**Interference Rejection Thresholds\
of Consumer Digital Television Receivers\
Available in 2005 and 2006**

**March 30, 2007**

**Technical Research Branch**

**Laboratory Division**

**Office of Engineering and Technology**

**Federal Communications Commission**

**OET Report Prepared by:**

**FCC/OET 07-TR-1003 Stephen R. Martin**

**ACKNOWLEDGEMENTS**

The author gratefully acknowledges the following contributions to this
work. Mark Hryszko of the Digital Television group of Advanced Micro
Devices provided the "Muddy Waters" RF vector file (mathematically
derived from an MPEG2 transport stream) that was used with the Wavetech
WS2100 RF player to provide a "desired signal" for the final few tests
performed for this report. John Gabrysch of the Commission's Media
Bureau set up and evaluated the performance of the Rohde and Schwarz SFU
DTV signal generator and developed channel assignment files for the
instrument. The work of Charles Rhodes on third-order intermodulation
inspired the paired-signal tests in this project. Gary Sgrignoli of MSW
provided a fast-track DTV education to prepare the author for the
prequel to this project. The author thanks the following Commission
employees for reviewing drafts of this document: Alan Stillwell, Rashmi
Doshi, and William Hurst (Office of Engineering and Technology); Doug
Miller, John Raymond, and Steve DeSena (Enforcement Bureau); Richard
Engelman and Sankar Persaud (International Bureau). The author also
acknowledges the support of wife, Dr. Bonnie Dorr, through many long
hours spent completing this work.

**TABLE OF CONTENTS**

[EXECUTIVE SUMMARY viii](#executive-summary)

[Tuner Type Tests viii](#tuner-type-tests)

[Interference Rejection Tests ix](#interference-rejection-tests)

[Interference From One Undesired Signal
ix](#interference-from-one-undesired-signal)

[Interference From IM3-Generating Pairs of Undesired Signals
xi](#__RefHeading___Toc163024326)

[CHAPTER 1 INTRODUCTION 1](#introduction)

[Background 1](#background)

[Objectives 2](#objectives)

[Measurement Program 3](#measurement-program)

[Overview 5](#overview)

[CHAPTER 2 SCOPE AND APPROACH 2-1](#scope-and-approach)

[Scope of Testing 2-1](#scope-of-testing)

[Interference Rejection Testing Approach
2-4](#interference-rejection-testing-approach)

[Presentation of Results 2-6](#presentation-of-results)

[Test Summary 2-8](#test-summary)

[CHAPTER 3 TUNER TYPE TESTS 3-1](#tuner-type-tests-1)

[Tuner Topologies 3-1](#tuner-topologies)

[LO Measurement For Tuner Type Identification
3-2](#lo-measurement-for-tuner-type-identification)

[Interference Rejection Tests For Tuner Type Identification
3-3](#interference-rejection-tests-for-tuner-type-identification)

[Summary 3-4](#summary)

[CHAPTER 4 INTERFERENCE REJECTION REFERENCE LEVELS AND TEST METHODOLOGY
4-1](#interference-rejection-reference-levels-and-test-methodology)

[Reference Levels for Interference Rejection Performance
4-1](#reference-levels-for-interference-rejection-performance)

[Test Setup Requirements 4-3](#test-setup-requirements)

[Test Setup 4-4](#test-setup)

[Test Setup Performance 4-5](#test-setup-performance)

[Test Setup Configurations 4-7](#test-setup-configurations)

[CHAPTER 5 REJECTION RESULTS ON CHANNEL 30 FOR SINGLE INTERFERERS WITH
FULL CHANNEL WIDTH
5-1](#rejection-results-on-channel-30-for-single-interferers-with-full-channel-width)

[Tests at ATSC-Specified Desired Signal Levels
5-1](#tests-at-atsc-specified-desired-signal-levels)

[Selection of a Weaker Desired Signal for Tests
5-3](#selection-of-a-weaker-desired-signal-for-tests)

[Effect of Desired Signal Source 5-5](#effect-of-desired-signal-source)

[Tests with Desired Signal at D~MIN~ + 3 dB
5-7](#tests-with-desired-signal-at-dmin-3-db)

[Summary of Fifth-Generation Receiver Results
5-8](#summary-of-fifth-generation-receiver-results)

[Earlier-Generation Receivers 5-9](#earlier-generation-receivers)

[Taboo Effects and Other Observations
5-9](#taboo-effects-and-other-observations)

[CHAPTER 6 REJECTION RESULTS ON CHANNEL 51 FOR SINGLE 8-VSB INTERFERERS
6-1](#rejection-results-on-channel-51-for-single-8-vsb-interferers)

[Tests at ATSC-Specified Desired Signal Levels
6-1](#tests-at-atsc-specified-desired-signal-levels-1)

[Comparison to Channel-30 Results
6-2](#comparison-to-channel-30-results)

[CHAPTER 7 TESTS WITH DIFFERENT SIGNAL TYPES AND SOURCES
7-1](#tests-with-different-signal-types-and-sources)

[1-MHz Bandwidth Undesired Signal 7-3](#mhz-bandwidth-undesired-signal)

[Desired Signal Source: SFU Versus ATSC997
7-3](#desired-signal-source-sfu-versus-atsc997)

[Repeat Baseline Test 7-5](#repeat-baseline-test)

[Undesired Signal Type: 8-VSB Versus Bandlimited Gaussian Noise
7-6](#undesired-signal-type-8-vsb-versus-bandlimited-gaussian-noise)

[Undesired Signal Type: DVB-H OFDM Versus Bandlimited Gaussian Noise
7-7](#undesired-signal-type-dvb-h-ofdm-versus-bandlimited-gaussian-noise)

[CHAPTER 8 THEORETICAL FRAMEWORK FOR OUT-OF-CHANNEL INTERFERENCE
8-1](#theoretical-framework-for-out-of-channel-interference)

[Interference Mechanisms and Order
8-1](#interference-mechanisms-and-order)

[Threshold of Visibility of Picture Degradation Due to Interference
8-2](#threshold-of-visibility-of-picture-degradation-due-to-interference)

[Slopes of Log-Log Plots of D, U, and D/U
8-3](#slopes-of-log-log-plots-of-d-u-and-du)

[Effect of AGC 8-3](#effect-of-agc)

[Weak Signals 8-4](#weak-signals)

[IM3 With Paired Signals 8-5](#im3-with-paired-signals)

[CHAPTER 9 THIRD-ORDER INTERMODULATION WITH PAIRED EQUAL-POWER
INTERFERERS
9-1](#third-order-intermodulation-with-paired-equal-power-interferers)

[Spectra of Third-Order Intermodulation Distortion
9-1](#spectra-of-third-order-intermodulation-distortion)

[Channel-30 Results at Three Desired Signal Levels
9-3](#channel-30-results-at-three-desired-signal-levels)

[Channel-51 Results at Three Desired Signal Levels
9-6](#channel-51-results-at-three-desired-signal-levels)

[Estimating 3^rd^ Order Intercept Point (IP3)
9-8](#estimating-3rd-order-intercept-point-ip3)

[Summary Data 9-12](#summary-data)

[CHAPTER 10 IM3 WITH PAIRED SIGNALS OF UNEQUAL AMPLITUDES
10-1](#im3-with-paired-signals-of-unequal-amplitudes)

[Measurements on Two Receivers 10-1](#measurements-on-two-receivers)

[Modeling and Extrapolation 10-2](#modeling-and-extrapolation)

[CHAPTER 11 SINGLE AND PAIRED REJECTION RATIOS VERSUS DESIRED SIGNAL
LEVEL---A DETAILED EXAMPLE
11-1](#single-and-paired-rejection-ratios-versus-desired-signal-levela-detailed-example)

[General Observations 11-2](#general-observations)

[IM3 With Paired Undesired Signals
11-3](#im3-with-paired-undesired-signals)

[Single Undesired Signals 11-6](#single-undesired-signals)

[Summary 11-9](#summary-1)

[CHAPTER 12 EXTENDING THE RESULTS TO LOWER SIGNAL LEVELS
12-1](#extending-the-results-to-lower-signal-levels)

[Order of Interference Processes and Effect of AGC
12-1](#order-of-interference-processes-and-effect-of-agc)

[Extrapolation to D = D~MIN~ + 1 dB 12-2](#extrapolation-to-d-dmin-1-db)

[CHAPTER 13 COMBINING MEASURED AND EXTRAPOLATED RESULTS
13-1](#combining-measured-and-extrapolated-results)

[CHAPTER 14 VERIFICATION TESTS USING ALTERNATIVE METHODS
14-1](#verification-tests-using-alternative-methods)

[Alternative Test Setup With Bandpass Filter on Undesired Signal
14-1](#alternative-test-setup-with-bandpass-filter-on-undesired-signal)

[Broadband Notched Noise 14-2](#broadband-notched-noise)

[Screen-Room Test 14-5](#screen-room-test)

[Summary 14-5](#summary-2)

[CHAPTER 15 SUMMARY AND CONCLUSIONS 15-1](#summary-and-conclusions)

[DTV Tuner Type 15-2](#dtv-tuner-type)

[Effect of Undesired Signal Type 15-2](#effect-of-undesired-signal-type)

[Cliff Effect 15-2](#cliff-effect-1)

[Interference from a Single Undesired Signal
15-3](#interference-from-a-single-undesired-signal)

[Interference From IM3-Generating Pairs of Undesired Signals
15-4](#interference-from-im3-generating-pairs-of-undesired-signals-1)

[APPENDIX A TABULATED REJECTION PERFORMANCE RESULTS
A-1](#tabulated-rejection-performance-results)

[Threshold D/U Statistics for 8 Fifth-Generation DTV Receivers
A-2](#threshold-du-statistics-for-8-fifth-generation-dtv-receivers)

[Threshold U Statistics for 8 Fifth-Generation DTV Receivers
A-7](#threshold-u-statistics-for-8-fifth-generation-dtv-receivers)

[APPENDIX B THEORETICAL BASIS FOR OUT-OF-CHANNEL INTERFERENCE
B-1](#theoretical-basis-for-out-of-channel-interference)

[Single Interferer B-2](#single-interferer)

[IM3 With Paired Signals B-9](#im3-with-paired-signals-1)

[Summary B-12](#summary-3)

BIBLIOGRAPHY

**ILLUSTRATIONS**

[Figure 2‑1. Spectra of the Four Undesired Signal Sources
2-11](#__RefHeading___Toc163024408)

[Figure 2‑2. Spectra of the Four Undesired Signal Sources---Expanded
Scale 2-11](#__RefHeading___Toc163024409)

[Figure 2‑3. Relationship Between Signal Excess and Coverage Area
2-12](#__RefHeading___Toc163024410)

[Figure 3‑1. Single-Conversion DTV Tuner Block Diagram Example
3-4](#__RefHeading___Toc163024411)

[Figure 3‑2. Double-Conversion DTV Tuner Block Diagram Example
3-4](#__RefHeading___Toc163024412)

[Figure 3‑3. Rejection Performance of Receivers with Undetected LO's
3-5](#__RefHeading___Toc163024413)

[Figure 4‑1. Block Diagram of Interference Rejection Test Setup
4-9](#__RefHeading___Toc163024414)

[Figure 4‑2. Leakage of U at N+2 into Channel N (30)
4-10](#__RefHeading___Toc163024415)

[Figure 4‑3. Leakage of U pair at N-2/N-4 into Channel N (30)
4-10](#__RefHeading___Toc163024416)

[Figure 4‑4. Leakage of U pair at N+1/N+2 into Channel N (30)
4-11](#__RefHeading___Toc163024417)

[Figure 5‑1. D/U of 8 Receivers at D = -68 dBm on Channel 30
5-12](#__RefHeading___Toc163024418)

[Figure 5‑2. D/U Statistics at D = -68 dBm on Channel 30
5-12](#__RefHeading___Toc163024419)

[Figure 5‑3. D/U of 8 receivers at D = -53 dBm on Channel 30
5-13](#__RefHeading___Toc163024420)

[Figure 5‑4. D/U Statistics at D = -53 dBm on Channel 30
5-13](#__RefHeading___Toc163024421)

[Figure 5‑5. D/U of 8 receivers at D = -28 dBm on Channel 30
5-14](#__RefHeading___Toc163024422)

[Figure 5‑6. D/U Statistics at D = -28 dBm on Channel 30
5-14](#__RefHeading___Toc163024423)

[Figure 5‑7. Spectra of Two Desired Signal Sources
5-15](#__RefHeading___Toc163024424)

[Figure 5‑8. Spectra of Two Desired Signal Sources on Expanded Scale
5-15](#__RefHeading___Toc163024425)

[Figure 5‑9. D/U of 8 receivers at D = D~MIN~ + 3 dB on Channel 30
5-16](#__RefHeading___Toc163024426)

[Figure 5‑10. D/U Statistics at D = D~MIN~ + 3 dB on Channel 30
5-16](#__RefHeading___Toc163024427)

[Figure 5‑11. Median D/U of 8 receivers at Four Signal Levels on Channel
30 5-17](#__RefHeading___Toc163024428)

[Figure 5‑12. Median Threshold U of 8 receivers at Four Signal Levels on
Channel 30 5-17](#__RefHeading___Toc163024429)

[Figure 5‑13. 2^nd^ Worst D/U of 8 receivers at Four Signal Levels on
Channel 30 5-18](#__RefHeading___Toc163024430)

[Figure 5‑14. 2^nd^ Worst Threshold U of 8 receivers at Four Signal
Levels on Channel 30 5-18](#__RefHeading___Toc163024431)

[Figure 5‑15. Worst D/U of 8 receivers at Four Signal Levels on Channel
30 5-19](#__RefHeading___Toc163024432)

[Figure 5‑16. Worst Threshold U of 8 receivers at Four Signal Levels on
Channel 30 5-19](#__RefHeading___Toc163024433)

[Figure 5‑17. D/U of Two Earlier-Generation Receivers at D = -68 dBm
Relative to Fifth-Generation Results 5-20](#__RefHeading___Toc163024434)

[Figure 6‑1. D/U of 7 Receivers at D = -68 dBm on Channel 51
6-3](#__RefHeading___Toc163024435)

[Figure 6‑2. D/U Statistics at D = -68 dBm on Channel 51
6-3](#__RefHeading___Toc163024436)

[Figure 6‑3. D/U of 7 Receivers at D = -53 dBm on Channel 51
6-4](#__RefHeading___Toc163024437)

[Figure 6‑4. D/U Statistics at D = -53 dBm on Channel 51
6-4](#__RefHeading___Toc163024438)

[Figure 6‑5. D/U of 7 Receivers at D = -28 dBm on Channel 51
6-5](#__RefHeading___Toc163024439)

[Figure 6‑6. D/U Statistics at D = -28 dBm on Channel 51
6-5](#__RefHeading___Toc163024440)

[Figure 6‑7. Comparison of Median D/U for 7 Receivers on Channels 30 and
51 at D = -68 dBm 6-6](#__RefHeading___Toc163024441)

[Figure 6‑8. Comparison of Median D/U for 7 Receivers on Channels 30 and
51 at D = -53 dBm 6-6](#__RefHeading___Toc163024442)

[Figure 7‑1. D/U With 1-MHz Undesired Signal Bandwidth
7-8](#__RefHeading___Toc163024443)

[Figure 8‑1. Deviation of Log-U Versus Log-D From Straight Line For
Linear Interference 8-7](#__RefHeading___Toc163024444)

[Figure 8‑2. Deviation of Log-U Versus Log-D From Straight Line For
2^nd^-Order Interference 8-7](#__RefHeading___Toc163024445)

[Figure 8‑3. Deviation of Log-U Versus Log-D From Straight Line For
3^rd^-Order Interference 8-8](#__RefHeading___Toc163024446)

[Figure 8‑4. Deviation of Log-U Versus Log-D From Straight Line For
Cross-Modulation 8-8](#__RefHeading___Toc163024447)

[Figure 9‑1. Third-Order Intermodulation Distortion Spectra of Single
and Paired Signals 9-15](#__RefHeading___Toc163024448)

[Figure 9‑2. Third-Order Intermodulation Distortion Spectra of Paired
Signals Versus Amplitude 9-16](#__RefHeading___Toc163024449)

[Figure 9‑3. Paired-Signal D/U of 8 receivers at D = -68 dBm on Channel
30 9-17](#__RefHeading___Toc163024450)

[Figure 9‑4. Paired-Signal D/U Statistics of 8 receivers at D = -68 dBm
on Channel 30 9-17](#__RefHeading___Toc163024451)

[Figure 9‑5. Paired-Signal D/U of 8 receivers at D = -53 dBm on Channel
30 9-18](#__RefHeading___Toc163024452)

[Figure 9‑6. Paired-Signal D/U Statistics of 8 receivers at D = -53 dBm
on Channel 30 9-18](#__RefHeading___Toc163024453)

[Figure 9‑7. Paired-Signal D/U of 8 receivers at D = -28 dBm on Channel
30---1st-Adjacent Only 9-19](#__RefHeading___Toc163024454)

[Figure 9‑8. Paired-Signal D/U of 8 receivers at D = -28 dBm on Channel
30---1st-Adjacent Only 9-19](#__RefHeading___Toc163024455)

[Figure 9‑9. Paired-Signal D/U of Receiver A3 on Channel 30 with Summed
D/U's as Reference 9-20](#__RefHeading___Toc163024456)

[Figure 9‑10. Paired-Signal D/U of Receiver D3 on Channel 30 with Summed
D/U's as Reference 9-20](#__RefHeading___Toc163024457)

[Figure 9‑11. Paired-Signal D/U of Receiver I1 on Channel 30 with Summed
D/U's as Reference 9-21](#__RefHeading___Toc163024458)

[Figure 9‑12. Paired-Signal D/U of Receiver J1 on Channel 30 with Summed
D/U's as Reference 9-21](#__RefHeading___Toc163024459)

[Figure 9‑13. Paired-Signal D/U of Receiver M1 on Channel 30 with Summed
D/U's as Reference 9-22](#__RefHeading___Toc163024460)

[Figure 9‑14. Paired-Signal D/U of Receiver N1 on Channel 30 with Summed
D/U's as Reference 9-22](#__RefHeading___Toc163024461)

[Figure 9‑15. Paired-Signal D/U of Receiver O1 on Channel 30 with Summed
D/U's as Reference 9-23](#__RefHeading___Toc163024462)

[Figure 9‑16. Paired-Signal D/U of Receiver G4 on Channel 30 with Summed
D/U's as Reference 9-23](#__RefHeading___Toc163024463)

[Figure 9‑17. Paired-Signal D/U of 7 receivers at D = -68 dBm on Channel
51 9-24](#__RefHeading___Toc163024464)

[Figure 9‑18. Paired-Signal D/U Statistics of 7 receivers at D = -68 dBm
on Channel 51 9-24](#__RefHeading___Toc163024465)

[Figure 9‑19. Paired-Signal D/U of 7 receivers at D = -53 dBm on Channel
51 9-25](#__RefHeading___Toc163024466)

[Figure 9‑20. Paired-Signal D/U Statistics of 6 receivers at D = -53 dBm
on Channel 51 9-25](#__RefHeading___Toc163024467)

[Figure 9‑21. Paired-Signal D/U of 7 receivers at D = -28 dBm on Channel
51 9-26](#__RefHeading___Toc163024468)

[Figure 9‑22. Paired-Signal D/U Statistics of 6 receivers at D = -28 dBm
on Channel 51 9-26](#__RefHeading___Toc163024469)

[Figure 9‑23. Paired-Signal D/U of Receiver A3 on Channel 51 with Summed
D/U's as Reference 9-27](#__RefHeading___Toc163024470)

[Figure 9‑24. Paired-Signal D/U of Receiver D3 on Channel 51 with Summed
D/U's as Reference 9-27](#__RefHeading___Toc163024471)

[Figure 9‑25. Paired-Signal D/U of Receiver I1 on Channel 51 with Summed
D/U's as Reference 9-28](#__RefHeading___Toc163024472)

[Figure 9‑26. Paired-Signal D/U of Receiver J1 on Channel 51 with Summed
D/U's as Reference 9-28](#__RefHeading___Toc163024473)

[Figure 9‑27. Paired-Signal D/U of Receiver M1 on Channel 51 with Summed
D/U's as Reference 9-29](#__RefHeading___Toc163024474)

[Figure 9‑28. Paired-Signal D/U of Receiver N1 on Channel 51 with Summed
D/U's as Reference 9-29](#__RefHeading___Toc163024475)

[Figure 9‑29. Paired-Signal D/U of Receiver O1 on Channel 51 with Summed
D/U's as Reference 9-30](#__RefHeading___Toc163024476)

[Figure 9‑30. Third-Order Intercept Point Parameter with Desired Signal
= ‑68 dBm on Channel 30 9-31](#__RefHeading___Toc163024477)

[Figure 9‑31. Third-Order Intercept Point Parameter with Desired Signal
= ‑53 dBm on Channel 30 9-31](#__RefHeading___Toc163024478)

[Figure 9‑32. Third-Order Intercept Point Parameter with Desired Signal
= -68 dBm on Channel 51 9-32](#__RefHeading___Toc163024479)

[Figure 9‑33. Third-Order Intercept Point Parameter with Desired Signal
= -53 dBm on Channel 51 9-32](#__RefHeading___Toc163024480)

[Figure 9‑34. Third-Order Intercept Point Parameter---Channel 30/51
Comparison 9-33](#__RefHeading___Toc163024481)

[Figure 10‑1. Threshold U for Paired, Unequal Undesired Signals on
Receiver G4 10-6](#__RefHeading___Toc163024482)

[Figure 10‑2. Threshold U for Paired, Unequal Undesired Signals on
Receiver M1 10-6](#__RefHeading___Toc163024483)

[Figure 10‑3. Threshold U for Paired, Unequal Undesired Signals on
Receiver M1 at D = -68 dBm 10-7](#__RefHeading___Toc163024484)

[Figure 10‑4. Modeled Thresholds for N-5/N-10 with D = -68 dBm
10-7](#__RefHeading___Toc163024485)

[Figure 10‑5. Modeled Thresholds for N-4/N-8 with D = -68 dBm
10-8](#__RefHeading___Toc163024486)

[Figure 10‑6. Modeled Thresholds for N-3/N-6 with D = -68 dBm
10-8](#__RefHeading___Toc163024487)

[Figure 10‑7. Modeled Thresholds for N+2/N+4 with D = -68 dBm
10-9](#__RefHeading___Toc163024488)

[Figure 10‑8. Modeled Thresholds for N+3/N+6 with D = -68 dBm
10-9](#__RefHeading___Toc163024489)

[Figure 10‑9. Modeled Thresholds for N+4/N+8 with D = -68 dBm
10-10](#__RefHeading___Toc163024490)

[Figure 10‑10. Modeled Thresholds for N+5/N+10 with D = -68 dBm
10-10](#__RefHeading___Toc163024491)

[Figure 10‑11. Modeled Thresholds for N-5/N-10 with D = D~MIN~ + 3 dB
10-11](#__RefHeading___Toc163024492)

[Figure 10‑12. Modeled Thresholds for N-4/N-8 with D = D~MIN~ + 3 dB
10-11](#__RefHeading___Toc163024493)

[Figure 10‑13. Modeled Thresholds for N-3/N-6 with D = D~MIN~ + 3 dB
10-12](#__RefHeading___Toc163024494)

[Figure 10‑14. Modeled Thresholds for N+2/N+4 with D = D~MIN~ + 3 dB
10-12](#__RefHeading___Toc163024495)

[Figure 10‑15. Modeled Thresholds for N+3/N+6 with D = D~MIN~ + 3 dB
10-13](#__RefHeading___Toc163024496)

[Figure 10‑16. Modeled Thresholds for N+4/N+8 with D = D~MIN~ + 3 dB
10-13](#__RefHeading___Toc163024497)

[Figure 10‑17. Modeled Thresholds for N+5/N+10 with D = D~MIN~ + 3 dB
10-14](#__RefHeading___Toc163024498)

[Figure 11‑1. D/U Versus D for Receiver D3 (Desired Signal on Channel
51) 11-10](#__RefHeading___Toc163024499)

[Figure 11‑2. Threshold U Versus D for Receiver D3 (Desired Signal on
Channel 51) 11-10](#__RefHeading___Toc163024500)

[Figure 11‑3. Slope of Log-D versus Log-U for Receiver D3 (Desired
Signal on Channel 51) 11-11](#__RefHeading___Toc163024501)

[Figure 11‑4. Slope of Log-U versus Log-D for Receiver D3 (Desired
Signal on Channel 51) 11-11](#__RefHeading___Toc163024502)

[Figure 11‑5. D/U Versus D for Receiver D3---Paired Signals And Their
Constituents 11-12](#__RefHeading___Toc163024503)

[Figure 11‑6. D/U Versus D for Receiver D3---Single Undesired Signals
11-12](#__RefHeading___Toc163024504)

[Figure 11‑7. Threshold U Versus D for Receiver D3---Single Undesired
Signals 11-13](#__RefHeading___Toc163024505)

[Figure 11‑8. Linear Undesired Power Versus Log-Desired Signal Power for
N+6 11-13](#__RefHeading___Toc163024506)

[Figure 12‑1. Slope of Threshold U Versus D from D = -68 dBm to -53 dBm
12-6](#__RefHeading___Toc163024507)

[Figure 12‑2. Slope of Threshold U Versus D from D =D~MIN~+3dB to -68
dBm 12-6](#__RefHeading___Toc163024508)

[Figure 12‑3. Slope of Threshold D Versus U from D =D~MIN~+3dB to -68
dBm 12-7](#__RefHeading___Toc163024509)

[Figure 12‑4. D/U of 8 Receivers at D = D~MIN~ + 1 dB on Channel 30
(Extrapolation) 12-7](#__RefHeading___Toc163024510)

[Figure 13‑1. D/U of Receiver A3 at Five Desired Signal Levels on
Channel 30 13-3](#__RefHeading___Toc163024511)

[Figure 13‑2. Threshold U of Receiver A3 at Five Desired Signal Levels
on Channel 30 13-3](#__RefHeading___Toc163024512)

[Figure 13‑3. D/U of Receiver D3 at Five Desired Signal Levels on
Channel 30 13-4](#__RefHeading___Toc163024513)

[Figure 13‑4. Threshold U of Receiver D3 at Five Desired Signal Levels
on Channel 30 13-4](#__RefHeading___Toc163024514)

[Figure 13‑5. D/U of Receiver I1 at Five Desired Signal Levels on
Channel 30 13-5](#__RefHeading___Toc163024515)

[Figure 13‑6. Threshold U of Receiver I1 at Five Desired Signal Levels
on Channel 30 13-5](#__RefHeading___Toc163024516)

[Figure 13‑7. D/U of Receiver J1 at Five Desired Signal Levels on
Channel 30 13-6](#__RefHeading___Toc163024517)

[Figure 13‑8. Threshold U of Receiver J1 at Five Desired Signal Levels
on Channel 30 13-6](#__RefHeading___Toc163024518)

[Figure 13‑9. D/U of Receiver M1 at Five Desired Signal Levels on
Channel 30 13-7](#__RefHeading___Toc163024519)

[Figure 13‑10. Threshold U of Receiver M1 at Five Desired Signal Levels
on Channel 30 13-7](#__RefHeading___Toc163024520)

[Figure 13‑11. D/U of Receiver N1 at Five Desired Signal Levels on
Channel 30 13-8](#__RefHeading___Toc163024521)

[Figure 13‑12. Threshold U of Receiver N1 at Five Desired Signal Levels
on Channel 30 13-8](#__RefHeading___Toc163024522)

[Figure 13‑13. D/U of Receiver O1 at Five Desired Signal Levels on
Channel 30 13-9](#__RefHeading___Toc163024523)

[Figure 13‑14. Threshold U of Receiver O1 at Five Desired Signal Levels
on Channel 30 13-9](#__RefHeading___Toc163024524)

[Figure 13‑15. D/U of Receiver G4 at Five Desired Signal Levels on
Channel 30 13-10](#__RefHeading___Toc163024525)

[Figure 13‑16. Threshold U of Receiver G4 at Five Desired Signal Levels
on Channel 30 13-10](#__RefHeading___Toc163024526)

[Figure 14‑1. Frequency Response of Channel-29 Bandpass Filter
14-6](#__RefHeading___Toc163024527)

[Figure 14‑2. Alternative Test Configuration With Bandpass Filter on
Undesired Signal 14-6](#__RefHeading___Toc163024528)

[Figure 14‑3. D/U Measurements on Receiver J1 with Primary Versus
Alternative Test Setup 14-7](#__RefHeading___Toc163024529)

[Figure 14‑4. Spectrum of Undesired Signal for Broadband Notched Noise
Test 14-7](#__RefHeading___Toc163024530)

[Figure 14‑5. Model Plot for "Plateau IM3" On Receiver G4 at D = -68 dBm
with N-5/N-10 14-8](#__RefHeading___Toc163024531)

[Figure 14‑6. Model Plot for "Plateau IM3" On Receiver D3 at D = -68 dBm
with N+2/N+4 14-8](#__RefHeading___Toc163024532)

[Figure 14‑7. Model Plot for "Plateau IM3" On Receiver G4 at D =
D~MIN~+3dB with N+4/N+8 14-9](#__RefHeading___Toc163024533)

[Figure 14‑8. Model Plot for "Plateau IM3" On Receiver G4 at D =-68 dBm
with N-3/N-6 14-9](#__RefHeading___Toc163024534)

[Figure 15‑1. Median D/U of 8 Receivers at Five Signal Levels on Channel
30 15-8](#__RefHeading___Toc163024535)

[Figure 15‑2. Median Threshold U of 8 Receivers at Five Signal Levels on
Channel 30 15-8](#__RefHeading___Toc163024536)

[Figure 15‑3. 2^nd^ Worst D/U of 8 Receivers at Five Signal Levels on
Channel 30 15-9](#__RefHeading___Toc163024537)

[Figure 15‑4. 2^nd^ Worst Threshold U of 8 Receivers at Five Signal
Levels on Channel 30 15-9](#__RefHeading___Toc163024538)

[Figure 15‑5. Worst D/U of 8 Receivers at Five Signal Levels on Channel
30 15-10](#__RefHeading___Toc163024539)

[Figure 15‑6. Worst Threshold U of 8 Receivers at Five Signal Levels on
Channel 30 15-10](#__RefHeading___Toc163024540)

[Figure 15‑7. Median D/U of 8 Receivers at D = -68 dBm With IM3 Signal
Pairs 15-11](#__RefHeading___Toc163024541)

[Figure 15‑8. Median Threshold U of 8 Receivers at D = -68 dBm With IM3
Signal Pairs 15-11](#__RefHeading___Toc163024542)

[Figure 15‑9. 2^nd^ Worst D/U of 8 Receivers at D = -68 dBm With IM3
Signal Pairs 15-12](#__RefHeading___Toc163024543)

[Figure 15‑10. 2^nd^ Worst Threshold U of 8 Receivers at D = -68 dBm
With IM3 Signal Pairs 15-12](#__RefHeading___Toc163024544)

[Figure 15‑11. Worst D/U of 8 Receivers at D = -68 dBm With IM3 Signal
Pairs 15-13](#__RefHeading___Toc163024545)

[Figure 15‑12. Worst Threshold U of 8 Receivers at D = -68 dBm With IM3
Signal Pairs 15-13](#__RefHeading___Toc163024546)

[Figure 15‑13. Median D/U of 8 Receivers at D = D~MIN~+3dB With IM3
Signal Pairs 15-14](#__RefHeading___Toc163024547)

[Figure 15‑14. Median Threshold U of 8 Receivers at D = D~MIN~+3dB With
IM3 Signal Pairs 15-14](#__RefHeading___Toc163024548)

[Figure 15‑15. 2^nd^ Worst D/U of 8 Receivers at D = D~MIN~+3dB With IM3
Signal Pairs 15-15](#__RefHeading___Toc163024549)

[Figure 15‑16. 2^nd^ Worst Threshold U of 8 Receivers at D = D~MIN~+3dB
With IM3 Signal Pairs 15-15](#__RefHeading___Toc163024550)

[Figure 15‑17. Worst D/U of 8 Receivers at D = D~MIN~+3dB With IM3
Signal Pairs 15-16](#__RefHeading___Toc163024551)

[Figure 15‑18. Worst Threshold U of 8 Receivers at D = D~MIN~+3dB With
IM3 Signal Pairs 15-16](#__RefHeading___Toc163024552)

[Figure 15‑19. Median D/U of 8 Receivers at D = D~MIN~+1dB With IM3
Signal Pairs 15-17](#__RefHeading___Toc163024553)

[Figure 15‑20. Median Threshold U of 8 Receivers at D = D~MIN~+1dB With
IM3 Signal Pairs 15-17](#__RefHeading___Toc163024554)

[Figure 15‑21. 2^nd^ Worst D/U of 8 Receivers at D = D~MIN~+1dB With IM3
Signal Pairs 15-18](#__RefHeading___Toc163024555)

[Figure 15‑22. 2^nd^ Worst Threshold U of 8 Receivers at D = D~MIN~+1dB
With IM3 Signal Pairs 15-18](#__RefHeading___Toc163024556)

[Figure 15‑23. Worst D/U of 8 Receivers at D = D~MIN~+1dB With IM3
Signal Pairs 15-19](#__RefHeading___Toc163024557)

[Figure 15‑24. Worst Threshold U of 8 Receivers at D = D~MIN~+1dB With
IM3 Signal Pairs 15-19](#__RefHeading___Toc163024558)

**TABLES**

[Table 2‑1. Measured Bandwidths of Undesired Signal Sources
2-2](#__RefHeading___Toc163024559)

[Table 2‑2. Relationship Between Excess Signal and Coverage Area
2-3](#__RefHeading___Toc163024560)

[Table 2‑3. DTV Receiver Samples 2-4](#__RefHeading___Toc163024561)

[Table 2‑4. UHF Reception Examples 2-7](#__RefHeading___Toc163024562)

[Table 2‑5. Summary of Tests 2-9](#__RefHeading___Toc163024563)

[Table 4‑1. Grand Alliance Receiver Interference Rejection Performance
4-1](#__RefHeading___Toc163024564)

[Table 4‑2. OET-69 DTV-Into-DTV Interference Protection Criteria
4-1](#__RefHeading___Toc163024565)

[Table 4‑3. ATSC A/74 Recommended Thresholds for Receiver Interference
Rejection 4-2](#__RefHeading___Toc163024566)

[Table 4‑4. Measurement Limitations of the Test Setup
4-7](#__RefHeading___Toc163024567)

[Table 4‑5. Test Setup Configurations and Settings
4-8](#__RefHeading___Toc163024568)

[Table 5‑1. Receiver Minimum Signal Level at TOV Versus Desired Signal
Source 5-6](#__RefHeading___Toc163024569)

[Table 5‑2. Signal Quality Measurements on 8-VSB Sources
5-6](#__RefHeading___Toc163024570)

[Table 7‑1. Comparative Signal Test Summary
7-2](#__RefHeading___Toc163024571)

[Table 7‑2. D/U Ratio With SFU as Desired Signal Source Relative to That
With Baseline Generator (ATSC997) 7-4](#__RefHeading___Toc163024572)

[Table 7‑3. D/U Ratio for Repeat of Baseline Test Relative to Baseline
7-5](#__RefHeading___Toc163024573)

[Table 7‑4. D/U Ratio With 8-VSB as Undesired Signal Relative to That
with Bandlimited Gaussian Noise 7-6](#__RefHeading___Toc163024574)

[Table 7‑5. D/U Ratio With DVB-H as Undesired Signal Relative to That
with Bandlimited Gaussian Noise 7-7](#__RefHeading___Toc163024575)

[Table 8‑1. Slopes of Log-Log Plots of D, U, and D/U for Various
Interference Mechanisms 8-3](#__RefHeading___Toc163024576)

[Table 8‑2. Deviation in Threshold U from Straight-Line Projection as D
approaches D~MIN~ 8-5](#__RefHeading___Toc163024577)

[Table 9‑1. Parameters for Paired-Interferer Tests (N+K/N+2K)
9-2](#__RefHeading___Toc163024578)

[Table 9‑2. Statistics of Paired-Signal D/U's Relative to Summed D/U's
for 8 Receivers on Channel 30 9-7](#__RefHeading___Toc163024579)

[Table 9‑3. IP3/SNR~R~^1/2^ Based on Paired-Signal Rejection
Measurements at Channel-30 9-10](#__RefHeading___Toc163024580)

[Table 9‑4. IP3/SNR~R~^1/2^ Based on Paired-Signal Rejection
Measurements at Channel-51 9-11](#__RefHeading___Toc163024581)

[Table 9‑5. IP3/SNR~R~^1/2^ Statistics
9-12](#__RefHeading___Toc163024582)

[Table 9‑6. Computed Threshold U Due to IM3 for Equal Paired Signals
9-13](#__RefHeading___Toc163024583)

[Table 9‑7. Computed Threshold D/U Due to IM3 for Equal Paired Signals
9-14](#__RefHeading___Toc163024584)

[Table 10‑1. Range of Impact of IM3 from Pairs of Undesired Signals When
D = -68 dBm 10-4](#__RefHeading___Toc163024585)

[Table 10‑2. Range of Impact of IM3 from Pairs of Undesired Signals When
D =D~MIN~ + 3 dB 10-5](#__RefHeading___Toc163024586)

[Table 12‑1. Characteristics of Log-Log Plots of Undesired Versus
Desired Signal Power At TOV 12-1](#__RefHeading___Toc163024587)

[Table 12‑2. Process for Extrapolation from D = D~MIN~+3dB to D~MIN~+1dB
12-4](#__RefHeading___Toc163024588)

[Table 12‑3. Error Test for Extrapolation From D = D~MIN~ + 3 dB to
D~MIN~ + 1 dB 12-5](#__RefHeading___Toc163024589)

[Table 14‑1. Broadband Notched Noise D/U Ratios at Threshold
14-3](#__RefHeading___Toc163024590)

[Table A‑1. Statistics of D~MIN~ for 8 Receivers on Channel 30
A-1](#__RefHeading___Toc163024591)

[Table A‑2. D/U Statistics for 8 Receivers at D = D~MIN~ + 1 dB on
Channel 30 A-2](#__RefHeading___Toc163024592)

[Table A‑3. D/U Statistics for 8 Receivers at D = D~MIN~ + 3 dB on
Channel 30 A-3](#__RefHeading___Toc163024593)

[Table A‑4. D/U Statistics for 8 Receivers at D = -68 dBm on Channel 30
A-4](#__RefHeading___Toc163024594)

[Table A‑5. D/U Statistics for 8 Receivers at D = -53 dBm on Channel 30
A-5](#__RefHeading___Toc163024595)

[Table A‑6. D/U Statistics for 8 Receivers at D = -28 dBm on Channel 30
A-6](#__RefHeading___Toc163024596)

[Table A‑7. Threshold U Statistics for 8 Receivers at D = D~MIN~ + 1 dB
on Channel 30 A-7](#__RefHeading___Toc163024597)

[Table A‑8. Threshold U Statistics for 8 Receivers at D = D~MIN~ + 3 dB
on Channel 30 A-8](#__RefHeading___Toc163024598)

[Table A‑9. Threshold U Statistics for 8 Receivers at D = -68 dBm on
Channel 30 A-9](#__RefHeading___Toc163024599)

[Table A‑10. Threshold U Statistics for 8 Receivers at D = -53 dBm on
Channel 30 A-10](#__RefHeading___Toc163024600)

[Table A‑11. Threshold U Statistics for 8 Receivers at D = -28 dBm on
Channel 30 A-11](#__RefHeading___Toc163024601)

[Table B‑1. Slopes of Log-Log Plots of D, U, and D/U for Various
Interference Mechanisms B-4](#__RefHeading___Toc163024602)

[Table B‑2. Deviation in Threshold U from Straight-Line Projection as D
Approaches D~MIN~ B-5](#__RefHeading___Toc163024603)

[Table B‑3. Slopes of Log-Log Plots of D, U, and D/U for Various
Interference Mechanisms B-13](#__RefHeading___Toc163024604)

[Table B‑4. Deviation in Threshold U from Straight-Line Projection as D
approaches D~MIN~ B-14](#__RefHeading___Toc163024605)

# EXECUTIVE SUMMARY

This report presents the results of two categories of tests performed on
consumer digital television receivers to assess their vulnerability to
out-of-channel interference:

1.  Tests of tuner type; and

2.  Interference rejection threshold tests.

The first category of test identifies the type of tuner (*e.g.*,
single-conversion versus double-conversion) in consumer DTV receivers. A
knowledge of tuner type aids in identifying the channel offsets at which
a TV receiver is likely to be susceptible to interference. The second
type of test measures the ability of DTV receivers to reject
interference from signals in TV channels other than the one to which the
TV is tuned.

The test results are intended to support assessments of interference to
DTV reception from:

1.  non-TV use of locally-unused spectrum within the TV broadcast
    spectrum, which is also often termed "white-space" use;

2.  non-TV use of spectrum adjacent to or near TV broadcast spectrum
    (*e.g.*, the TV channel 52 to 67 spectrum that will be auctioned for
    other uses); and,

3.  other DTV stations.

The results also enable evaluation of the degree to which consumer DTV
receivers comply with the voluntary standards contained in the receiver
standards document, "ATSC Recommended Practice: Receiver Performance
Guidelines"[^1]

It should be noted that this study characterizes susceptibility of
consumer DTVs to interference in terms of signal and interference levels
appearing *[at the antenna input terminal]{.underline}* of the receiver.
Assessments of potential for interference to DTV reception will require
additional analysis involving specific protection scenarios,[^2]
propagation modeling, and antenna modeling, which are beyond the scope
of the study.

## Tuner Type Tests

Measurements on the "Grand Alliance" prototype DTV receiver provided the
basis for establishing interference protection criteria for the DTV
channel allotment process. That receiver used a double-conversion tuner.
Consumer DTV receivers often use single-conversion tuners, which can be
more susceptible to interference at certain channel spacings than a
double-conversion tuner. Most of the analog TV taboos that limited
allotments of channels at certain spacings in a given local area were
the result of interference vulnerabilities associated with
single-conversion tuners.

Tests were performed on thirty consumer DTV receivers to determine their
tuner types. All were found to have single-conversion tuners. While the
use of single-conversion tuners implies the possibility of interference
susceptibilities at the same frequency offsets as those experienced by
analog TV, it should be noted that such interference vulnerabilities are
lower for digital TV than for analog TV because the ATSC DTV system is
inherently more resistant to interference than the NTSC analog system.

## Interference Rejection Tests

The out-of-channel interference rejection threshold of consumer digital
television (DTV) receivers was measured by supplying an ATSC 8-VSB[^3]
signal (the *[desired]{.underline}* signal), along with one or two
*[undesired]{.underline}* signals, to the antenna terminal of a DTV
receiver and then adjusting the level of the undesired signal(s) to the
point at which picture degradation begins to be observed---a point known
as the threshold of visibility (TOV) of degradation. In such testing,
the DTV receiver is tuned to the channel number of the desired signal.
The undesired signal (the potential interferer) is placed on another
channel, either above or below the desired channel.

We refer to the desired signal power at the input to the DTV receiver as
D and the undesired power when adjusted to the threshold (TOV) as U. It
is traditional to express interference rejection performance in terms of
the ratio D/U. When D/U is expressed in decibels (dB), it is typically a
negative number for out-of-channel interference; that is, the undesired
signal level is greater than the desired signal at TOV. Low values
(*i.e.*, large negative numbers) represent good rejection performance;
high values (small negative numbers) represent high *susceptibility* to
interference. D/U ratios measured for this report ranged from below -74
dB to -20 dB. Results in this report are presented both as D/U ratios
and as threshold values of the undesired signal power U in order to meet
the needs or preferences of different analysts.

Most of the interference rejection tests were performed on eight
consumer DTV receivers that were on the market in 2005 and 2006. The
eight receivers were identified as having fifth-generation
multipath-handling capability. Limited tests were also performed on two
earlier-generation receivers.

It should be noted that the out-of-channel interference tests for this
report were performed using a test setup that suppressed leakage of the
undesired signal into the desired channel to a sufficient degree to make
spectral leakage effects negligible. Thus, the first-adjacent channel
tests do not include the effects of spectral splatter representative of
a DTV transmitter---an effect which drives the first-adjacent channel
protection ratios used for DTV channel allotments.

## Interference From One Undesired Signal

### Channel Selection

All tests for this report were performed in the UHF TV band. For the
bulk of the testing, the TV was tuned to a desired signal on channel 30
(designated as channel "N"), and the undesired signal was sequenced
through channels N-1 through N-16 and N+1 through N+16. The earliest
testing in the program was performed with the desired signal on channel
51 and the undesired signal placed on channels N+1 through N+16.

The measurements on channel 51 generally matched those on channel 30
within about 4 dB---and in most instances much closer than that.

### Undesired Signals

All tests were performed using undesired signals that were continuous,
as opposed to occurring in bursts (as might be typical for packet-based
communications).

#### Signal Type {#signal-type .unnumbered}

For most tests the undesired signal was either an 8-VSB DTV signal or a
white Gaussian noise signal that had been bandlimited to match the 3-dB
width of the 8-VSB signal. The selection between these two signal types
was driven by equipment availability and spectrum shape
requirements.[^4]

A smaller number of tests were performed to compare the interference
effects of three signal types:

1.  The 8-VSB DTV signal;

2.  The Gaussian noise signal bandlimited to match the 8-VSB signal
    width (at the 3-dB points);

3.  An OFDM signal (DVB-H) that was about 5-MHz wide.

The results show that the DTV receivers are more vulnerable to
out-of-channel interference from the Gaussian noise and OFDM signals
than from the 8-VSB DTV signal by an amount just over 1 dB.

#### Signal Bandwidth {#signal-bandwidth .unnumbered}

For most tests, the undesired signal filled most of the 6-MHz width of a
TV channel. Tests were also performed on one TV using a narrower
signal---Gaussian noise bandlimited to a 3-dB bandwidth of 1 MHz. D/U
ratios with this reduced-bandwidth signal were comparable to those for
the wider undesired signals except in channel offsets where significant
narrowband interference effects occurred. One prominent such effect
occurred with the interference on channel N+7, where an interference
susceptibility peak was observable on 7 of the 8 DTV receivers that were
tested with the broader signals. Tests with the narrow signal showed
that the N+7 interference effect is narrowly centered at the local
oscillator frequency of the receiver (44 MHz above the center of the
tuned channel).

#### Signal Levels {#signal-levels .unnumbered}

If D/U ratios were constant with changes in desired signal level,
measurements at a single desired signal level would be sufficient to
characterize the interference susceptibility of a TV receiver at a given
channel offset; however, the tests showed that threshold D/U ratios vary
with signal level, and do so in ways that vary among the different
channel offsets on different TVs. The nature of the variation also
changes with signal level. As a result, tests were performed at three
desired signal levels specified by the ATSC (-28, -53, and ‑68 dBm) as
well as one additional signal level, D~MIN~ + 3 dB, where **D~MIN~**
refers to the receiver-specific desired signal level at TOV in the
absence of interference (essentially, the minimum signal level at which
a given DTV receiver can operate). In addition, modeling was performed
to extend the results down to D~MIN~ + 1 dB.

### Cliff Effect

The digital television broadcast system can achieve flawless picture
reception under interference conditions (D/U ratios) that would produce
an unusable picture for analog broadcast TV; however, once an undesired
signal reaches a level at which picture impairments become visible on a
DTV receiver, the picture degrades extremely rapidly with further
increases in undesired signal level. This characteristic of DTV receiver
performance is known as the "cliff effect". The interference rejection
thresholds of the tested receivers exhibited a strong "cliff effect". In
most cases, increasing interference level about 1 dB above the TOV
level, at which picture impairments are first observed, caused complete
loss of the TV picture.

### Rejection Performance

No receiver appeared to fully achieve the ATSC recommended guidelines
for interference rejection performance---guidelines that are less
stringent than the receiver performance assumptions on which current DTV
interference protection criteria are based.[^5] After taking into
account differences between the Gaussian-noise interferer used for most
of the tests and the 8-VSB interferer specified by the ATSC, the
best-performing receiver appears to fail the guidelines at only one
channel offset, and there by only 1 dB. A second receiver failed to meet
the voluntary guidelines by 1 to 2 dB at two channel offsets. The
remaining five receivers failed to meet the guidelines at two to 16
channel offsets; the worst failure for each of those receivers ranged
from about 8 to 24 dB.

The rejection performance of the receivers is summarized by plots in the
final chapter of this report. The following observations apply to the
results.

1.  In terms of absolute signal levels that can cause interference, the
    DTV receivers are at their most vulnerable when operating at low
    desired signal levels.

2.  At low desired signal levels the DTV receivers are *as* susceptible
    to interference from the second-adjacent channels (N-2 and N+2) as
    from first-adjacent channels (N-1 and N+1). In terms of worst and
    second-worst performance, the receivers are actually *more*
    susceptible to interference from second-adjacent channels than from
    first-adjacent channels. (This contradicts the assumptions of
    OET-69[^6] and the ATSC Receiver Guidelines.)

3.  The receivers tend to be more susceptible to interference from N+2,
    N+1, N-1, N-2, N-3, N-4, and sometimes N-6 than from the mixer image
    channel offsets of N+14 and N+15.

4.  At moderate desired signal levels, the receivers exhibit relatively
    high susceptibility to interference from channel N+7. This
    interference threshold is nearly constant in terms of absolute power
    of the undesired signal necessary to cause interference at different
    levels of desired signals. At lower desired signal levels, other
    channel offsets become more vulnerable.

## Interference From IM3-Generating Pairs of Undesired Signals

Pairs of undesired signals placed on channels N+K and N+2K, where K is a
positive or negative integer, create an opportunity for ***third-order
intermodulation (IM3)*** occurring in the DTV tuner to create spectral
products that fall in the desired channel N. These spectral products can
interfere with TV reception. Though the D/U ratios associated with
paired-signal IM3 effects tend to decrease as the desired signal
decreases, the test results show that IM3 can constitute a dominant
interference mechanism even at desired signal levels very near the
minimum signal threshold for the TV (D~MIN~).

Measurements of interference thresholds were performed with
equal-powered undesired signals on N+K/N+2K combinations for eight TVs
on channel 30 and seven TVs on channel 51. Tests were performed for K =
-5 to 5 when N was 30 and for K = 1 to 8 when N was 51. In both sets of
tests, the desired signal levels were -68 dBm and -53 dBm. Not all
measured cases produced interference effects that were sufficiently
higher than the single-channel effects to allow isolation of the IM3
effects. For those that did, a third-order intercept point (IP3) was
computed.

The IP3 data was used to predict paired-signal IM3 interference effects
at lower *desired* signal levels than the measurements and at *unequal*
*undesired* signal levels---predictions that were tested by measuring
two receivers using unequal undesired signals. The results show that
when such signal pairs occur, they represent the dominant interference
mechanism for channel offsets from about N+4 to N+16 (with the exception
of the mixer image at N+14 and N+15) and from about N-5 to N-10. For
spacings close to channel N (*e.g.*, N+/-1 and N+/-2), the paired-signal
effects appear less likely to dominate---at least if the pair has equal
power levels. No paired signal measurements were performed beyond N+16
and N-10, so it is not know how far out the effect continues; however,
the effect is seen to diminish with increasing channel offset from the
desired channel.

Paired signals at IM3-generating spacings have the potential to create
even greater interference susceptibilities if an existing undesired
signal on one of the IM3-generating channels (*e.g.*, a nearby DTV
broadcast station when the receiver is tuned to a more distant station)
exceeds the measured equal-power-level threshold for paired signals. In
such a case, the presence of that signal can greatly increase
susceptibility to interference on the other channel of the
IM3-generating pair. This situation generally creates the greatest
vulnerabilities when the stronger undesired signal is on channel N+K and
it exceeds the equal-power paired-signal threshold; in that case, the
receiver susceptibility to interference on the N+2K channel increases by
twice the N+K signal excess above the equal-power threshold (in dB).

The ATSC Receiver Guidelines document (A/74) provides no recommended
performance levels for rejection of paired-signal interference.

# ** **INTRODUCTION

This report presents the results of laboratory tests of consumer digital
television (DTV) receivers to determine:

1.  Tuner type (*e.g.*, single conversion); and

2.  UHF out-of-channel interference rejection thresholds at the antenna
    input terminal of the receiver.

The term, "out-of-channel" interference, as used in this report,
includes any interference occurring outside of the 6‑MHz width of the TV
channel to which the receiver is tuned. Thus, it includes:
first-adjacent channels; "taboo" channels associated with analog TV
(*i.e.*, TV channels more than one channel away from the desired channel
at specific channel spacings associated with interference
vulnerabilities of analog TV); other TV channels; and interference from
sources outside of spectrum allocated to broadcast TV.

The tuner type tests were performed on 30 consumer DTV receivers---29 of
which were on the market in mid-to-late 2005 and the other of which was
procured in 2006. 28 of the receivers had been subjected to other
terrestrial reception performance testing during an earlier program
conducted as part of the Commission's compliance with the Satellite Home
Viewer Extension and Reauthorization Act of 2004 (SHVERA).[^7]

Extensive interference rejection tests were performed on eight of the
receivers. Limited interference rejection testing was performed on two
other receivers as part of the tuner type tests.

## Background

The ability of television receivers to operate in the presence of
interference is an important factor in determining whether consumers can
receive TV broadcast service. It is generally recognized that the ATSC
DTV system (also known as 8-VSB)[^8] used for terrestrial broadcast
digital TV in the United States is less susceptible to interference than
the NTSC analog TV system that it is replacing. This increased
robustness has enabled a relaxation of the "taboo" rules that govern
channel spacings of broadcast television stations in a local
area---allowing part of the spectrum formerly assigned for broadcast TV
use (UHF channels 52 through 69) to be made available for other uses
after the completion of the DTV transition.

The Federal Communications Commission's (FCC) rules that are intended to
prevent interference to broadcast DTV reception[^9] are based on the
interference rejection performance of the so-called "Grand Alliance" DTV
prototype receiver. These rules define the interference protection
afforded to broadcast TV stations, and receiver manufacturers are
expected to consider the signal protection ratios in the rules when
designing their TV receiver products. While the prototype DTV receiver
used a double-conversion tuner configuration, some authors have surmised
that many modern consumer DTVs employ single-conversion tuners that may
be more susceptible to out-of-channel interference at some frequencies
than a double-conversion tuner.[^10][^11] In addition, other design
differences between the "Grand Alliance" prototype DTV receiver and
today's consumer receivers could potentially affect the degree of a
receiver's ability to reject out-of-channel interference.

Interference can be broadly divided into two categories:

1.  Co-channel interference; and,

2.  Out-of-channel interference.

Co-channel interference results from undesired emissions at frequencies
within the channel that a television receiver is currently attempting to
receive. Out-of-channel interference results from emissions occurring in
a frequency range outside that of the TV channel to which the receiver
is tuned. Out-of-channel emissions may come from another TV broadcast or
a non-TV source.

### Co-Channel Interference Rejection

Tests conducted by the FCC Laboratory in 2005 on 28 consumer DTV
receivers demonstrated that the receivers differ very little in their
immunity to broadband *[co-channel]{.underline}* interference. In those
tests, receivers were found to produce pictures that were free of visual
errors when the TV signal power exceeded broadband interference power
within the same TV channel by a threshold ranging from 14.9 to 15.8 dB,
with the median threshold being 15.3 dB.[^12] These results closely
match the 15.2 dB threshold of the Grand Alliance receiver.[^13]

The small variation of co-channel interference rejection performance
among the receivers and the close match to the older Grand Alliance
results are in line with the expectation that co-channel interference
rejection threshold is determined primarily by the structure of the ATSC
DTV signal format adopted by the FCC.

### Out-of-Channel Interference Rejection

Unlike co-channel interference rejection, out-of-channel interference
rejection of a DTV receiver is expected to depend heavily on receiver
characteristics, such as tuner selectivity, tuner image performance,
automatic gain control (AGC) implementation, and tuner overload
characteristics.

Because of this dependence on receiver characteristics and because
modern consumer DTV receivers may differ substantially in design from
the Grand Alliance receiver, new measurements are required to
characterize out-of-channel interference rejection of today's DTV
receivers.

## Objectives

The DTV receiver measurements described in this report are intended to
support assessments of interference to DTV reception from:

4.  non-TV use of locally-unused spectrum within the TV broadcast
    spectrum, which is also often termed "white-space" use;

5.  non-TV use of spectrum adjacent to or near TV broadcast spectrum
    (*e.g.*, the TV channel 52 to 67 spectrum that will be auctioned for
    other uses); and,

6.  other DTV stations.

The results also enable evaluation of the degree to which consumer DTV
receivers comply with the voluntary standards contained in the receiver
standards document, "ATSC Recommended Practice: Receiver Performance
Guidelines"[^14]

A device that transmits radio energy on an otherwise unused TV channel
(or in spectrum adjacent to a TV band) can interfere with DTV reception
in one of two ways, or in a combination of the two:

\(1\) The radio energy it creates in its intended band of operation may
impact the DTV receiver through various receiver vulnerabilities caused
by nonlinearities in the receiver, mixer images, or other mechanisms;

\(2\) The device may unintentionally "splatter" enough energy into the
channel to which the DTV receiver is tuned to interfere with TV
operation.

The first of these ways is true out-of-channel interference; the second
is a form of co-channel interference. Given that either of these
factors---or a combination thereof---could determine interference
rejection performance, one way to test DTV receivers would be to subject
them to simulated interferers that contain both an intended emission on
a channel outside of the desired channel and spectral splatter into the
desired channel. The resulting interference performance measurements
would reflect the combination of the two interference effects. However,
given that there is debate within the technical community regarding both
the intended emissions and the out-of-band (*e.g.*, spurious) emissions
for devices operating in the "white spaces", we believe it is
appropriate to deal with these two types of interference separately. As
was stated in the previous section, co-channel interference is
relatively well understood and relatively constant among ATSC DTV
receivers compared to out-of-channel interference; consequently, we
chose to measure only true out-of-channel interference in this study. As
such, we applied filtering to the outputs of out-of-channel signal
sources used in the tests in order to reduce their spectral splatter
into the desired channel to negligible levels.

It should be noted that this study characterizes susceptibility of
consumer DTVs to interference in terms of signal and interference levels
appearing *[at the antenna input terminal]{.underline}* of the receiver.
Assessments of potential for interference to DTV reception will require
additional analysis involving specific protection scenarios,[^15]
propagation modeling, and antenna modeling, which are beyond the scope
of the study.

## Measurement Program

The tests were performed on subsets of the 28 DTV receivers that had
been tested in 2005 in support of the *Satellite Home Viewer Extension
and Reauthorization Act of 2004 (SHVERA)*.[^16] An additional receiver
that was received too late for inclusion in that study, as well as one
that was purchased in 2006, were also tested, bringing the total to 30
receivers. Five of the 30 receivers were set top DTV tuners. The
remaining 25 were DTVs with integrated digital tuners.

The measurement program described here consisted broadly of two parts:
(1) tuner type characterization; (2) interference rejection threshold
tests.

[Tuner type characterization]{.underline} was intended to identify tuner
topology used in consumer DTV receivers. The first phase of these tests
involved searching for a local oscillator (LO) signal at the antenna
inputs of each of the 30 DTV receivers while switching between two
channels. The tests demonstrated that at least 28 of the 30 receivers
use single-conversion tuners with an intermediate frequency (IF) of 44
MHz. For the two receivers that produced inconclusive results in the LO
tests, interference rejection tests were used to identify any
interference susceptibilities that would be a "signature" of
single-conversion receivers with 44-MHz IF. Those two receivers were
also determined to use single-conversion tuners.

[Interference rejection threshold testing]{.underline} consists of
measuring the maximum signal level at which an undesired (*i.e.*,
interfering) signal can be injected into the TV receiver's antenna input
without adversely affecting TV reception of a "desired" signal. The
behavior of DTV signal reception in this regard differs considerably
from that of analog TV reception. The DTV broadcast system can achieve
flawless picture reception under interference conditions that would
produce an unusable picture for analog broadcast TV; however, once an
undesired signal reaches a level at which picture impairments become
visible on a DTV receiver, the picture degrades extremely rapidly with
further increases in undesired signal level---typically going from
barely perceptible picture impairments to complete loss of picture with
a span of about 1 dB. Similar degradation of analog reception occurs
over a span as large as 30 dB, a difference that emphasizes the
importance of these measurements for DTV.

Because of the number of variables involved in interference rejection
testing, measurements were performed on only ten DTV receivers. Seven of
these included one of each brand selected from among receivers
exhibiting "fifth-generation" DTV demodulator performance in the SHVERA
Study. An eighth TV was procured in 2006. The remaining two, on which
only limited interference rejection testing was performed, were the two
receivers for which the LO tests were inconclusive.

Initial focus of the work reported herein was on the immunity of the
receivers to interference from future radio services that will operate
in the channel 52 to 67 spectrum after completion of the DTV transition.
Consequently, the initial tests were performed with the receivers tuned
to channel 51 and interference placed on channels 52 through 67.
Subsequent measurements, focused on the white-space use of the TV
spectrum, were performed with the receivers tuned to channel 30---near
the center of the UHF core TV spectrum---with interferers placed both
above and below channel 30.

Interfering sources used for most of the testing included an ATSC 8-VSB
DTV signal and a pseudo-random Gaussian noise signal bandlimited to the
same spectral width as a DTV signal (5.38 MHz, 3-dB width). Except for
the small pilot tone of the DTV signal, both signals exhibit noise-like
signal characteristics and relatively flat spectra similar to those of
most modern communication systems using digital modulation. A few tests
were performed using an OFDM signal and using a narrower width Gaussian
noise signal, for comparison.

In accordance with standard industry practice, the interference
rejection threshold of the receiver is expressed as the ratio of desired
signal power to undesired signal power (***D/U ratio***) at the
threshold of visibility (TOV) of degradation of the TV picture. For a
few interference mechanisms, the threshold D/U ratio remains constant as
the desired signal level is varied except at low signal levels, but many
other mechanisms are non-linear, resulting in variable D/U ratios that
are further affected by the receiver's automatic gain control (AGC) in a
way that is not predictable without a detailed knowledge of the design
of the each receiver; consequently, measurements were performed at
multiple desired signal power levels.

Interference rejection thresholds are also a function of the frequency
spacing between the desired TV signal and the undesired interfering
signal. Single-conversion TV receivers are known to exhibit interference
susceptibilities up to 90 MHz (15 TV channel widths) from the desired TV
channel;[^17] consequently, measurements with single interferers were
performed at various frequency spacings within, and just beyond, this
range.

In addition, pairs of interfering signals at particular spacings can be
expected to create interference through non-linear effects in a TV
tuner; consequently, some tests were performed using pairs of
interferers spaced at intervals that could cause third-order
intermodulation distortion to fall in the desired channel.

## Overview

Chapter 2 of this report describes the scope of the test program and the
general testing approach.

Chapter 3 describes the tests performed to determine DTV tuner type
(single conversion versus double conversion or other types) and the
results of those tests.

All remaining chapters deal with interference rejection performance of
the DTV receivers, as described below.

Chapter 4 describes the test methodology employed for interference
testing, the performance of the test setup, and some reference values
for rejection performance from other documents.

Chapter 5 presents the results of rejection performance measurements on
eight DTV receivers tuned to channel 30 (N=30) for a single undesired
signal placed on each of the channels from N-1 to N-16 and N+1 to N+16
The undesired signal was an 8-VSB signal for channels N-1 and N+1 and a
white Gaussian noise signal bandlimited to match the 3-dB width of an
8-VSB signal for all other channels. The desired signal power levels for
these tests were -28 dBm, -53 dBm, -68 dBm, and D~MIN~ +3 dB, where
**D~MIN~** refers to the individually measured threshold for each
receiver when operated without interference.

Chapter 6 presents results of rejection performance measurements on
seven DTV receivers (a subset of the eight) tuned to channel 51 (N=51)
for a single undesired 8-VSB signal placed on each of the channels from
N+1 to N+16. The desired signal power levels for these tests were -28
dBm, -53 dBm, and ‑68 dBm.

Chapter 7 presents the results of measurements of the differences in
interference effects of four undesired signal types:

1.  White Gaussian noise bandlimited to the 3-dB width of an 8-VSB
    source;

2.  8-VSB;

3.  DVB-H---an orthogonal frequency division multiplexing (OFDM)
    signal---set for a 5-MHz channel width; and

4.  White Gaussian noise bandlimited to a 3-dB width of 1 MHz.

The chapter also presents the effects of signal quality differences of
two different 8-VSB signal generators that served as the desired source.

Chapter 8 presents a theoretical framework that aids in interpreting and
extending the out-of-channel interference measurements.

Chapter 9 presents the results of interference rejection measurements
performed using equal-power pairs of undesired signals spaced so as to
place third-order intermodulation (IM3) products in the desired channel.
The tests were performed on eight DTV receivers tuned to channel 30 and
seven DTVs tuned to channel 51. Undesired signals were placed at channel
pairs N+K/N+2K for K = -1 through -5 and +1 through +5 for channel 30
and K = 1 through 8 for channel 51. The undesired sources were the same
as those described for Chapters 5 and 6. Values of a third-order
intercept parameter (IP3) were estimated based on some of the
measurements.

Chapter 10 presents interference rejection measurements on two receivers
(one N+K/N+2K channel offset pair for each) using a pair of undesired
signals of *unequal* amplitudes. It also presents a model that is then
used to make predictions regarding interference rejection performance of
the other tested DTV receivers for unequal, paired undesired signals.
The model makes use of measurements from Chapters 5 and 9.

Chapter 11 presents measurements of rejection performance for one DTV
receiver over a wide, finely-stepped desired-signal amplitude range. The
tests included single interferers, as well as paired interferers spaced
to place IM3 products in the desired signal channel. The measurements
provide insight into the behavior of interference susceptibilities
including their nonlinearities and the effects of receiver AGC.

Chapter 12 extrapolates the channel-30, single-channel interference
rejection measurements from Chapter 5 of this report to a lower desired
signal level, D~MIN~ + 1 dB. It also employs measured data from Chapter
11 to evaluate the extrapolation method.

Chapter 13 combines the single-channel rejection performance
*measurements* of the eight DTV receivers on channel 30 from Chapter 5
(at D = -28 dBm, -53 dBm, ‑68 dBm, and D~MIN~ + 3 dB) with the
*extrapolations* of Chapter 12 (to D = D~MIN~ + 1 dB) to present
combined results.

Chapter 14 presents the results of tests and analyses performed to
validate the test methodology and test setup used for the measurements
in this report. (Direct measurements of test setup performance are shown
in Chapter 4.)

Chapter 15 presents the summary and conclusions. It also includes new
graphs that integrate the results of some of the other chapters in terms
of median, 2^nd^ worst, and worst performance among the eight receivers.

#  SCOPE AND APPROACH

## Scope of Testing

Two types of tests were performed on DTV receivers in the measurement
program reported herein: (1) frequency measurements of tuner local
oscillator (LO) signals leaking out of the TV receiver antenna terminal;
(2) signal levels of desired and undesired signals at the TV receiver
antenna port with the undesired signal set to the threshold of
visibility (TOV) of degradation of the received TV picture.

Measurements of the LO, where possible, serve to characterize the type
of receiver (single or double conversion) and intermediate frequency
(IF) for single conversion receivers.

The signal level measurements at TOV quantify the immunity of the
receiver to out-of-channel interference and also can be used to aid in
characterizing receiver type when LO leakage is not measurable. These
results are expressed as interference rejection ratio threshold---the
ratio of desired signal power to undesired (interfering) signal power
(D/U ratio) at TOV.

### Interfering Signal Types

The objectives of the testing were to generate data that could be used
to assess potential interference to DTV by future devices operating in
TV white spaces, future services operating in channels 52 through 67
after the completion of the DTV transition, and other DTV signals.
Ideally, measurements would have been performed using each potential
type of interfering signal; however, white-space devices and signals to
be transmitted in channels 52 through 67 are not fully defined, and,
even if representative devices had been available, the number of tests
would have been prohibitive.

Most modern digital communications systems produce signals that are
somewhat noise-like. The spectra are often flat over most of their
channel width; they have relatively high peak-to-average ratios and peak
levels that are random, rather than fixed---as in the case of most
analog transmissions. A growing number of digital systems are using
orthogonal-frequency-division-multiplexing (OFDM) signals. Both the
8-VSB DTV signal used for broadcast DTV in the United States and OFDM
signals share these noise-like, flat-spectrum characteristics (except
for the 8-VSB pilot).

We initially expected that bandlimited white noise, 8-VSB DTV signals,
and OFDM signals of equal bandwidths would be likely to exhibit similar
interference effects on DTV reception. (Later, testing described in
Chapter 7 caused a small adjustment to this expectation.) Initial
single-interferer testing was performed using an 8-VSB DTV signal as the
interferer and TV receivers tuned to channel 51. For tests with pairs of
interferers to create intermodulation distortion within the TV
receivers, a Gaussian noise generator---bandlimited to the same 3-dB
width as an 8-VSB signal---was used as the second interferer because an
additional 8-VSB source was not available. The measurements on channel
51 were terminated after failure of the 8-VSB source that had been used
as an interferer.

All further tests were performed with the TV receivers tuned to channel
30 because of the change in focus of the project from interference
effects of services in channel 52 through 69 to interference effects of
white-space devices, which would be limited to VHF and core UHF
channels. Channel 30 was selected for testing because it is a
locally-unused channel near the center of the core UHF band.

The testing with TV receivers tuned to channel 30 was initiated using a
Gaussian noise generator---bandlimited to the 3-dB width of an 8-VSB
signal---as the interferer, because the only available 8‑VSB source was
being used to generate the desired signal. For intermodulation tests,
two such signal sources were used as interferers. The bandlimited
Gaussian noise sources did not exhibit a band-edge rolloff steep enough
to support tests of interference on first-adjacent-channels (*i.e.*, N-1
or N+1 when the TV is tuned to channel N); consequently, first adjacent
channel tests were postponed until a new 8-VSB DTV signal source was
procured. That source, which arrived late in the test program, was then
used for all tests on first-adjacent channels for N=30.

A limited number of tests were performed to compare the interference
results of four interferer types:

\(1\) 8-VSB DTV signal;

\(2\) Gaussian noise bandlimited to match the 3-dB width of an 8-VSB
signal;

\(3\) an OFDM DVB-H signal; and

\(4\) Gaussian noise bandlimited to a 3-dB width of 1 MHz.

The OFDM DVB-H signal was generated using a commercial software package
for a vector signal generator with parameters set for a 2k OFDM signal
with 5-MHz channel width and 64 QAM modulation.

Figures 2-1 and 2-2 show measured spectra of the four interferers at
equal total power levels. Table 2‑1 shows bandwidths of each signal.

[]{#__RefHeading___Toc163024559 .anchor}Table 2‑1. Measured Bandwidths
of Undesired Signal Sources

  ------------------------------- ------------------- --------------------
  **Signal**                      **3-dB Bandwidth    **20-dB Bandwidth
                                  (MHz)**             (MHz)**

  8-VSB (Bandwidths, neglecting   5.38                5.90
  pilot)                                              

  Gaussian noise (8-VSB width)    5.38                6.32

  Gaussian noise (1-MHz width)    1.00                1.18

  OFDM DVB-H                      4.76                4.80
  ------------------------------- ------------------- --------------------

### Desired Signal Levels

The ATSC specifies guidelines for interference rejection performance of
DTV receivers at three desired signal levels: -68 dBm, -53 dBm, and -28
dBm, which they designate as "weak", "moderate", and "strong",
respectively. Our initial intent was to test only at these three signal
levels; however, after tests demonstrated that D/U rejection ratios are
by no means constant as a function of desired signal power, a decision
was made to extend the measurements to a lower level that was receiver
dependent.

The motivation for the tests at lower desired signal levels, near
D~MIN~, can be seen in Figure 2‑3 and Table 2-2, both of which show the
relationship of desired signal levels to broadcast coverage area with
flat terrain.[^18] The computations are based on the Egli propagation
model,[^19] which has propagation loss proportional to the fourth power
of distance. If we view the outer boundary of a broadcast station's
coverage area to be determined by the point at which consistent
reception is just barely possible with a given receiver and antenna
system (*i.e.*, no signal margin remains after normal amplitude
variations of the signal due to fading), then the signal margin will be
less than 1 dB in the outer 11 percent of the coverage area. Similarly,
the outer 29 percent of the coverage area has less than 3 dB of margin,
and fully 84 percent of the coverage area would experience lower signal
levels than the ATSC-designated "weak" signal level of -68 dBm (where
the excess signal is nominally 16 dB).[^20]

Given the above analysis and the increased vulnerability to interference
when the desired signal levels are low, a decision was made to extend
the results---through both measurement and extrapolation---to signal
levels close to the DTV receiver thresholds. Specifically, the desired
signal threshold (D~MIN~) for each TV was measured in the absence of
interference. Interference rejection tests were then conducted at a
desired signal level 3 dB higher than this threshold---*i.e.*, at
D = D~MIN~ + 3 dB. In addition, analytical work was performed to
extrapolate the test results down to a desired signal level of D~MIN~ +
1 dB.

[]{#__RefHeading___Toc163024560 .anchor}Table 2‑2. Relationship Between
Excess Signal and Coverage Area

  ------------------ ------------- ---------------------------------------
  Excess Signal (dB) R/R~MAX~      Percentage of Coverage Area Having Less
                                   Excess Signal Than That Shown

  0                  1             0%

  1                  0.94          11%

  3                  0.84          29%

  10                 0.56          68%

  16                 0.40          84%
  ------------------ ------------- ---------------------------------------

> R = range from the broadcast antenna to the TV reception antenna;
>
> R~MAX~ = R at the edge of coverage

### TV Receiver Samples

A total of 30 receivers were available for this test program. One TV was
procured in 2006 and 29 were provided by the manufacturers for the
Congressionally-mandated 2005 SHVERA Study (though only 28 had arrived
in time to be included in that study). The 29 receivers from the SHVERA
Study had been selected to be representative of consumer DTV receivers
that were on the market in the summer of 2005. Five of the receivers
were set top boxes and 25, including the one procured in 2006, were DTVs
with built-in digital ATSC tuners. The DTV receivers comprise 16 brand
names and a wide range of prices, sizes, and display technologies, as
shown in Table 2-3.

All 30 receivers were tested to determine tuner type. Local oscillator
sensing was sufficient to identify all but two of the receivers as
having single-conversion tuners with 44-MHz IF. The remaining two were
subjected to limited interference rejection performance tests to look
for signatures of single-conversion tuners. Such signatures were found
in both receivers.

Because of the complexity of interference testing, only eight of the
receivers were selected for interference rejection tests (beyond the
limited testing on two receivers mentioned in the preceding paragraph).
The selection process was as follows. Of the 28 receivers that had been
tested in the SHVERA Study, only ten had been found to exhibit "upper
tier" (or "fifth generation") multipath performance. Those ten, which
were among the more recently introduced receivers used for the SHVERA
Study[^21], along with the receiver procured in 2006 (which also
exhibited "upper tier" multipath performance), were taken to be
representative of the new generation receiver technology. The eleven
comprised eight brands of receivers. All were DTVs (*i.e.*, none were
set top boxes).[^22] One receiver of each brand from among the
eleven---a total of eight receivers---was selected for interference
rejection testing. The eight included receivers from all price ranges.

Specific receivers are identified in both this report and the SHVERA
Study by two-character codes---a letter followed by a number---in order
to avoid revealing specific brands or models. Additional information
regarding the samples can be found in the SHVERA Study.[^23]

[]{#__RefHeading___Toc163024561 .anchor}Table 2‑3. DTV Receiver Samples

+---------------+--------+--------+--------+---------+----------------+
| **Sample      | **     |        | **D    | **      | **Display      |
| Type**        | Number |        | isplay | Display | T              |
|               | of     |        | Size** | Aspect  | echnology^A^** |
|               | Sam    |        |        | Ratio** |                |
|               | ples** |        |        |         |                |
+---------------+--------+--------+--------+---------+----------------+
|               | **LO   | **Rej  |        |         |                |
|               | T      | ection |        |         |                |
|               | ests** | T      |        |         |                |
|               |        | ests** |        |         |                |
+---------------+--------+--------+--------+---------+----------------+
| **Set-Top Box | 5      | 0      | N/A    | N/A     | N/A            |
| (STB)**       |        |        |        |         |                |
+---------------+--------+--------+--------+---------+----------------+
| **DTV with    |        |        |        |         |                |
| Integrated    |        |        |        |         |                |
| ATSC Digital  |        |        |        |         |                |
| Tu            |        |        |        |         |                |
| ner**^B^**:** |        |        |        |         |                |
+---------------+--------+--------+--------+---------+----------------+
| 1.  \$370 -   | 7      | 2      | 26" -- | 4:3 or  | Direct-View    |
|     \$1000    |        |        | 36"    | 16:9    | CRT            |
+---------------+--------+--------+--------+---------+----------------+
| 2.  \$1001 -  | 8      | 2+1^C^ | 26" -- | 16:9    | Direct-View    |
|     \$2000    |        |        | 52"    |         | LCD,           |
|               |        |        |        |         |                |
|               |        |        |        |         | Plasma,        |
|               |        |        |        |         |                |
|               |        |        |        |         | CRT Rear       |
|               |        |        |        |         | Projection,    |
|               |        |        |        |         |                |
|               |        |        |        |         | DLP Rear       |
|               |        |        |        |         | Projection,    |
|               |        |        |        |         |                |
|               |        |        |        |         | LCD Rear       |
|               |        |        |        |         | Projection     |
+---------------+--------+--------+--------+---------+----------------+
| 3.  \$2001 -  | 10     | 4+1^C^ | 32" -- | 16:9    | Direct-View    |
|     \$4200    |        |        | 62"    |         | LCD,           |
|               |        |        |        |         |                |
|               |        |        |        |         | Plasma,        |
|               |        |        |        |         |                |
|               |        |        |        |         | DLP Rear       |
|               |        |        |        |         | Projection,    |
|               |        |        |        |         |                |
|               |        |        |        |         | LCD Rear       |
|               |        |        |        |         | Projection     |
+---------------+--------+--------+--------+---------+----------------+
| **TOTAL**     | **30** | **8+   |        |         |                |
|               |        | 2^C^** |        |         |                |
+---------------+--------+--------+--------+---------+----------------+

*Note:*

*A -- Display Technologies*

1.  *CRT = cathode ray tube (conventional picture tube)*

2.  *DLP = digital light processing*

3.  *LCD = liquid crystal display*

*B \-- Prices shown are market prices in August or September 2005.*

*C -- 1^st^ number represents receivers selected for test based on
having "upper-tier" DTV demodulator performance; 2^nd^ number represents
receivers tested to characterize receiver type where LO tests were
inconclusive.*

## Interference Rejection Testing Approach

### TV Channel Selection

Initial tests were performed with TV receivers tuned to channel 51 and
interferers placed on channels 52 through 67 in order to provide data on
the receivers' ability to reject interference from services that may
operate in the spectrum of channels 52 through 67 after the DTV
transition is complete.

Subsequent testing was performed with TVs tuned to channel 30, to
represent performance near the middle of the UHF core band.

In order to provide comparative data using a different test method, one
set of tests was performed with the interfering source fixed at channel
29 and the TV receiver tuned to various channels from 14 to 37.

### Filtering of Undesired Signals

DTV interference rejection testing requires extremely high suppression
of out-of-band emissions from the undesired signal that might otherwise
spill into the desired channel. Available signal generators do not
provide sufficient suppression.

The conventional approach to dealing with this issue is to place a
bandpass filter around the *undesired* signal. In that approach the
undesired signal is typically placed on a fixed channel so that a fixed
filter can be used. The desired signal and the TV tuner are then
switched to various channels to achieve the channel-spacings to be
tested.

For this report a different approach was taken to the problem. The
desired channel was fixed and the undesired channel was varied. A fixed
band-reject filter was used to suppress the out-of-band emissions of the
undesired signal that fell *within the desired channel*. The details of
the technique are provided in Chapter 4. Tests using the conventional
approach are reported in Chapter 14 for comparison.

### Operation and Connection of Samples

For receivers having multiple antenna inputs that could handle ATSC
signals, only the input labeled "antenna A" or "antenna 1" was tested.
For receivers having a radio frequency (RF) output associated with the
selected antenna input, the output was externally terminated in 75 ohms.

Only one TV was turned on during any given test in order to avoid
possible interference from emissions of other TV receivers.

### Identifying Interference Rejection Thresholds

In determining interference thresholds, we are interested in picture
degradation that is visible to the TV viewer. With digital television,
some data transmission errors are fully corrected by error correction
algorithms---resulting in no errors in the video transport stream data.
Other transmission errors that cannot be corrected may, in some cases,
be effectively masked by error concealment techniques used in the
receiver's video processor. We are only interested in picture errors
that will be perceived by the viewer. The subjectivity of visual error
detection could be eliminated through relationships that have been
established between visible TOV and bit-error-rate (BER); however, such
techniques cannot be applied in testing of consumer DTV receivers that
do not provide access to bit streams; consequently, thresholds for this
report were determined by visual observation of DTV pictures.

In all interference rejection tests, the level of the desired signal D
was adjusted as closely as possible to the intended value by using a
step attenuator operating in 0.1‑dB steps. The level of the undesired
(interfering) signal was then adjusted upward until picture errors were
easily observed within a few seconds. That level was then backed off and
readjusted in 0.1‑dB steps to determine the minimum undesired signal
level at which one or more visible picture errors occurred in two
consecutive 30-second intervals. The power level of the undesired signal
was then measured and this level was identified as the undesired power
level U at TOV---except in rare cases as described below.

The thresholds exhibited a strong "cliff effect". In most cases, the
increasing interference level about 1 dB above the TOV level identified
by the method above caused complete loss of picture. In some cases,
picture loss did not occur until the undesired signal level rose as much
as much as 3 dB and in one case, 5 dB. In a few cases, picture loss
occurred concurrently with the appearance of errors or with only an
additional 0.1 dB increase in interference---an extremely abrupt cliff!

When the picture was lost due to high interference levels, it was
recovered in most cases by reducing the undesired signal level back to
the TOV level that was identified by the procedure described above,
though in some cases that recovery took 20-seconds or more. In a few
cases, it was observed that---after loss of picture due to either high
interference levels or a channel change---the TV was unable to
re-establish a picture without reducing the undesired signal level a few
tenths of a dB below the apparent TOV point. In such cases, the
threshold was rerecorded as one 0.1-dB step above the level necessary to
permit picture recovery. (*i.e.*, inability to recover the picture was
treated as an error.)

D/U ratios were computed based on the actual measured value of the
desired signal D rather than on the intended setting of D (though the
difference was generally less than 0.05 dB).

### Signal Power Measurements

All measurements of desired and undesired power levels were made by
means of the band power integration function of a spectrum analyzer that
was set to perform an RMS average of spectrum traces. The number of
points in the spectrum sweep was set so that bin spacing matched the 30
kHz resolution bandwidth used for the measurements. The spectrum
analyzer's internal preamp was used to ensure a sufficiently low
instrumentation noise level (approximately -98 dBm in 6-MHz bandwidth +
analyzer attenuation). The analyzer was used in the automatic
attenuation mode with the reference level set to the lowest multiple of
5 dBm that was at least 1 dB above the total signal power. In cases
where power levels below -70 dB were to be measured, the analyzer
attenuation was manually set to 0 dB. For measurements below -78 dBm
(measurements of desired signal level at or near the receiver
threshold), analyzer noise was measured separately and subtracted---in
linear power units---from the measured values.

## Presentation of Results

Interference *rejection performance* measurements on TV receivers are
typically presented in terms of the ratio of desired to undesired signal
powers (D/U) at TOV. *Protection criteria* designed to prevent
interference are sometimes specified in terms of D/U ratios and at other
times specified as absolute signal levels (*e.g.*, of transmit power or
field strength) permitted in a band.

D/U rejection ratios would provide a particularly useful
characterization of interference rejection performance of a receiver if
those rejection ratios remained constant as signal levels were varied.
Unfortunately, we found this not to be the case for DTV receivers.
Interference at many channel offsets is driven by nonlinear mechanisms
that cause D/U to increase with increasing signal levels; such
variability is particularly common at low desired signal levels where a
TV is most susceptible to interference.[^24] Even for linear
interference mechanisms, D/U increases as the desired signal level
approaches D~MIN~ for a receiver.

Since D/U rejection ratios of DTV receivers are not constant,
interference assessment requires knowledge of the *absolute levels* of
desired and undesired signals at the input to the receiver rather than
just a knowledge of the *ratio* of the signal powers. But, the absolute
signal levels at the input to a DTV receiver can vary widely depending
on the gain, height, or indoor-versus-outdoor placement of the antenna
to which it is attached. Table 2-4 shows UHF reception examples for
three different antenna systems:

1.  An outdoor antenna system with a mast-mounted preamp sufficient to
    overcome downlead loss;

2.  An outdoor antenna system according to OET-69 planning factors;

3.  A low-gain, indoor antenna.

The table shows that the signal level at the TV's RF input can easily
vary over a 26-dB range simply by changing from an indoor antenna to an
outdoor, mast-mounted antenna.[^25] The span can be even wider (30‑dB or
more) if a mast-mounted preamp is used to minimize the effect of
downlead attenuation.

Knowledge of the receive antenna system and deployment (*e.g.*, indoor
versus outdoor) used by a given TV receiver is not generally available
to an outside entity, whether that entity is a smart-radio device
transmitting in locally unused TV spectrum or an analyst assessing
potential for interference between two DTV broadcast stations. Even if a
potential interferer to DTV reception had access to complete, accurate
information regarding desired and undesired signal field strengths in a
given DTV reception area, there would be no way to know where within a
30-dB signal level span that a given DTV receiver is operating without
knowing the gain, height, or indoor-versus-outdoor placement of its
antenna. Thus, for example, a given receiver could be operating with a
1-dB signal margin (at D = D~MIN~ + 1 dB, or about ‑83 dBm) or at the
ATSC "moderate" signal level (D = -53 dBm), based only on changes in the
antenna system.

[]{#__RefHeading___Toc163024562 .anchor}Table 2‑4. UHF Reception
Examples

  ------------------------------------- ---------------- ------------ ---------------
                                        **Outdoor        **Outdoor    **Indoor
                                        Reception        Reception    Reception (Low
                                        w/Mast-Mounted   (OET-69)**   Gain
                                        Preamp^1^**                   Antenna)^2^**

  Antenna gain (dBd)                    10               10           0.0

  Downlead loss (dB)                    0                4            0.6

  Antenna height (m)                    10               10           2.0

  Relative field strength due to height 0                0            -14.0
  difference (dB)^3^                                                  

  Building loss (dB)^4^                 0                0            5.0

  **Relative signal level at input to   **10**           **6**        **-19.6**
  TV (dB)**                                                           
  ------------------------------------- ---------------- ------------ ---------------

*Notes*

*^1^ Mast-mounted preamp is assumed to have gain sufficient to overcome
downlead loss.*

*^2^ Downlead loss for indoor antenna is based on 2 meters of RG-59 at
573 MHz (geometric mean frequency between channel 14 and channel 51).*

*^3^ Signal-strength dependence on height is based on the Egli
propagation model, in which received signal power is proportional to the
square of antenna height (Egli, J., "Radiowave propagation above 40 Mc
over irregular terrain", Proceedings of the IRE, Vol. 45, Oct. 1957,
pp.1383-1391)*

*^4^ Building loss attenuation shown is intended only as an
example---not as an endorsement of a particular value*

Despite the variation of D/U rejection ratios of TV receivers with
absolute signal amplitudes, the *D/U ratio* formulation is convenient to
use in applications like DTV-into-DTV interference assessment because
estimation of D/U ratios may be easier and more accurate than estimation
of absolute levels where long-distance propagation is
involved---especially if the broadcast stations are co-sited. In such
applications a change in antenna gain, height, or indoor-versus-outdoor
placement are likely to affect the desired and undesired signal levels
in the same way, so that the D/U ratio to which the TV is exposed
remains constant with antenna changes (assuming that the undesired and
desired signal sources both fall within the main response of the TV
directional pattern). The lack of knowledge of the reception antenna
means that interference assessment might have to consider a range of
rejection ratios that are possible for the receiver given the range of
signal levels that could reach the TV RF input from the range of likely
antenna systems to which the potential victim TV receiver might be
attached.

On the other hand, some may find *absolute undesired signal level
thresholds* to be more useful for assessing shorter distance
interference from low-power devices because the effects of TV antenna
height and placement on the undesired signal are likely to be different
from their effects on the desired signal. In such cases, it may be
useful to assess interference by determining the *absolute* level of an
undesired signal that could cause picture degradation under the
assumption that the TV could be operating at a low signal margin.

Because of these differences in approach, this report presents the
interference rejection performance measurements in two ways: as D/U
ratios and as threshold values for the undesired signal level U.[^26]

## Test Summary

Table 2-5 summarizes the tests performed for this report, including
local-oscillator sensing and over 2000 measurements of D/U ratio.

[]{#__RefHeading___Toc163024563 .anchor}Table 2‑5. Summary of Tests

+----------+----+-------+------+---------+---------+---------+------+
| **Test** | ** | **\#  | *    | **Inter | **Int   | **      | **\# |
|          | Ch | of TV | *TV\ | ference | erferer | Desired | of   |
|          | ap | Rece  | T    | Ch      | Type**  | Signal  | D/U  |
|          | -t | ivers | uned | annel** |         | L       | Mea  |
|          | er | Tes   | Chan |         |         | evels** | sure |
|          | ** | ted** | (    |         |         |         | -men |
|          |    |       | N)** |         |         |         | ts** |
+----------+----+-------+------+---------+---------+---------+------+
| **Tuner  |    |       |      |         |         |         |      |
| Type     |    |       |      |         |         |         |      |
| Tests    |    |       |      |         |         |         |      |
| (e.g.,   |    |       |      |         |         |         |      |
| Singl    |    |       |      |         |         |         |      |
| e/Double |    |       |      |         |         |         |      |
| Conve    |    |       |      |         |         |         |      |
| rsion)** |    |       |      |         |         |         |      |
+----------+----+-------+------+---------+---------+---------+------+
| Local-os | 3  | 30\   | 51 & | N/A     | N/A     | N/A     |      |
| cillator |    | (1    | 53   |         |         |         |      |
| (LO)     |    | 1,5^t |      |         |         |         |      |
| sensing  |    | h^-G) |      |         |         |         |      |
+----------+----+-------+------+---------+---------+---------+------+
| Inte     | 3  | 2     | 30   | N+2 to  | WGN\*   | N/A     | 30   |
| rference |    | (     |      | N+16    |         |         |      |
| r        |    | 4^th^ |      |         |         |         |      |
| ejection |    | G or  |      |         |         |         |      |
| when not |    | ear   |      |         |         |         |      |
| resolved |    | lier) |      |         |         |         |      |
| by LO    |    |       |      |         |         |         |      |
| sensing  |    |       |      |         |         |         |      |
+----------+----+-------+------+---------+---------+---------+------+
| **Inte   |    |       |      |         |         |         |      |
| rference |    |       |      |         |         |         |      |
| Re       |    |       |      |         |         |         |      |
| jection- |    |       |      |         |         |         |      |
| --Single |    |       |      |         |         |         |      |
| Inte     |    |       |      |         |         |         |      |
| rferer** |    |       |      |         |         |         |      |
+----------+----+-------+------+---------+---------+---------+------+
| Channel  | 5  | 8     | 30   | N-16 to | 8-VSB:  | D~MIN   | 1024 |
| 30 tests |    | (     |      | N-1,\   | N±1.    | ~+3 dB, |      |
|          |    | 5^th^ |      | N+1 to  |         | ‑68,    |      |
|          |    | G)    |      | N+16    | WGN^1^: | ‑53,    |      |
|          |    |       |      |         | N±2 to  | ‑28 dBm |      |
|          |    |       |      |         | N±16    |         |      |
+----------+----+-------+------+---------+---------+---------+------+
| Ch       | 6  | 7     | 51   | N+1 to  | 8-VSB   | -68,    | 225  |
| annel-51 |    | (     |      | N+16    |         | -53,    |      |
| tests    |    | 5^th^ |      |         |         |         |      |
|          |    | G)    |      |         |         | -28     |      |
|          |    |       |      |         |         |  dBm^2^ |      |
+----------+----+-------+------+---------+---------+---------+------+
| Ch       | 11 | 1     | 51   | N+1 to  | 8-VSB   | D       | 98   |
| annel-51 |    | (     |      | N+7,    |         | ~MIN~+1 |      |
| detailed |    | 5^th^ |      | N+14,   |         | dB,     |      |
| tests of |    | G)    |      | N+15    |         |         |      |
| one TV   |    |       |      |         |         | D       |      |
|          |    |       |      |         |         | ~MIN~+3 |      |
|          |    |       |      |         |         | dB,     |      |
|          |    |       |      |         |         |         |      |
|          |    |       |      |         |         | -78 to  |      |
|          |    |       |      |         |         | ‑8 dBm  |      |
|          |    |       |      |         |         | in 5-dB |      |
|          |    |       |      |         |         | steps   |      |
+----------+----+-------+------+---------+---------+---------+------+
| **Inte   |    |       |      |         |         |         |      |
| rference |    |       |      |         |         |         |      |
| R        |    |       |      |         |         |         |      |
| ejection |    |       |      |         |         |         |      |
| for      |    |       |      |         |         |         |      |
| Paired   |    |       |      |         |         |         |      |
| Signals  |    |       |      |         |         |         |      |
| (3^r     |    |       |      |         |         |         |      |
| d^-Order |    |       |      |         |         |         |      |
| Intermo  |    |       |      |         |         |         |      |
| dulation |    |       |      |         |         |         |      |
| in TV    |    |       |      |         |         |         |      |
| Rec      |    |       |      |         |         |         |      |
| eiver)** |    |       |      |         |         |         |      |
+----------+----+-------+------+---------+---------+---------+------+
| Ch       | 9  | 8     | 30   | N       | 8-VSB   | -68,    | 176  |
| annel-30 |    | (     |      | -5/N-10 | for     | -53,    |      |
| tests    |    | 5^th^ |      | to      | N±1;    | ‑28     |      |
|          |    | G)    |      | N-1/N-2 | WGN^1^  |  dBm^3^ |      |
|          |    |       |      | and     | for all |         |      |
|          |    |       |      | N+1/N+2 | others  |         |      |
|          |    |       |      | to      |         |         |      |
|          |    |       |      | N       |         |         |      |
|          |    |       |      | +5/N+10 |         |         |      |
+----------+----+-------+------+---------+---------+---------+------+
| Ch       | 9  | 7     | 51   | N+1/N+2 | 8-VSB   | -68,    | 162  |
| annel-51 |    | (     |      | to      | for     | -53,    |      |
| tests    |    | 5^th^ |      | N       | N+K;    | ‑28     |      |
|          |    | G)    |      | +8/N+16 | WGN^1^  |  dBm^2^ |      |
|          |    |       |      |         | for     |         |      |
|          |    |       |      |         | N+2K    |         |      |
+----------+----+-------+------+---------+---------+---------+------+
| Ch       | 11 | 1     | 51   | N+1/N+2 | 8-VSB   | D       | 57   |
| annel-51 |    | (     |      | to      | for     | ~MIN~+1 |      |
| detailed |    | 5^th^ |      |         | N+1;    | dB,     |      |
| tests of |    | G)    |      | N+4/N+8 | WGN^1^  | D       |      |
| one TV   |    |       |      |         | for all | ~MIN~+3 |      |
|          |    |       |      |         | others  | dB, ‑78 |      |
|          |    |       |      |         |         | to      |      |
|          |    |       |      |         |         | ‑8 dBm  |      |
|          |    |       |      |         |         | in 5-dB |      |
|          |    |       |      |         |         | steps   |      |
+----------+----+-------+------+---------+---------+---------+------+
| **Inte   |    |       |      |         |         |         |      |
| rference |    |       |      |         |         |         |      |
| Reject   |    |       |      |         |         |         |      |
| ion---Co |    |       |      |         |         |         |      |
| mparison |    |       |      |         |         |         |      |
| Tests    |    |       |      |         |         |         |      |
| with     |    |       |      |         |         |         |      |
| D        |    |       |      |         |         |         |      |
| ifferent |    |       |      |         |         |         |      |
| S        |    |       |      |         |         |         |      |
| ources** |    |       |      |         |         |         |      |
+----------+----+-------+------+---------+---------+---------+------+
| Repeat   | 7  | 8     | 30   | N-6,    | WGN^1^  | -68 dBm | 40   |
| test for |    | (     |      | N-4,    |         |         |      |
| con      |    | 5^th^ |      | N‑3,    |         |         |      |
| sistency |    | G)    |      | N-2,    |         |         |      |
|          |    |       |      | N+2     |         |         |      |
+----------+----+-------+------+---------+---------+---------+------+
| OFDM     | 7  | 8     | 30   | N-6,    | DVB-H   | -68 dBm | 40   |
| Inte     |    | (     |      | N-4,    | (5‑MHz  |         |      |
| rference |    | 5^th^ |      | N‑3,    | width)  |         |      |
|          |    | G)    |      | N-2,    |         |         |      |
|          |    |       |      | N+2     |         |         |      |
+----------+----+-------+------+---------+---------+---------+------+
| 8-VSB    | 7  | 8     | 30   | N-6,    | 8-VSB   | -68 dBm | 40   |
| Inte     |    | (     |      | N-4,    |         |         |      |
| rference |    | 5^th^ |      | N‑3,    |         |         |      |
|          |    | G)    |      | N-2,    |         |         |      |
|          |    |       |      | N+2     |         |         |      |
+----------+----+-------+------+---------+---------+---------+------+
| 1-MHz    | 7  | 1     | 30   | N-15 to | G       | -68 dBm | 88   |
| wide     |    | (     |      | N-1,\   | aussian |         |      |
| In       |    | 5^th^ |      | N+1 to  | noise   |         |      |
| terferer |    | G)    |      | N+15    | (1 MHz) |         |      |
+----------+----+-------+------+---------+---------+---------+------+
| Higher   | 7  | 8     | 30   | N-6,    | WGN^1^  | -68 dBm | 40   |
| quality  |    | (     |      | N-4,    |         |         |      |
| desired  |    | 5^th^ |      | N‑3,    |         |         |      |
| signal   |    | G)    |      | N-2,    |         |         |      |
|          |    |       |      | N+2     |         |         |      |
+----------+----+-------+------+---------+---------+---------+------+
| **Inte   |    |       |      |         |         |         |      |
| rference |    |       |      |         |         |         |      |
| Reject   |    |       |      |         |         |         |      |
| ion---To |    |       |      |         |         |         |      |
| Evaluate |    |       |      |         |         |         |      |
| Test     |    |       |      |         |         |         |      |
| Method** |    |       |      |         |         |         |      |
+----------+----+-------+------+---------+---------+---------+------+
| Alt      | 14 | 1     | 14,  | Channel | 8-VSB   | -68 dBm | 18   |
| ernative |    | (     | 15,  | 29 (N-8 |         |         |      |
| test     |    | 5^th^ | 21   | to      |         |         |      |
| setup    |    | G)    | to   | N-1,\   |         |         |      |
| w/       |    |       | 37   | N+1 to  |         |         |      |
| bandpass |    |       |      | N+8,    |         |         |      |
| filter   |    |       |      | N+14,   |         |         |      |
|          |    |       |      | N+15)   |         |         |      |
+----------+----+-------+------+---------+---------+---------+------+
| B        | 14 | 8     | 30   | Chan 2  | G       | -68,    | 16   |
| roadband |    | (     |      | -69     | aussian | ‑53 dBm |      |
| Notched  |    | 5^th^ |      | w/notch | noise + |         |      |
| Noise    |    | G)    |      | for     | band    |         |      |
|          |    |       |      | chan    | -reject |         |      |
|          |    |       |      | 29-31   | filter  |         |      |
+----------+----+-------+------+---------+---------+---------+------+
| Scr      | 14 | 1     | 30   | N+7     | WGN^1^  | -68 dBm | 1    |
| een-Room |    | (     |      |         |         |         |      |
|          |    | 5^th^ |      |         |         |         |      |
|          |    | G)    |      |         |         |         |      |
+----------+----+-------+------+---------+---------+---------+------+
| *        |    |       |      |         |         |         | **20 |
| *TOTAL** |    |       |      |         |         |         | 55** |
+----------+----+-------+------+---------+---------+---------+------+

*Notes (see next page):*

*Notes from Table 2-5:*

*5^th^ G" refers to receivers having multipath performance equivalent to
that of 5^th^-generation Zenith demodulators; all others tested as
having earlier-generation demodulators.*

***D~MIN~** is the desired signal level corresponding to the threshold
of visibility (TOV) of picture degradation in the absence of
interference.*

*^1^ WGN = white Gaussian noise bandlimited to 5.38-MHz 3-dB width.*

*^2^ Tests of one of the seven receivers tested channel 51 were
incomplete. For that receiver: all tests at D = ‑68 dBm were completed;
at D = ‑53 dBm, the single-interferer tests were completed, but the
paired-interferer tests were performed only for N+1/N+2; at D= ‑28 dBm,
the only tests performed were N+1 and N+1/N+2.*

*^3^ Channel-30 paired-signal tests at D = -28 dBm were limited to
N+1/N+2 and N-1/N-2.*

![](media/image1.wmf){width="6.497916666666667in"
height="4.2347222222222225in"}

[]{#__RefHeading___Toc163024408 .anchor}Figure 2‑1. Spectra of the Four
Undesired Signal Sources

![](media/image2.wmf){width="6.497916666666667in"
height="4.280555555555556in"}

[]{#__RefHeading___Toc163024409 .anchor}Figure 2‑2. Spectra of the Four
Undesired Signal Sources---Expanded Scale

![](media/image3.wmf){width="5.415972222222222in"
height="4.814583333333333in"}

> R = range from the broadcast antenna to the TV reception antenna;
>
> R~MAX~ = R at the edge of coverage

[]{#__RefHeading___Toc163024410 .anchor}Figure 2‑3. Relationship Between
Signal Excess and Coverage Area

#  TUNER TYPE TESTS

This chapter presents the results of tests of 30 DTV receivers to
determine their tuner topologies.

## Tuner Topologies

Two tuner topologies are known to have been used in ATSC DTV receivers:
single-conversion tuners and double conversion tuners.

Both types of tuners are designed to shift a desired, 6-MHz wide TV
signal from its original frequency (centered between 57 MHz for channel
2 and 803 MHz for channel 69) to a lower, fixed frequency range where it
is feasible to implement a filter that passes the desired channel
without significant distortion of its spectral shape while providing a
high degree of rejection of adjacent-channel signals. Typically such a
filter is implemented at a center frequency of 44 MHz and passes
frequencies from 41 to 47 MHz. A single-conversion tuner performs the
frequency shift in one operation. A double-conversion tuner performs it
in two steps.

### Single-Conversion Tuners

Figure 3-1 shows a simplified block diagram of single-conversion tuner.
The input filter may be broad enough to pass an entire TV band, such as
the UHF band containing channels 14 through 69. A "tracking filter" in
the RF section adjusts with the TV channel selection and passes the
desired TV channel and perhaps several channels on either side. A local
oscillator (LO) at a frequency 44 MHz above the center of the desired TV
channel (*e.g.*, 739 MHz when the receiver is tuned to channel 51) is
then non-linearly mixed with the amplified and filtered RF signal. This
mixing down-converts the desired TV channel from its original frequency
(*e.g.*, 695 MHz +/- 3 MHz, for channel 51) to 44 MHz +/-3 MHz, which
can pass through the fixed-frequency IF filter that serves to perform
the primary channel selection function.[^27]

In addition to the desired TV channel---centered 44 MHz *below* the LO
frequency---incoming signals that are located 44 MHz +/- 3 MHz *above*
the LO are also down-converted into the IF filter band. For UHF
channels, which occupy contiguous 6-MHz spectrum assignments, this
corresponds to parts of the energy in TV channel numbers N+14 and N+15,
where N is the desired channel number. The presence of these image
signals can interfere with reception of the desired signal. One of the
purposes of the tracking filter in a single-conversion TV tuner is to
attenuate signals at the image frequencies before they reach the mixer
in order to mitigate the interference potential.

Certain other signal interactions in a single-conversion tuner can
create interference sensitivities at other channel spacings. These will
be discussed later in this report.

### Double-Conversion Tuners

Figure 3-2 shows a simplified block diagram of a double-conversion
tuner---as implemented in the Grand Alliance receiver.[^28] This tuner
configuration does not use a tracking filter. Rather, the entire TV
spectrum is up-converted in such a way as to center the desired TV
signal at 920 MHz. After filtering, the resulting signal is then
down-converted by the second mixer so that the desired signal is
centered at 44 MHz.

### Comparisons

The double-conversion design results in image frequencies that are
further separated from desired signal as compared to a single-conversion
design. This separation makes it easier to filter out those undesired
signal components. A double-conversion receiver is therefore less likely
to have detectable image responses. [^29] [^30]

On the other hand, the lack of a tracking filter in double-conversion
designs means that the first mixer must process all received TV signals
rather than just the few channels surrounding the desired signal.
Non-linear interactions between these various signals can create other
interference issues.[^31] [^32] Additionally, achieving low noise figure
and phase noise is more difficult in double-conversion than
single-conversion receivers.[^33] [^34]

## LO Measurement For Tuner Type Identification

In a single-conversion tuner, the LO frequency is located within the TV
bands except when tuning the upper channels of a band. A small amount of
the LO signal can leak out through the antenna port of the TV receiver.
If the LO is detectable at the antenna port, its presence and frequency
can be used to identify the tuner as single conversion and to confirm
the IF frequency.

With double-conversion tuners, the LO is located above the UHF TV bands
and is thus more easily filtered out and less likely to be detectable at
the antenna port.[^35] [^36]

### LO Frequency Test Methodology

The antenna port of each of the 30 DTV receivers discussed in Chapter 2
was observed using a spectrum analyzer in search of LO emissions. (For
receivers having multiple antenna inputs that could handle ATSC signals,
only the input labeled "antenna A" or "antenna 1" was tested.) During
these tests, no signal was supplied to the antenna port; however, prior
to these tests, a channel scan was performed on each TV while
simultaneously applying ATSC signals on UHF channels 51 and 53. This
step was necessary because many DTVs prevent selection of a given TV
channel unless a valid signal was observed on that channel in a previous
channel scan.

To improve the detectability of very weak LO emissions, the spectrum
analyzer was operated with 0 dB input attenuation, the internal preamp
turned on, resolution bandwidth set to 10 kHz, and trace averaging
enabled. The analyzer was set to sweep a 20 MHz span that included the
frequencies of interest. Use of a 2001-point sweep enabled a 0.01‑MHz
bin-to-bin spacing. Each TV was initially tuned to channel 51 and the
spectrum was observed for the presence of a line at 739 MHz---the LO
frequency expected for a single-conversion tuner with a 44‑MHz IF when
tuned to channel 51. The TV was then changed to channel 53, the spectrum
averaging was restarted, and the spectrum was observed to determine
whether the line shifted upward by 12 MHz to the LO frequency expected
for channel 53.

### LO Test Results

For 28 of the tested 30 DTV receivers, LO signals were detected at
frequencies consistent with a single-conversion receiver with an IF
frequency of approximately 44 MHz. For 25 of those, each observed
LO-associated line was within 0.02 MHz of the value expected (44 MHz
above the center frequency of the tuned channel) for each tested
channel. One of the receivers (designated O1 in the SHVERA Study)
exhibited LO-associated lines that were 0.18 MHz above the expected
frequencies. The LO-associated emissions from two other receivers
(designated D2 and D3) exhibited a hunting behavior around the expected
frequency---extending as far as 0.25 or 0.26 MHz from the expected
frequency.

These results provide clear evidence that at least 28 of the 30 consumer
DTV receivers that were tested have single-conversion tuners with an IF
frequency at, or very near, 44 MHz.

For two of the receivers (designated G3 and P1), no LO signal was
observed in the expected frequency range. Based only on these results,
each of these two receivers could have had a different tuner topology,
such as a double conversion tuner, or they could have had
single-conversion tuners but either with a different IF frequency than
was expected or with better control of LO leakage to the antenna port
than the other receivers; consequently, a conclusion regarding topology
of these two receivers required additional tests.

## Interference Rejection Tests For Tuner Type Identification

Interference rejection tests were performed for the receivers G3 and P1,
the two receivers for which LO sensing was inconclusive. These two DTVs
would be classified as fourth-generation or earlier[^37] based on their
multipath performance, which was tested as part of the SHVERA Study.
Both were on the market in 2005, though P1 was actually introduced to
the market in 2004.

The measurements were performed using techniques to be described in the
next chapter. A desired signal of ‑68 dBm was applied to the receivers
on channel 30 along with a white noise signal bandlimited to a 3‑dB
width of 5.38 MHz on another channel. The undesired signal level was
adjusted to the TOV of degradation of the television picture. The
resulting D/U ratios are plotted in Figure 3.3.

Both receivers exhibit a peak in sensitivity to interference at N+7.
This channel contains the LO frequency of a single-conversion tuner with
44-MHz IF. Such a peak can be observed in D/U plots presented in a later
chapter of this report for seven of the other eight single-conversion
receivers tested.

In addition, receiver P1 exhibits elevated sensitivity to interference
at N+14 and N+15. This corresponds to the mixer image for a
single-conversion tuner with 44-MHz IF. Mixer image peaks are seen in
D/U plots presented later in this report for seven of the eight
single-conversion receivers tested.

Based on these observations, receivers G3 and P1 are judged to have
single-conversion tuners with 44‑MHz IF. No further testing was
performed on these two receivers.

## Summary

All 30 tested receivers were judged to have single-conversion topologies
with 44-MHz IF.

![](media/image4.wmf){width="5.986111111111111in"
height="1.948611111111111in"}

[]{#__RefHeading___Toc163024411 .anchor}Figure 3‑4. Single-Conversion
DTV Tuner Block Diagram Example

![](media/image5.wmf){width="5.990972222222222in"
height="1.6569444444444446in"}

[]{#__RefHeading___Toc163024412 .anchor}Figure 3‑5. Double-Conversion
DTV Tuner Block Diagram Example

![](media/image6.wmf){width="6.492361111111111in"
height="4.343055555555556in"}

[]{#__RefHeading___Toc163024413 .anchor}Figure 3‑6. Rejection
Performance of Receivers with Undetected LO's

#  INTERFERENCE REJECTION REFERENCE LEVELS AND TEST METHODOLOGY

This chapter describes the test methodology employed for interference
testing, the performance of the test setup, and some reference values
for rejection performance from other documents.

Channel-to-channel signal level differences required for out-of-channel
interference rejection testing present some challenges that require the
use of specialized filters. The amount of filtering depends on the
threshold desired-to-undesired (D/U) power ratios that are to be
measured.

## Reference Levels for Interference Rejection Performance

Interference rejection performance is defined in terms of the ratio of
desired signal power (D) to undesired signal power (U) at the point at
which visible degradation begins to occur in the television picture.

### Grand Alliance Receiver Performance

The interference rejection capability achieved by the Grand Alliance
prototype DTV receiver for a DTV interferer is shown in Table 4‑1.

[]{#__RefHeading___Toc163024564 .anchor}Table 4‑6. Grand Alliance
Receiver Interference Rejection Performance

  --------------- --------------------------- ---------------------------
  **K**           **D/U Ratio (dB)**          

                  **N -- K**                  **N + K**

  1               -41.98                      -43.17

  2               -60.52                      -59.13

  3               -60.61                      -61.53

  4 to 15         Not measurable              Not measurable
  --------------- --------------------------- ---------------------------

It can be seen that, for DTV interference, the receiver achieved
rejection ratios of about -42 and -43 dB for the two first-adjacent
channels (N+1 and N-1) and rejection ratios of about -60 dB or better at
all other tested channel spacings.

### OET-69 Guidance for Evaluating TV Service Coverage and Interference

OET Bulletin No. 69, "Longley-Rice Methodology for Evaluating TV
Coverage and Interference", defines the FCC methodology for evaluating
TV service coverage and interference protection. Though it does not
directly define TV receiver characteristics or requirements, it does
define D/U ratios that are to serve as protection criteria to avoid
DTV-to-DTV interference. Those protection criteria are shown in
Table 4‑2.

[]{#__RefHeading___Toc163024565 .anchor}Table 4‑7. OET-69 DTV-Into-DTV
Interference Protection Criteria

  ------------------- ---------------------------------------------------
  **Interfering\      **D/U Ratio (dB)\
  Channel**           for DTV-into-DTV Interference**

  N-1                 -28

  N+1                 -26
  ------------------- ---------------------------------------------------

For other channel offsets, OET-69 states the following.

*"The evaluation of service and interference in Appendix B of the Sixth
Report and Order considered taboo channel relationships for interference
into DTV. However, the D/U ratios (approximately -60 dB) were such that
they rarely if ever had an effect on the results, and the FCC rules
adopted in the*

*Sixth Report and Order do not require attention to UHF taboo
interference to DTV stations."*[^38]

Thus, the interference rejection threshold of -60 dB assumed for DTV
receivers was considered adequate to protect against DTV-into-DTV
interference for channel spacings beyond N+1 and N-1 based on the
allotment scenarios that were evaluated.

### ATSC Recommended Performance

The ATSC Receiver Guidelines[^39] recommend that DTV receivers achieve
the interference rejection capabilities shown in Table 4‑3. The
performance thresholds are specified at three different desired signal
levels, which the ATSC designates as "weak", "moderate", and "strong".

[]{#__RefHeading___Toc163024566 .anchor}Table 4‑8. ATSC A/74 Recommended
Thresholds for Receiver Interference Rejection

+-----------------+-----------------+-----------------+-----------------+
| **Interfering   | **Threshold D/U |                 |                 |
| Channel         | for Specified   |                 |                 |
| Number**        | Desired Signal  |                 |                 |
|                 | Level (dB)**    |                 |                 |
+-----------------+-----------------+-----------------+-----------------+
|                 | **Weak**        | **Moderate**    | **Strong**      |
|                 |                 |                 |                 |
|                 | **(-68 dBm)**   | **(-53 dBm)**   | **(-28 dBm)**   |
+-----------------+-----------------+-----------------+-----------------+
| N+/-1           | -33             | -33             | ***-20***       |
+-----------------+-----------------+-----------------+-----------------+
| N+/-2           | -44             | -40             | ***-20***       |
+-----------------+-----------------+-----------------+-----------------+
| N+/-3           | -48             | -40             | ***-20***       |
+-----------------+-----------------+-----------------+-----------------+
| N+/-4           | -52             | -40             | ***-20***       |
+-----------------+-----------------+-----------------+-----------------+
| N+/-5           | -56             | -42             | ***-20***       |
+-----------------+-----------------+-----------------+-----------------+
| N+/-6 to N+/-13 | -57             | ***-45***       | ***-20***       |
+-----------------+-----------------+-----------------+-----------------+
| N+/-14 to       | -50             | ***-45***       | ***-20***       |
| N+/-15          |                 |                 |                 |
+-----------------+-----------------+-----------------+-----------------+

> *Notes*
>
> *Channel "N" is the channel number of the "desired" signal---to which
> the DTV receiver is tuned.*
>
> ***Bold Italics** denote D/U thresholds that correspond to an
> undesired signal level of -8 dBm.*

It should be noted that the ATSC-designated "weak" and "strong" levels
do *[not]{.underline}* bound the range of expected signal levels. The
document recommends that receivers be able to operate with DTV signals
ranging from ‑83 dBm to ‑8 dBm in level.

The ATSC document explains the basis for the -33 dB rejection ratio for
first-adjacent channel interference in Table 4-3. It points out that the
OET-69 protection criteria for allotting DTV stations permits a D/U
ratio as low as -26 and ‑28 dB for first-adjacent channel interference.
The recommended -33 dB receiver threshold was obtained by subtracting 6
dB from the mean of these values. Since the criteria in OET-69 are
derived from receiver susceptibility to transmitter splatter into the
first adjacent channel (based on the DTV emission mask), a receiver
threshold of -33 dB, measured without splatter, ensures that the factor
determining adjacent channel interference will be transmitter splatter
rather than receiver performance.

The ATSC document does not explain the basis of the other D/U values it
recommends; however, those identified by red italics in the above table
correspond to interference at the maximum expected DTV signal level of
‑8 dBm. We understand the other values to be a result of negotiations
that considered the performance levels that would likely be achievable
by consumer-grade TV receivers.

## Test Setup Requirements

### Measurement Requirements

Goals for performance of the test setup were established based on the
above reference levels. For first-adjacent channels (N+1 and N-1), our
goal was to able to measure threshold D/U ratios at least as low as the
‑33 dB level recommended by the ATSC Receiver Guidelines. For all other
channel spacings, or goal was to be able to measure down to a D/U ratio
of -60 dB.

We also wished to be able to supply desired and undesired signals at
levels up to ‑8 dBm.

### The Challenge

Consider the case of a D/U ratio of -60 dB---meaning that the desired TV
signal power is 60 dB below the power of the interferer. The SHVERA
Study demonstrated that the median DTV receiver requires that the
desired signal be at least 15.3 dB above any co-channel noise in order
for successful reception to occur.[^40] For testing at a D/U ratio of
-60 dB, this means that the co-channel noise created by the test setup
must be at least 60 + 15.3 dB below the power of the interferer;
otherwise, the test setup itself will prevent successful DTV reception.
In fact, in order to make test setup noise relatively insignificant at a
D/U ratio of ‑60 dB, we want an additional 10 dB margin---meaning that
co-channel noise created by the test setup must be at least 85.3 dB
below the power of the undesired signal when that signal is placed on
any channel other than a first-adjacent one.

No available signal sources met this requirement. The source used to
generate the "undesired" signal for the testing on channel 51 achieved
only a 49-dB spread between signal power and power splattered into the
second-adjacent channel (*i.e.*, power splattered into channel N when
the undesired source was placed at channel N+2). The source used for
most of the testing on channel 30 was somewhat better but still achieved
only a 56 dB spread between signal power and splatter into the
second-adjacent channel.

The -33 dB D/U specification placed on first-adjacent channel
interference requires a less formidable sounding dynamic range. For that
measurement, any noise created by the test setup must be at least 33 +
15.3 + 10 dB = 58.3 dB below the power of the interferer. This
specification was not met in the first adjacent channel of any source
available during most of the testing.

To achieve the required test setup performance levels, a filter is
needed to further reduce the out-of-band components of the undesired
signal source.

### Solutions

A typical solution to this filtering problem is to bandpass filter the
undesired signal to reduce energy leakage into the desired channel.
Because variable filters tend to have poorer shape factors than
high-quality fixed filters, one approach would be to select a fixed
interfering channel for the tests and to procure a fixed filter to shape
the undesired signal on that channel. Testing at various channel
spacings between the desired and undesired signals could be accomplished
by switching the *desired* channel number over some required range.

While this approach would work well for tests with a single interferer,
it creates a problem for testing against a pair of interferers.
Intermodulation effects in the DTV receiver are expected to be most
prominent for specific pairs of interfering signal channels, such as N+1
and N+2, N+2 and N+4, or N+3 and N+6. For tests of those effects, one
interferer could operate on a fixed channel, but the other would have to
be movable.

To deal with this problem, the desired channel was fixed and the
undesired channels were allowed to change. The undesired signals were
then subjected to a band-*reject* filter at the desired channel
frequency. This fixed band-reject filter served to reduce leakage of the
undesired signals into the desired TV channel.

In actuality, for a given desired channel, two custom filters were
procured: one for adjacent-channel tests and the other for interferers
located beyond the first-adjacent channel. Of the two filters, the
filter for non-adjacent tests has greater rejection in the desired
channel, but would cause unacceptable spectral distortion of an
undesired signal on the adjacent channel (N+1). The filter for adjacent
tests avoids excessive distortion to a first-adjacent undesired signal;
it has less rejection in the desired channel than the other filter, but
the rejection is sufficient for measurements at the more modest D/U
ratios required for the first-adjacent channel.

In addition, the more conventional bandpass filter approach was
implemented for one set of tests for comparison.

## Test Setup

Figure 4-1 shows an overall block diagram of the test setup used for
interference rejection tests.

The top left portion of the diagram shows the desired DTV signal source
and associated amplifiers, along with a step attenuator allowing signal
level to be adjusted in 0.1‑dB steps over an 81‑dB range. A Sencore
ATSC997 8-VSB generator playing a built-in high-definition video stream
of a football game was used for most of the testing. A Rohde and Schwarz
SFU generator, acquired relatively late in the test program, was used
for tests at a low desired signal level (D~MIN~ + 3 dB) and for some
comparative tests; a built-in high-definition video stream of a shark
tank served as the video content for those tests. In the final two weeks
before the due date of this report, some adjacent-channel testing was
performed using a newly acquired Wavetech WS2100 RF Player, combined
with an external upconverter and a file containing an 8‑VSB signal
mathematically derived from an MPEG2 transport stream,[^41] to create a
higher quality desired signal source than the Sencore ATSC997, while
freeing the SFU to act as undesired signal on the adjacent channel.

Up to two generators were used at any given time to create the undesired
(*i.e.*, interfering) signals. The generators included a Sencore RFP910
RF Player playing a supplied recording ("Hawaii Reference A"), the Rohde
and Schwarz SFU mentioned above, two Agilent E4437B vector signal
generators used to generate band-limited white Gaussian noise, and an
Agilent 4438C vector signal generator equipped with Signal Studio for
DVB software to generate an OFDM DVB-H signal. The Sencore RF Player
failed near the end of the planned tests at channel 51 and was
unrepairable. The Rohde and Schwarz SFU was procured later in the
testing period.

The two undesired signals are combined and amplified by a 5-watt power
amplifier which is operated at an output power of only 0.07 watts in
order to limit third-order intermodulation distortion products, which
would fall within the desired signal channel. A step-attenuator
(Atten-C) is used to adjust the input level of the amplifier.

The amplified, undesired signal pair is then passed through one of four
band-reject filters to reduce out-of-band splatter into the desired
channel to which the TV is tuned. The filter is followed by a fixed
attenuator and a step attenuator that allows the undesired signal level
to be adjusted in 0.1‑dB steps over an 81‑dB range. No active devices
(*e.g.*, amplifiers) are included in the test setup beyond the filter
output in order to avoid creation of intermodulation products.

The desired signal is then combined with the filtered undesired signal
pair. The combined signals are split into two paths---one feeding the
DTV receiver under test through an impedance-matching pad and the other
feeding a spectrum analyzer used for all power measurements. A total of
about 9‑dB of attenuation is provided in each splitter output path in
order to reduce the impact of any reflections caused by impedance
mismatches at the DTV receiver input. The attenuators following the
splitter were selected to provide a signal level match between the TV
port and the measurement port to within 0.1 dB across all TV channels.

Double-shielded cables were used throughout the test setup because of
the wide range of signal levels present simultaneously. A 50-ohm
impedance was maintained throughout the setup, except at two 8-VSB
sources and the consumer TV inputs, which were each specified to be
nominally 75 ohms. The 75‑ohm devices were matched to the rest of the
test setup through impedance-matching pads or---in the case of one of
the 8-VSB sources---an impedance-matching transformer. In addition to
the impedance-matching pads, 50-ohm attenuator pads were used at various
places throughout the test setups to reduce the effects of any impedance
mismatches at places where such mismatches were considered likely or
would be expected to have a significant impact, as well as to reduce
third-order intermodulation in amplifiers A1 and A2.

The test setup is capable of delivering undesired signals to the TV
receiver at a maximum level ranging from -7 to -1 dBm per interferer.

## Test Setup Performance

As was described in the *Test Setup Requirements* section, the test
setup was required to suppress splatter from the undesired signals into
the desired channel by as much as 85.3 dB. No available spectrum
analyzer had sufficient dynamic range to measure this degree of
suppression. Instead, the spectrum of the output of the test setup was
first measured with the filter bypassed. These measurements were
performed with no desired signal present and for several different
channel selections for the undesired signal with undesired signal set to
a high level. Separately, the frequency response of the test setup was
then measured both with the filter in place and with the filter
bypassed; the difference between these measurements represents the
in-situ filter frequency response. The filter frequency response was
then applied to the spectrum measurements made with the filter
bypassed---resulting in a computed value for the net output spectrum.

Figure 4-2 shows the output spectrum of the test setup with channel 30
as the desired channel and a bandlimited white Gaussian undesired signal
at channel N+2. Integration of the blue---undesired-signal-only curve
shows that the power splattered by test setup into channel N is 99.3 dB
below the total undesired signal power. About 56 dB of this suppression
is due to the performance of the undesired signal generator---degraded
slightly by the amplifier that follows it. The remaining 43 dB of
suppression comes from the band-reject filter.

In the figure, the spectrum of a desired DTV signal is plotted at a
total power level 60 dB below the power of the undesired signal, *i.e.*,
at a D/U ratio of -60 dB. Since a typical DTV requires that D be 15.3 dB
above any co-channel noise, the test setup noise is 24 dB below the
point at which DTV operation would fail. This significantly exceeds the
10‑dB margin that was considered essential for meaningful D/U
measurements.[^42]

Figure 4-3 shows another example of the output spectrum of the test
setup---again with channel 30 as the desired channel, but this time with
a pair of interfering signals spaced to create intermodulation
distortion in channel N. In this case the unintended power leaked into
the desired channel is 98.2 dB below the undesired signal power.

Figure 4-4 shows an adjacent-channel example. A pair of interferers is
placed at N+1/N+2. The interferer at N+1 (U~1~) is an 8-VSB source; some
rounding of the left side of the 8-VSB signal by the band-reject filter
can be seen. The interferer at N+2 (U~2~) is a white-Gaussian-noise
source bandlimited to match the 3-dB width of an 8-VSB signal. Two
different interferer types had to be used for this test: though two
bandlimited noise generators were available, their spectrum rolloff is
not steep enough for use as an adjacent channel (N+1) source because too
much power would be spilled into the desired channel; and, only one
8-VSB source (besides the one used as a desired signal) was available.

In the case of N+1/N+2 interference, there is no need to measure D/U
ratios as low as -60 dB. In this case, the desired signal is shown at a
D/U ratio of -33 dB---the ATSC-recommended rejection performance for
first-adjacent-channel interference. Based on integration of the signal
spectra, the total noise power leaked into the desired channel is
70.2 dB below the undesired signal power. This provides a 21.9 dB margin
to the point of reception failure caused by the test setup. (Actual
margin is likely higher than this because, as can be seen from the plot,
much of the undesired power that leaks into the desired channel N is at
the band edges where filtering within the DTV receiver will reduce its
effect.) With 10 dB being considered the minimum acceptable margin,
receiver measurements could be made with this signal configuration down
to a D/U ratio of about -45 dB per undesired signal.

Table 4-4 summarizes the minimum D/U ratios that can be measured by the
various test setup configurations used in this report based on the
undesired signal leakage into the desired channel. Two limitations are
listed for adjacent-channel test configurations: a limit based on total
power leaked into the desired channel and a limit that includes the
effect of a DTV receiver's raised-cosine filter response on spectrum
leakage at the edges of the desired channel. The former limit ("worst
case limit") is displayed on plots as the "Measurement Limit" for
measurements on channel 30. The latter limit is used as a measurement
limit for measurements at channel 51 to avoid unnecessarily excluding
measurement results from further analysis. (This decision was made
because the channel-51 test setup had poorer performance than that for
channel 30, in that it spilled more energy from the undesired signal
into the edge of the desired channel.)

In addition, minimum D/U ratio is limited by the maximum undesired
signal level that the test setup can produce. The maximum undesired
signal level ranges from about -7 dBm to -1 dBm depending on the test
setup configuration and channel spacing being tested. Typically, at a
desired signal level of ‑68 dBm the D/U measurement range is limited by
leakage of undesired signal into the desired channel for measurements at
N+1 or N-1 and by maximum undesired signal that the test setup can
generate for all other channel spacings.

## Test Setup Configurations

Table 4-5 summarizes the equipment configurations used for the various
tests of interference rejection performance.

[]{#__RefHeading___Toc163024567 .anchor}Table 4‑9. Measurement
Limitations of the Test Setup

+-------+----+---------+---------+---------+-------+------+---------+
| **De  | ** | **Un    | **Un    | **App   | **    | **Wo | **D/U   |
| sired | Fi | desired | desired | licable | Cases | rst- | Limit   |
| Ch    | lt | Source  | Source  | Inter   | exami | Case | If the  |
| annel | er | 1**     | 2**     | ference | ned** | L    | DTV's   |
| N**   | ** |         |         | Cha     |       | imit | Raised  |
|       |    |         |         | nnels** |       | on   | Cosine  |
|       |    |         |         |         |       | D/U\ | Filter  |
|       |    |         |         |         |       | (d   | Is      |
|       |    |         |         |         |       | B)** | Assumed |
|       |    |         |         |         |       |      | in TV\  |
|       |    |         |         |         |       |      | (dB)**  |
+-------+----+---------+---------+---------+-------+------+---------+
| 30    | 3  | 8-VSB   | None    | N+1,    | Both  | -    | -59.4   |
|       | 0N | (Rohde  |         | N-1     |       | 48.3 |         |
|       |    | SFU)    |         |         |       |      |         |
+-------+----+---------+---------+---------+-------+------+---------+
| 30    | 3  | WGN     | None    | N+2 to  | N-16, | -    |         |
|       | 0W |         |         | N+16    | N-8,  | 74.0 |         |
|       |    |         |         | and\    | N-2,  |      |         |
|       |    |         |         | N-2 to  | N+2,  |      |         |
|       |    |         |         | N-16    | N+8,  |      |         |
|       |    |         |         |         | N+16  |      |         |
+-------+----+---------+---------+---------+-------+------+---------+
| 30    | 3  | 8-VSB   | WGN     | Pairs:  | Both  | -    | -52.5   |
|       | 0N | (Rohde  |         | N+1/N+2 |       | 44.9 |         |
|       |    | SFU)    |         | and     |       |      |         |
|       |    |         |         |         |       |      |         |
|       |    |         |         | N-1/N-2 |       |      |         |
+-------+----+---------+---------+---------+-------+------+---------+
| 30    | 3  | WGN     | WGN     | Pairs:  | P     | -    |         |
|       | 0W |         |         |         | airs: | 71.7 |         |
|       |    |         |         | N+2/N+4 | N-8/  |      |         |
|       |    |         |         | to      | N-16, |      |         |
|       |    |         |         | N+8     | N-4   |      |         |
|       |    |         |         | /N+16;\ | /N-8, |      |         |
|       |    |         |         | N-2/N-4 | N-2   |      |         |
|       |    |         |         | to\     | /N-4, |      |         |
|       |    |         |         | N       | N+2   |      |         |
|       |    |         |         | -8/N-16 | /N+4, |      |         |
|       |    |         |         |         | N+4   |      |         |
|       |    |         |         |         | /N+8, |      |         |
|       |    |         |         |         | N+8   |      |         |
|       |    |         |         |         | /N+16 |      |         |
+-------+----+---------+---------+---------+-------+------+---------+
| 51    | P5 | 8-VSB   | None    | N+1     | N+1   | -    | -43.9   |
|       | 2- | (       |         |         |       | 37.6 |         |
|       | 53 | Sencore |         |         |       |      |         |
|       |    | RFP)    |         |         |       |      |         |
+-------+----+---------+---------+---------+-------+------+---------+
| 51    | P5 | 8-VSB   | WGN     | N+1/N+2 | N+    | -    | -42.6   |
|       | 2- | (       |         |         | 1/N+2 | 36.7 |         |
|       | 53 | Sencore |         |         |       |      |         |
|       |    | RFP)    |         |         |       |      |         |
+-------+----+---------+---------+---------+-------+------+---------+
| 51    | P5 | 8-VSB   | WGN     | N+2 to  | All   | -    |         |
|       | 3- | (       |         | N+16    | pairs | 71.0 |         |
|       | 56 | Sencore |         | and     | and   |      |         |
|       |    | RFP)    |         | pairs:  | N+9   |      |         |
|       |    |         |         | N+2/N+4 | to    |      |         |
|       |    |         |         | to      | N+16  |      |         |
|       |    |         |         | N       |       |      |         |
|       |    |         |         | +8/N+16 |       |      |         |
+-------+----+---------+---------+---------+-------+------+---------+

*Note: WGN refers to bandlimited white Gaussian noise from an Agilent
E4437B vector signal generator*

[]{#__RefHeading___Toc163024568 .anchor}Table 4‑10. Test Setup
Configurations and Settings

  ------------------------ ------------------- --------- ----------- ------------- ------------- ---------
  **N**                    **Interferer(s)**   **Test    **Desired   **Undesired   **Undesired   **Step
                                               Setup**   Signal      Source 1**    Source 2**    Atten-C
                                                         Source**                                (dB)**

  **Interference                                                                                 
  Rejection---Single                                                                             
  Interferer**                                                                                   

  30                       Single adjacent     Primary   8-VSB Src A 8-VSB Src C @               5
                                                         @ 38dBmV    +2 dBm                      

  30                       Single adjacent w/D Primary   8-VSB Src D 8-VSB Src C @               5
                           at D~MIN~+3 dB                            +2 dBm                      

  30                       Single non-adjacent Primary   8-VSB Src A WGN Src A @                 2
                                                         @ 38dBmV    -7 dBm                      

  30                       Single non-adjacent Primary   8-VSB Src C WGN Src A @                 2
                           w/D at D~MIN~+3 dB            @+2dBm      -7 dBm                      

  51                       Single              Primary   8-VSB Src A 8-VSB Src B @               2
                                                         @ 38dBmV    -30 dBm                     

  **Interference Rejection                                                                       
  for Paired Signals**                                                                           

  30                       Paired adjacent\    Primary   8-VSB Src A 8-VSB Src C @ WGN Src A @   5
                           (*e.g.*, N+1/N+2)             @ 38dBmV    +2 dBm        variable      
                                                                                   level         

  30                       Paired non-adjacent Primary   8-VSB Src C WGN Src B @   WGN Src A @   8
                                                         @+2dBm      -7 dBm        variable      
                                                                                   level         

  51                       Paired              Primary   8-VSB Src A 8-VSB Src B @ WGN Src A @   2
                                                         @ 38dBmV    -30 dBm       variable      
                                                                                   level         

  **Interference                                                                                 
  Rejection---Comparison                                                                         
  Tests With Different                                                                           
  Sources**                                                                                      

  30                       Single non-adjacent Primary   8-VSB Src A 8-VSB Src C @               2
                           DTV interferer                @ 38dBmV    +2 dBm                      

  30                       Single non-adjacent Primary   8-VSB Src A OFDM Src A @                2
                           OFDM interferer               @ 38dBmV    -6.9 dBm                    

  **Interference                                                                                 
  Rejection---To Evaluate                                                                        
  Test Method**                                                                                  

  Variable (U at 29)       Single adjacent &   Alt       8-VSB Src A 8-VSB Src C @               NA
                           nonadjacent using             @ variable  variable                    
                           Simplified Test               output      output level                
                           Setup w/BPF on U              level                                   
  ------------------------ ------------------- --------- ----------- ------------- ------------- ---------

*Test Setups*

1.  *Primary: Figure 4-1*

2.  *Alt.: Figure 14-2*

*Signal sources*

1.  *8-VSB Source A: Sencore ATSC997 ATSC Source*

2.  *8-VSB Source B: Sencore RFP910 RF Player ("Hawaii_ReferenceA"
    file)*

3.  *8-VSB Source C: Rohde & Schwarz SFU 8-VSB Generator*

4.  *8-VSB Source D: Wavetech WS-2100 RF Player ("Muddy Waters" file) +
    Drake DUC860 Upconverter*

5.  *AWGN Source A: Agilent E4437B Vector Signal Generator in AWGN mode*

6.  *AWGN Source B: Agilent E4437B Vector Signal Generator in AWGN mode*

7.  *OFDM Source A: Agilent E4438C Vector Signal Generator +* *Agilent
    Signal Studio for DVB software*

![](media/image7.wmf){width="6.498611111111111in"
height="4.231944444444444in"}

1.  Amplifiers

    1.  A1 = MiniCircuits ZFL-1000H (28 dB minimum gain; 20 dBm 1-dB
        compression)

    2.  A2 = MiniCircuits ZFL-1000VH (20 dB minimum gain; 25 dBm 1-dB
        compression)

    3.  A3 = HP8447B (22 dB gain; 400-1300 MHz)

    4.  A4 = Amplifier Research 5W1000 (37 dB gain; 500 kHz -- 1000 MHz;
        5 watts output)

2.  Attenuators

    1.  Attenuators preceding A1 and A2 are selected to reduce IM3 to
        acceptable levels

    2.  Step Attenuator-C set to reduce IM3 of A4 to acceptable levels

    3.  Step Attenuators D & U: Alan Industries models 50V70 N, 50V10 N,
        and 50V1 N cascaded to provide 0 - 81 dB in 0.1-dB steps (0.5W
        max power)

3.  Combiners & Splitter: MiniCircuits ZAPD-900-5W (100-900 MHz)

4.  Custom Band-Reject Filters

    1.  "30N" = Tin Lee CE7-569(4.8)N50

    2.  "30W" = Microwave Filter Company model 16195

    3.  "P52-53" = Tin Lee CE7-692/697.4(20) N50

    4.  "P53-56" = Tin Lee CE7-692/698 N50

5.  Impedance Matching

    1.  Minimum Loss Pads = Trilithic ZM-57

    2.  75-50 ohm transformer = Trilithic ZMT-57

6.  25-ft coax = Times Microwave LMR-400-UF

7.  Equipment settings

    1.  Agilent E4437B settings for bandlimited white Gaussian noise

        1.  AWGN mode w/length 1048576

            1.  Bandwidth setting = 4.686 MHz for 5.38-MHz 3-dB width

            2.  Bandwidth setting = 875 kHz for 1-MHz 3-dB width

        2.  Output setting = -7 dBm. (Higher could damage Step-Atten-U &
            raise IM3 of E4437B output)

    2.  Agilent E4438C vector signal generator using Agilent Signal
        Studio for DVB software

        1.  Signal Type: DVB-H

        2.  Waveform parameters: Size=2k; Modulation=64 QAM; Chan.
            width=5 MHz; Guard interval=1/8

        3.  Output setting = -6.9 dBm

[]{#__RefHeading___Toc163024414 .anchor}Figure 4‑7. Block Diagram of
Interference Rejection Test Setup

![](media/image8.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024415 .anchor}Figure 4‑8. Leakage of U at N+2
into Channel N (30)

![](media/image9.wmf){width="6.492361111111111in"
height="4.284722222222222in"}

[]{#__RefHeading___Toc163024416 .anchor}Figure 4‑9. Leakage of U pair at
N-2/N-4 into Channel N (30)

![](media/image10.wmf){width="6.492361111111111in"
height="4.284722222222222in"}

[]{#__RefHeading___Toc163024417 .anchor}Figure 4‑10. Leakage of U pair
at N+1/N+2 into Channel N (30)

#  REJECTION RESULTS ON CHANNEL 30 FOR SINGLE INTERFERERS WITH FULL CHANNEL WIDTH

This chapter presents the results of interference rejection tests of
eight "fifth-generation" DTV receivers tuned to channel 30. The
interferer for these tests was:

1.  For channels N+1 and N-1, an 8-VSB signal;

2.  For channels N+2 through N+16 and N-2 through N-16, a white Gaussian
    noise signal bandlimited to match the 3-dB width of an 8-VSB signal.

Spectra of the sources were shown in Figures 2-1 and 2-2.

A limited set of interference rejection tests was also performed on two
earlier-generation receivers, designated G3 and P1, for purposes of
identifying tuner type as described in Chapter 3. This data was plotted
in Figure 3-3, but it is repeated near the end of this chapter with an
overlay showing the range of values measured for the fifth-generation
receivers for comparison.

The primary focus of these tests was to investigate the interference
susceptibility of DTV receivers operating in the UHF band to
interference from other occupants of the UHF TV spectrum, including
other TV broadcasts as well as non-TV use of the "white spaces". As
such, the desired channel (30) was selected as a locally unused channel
near the center of the UHF core spectrum.

Test results are presented in this chapter either as D/U ratios, in
which case better performance corresponds to lower points on the graph,
or as threshold values of the undesired signal level U, in which case
better performance corresponds to points nearer the top of the graph.

## Tests at ATSC-Specified Desired Signal Levels

### "Weak" Desired Signal (D = -68 dBm)

Figure 5-1 shows measured values of D/U ratios at TOV for the eight DTV
receivers for undesired signal channels ranging from N-16 to N+16. (The
case of co-channel interference, *i.e.*, interference on channel N, is
omitted.) The desired signal power was set to -68 dBm, a signal level
that the ATSC chose to designate as "weak", although DTVs are assumed to
operate down to a signal level of -84 dBm.[^43]

The shaded area at the bottom of the plot represents the measurement
limitations imposed by the test setup---as described in Chapter 4.
Measurements falling in---or at the border of---this region are not
valid; the actual performance of a receiver at these points is better
(*i.e.*, lower on the graph) than the plotted point indicates. For N-1
and N+1 with D = -68 dBm, the limit is based on leakage from the
undesired source into the desired channel. For other offsets and higher
desired signal levels, the measurements are limited by the maximum
undesired signal power the test setup could inject into the DTV
receiver.

The ATSC-recommended DTV-into-DTV interference rejection thresholds are
shown on the plot as a reference. Those limits are defined for channels
ranging from N-15 and N+15. Compliance with those voluntary limits would
be indicated by all points on a measurement curve falling on or below
the ATSC line. It should be recognized, however, that the ATSC
recommendations apply when the undesired signal is an 8‑VSB DTV signal,
which was the case only for the N-1 and N+1 points on each curve. It can
be seen that all eight receivers comply with the ATSC recommendation at
N‑1 and N+1.

At the other channel offsets, N-2 through N-15 and N+2 through N+15, no
receiver appears to fully comply with the recommended performance limit.
The best-performing receiver, designated G4, complied everywhere except
at N+5 and N+6, where its performance failed to meet the limits by about
2 dB and 1 dB, respectively. On average, the receivers failed to meet
the recommended performance on at about seven of the 30 channel offsets,
with one receiver (D3) failing at twelve points. The worst failure for
each receiver ranged from about 2 dB to 25 dB.

The above results cannot be viewed as definite failures to meet the
performance guidelines because the tests (other than at N-1 and N+1)
were performed using a bandlimited white noise source as the interferer,
rather than an 8-VSB signal. (An 8-VSB source was not available for most
of the test period.) Limited tests presented in Chapter 7 show an
average performance improvement of 1.1 dB when the interference comes
from an 8-VSB signal rather than from the white Gaussian noise source of
the same 3-dB bandwidth. However, even taking this difference into
account, it is unlikely that any of the receivers would fully comply
with the ATSC guidelines at every channel offset, though one or two
would probably come close.

Figure 5-2 summarizes the measurements that were shown in Figure 5-1.
The blue curve shows the median performance of the eight receivers.
Error bars show the best and worst performance among the receivers at
each channel offset. A dashed curve shows the performance of the second
worst performing receiver at each channel offset. On a median basis, the
offsets that break the recommended limits by the largest amounts are
N-4, N-6, and N+7.

### "Moderate" Desired Signal (D = -53 dBm)

Figure 5-3 shows measured values of D/U ratios at TOV for the same eight
DTV receivers with the desired signal power set to -53 dBm, a signal
level that the ATSC designates as "moderate". Again, all eight receivers
comply with the ATSC recommended performance on the first-adjacent
channels (N+1 or N-1). At the other channel offsets, only one receiver
(G4) appears to fully comply with the recommended performance limit. A
second receiver (I1) appears to fail only at N-2 by 1 dB and at N‑4 by a
negligible amount. Other receivers fail at from one to 16 points with
worst-case failures ranging from three to 18 dB. The worst performing
receiver was D3. Again, these results cannot be viewed as definite
failures to meet the guidelines because the tests were performed using a
bandlimited white noise source as the interferer, rather than an 8-VSB
signal. Based on the differences in interference effect of the 8-VSB and
Gaussian signals, it is likely that a second receiver would have
complied with the guidelines at this desired signal level if an 8-VSB
signal had been used as the interferer.

Figure 5-4 shows the best, median, second worst, and worst performance
at each channel offset. On a median basis the only failure to satisfy
the ATSC recommended performance is at N+7.

### "Strong" Desired Signal (D = -28 dBm)

Figure 5-5 shows that, with the desired signal set to the level that the
ATSC designates as "strong", every receiver complied with the ATSC
Recommended Guidelines at every point, with the exception of one
receiver (G4) that appeared to fail by only 0.2 dB at N+1. In most cases
the test setup was not capable of generating strong enough undesired
signals to cause visible degradation of the TV picture; consequently,
most data points are plotted on the measurement limit line. Figure 5-6
shows the best, median, second worst, and worst performance at each
channel offset.

## Selection of a Weaker Desired Signal for Tests

### Motivation

The data in this chapter and later chapters of this report show that, as
desired signal power at the input to a TV decreases, the amount of
undesired power that the TV can tolerate on another channel also
decreases. This means that a TV is most vulnerable to interference when
operating at a low desired signal level---not a surprising result.

One might also hypothesize that, as the desired signal power D at the
input to the TV decreases, the undesired signal power U necessary to
cause picture degradation would decrease at the same rate. If this were
true, the D/U ratio would remain constant, and interference rejection
measurements would only need to be performed at a single power level to
gain an understanding of the TV's rejection performance. From the test
results in this report, it is clear that this hypothesis is false. In
fact, the rate of change of threshold undesired signal with desired
signal differs with channel offset between the desired and undesired
channel and also varies with desired signal amplitude.

The variation of D/U ratio with signal amplitude---often in unexpected
ways---suggests the need for rejection performance measurements at a
variety of amplitudes. In Chapter 11, we subject a single TV to D/U
measurements over a wide amplitude range to gain some insight into
interference behavior. However, given that TV's are most susceptible to
interference at low desired signal levels, we focus here on weak
signals.

The range of desired signal levels that a DTV receiver can or should
accommodate extends from:

1.  D~MIN~ (nominally -84 dBm)

> --- the desired signal level at which a DTV receiver begins to
> experience visible picture degradation; -84 dBm is the threshold
> assumed by OET-69 for edge-of-coverage UHF reception and also the
> median channel-30 threshold of 28 consumer DTV receivers measured
> under the SHVERA Study; to,

2.  -8 dBm --- the maximum DTV signal level anticipated by the ATSC
    Receiver Guidelines.

In between are the three levels at which ATSC A/74 defines interference
rejection performance guidelines for DTV receivers:

1.  -68 dBm \-- "weak"

2.  -53 dBm \-- "moderate"

3.  -28 dBm \-- "strong"

The measurements of rejection performance presented thus far in this
chapter were performed at these three levels.

Note that the -68 dBm signal level designated by the ATSC as "weak" is
16 dB above the -84 dBm minimum signal level at which a typical DTV
receiver can operate; that minimum signal level of -84 dBm is also the
signal level assumed by OET-69 (FCC's document for predicting coverage
of a TV station) to be available to a DTV receiver at the edge of
coverage of a TV broadcast station.[^44] Table 2-2 and Figure 2-3 of
Chapter 2 showed that fully 84 percent of the coverage area of a
broadcast station may experience desired signal levels weaker than
‑68 dBm, assuming that the same type of antenna system is used at all
locations in the viewing area. This suggests a need to test at lower
signal levels.

### Signal Level Selection

Selecting a signal level for interference tests that represent a near
edge-of-coverage condition is not straight-forward. Only about half of
the 28 receivers tested for the SHVERA Study could produce an error-free
picture with a channel-30 desired signal level matching the -84 dBm
edge-of-coverage signal level assumed by OET-69, even without adding any
interference, and a few TVs would produce no picture at all at this
signal level. Among those receivers, the TV with the least UHF
sensitivity required an input signal level about 2.6 dB larger than the
‑84 dBm level, while the most sensitive TV could operate at a signal
level 1.3 dB weaker than ‑84 dBm. The spread between the most-sensitive
and least-sensitive receivers was larger in the VHF band---as high as 15
dB.

If, in order to accommodate relatively insensitive receivers, a
relatively high desired signal level is chosen as the measurement basis
for rules to prevent interference to television, the resulting rules for
a new service might permit interference levels that would limit the
operation of the better receivers that can operate on weaker signals.
Hence a decision was made to also test at a receiver-dependent desired
signal level near the threshold of visible picture degradation (TOV)
that occurs in the absence of interference, a level we have designated
as D~MIN~.

Table 2-2 and Figure 2-3 of Chapter 2 showed that a TV located beyond 84
percent of the maximum reception range (R~MAX~) of the broadcast station
(for a given antenna system) will receive signal levels at less than 3
dB of signal margin (*i.e.*, signal level relative to that needed for
consistent, clear reception of the broadcast signal).[^45] 29 percent of
the coverage area falls in this region of less than 3 dB signal excess.
Similarly, and 11 percent of the coverage area will exhibit a signal
excess of less than 1 dB.[^46]

The assumptions regarding coverage area are typically based on use of a
high-gain outdoor antenna on a 10-meter mast. The percentages discussed
above apply to such coverage area as long as the receiving system
(including antenna gain and mast height) remains constant as one moves
in to closer distances from the broadcast location. Thus, for example,
29 percent of the receiving coverage area would operate with less than
3‑dB signal excess for customers with that receiving system. If,
however, closer-in customers choose a lower-gain antenna, a lower mast
height, or an indoor antenna location, those customers will operate with
a shorter maximum possible range for consistent reception (R~MAX~). Such
customers would also operate with less than 3-dB excess signal whenever
they are beyond 84% of the maximum reception range possible with
*[that]{.underline}* antenna system. In essence, the region with less
than 3-dB excess signal repeats itself as 29 percent of the area of a
smaller coverage circle corresponding to use of the lesser antenna
system. Hence, the area where excess signal is less than 1 or 3 dB will
be larger than the 11 and 29 percent values discussed here if closer-in
customers choose lower-gain antennas or place those antennas at less
optimal locations such as on a shorter outdoor mast or indoors. (We note
that, while the simple model used in the above analysis is useful for
estimating the relative importance of various values for signal excess,
terrain and man-made structures in real-world locations will cause the
numbers to vary from those shown here.)

Given that rejection performance tests are time consuming, a decision
was made to make measurements at only one additional signal level beyond
the three ATSC-specified levels. We chose to make this level dependent
on the threshold reception performance of the individual receivers.
Thus, we measured the desired signal level D~MIN~ at which TOV occurs
for each receiver in the absence of interference. Interference rejection
tests were then performed at a desired signal level 3 dB above this
threshold. The desired signal level for these tests is designated as
D~MIN~ + 3 dB. In addition, we extrapolated the measurements to a
desired signal power of D~MIN~ + 1 dB in Chapter 12 by means of a
modeling approach developed from a theoretical framework presented in
Chapter 8.[^47]

## Effect of Desired Signal Source

In preparing for the D~MIN~-referenced measurements, D~MIN~ was measured
for three receivers that been tested for the SHVERA Study, but the new
measurements were found to be about 1 dB higher than the earlier SHVERA
measurements.[^48] While these differences could have been considered to
be within measurement error, there was uncertainty about whether the
difference could be attributed to differences between the SHVERA test
setup and the current test setup or the use of different desired signal
sources in the two test programs.

The signal source used in the SHVERA Study had failed irreparably while
being used as an undesired signal source for channel-51 tests in the
current program; however, a new signal source (Rohde and Schwarz SFU)
had been procured late in the current test program. To evaluate the
cause of 1-dB difference, the new SFU generator was substituted for the
Sencore ATSC997 source that was used as the desired source for most of
the testing described in this report. The result of the switch was a
1‑dB improvement in measured sensitivity of the receivers---to results
that matched the SHVERA test results.

Table 5-1 shows the observed differences in receiver threshold for
various desired-signal configurations, *with the SFU-based measurements
as the reference*. In all cases, the measurements were made at the
output of the test configuration that was shown in Figure 4-1. The first
measurement column shows the differences in measured D~MIN~ using the
ATSC997 in the test setup as shown in Figure 4-1 (including amplifiers
A1 and A2, as well as three 6-dB pads) instead of the SFU. On average
the ATSC997 in the "normal" test-setup configuration widely used in this
report resulted in a receiver threshold about 0.9 dB higher than that
when the SFU was used. The second column represents measurements to
determine whether the difference was due to the ATSC997 itself, or the
amplifiers that followed it. The third is a comparison to the SHVERA
measurements.

In general, all three tested TVs appeared to require an input DTV signal
level about 0.9 dB higher when the signal was supplied by the Sencore
ATSC997 than when it was supplied by either the Rohde and Schwarz SFU
or, based on the SHVERA test results, the Sencore RF Player (playing the
"Hawaii_ReferenceA" file). This fact suggested that the signal quality
of the ATSC997 was inferior to that of the other sources in a way that
affected TV performance in a small, but measurable way. ***While a
0.9‑dB discrepancy in TV receiver threshold may seem small, there was
concern that it might be relevant when performing interference testing
at levels only 3‑dB above the receiver threshold.***

Measurements were performed on the desired signal at the output of the
test setup in an attempt to determine the cause of the
generator-dependence of receiver thresholds.

Figures 5-7 and 5-8 show the spectra of the desired signal at the output
of the test setup using each of the two remaining 8-VSB sources. Figure
5-7 illustrates the higher noise floor of the ATSC997 relative to the
SFU. If the ATSC997's noise floor extended through the desired signal
band at a level roughly 40 dB below the desired signal, it would add to
the TV receiver noise, which is generally expected to be about

[]{#__RefHeading___Toc163024569 .anchor}Table 5‑11. Receiver Minimum
Signal Level at TOV Versus Desired Signal Source

+--------+---------------------+------------------+-------------------+
| **TV   | **D~MIN~ Measured   |                  |                   |
| Rece   | Using Signal Source |                  |                   |
| iver** | Shown**             |                  |                   |
|        |                     |                  |                   |
|        | **Relative to       |                  |                   |
|        | D~MIN~ Measured     |                  |                   |
|        | Using Rohde &       |                  |                   |
|        | Schwarz SFU (dB)**  |                  |                   |
+--------+---------------------+------------------+-------------------+
|        | **Sencore ATSC997   | **Sencore        | **SHVERA Result   |
|        | (with amplifiers A1 | ATSC997          | (Sencore RF       |
|        | & A2 as shown in    | (bypassing       | Player in a       |
|        | Figure 4-1)**       | external         | Different Test    |
|        |                     | amplifiers)**    | Setup)**          |
+--------+---------------------+------------------+-------------------+
| I1     | 0.77                | 0.87             | -0.16             |
+--------+---------------------+------------------+-------------------+
| M1     | 1.06                | 1.24             | 0.05              |
+--------+---------------------+------------------+-------------------+
| N1     | 0.80                | 0.74             | 0.26              |
+--------+---------------------+------------------+-------------------+
| **     | **0.87**            | **0.95**         | **0.05**          |
| Mean** |                     |                  |                   |
+--------+---------------------+------------------+-------------------+

15 dB below the desired signal level at threshold. This would cause the
total noise seen by the receiver to rise, relative to
receiver-noise-only, by 10 Log(1 + 10^-(40-15)/10^) = 0.014 dB. Clearly
this is not the cause of the 0.9-dB change in receiver threshold.

The "flat top" of the ATSC997 signal exhibits a downward slope (visible
in Figure 5-8) that projects to 0.7 dB across a 6-MHz channel
width---far greater than the slope of the SFU spectrum, which projects
to 0.04 dB across 6-MHz. We are unaware of a way to predict the impact
of the spectral slope.

The pilot peak of the ATSC997 spectrum is 0.4 dB higher than that of the
SFU---probably owing in part to the spectral slope.

Table 5-2 shows some additional measurements that were made on the
desired signal at the output of the test setup for each desired signal
source using an Agilent 89441A vector signal generator. Each measurement
was an average of at least four successive readings that were obtained
using the default settings of a control software package designed for
DTV measurements.[^49]

[]{#__RefHeading___Toc163024570 .anchor}Table 5‑12. Signal Quality
Measurements on 8-VSB Sources

  -------------------------------------- ------------- -------- --------- --------
  **Desired Signal Source\--\>**         **ATSC997**            **SFU**   

  **Vector Signal Analyzer Equalizer     **OFF**       **ON**   **OFF**   **ON**
  Setting\--\>**                                                          

  **Modulation Error Ratio (MER) (dB)**  29.88         32.50    39.10     40.86

  **Phase Error (deg)**                  2.43          1.51     1.01      0.92

  **Pilot Level (dB)**                   0.59          0.30     0.04      0.08
  -------------------------------------- ------------- -------- --------- --------

The modulation error ratios (MER) were examined to determine whether MER
differences could account for the observed receiver performance
differences. MER is definitely poorer for the ATSC997 source than for
the SFU; however, even with the vector signal analyzer's equalizer
turned off, the MER of the ATSC997 is still quite respectable. The ATSC
states that the MER of a DTV transmitter should be greater than 27 dB in
order to limit the impact on receiver threshold to about 0.25 dB.[^50]
The even higher 29.9 dB MER measured from the test setup using the
ATSC997 source suggests that the impact on the receiver should be well
under 0.25 dB.

Eilers and Sgrignoli state that an MER of 27 dB will cause an increase
in receiver threshold of 0.28 dB and explain that the increase can be
computed "*by converting the 27-dB transmitter figure of merit value and
the 15-dB receiver threshold value to equivalent linear relative powers,
adding them together, and converting back to a logarithmic value
resulting in 0.28 dB (= 0.3 dB) of increased noise*."[^51] Applying this
technique to an MER of 29.88 dB, yields a 0.14‑dB predicted increase in
receiver threshold---nowhere near the observed 0.9‑dB increase.

The cause of the roughly 1-dB degradation in receiver threshold when the
ATSC997 supplies the desired signal remains unresolved. Similar results
were obtained on repetition of the measurements---again swapping signal
sources but changing nothing else in the test setup; this suggests that
the difference was real rather than a result of measurement error.

### Selection of a Desired Signal Source for Tests at D~MIN~ + 3 dB

Due to concern over possible impacts on interference rejection
measurements to be made only 3-dB above the receiver threshold, a
decision was made to make the "D~MIN~+3 dB" measurements using the SFU
as the desired signal source. The use of the SFU as the desired signal
source for these measurements precluded testing on first-adjacent
channel (N+1 and N-1) because neither the ATSC997 nor the bandlimited
white noise source had adequate out-of-band spectral characteristics to
support such testing. Hence, these measurements were performed
(initially) only for an undesired signal (white Gaussian noise source
bandlimited to match the 3-dB width of an 8-VSB signal) on channels N-2
through N-16 and N+2 through N+16.

Receipt of a Wavetech WS2100 RF Player shortly before the delivery
deadline for this report enabled first-adjacent channel testing with a
high-quality desired signal source at D~MIN~+3 dB. The primary purpose
of this player is playback of digitally-recorded RF captures of
broadcast DTV signals received on TV antennas for evaluation of the
multipath performance of DTV demodulators; however, the system is
capable of performing as an unimpaired 8‑VSB signal source if equipped
with a recording of a high quality DTV signal. The Digital Television
group of Advanced Micro Devices (AMD) created such a "recording" by
mathematically deriving an 8‑VSB signal from an MPEG2 transport stream.
They provided this recording to us through Wavetech in the form of a
file called "Muddy Waters". The WS2100, equipped with this file, was
combined with an external upconverter to act as a desired signal source
at a level of D~MIN~ + 3 dB for tests with the SFU as an undesired
signal source on channels N-1 and N+1; those results are presented in
the next section of this chapter.

In tests of the three receivers indicated in Table 5-1 using the
Wavetech and the SFU, alternately, as desired signal sources, D~MIN~
values obtained with the two sources matched within 0.1 dB for each TV,
with an average difference of 0.0 dB.[^52] Thus, the TV receivers were
unable to distinguish the signal quality of the Wavetech source from
that of the SFU.

## Tests with Desired Signal at D~MIN~ + 3 dB

The results of the interference rejection measurements with the desired
signal at D~MIN~ + 3 dB are shown in Figures 5-9 and 5-10. Though the
ATSC provides no performance guidelines for interference rejection with
D = D~MIN~ + 3 dB, the performance guideline for D = -68 dBm is included
on the plots as a reference. Note that the vertical scale of the plots
was extended 5 dB lower than the earlier D/U plots, because the
measurement limit of the test setup extends lower at D~MIN~ + 3 dB. The
measurement limitations at D = D~MIN~ + 3 dB are based on leakage from
the undesired source into the desired channel.

Qualitatively, the interference behavior at the lower desired signal
level is similar to that at -68 dBm, with at least one notable
exception; the N+7 interference susceptibility that appeared so
significant at -68 dBm is quite low at D~MIN~ + 3 dB.

We also note that there was another of several discrepancies involving
measurements of receiver G4. When D~MIN~ was measured for the N-1 and
N+1 tests, the result was 5.5 dB higher than the two measurements
performed three months earlier for the N+2 through N+16 and N-2 through
N-16 tests. A repeat of the tests the next morning produced a match to
the older results. Though receiver G8 was the best performing receiver
among the eight in terms of interference rejection performance,
measurements involving G8 were consistently inconsistent (a topic
discussed further in Chapter 7).

## Summary of Fifth-Generation Receiver Results

Figure 5-11 combines the measurements for each of the four desired
signal levels---showing the *median* D/U ratio across the eight
receivers at each channel offset and signal level. The three upper solid
black lines correspond to the measurement limits applicable to the three
upper curves on the plot---for D = ‑28 dBm, ‑53 dBm, and ‑68 dBm. Points
falling on the respective black curves are at the measurement limit. The
black line at the top of the shaded region is the measurement limit
corresponding the measurements at D = D~MIN~ + 3 dB; it is based on
leakage from the undesired source into the desired channel.

Figure 5-12 is similar to Figure 5-11, except the plot is in terms of
undesired signal level (U) at the threshold. This portrayal differs in
two significant ways from the D/U plots:

\(1\) Better performance is indicated by higher points on the plot
rather than by lower ones;

\(2\) It makes clear that the greatest susceptibility to interference
occurs at low desired signal levels---even though D/U ratio is often
lowest (*i.e.*, best) at low desired signal levels.

We note that the measurement limitation shown in Figure 5-12 is the
maximum undesired signal power that the test setup could inject into the
receiver. The N-1 and N+1 offsets for D = -68 dBm and all of the offsets
for D = D~MIN~ + 3 dB are subject to an additional limitation, shown
only in the D/U plots, based on leakage of the undesired signal into the
desired channel.

Based on the D/U plots one might conclude that interference at N+7 is a
problem area; however, in terms of absolute levels of undesired signals
that can cause interference there are 14 other channel spacings that are
more vulnerable (N-7 through N+5, N+14, and N+15) to interference.

Figures 5-13 and 5-14 are repeats of the previous two plots except that
they show the second-worst performance among the eight receivers, rather
than the median. Figure 5-15 and 5-16 show the worst performance among
the eight receivers.

Chapter 13 includes plots of these measurement results for the
*individual receivers* along with extrapolations to D = D~MIN~ + 1 dB.
Chapter 15 presents plots of the measurements and extrapolations for
median, second-worst, and worst performance among the receivers.
Appendix A includes tabulations of some of the data.

## Earlier-Generation Receivers

A limited set of interference rejection tests was also performed on two
earlier-generation receivers for purposes of identifying tuner type, as
described in Chapter 3. The receivers are designated G3 and P1. These
two DTVs would be classified as fourth-generation or earlier based on
their multipath performance, which was tested as part of the SHVERA
Study. Both were on the market in 2005, though P1 was actually
introduced to the market in 2004.

Data from those measurements was plotted in Figure 3-7, but Figure 5-17
shows the same measurements overlaid with the median and range of
measurements of the eight fifth-generation receivers, for comparison.
All measurements were made with a desired signal power of -68 dBm; the
third/fourth generation measurements were limited to channel offsets of
N+2 through N+16.

It can be seen that the measurements on receiver P1 fall within the
range of performance for the fifth-generation receivers except at two
points: N+2, where the results for P1 are slightly better than any of
the fifth-generation results, and N+10, where the results for P1 are
worse than the fifth-generation results but are still within the ATSC
A/74 guidelines.

On the other hand, most of the measurements on receiver G3 correspond to
worse performance than any of the tested fifth-generation receivers, and
most fall well outside of the ATSC A/74 guidelines. Given the small
number of receivers tested, it is impossible to say whether similarly
poor performance is common among earlier-generation receivers.

## Taboo Effects and Other Observations

Some of the interference susceptibilities that can be seen in the plots
were expected based on previous knowledge of the analog UHF taboos.[^53]
For example, in Figures 5-1 and 5-9, an increased susceptibility to
interference can be seen at channels N+14 and N+15 in seven of the eight
fifth-generation receivers; a similar peak is seen for one of the two
earlier generation receivers in Figure 5-17. The mixer image frequency
band,[^54] which is centered 88 MHz (14 ^2^/~3~ channels) above the
center of the desired channel, straddles channels N+14 and
N+15---causing the increased susceptibility to interference from
undesired signals on those channels.

Similarly, a peak in susceptibility can be seen at N+7 in nine of the
ten receivers. The analog taboo at N+7 exists primarily because of the
possibility that unintentional local oscillator radiation from one TV
receiver might interfere with reception on another TV tuned seven
channels higher. Since all tests for this report were performed with
only one TV turned on at a time, local oscillator radiation was not a
factor.

Another potential explanation for the N+7 peak was the possibility that
an undesired signal on channel N+7 could beat with the desired
signal---creating interference that could pass through the IF filter of
the receiver. This "IF beat" effect[^55] has previously been recognized
with analog TV receivers and was initially thought to be the explanation
of the N+7 peak observed here---both because of its location (at N+7)
and the fact that the susceptibility threshold exhibits more of a
constant undesired signal level rather than a constant D/U ratio (see,
for example, Figures 5-11 and 5-12). The mixing product between the
desired signal and an undesired signal would be expected to have a power
level that is directly proportional to both the desired signal power and
the undesired signal power. The resulting interference passing through
the receiver's IF filter would thus increase in direct proportion to the
desired signal power, so that once the undesired signal reaches a
sufficient level to result in the interference coming within about 15 dB
of the desired signal power, reception would no longer be possible;
attempts to re-establish reception by increasing the desired signal
power would result in corresponding increases in the interference power.

Tests results presented in Chapter 7 contradict the IF-beat explanation
for the N+7 peak---suggesting instead some sort of direct interaction
between the TV's local oscillator and the undesired signal. The absence
of an N‑7 peak also runs counter to the IF-beat explanation.

Another analog taboo is associated with the "half IF" beat response.
This is the result of the second harmonic of an undesired signal, spaced
above the desired channel by half the IF frequency, beating with the
second harmonic of the TV's local oscillator. The result is an increased
susceptibility to interference spaced 22 MHz (3 ^2^/~3~ channels) above
the center of the desired channel. The susceptibility peak from this
effect would be expected to be seen primarily at channel N+4. Peaks at
N+4 were observed on only two receivers: A3 (Figure 5-3) and G3 (Figure
5-17).

An unexpected sensitivity occurred at N-6 on some receivers. Receiver J1
exhibits a large peak at N-6, as seen in Figure 5-1. A smaller peak can
be seen for receiver N1 in the same graph, and a third receiver (A3)
exhibits a slight susceptibility peak in Figure 5-3. The cause of this
sensitivity is not known.

Also unexpected is that two of the receivers (J1 and N1) are
significantly more susceptible to interference on the second-adjacent
channels (N-2 and N+2) than on the first-adjacent ones (N-1 and N+1),
and one more receiver (O1) exhibits such behavior on the positive side
(i.e., N+2 only). (See Figure 5-1, for example.) In fact, at low signal
levels (D~MIN~ + 3 dB), the second adjacent channels are as susceptible
to interference as the first adjacent channels even when viewed on a
median basis across all eight TVs. (See the lower curve on Figure 5-12,
for example.)

Some broader band effects can also been seen. For example, in
Figure 5‑3, the susceptibility of receiver D3 to interference is seen to
smoothly decrease from N-4 to N-16. The absence of peaks at specific
channels suggests that this is a cross-modulation effect.
Cross-modulation creates an interference power that is directly
proportional to the desired signal power. As a result, it is expected to
exhibit a fixed undesired signal level threshold that does not change as
the desired signal decreases (until desired signal approaches D~MIN~).
In Chapter 13 (Figure 13-4), we see that this is indeed the case at
desired signal levels of ‑53 dBm and below. The smooth decrease in the
cross-modulation effect as the desired signal moves from N-4 to N-16 is
likely to be a result of rolloff caused by the RF tracking filter in the
receiver.

This apparent cross-modulation effect on receiver D3 exhibits some
rather unexpected behavior as the undesired signal moves from channel
N-4 to N-3. With a desired signal power of -53 dBm, the interference
susceptibility, which had been rising smoothly as the undesired signal
was moved closer to the desired channel, suddenly drops precipitously at
channel N-3 by 20 dB or more[^56] and remains lower at channels N-2,
N-1, N+1, and N+2 than it had been at N-4. We believe that the reduction
in susceptibility is due to the influence of the undesired signal on the
receiver's automatic gain control (AGC)---a topic that will be discussed
further in Chapters 8 and 11.

Though the "hardness" of the thresholds was not one of the measurement
parameters for this study, we noted a strong "cliff effect" in most of
the threshold measurements. For example, in most cases, increasing
interference level about 1 dB above the threshold of visibility
(TOV)---the point at which picture degradation becomes
perceptible---caused complete loss of picture. In some cases picture
loss didn't occur until the undesired signal level rose as much as much
as 3 dB and in one case, 5 dB (though picture errors occurred
continuously in that case after only a 1.5 dB increase). In a few cases,
picture loss occurred concurrently with appearance of errors or with
only an additional 0.1 dB increase in interference---an extremely abrupt
cliff!

![](media/image11.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024418 .anchor}Figure 5‑11. D/U of 8 Receivers
at D = -68 dBm on Channel 30

![](media/image12.wmf){width="6.495138888888889in"
height="4.476388888888889in"}

[]{#__RefHeading___Toc163024419 .anchor}Figure 5‑12. D/U Statistics at D
= -68 dBm on Channel 30

![](media/image13.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024420 .anchor}Figure 5‑13. D/U of 8 receivers
at D = -53 dBm on Channel 30

![](media/image14.wmf){width="6.495138888888889in" height="4.4625in"}

[]{#__RefHeading___Toc163024421 .anchor}Figure 5‑14. D/U Statistics at D
= -53 dBm on Channel 30

![](media/image15.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024422 .anchor}Figure 5‑15. D/U of 8 receivers
at D = -28 dBm on Channel 30

![](media/image16.wmf){width="6.490277777777778in"
height="4.561805555555556in"}

[]{#__RefHeading___Toc163024423 .anchor}Figure 5‑16. D/U Statistics at D
= -28 dBm on Channel 30

![](media/image17.wmf){width="6.492361111111111in"
height="4.2652777777777775in"}

[]{#__RefHeading___Toc163024424 .anchor}Figure 5‑17. Spectra of Two
Desired Signal Sources

![](media/image18.wmf){width="6.492361111111111in"
height="4.239583333333333in"}

[]{#__RefHeading___Toc163024425 .anchor}Figure 5‑18. Spectra of Two
Desired Signal Sources on Expanded Scale

![](media/image19.wmf){width="6.497916666666667in"
height="4.4430555555555555in"}

[]{#__RefHeading___Toc163024426 .anchor}Figure 5‑19. D/U of 8 receivers
at D = D~MIN~ + 3 dB on Channel 30

![](media/image20.wmf){width="6.490277777777778in"
height="4.561805555555556in"}

[]{#__RefHeading___Toc163024427 .anchor}Figure 5‑20. D/U Statistics at D
= D~MIN~ + 3 dB on Channel 30

![](media/image21.wmf){width="6.497916666666667in"
height="4.338888888888889in"}

[]{#__RefHeading___Toc163024428 .anchor}Figure 5‑21. Median D/U of 8
receivers at Four Signal Levels on Channel 30

![](media/image22.wmf){width="6.497916666666667in"
height="4.384027777777778in"}

[]{#__RefHeading___Toc163024429 .anchor}Figure 5‑22. Median Threshold U
of 8 receivers at Four Signal Levels on Channel 30

![](media/image23.wmf){width="6.497916666666667in"
height="4.325694444444444in"}

[]{#__RefHeading___Toc163024430 .anchor}Figure 5‑23. 2^nd^ Worst D/U of
8 receivers at Four Signal Levels on Channel 30

![](media/image24.wmf){width="6.497916666666667in"
height="4.4430555555555555in"}

[]{#__RefHeading___Toc163024431 .anchor}Figure 5‑24. 2^nd^ Worst
Threshold U of 8 receivers at Four Signal Levels on Channel 30

![](media/image25.wmf){width="6.497916666666667in"
height="4.338888888888889in"}

[]{#__RefHeading___Toc163024432 .anchor}Figure 5‑25. Worst D/U of 8
receivers at Four Signal Levels on Channel 30

![](media/image26.wmf){width="6.497916666666667in"
height="4.4430555555555555in"}

[]{#__RefHeading___Toc163024433 .anchor}Figure 5‑26. Worst Threshold U
of 8 receivers at Four Signal Levels on Channel 30

![](media/image27.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024434 .anchor}Figure 5‑27. D/U of Two
Earlier-Generation Receivers at D = -68 dBm Relative to Fifth-Generation
Results

#  REJECTION RESULTS ON CHANNEL 51 FOR SINGLE 8-VSB INTERFERERS

This chapter presents the results of interference rejection tests of
seven DTV receivers tuned to channel 51. The interferer for these tests
was an 8-VSB signal placed sequentially on channels N+1 through N+16.
The tested receivers comprise seven of the eight receivers that were
tested for Chapter 5. Tests on one of the seven receivers were not
completed due to equipment failure. (Note that presentation of detailed
test results showing the variation of D/U with desired signal level for
one TV receiver at channel 51 are postponed until Chapter 11.)

The channel-51 tests for this chapter occurred chronologically before
those on channel-30, described in Chapter 5. The primary focus of these
tests was to investigate interference susceptibility of DTV receivers
operating in the upper UHF core channels to interference from future
services to be offered in spectrum currently assigned to television
channels 52 through 67. Because of this focus, tests were limited to
undesired signals above the desired channel.

Notwithstanding the above focus, an 8-VSB source was used as the
undesired signal for all of these tests (unlike the tests in Chapter 5,
which used an 8-VSB source only at N-1 and N+1 and used a bandlimited
Gaussian noise source at all other channel offsets).[^57] That choice
was based on the steep rolloff of the 8-VSB source at its channel edges
and the lack of availability of surrogate devices representative of
signals planned for use in channels 52 through 67.

## Tests at ATSC-Specified Desired Signal Levels

### "Weak" Desired Signal (D = -68 dBm)

Figure 6-1 shows measured values of D/U ratios at TOV for seven DTV
receivers for undesired signal channels ranging from N+1 to N+16 with
the desired signal power set to -68 dBm, the signal level that the ATSC
designates as "weak". The configuration of the plots is similar to those
in Chapter 5, except for the single-sided range of channel offsets, so
the reader is referred to the corresponding section of that chapter for
further explanation of the format.

The ATSC-recommended DTV-into-DTV interference rejection thresholds are
shown on the plot as a reference. Compliance with those voluntary limits
would be indicated by all points on each measurement curve falling on or
below the ATSC line. For the desired signal level of -68 dBm, only one
of the receivers (M1) fully complies with the guidelines. Receiver D3
fails to comply at seven of the sixteen tested channel offsets. The
other receivers fail to comply at from one to three of the channel
offsets. The N+7 channel offset seems to offer the most challenge in
that five of the receivers failed to comply with the guidelines at that
offset. We note that these measurements are directly comparable to the
ATSC performance guidelines since they were made with an 8-VSB signal as
the undesired signal.

The measurements on the seven receivers for the first adjacent channel
(N+1) are closely clustered, and all satisfy the ATSC guidelines. The
second-adjacent channel results (N+2) are much more scattered---with
three of the receivers failing to meet the ATSC guidelines and actually
exhibiting more susceptibility to interference at N+2 than at N+1.

Figure 6-2 shows the best, median, second worst, and worst performance
at each channel offset. On a median basis the only failure to satisfy
the ATSC recommended performance is at N+7.

### "Moderate" Desired Signal (D = -53 dBm)

Figure 6-3 shows measured values of D/U ratios at TOV for the same seven
DTV receivers with the desired signal power set to -53 dBm, the signal
level that the ATSC designates as "moderate". None of the receivers
comply with the performance guidelines at all channel offsets. Again,
N+7 appears to be the most challenging channel offset in that six of the
seven receivers failed to comply at that offset. Receiver D3 was, again,
the poorest performer---failing to comply with the guidelines at five of
the sixteen tested channel offsets. The other receivers failed to comply
at one or two channel offsets.

Figure 6-4 shows the best, median, second worst, and worst performance
at each channel offset. On a median basis the only failure to satisfy
the ATSC recommended performance is at N+7.

### "Strong" Desired Signal (D = -28 dBm)

Figure 6-5 shows that, with the desired signal set to the level that the
ATSC designates as "strong", every receiver complied with the ATSC
guidelines. Since the measurement limit was close to the ATSC
guidelines, almost all of the measurements fell at the measurement limit
(*i.e.*, the test setup was not capable of generating a strong enough
undesired signal to cause interference.)

Figure 6-6 shows the corresponding statistical data.

## Comparison to Channel-30 Results

Figures 6-7 and 6-8 compare the median D/U measurements on channel 30
with those on channel 51 for desired signal levels of -68 dBm and -53
dBm, respectively, for the seven DTV receivers that were tested on
channel 51. (Note that the medians for channel 30 shown in these two
charts are for only seven receivers---in order to match the channel-51
test group. The channel-30 data in Chapter 5 includes an eight
receiver.) The largest differences among points that were measurable
were 5 dB at N+15 (mixer image frequency) and 4 dB at N+2; both of those
measurements indicate better performance at channel 51 than at channel
30 (perhaps surprisingly). For all other measurements, the match between
channels was within about 2 dB or less.

![](media/image28.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024435 .anchor}Figure 6‑28. D/U of 7 Receivers
at D = -68 dBm on Channel 51

![](media/image29.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024436 .anchor}Figure 6‑29. D/U Statistics at D
= -68 dBm on Channel 51

![](media/image30.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024437 .anchor}Figure 6‑30. D/U of 7 Receivers
at D = -53 dBm on Channel 51

![](media/image31.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024438 .anchor}Figure 6‑31. D/U Statistics at D
= -53 dBm on Channel 51

![](media/image32.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024439 .anchor}Figure 6‑32. D/U of 7 Receivers
at D = -28 dBm on Channel 51

![](media/image33.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024440 .anchor}Figure 6‑33. D/U Statistics at D
= -28 dBm on Channel 51

![](media/image34.wmf){width="6.497916666666667in"
height="4.4430555555555555in"}

[]{#__RefHeading___Toc163024441 .anchor}Figure 6‑34. Comparison of
Median D/U for 7 Receivers on Channels 30 and 51 at D = -68 dBm

![](media/image35.wmf){width="6.497916666666667in"
height="4.4430555555555555in"}

[]{#__RefHeading___Toc163024442 .anchor}Figure 6‑35. Comparison of
Median D/U for 7 Receivers on Channels 30 and 51 at D = -53 dBm

#  TESTS WITH DIFFERENT SIGNAL TYPES AND SOURCES

This chapter presents the results of tests performed to determine the
influence of test signal sources and signal types on the interference
rejection performance of DTV receivers. Specifically, the tests compare
the following:

5.  Effect of two different 8-VSB signal generators as the *desired*
    signal;

6.  Effect of several types of *undesired* signals, including

    1.  White Gaussian noise bandlimited to the 3-dB width of an 8-VSB
        source;

    2.  8-VSB;

    3.  DVB-H---an orthogonal frequency division multiplexing (OFDM)
        signal---set for a 5-MHz channel width; and

    4.  White Gaussian noise bandlimited to a 3-dB width of 1 MHz.

In addition, the tests include a repeat of the baseline test conditions
(described below) to determine the amount of variation that may have
been due to repeatability or equipment changes (spectrum analyzer). All
of the tests discussed in this section were performed with the desired
signal on channel 30 and set to a level of -68 dBm.

Spectra and bandwidths of the various sources can be found in Chapters 2
and 5. Figures 2‑1 and 2‑2 show spectra of the four undesired signals;
bandwidths characteristics are shown in Table 2‑1. Figures 5‑7 and 5-8
show spectra of the two desired signal sources.

The baseline for comparison is:

1.  Desired signal source---Sencore ATSC997;

2.  Undesired signal type---white Gaussian noise (from an Agilent E4437B
    vector signal generator) bandlimited to match the 3-dB width of an
    8-VSB signal.

The 1-MHz bandwidth tests were performed on one DTV receiver (N1) for
channel offsets from N-16 to N+16. All other tests were performed on all
eight DTV receivers, but were limited to the five non-adjacent channel
offsets that exhibited the most interference potential among the
receivers at low signal levels (Figure 5‑16): N+2, N-2, N-3, N-4, and
N-6. (Note that channels N-1 and N+1 were not tested because the
Gaussian source did not have adequate band-edge rolloff to permit
testing on first-adjacent channels.)

The baseline tests, a subset of the measurements presented in Chapter 5,
were performed between August 30 and October 23, 2006. The comparative
tests presented here, including the "repeat baseline" test, were
performed between January 31 and February 6, 2007.[^58]

The results for all tests except the 1-MHz bandwidth tests are
summarized in Table 7-1. Individual results are presented in each
section. Results for the 1 MHz tests are in the next section of this
chapter.

Table 7-1 shows the means and standard deviations for the differences in
D/U measurements between a "comparative test" configuration and the
baseline configuration. The statistics are based on 35 measured values
(7 receivers X 5 channel offsets), except in the case of the DVB-H
signal, where 34 measurements were used for reasons explained in the
DVB-H section below. The standard deviations shown are for the
individual differences; standard deviation of the mean would be reduced
from this by a factor of square-root of 34 or 35 (5.8 or 5.9) if the
individual differences can be considered independent. Results are shown
in hundredths of a dB to reduce round-off error, although D/U
measurement resolution was 0.1 dB since the measurements were made by
stepping the undesired signal in increments of 0.1 dB to locate the
receiver's TOV.

[]{#__RefHeading___Toc163024571 .anchor}Table 7‑13. Comparative Signal
Test Summary

+------------+----------+------------+-----------+-----------+--------+
|            |          | *          |           | **D/U     |        |
|            |          | *Signals** |           | Ratio     |        |
|            |          |            |           | Relative  |        |
|            |          |            |           | to        |        |
|            |          |            |           | Baseline  |        |
|            |          |            |           | (dB)**    |        |
+------------+----------+------------+-----------+-----------+--------+
| **Test     | **Test   | **Desired  | **        | **Mean**  | **St   |
| Case**     | Dates**  | Signal     | Undesired |           | andard |
|            |          | Source**   | Signal**  |           | Devia  |
|            |          |            |           |           | tion** |
+------------+----------+------------+-----------+-----------+--------+
| Baseline   | 8        | ATSC997    | WGN       | 0         | N/A    |
|            | /30/2006 |            |           |           |        |
|            | --       |            |           |           |        |
|            | 10       |            |           |           |        |
|            | /23/2006 |            |           |           |        |
+------------+----------+------------+-----------+-----------+--------+
| Repeat     | 2        | ATSC997    | WGN       | -0.12     | 0.33   |
| Baseline   | /02/2007 |            |           |           |        |
|            | --       |            |           |           |        |
|            | 2        |            |           |           |        |
|            | /05/2007 |            |           |           |        |
+------------+----------+------------+-----------+-----------+--------+
| SFU as D   | 1        | ***SFU***  | WGN       | -1.14     | 0.40   |
|            | /31/2007 |            |           |           |        |
|            | --       |            |           |           |        |
|            | 2/1/2007 |            |           |           |        |
+------------+----------+------------+-----------+-----------+--------+
| 8-VSB as U | 2        | ATSC997    | **        | -1.28     | 0.68   |
|            | /06/2007 |            | *8-VSB*** |           |        |
|            | --       |            |           |           |        |
|            | 2        |            |           |           |        |
|            | /07/2007 |            |           |           |        |
+------------+----------+------------+-----------+-----------+--------+
| DVB-H OFDM | 2        | ATSC997    | **        | -0.40\    | 1.09   |
| as U       | /05/2007 |            | *DVB-H*** | (-0.25\*) |        |
|            | --       |            |           |           | (0     |
|            | 2        |            |           |           | .66\*) |
|            | /06/2007 |            |           |           |        |
+------------+----------+------------+-----------+-----------+--------+

*Notes:*

1.  *WGN = White Gaussian noise bandlimited to 5.38 MHz 3-dB width.*

2.  *The means and standard deviations were across five channel offsets
    and seven receivers---a total of 35 measurements, except results
    marked "\*" are for 34 measurements. Measurement results for
    receiver G4 were not included in these statistics for reasons
    discussed in the section of this chapter entitled, "Desired Signal
    Source: SFU Versus ATSC997"*

The "repeat baseline" test results differed from the baseline test
results by an average of only 0.12 dB---a reassuringly small difference
given the four-month delay and spectrum analyzer change between the
baseline and "repeat baseline". Though the results in the table are
presented relative to the original baseline tests, we can use the newer
"repeat baseline" as the point of reference by subtracting -0.12 dB from
the means. Doing so, we find the following.

1.  Use of the SFU as the *desired* signal source resulted in D/U ratios
    that were 1.0 dB lower (better) than were achieved with the ATSC997
    (the source used for most of the tests presented in this
    report).[^59] Thus the DTV receivers could tolerate about 1.0 dB
    more interference when the SFU was the desired signal source. This
    suggests that the ATSC997 may have had a slightly degraded
    performance that affected the results, at topic that was discussed
    in Chapter 5.

2.  An 8-VSB *interferer* results in D/U ratios that are 1.2 dB lower
    than those measured with a bandlimited white Gaussian noise
    interferer. Thus, the TV's are 1.2 dB less susceptible to
    out-of-band interference from an 8-VSB DTV signal than from a
    Gaussian-noise signal of comparable bandwidth.

3.  The OFDM DVB-H signal causes an interference effect comparable to
    that of bandlimited Gaussian noise based on the mean listed in
    parentheses in the table; this mean omits one measurement (in
    addition to those of receiver G4) for reasons discussed in the DVB-H
    section of this chapter.

The results of tests with the reduced-bandwidth interferer are presented
in the next section followed by detailed results of the tests described
above.

## 1-MHz Bandwidth Undesired Signal

Most tests performed for this report involved undesired signals that
filled, or nearly filled, a 6-MHz wide TV channel. Interference
rejection tests were also performed on one DTV receiver (receiver N1)
using a reduced-bandwidth source to determine the effect of a narrower
undesired signal spectrum. Specifically, a Gaussian noise signal with a
1-MHz 3‑dB width was created using the same vector signal generator that
was used to generate 5.38-MHz wide Gaussian noise signal. Spectral plots
were shown in Figures 2-1 and 2-2.

The interference rejection measurements were performed with the 1-MHz
bandwidth undesired signal centered on each channel from N-16 to N+16,
except for channel N. In addition, where the 8-VSB-width source had
identified interference vulnerabilities, tests were performed with the
1-MHz wide source stepped in 1-MHz or 2‑MHz steps to look for finer
frequency dependence of the vulnerability. The desired signal was set to
-68 dBm.

Figure 7-1 shows the threshold D/U ratio measurements for the 1-MHz wide
Gaussian noise source along with the results (from Chapter 5) for the
5.38-MHz-wide baseline source. (The baseline source was a Gaussian noise
source bandlimited to match the 3-dB width of an 8-VSB signal, except
that for N-1 and N+1, an actual 8-VSB source was used in order to
achieve band-edge characteristics adequate for adjacent channel
testing.) Though measurements were made from N-16 to N+16, the plot is
limited to a range over which the 1-MHz width tests yielded D/U ratios
that were above the measurement limit; consequently, the plot extends
from channel N-9 through the center point of channel N+16. Vertical
gridlines correspond to the boundaries between TV channels.

### N+7 Interference

In general the two plots in Figure 7-1 track each other reasonably well
except where narrowband vulnerabilities are apparent. One point of
interest is the interference susceptibility peak at N+7. The 1‑MHz data
shows high susceptibility when the undesired signal is centered at 44
MHz, but no measurable interference susceptibility at 43 or 45 MHz (or
elsewhere within channel N+7). Based on the bandwidth ratio of the two
signal sources (5.38 MHz / 1 MHz), one would expect the 1-MHz wide
signal to have a 7.3 dB greater power spectral density than the 5.38 MHz
wide signal used for the baseline tests when the power levels are the
same. This closely matches the 6.7 dB difference in D/U peaks in N+7 for
the two signal bandwidths.

It appears that N+7 interference is seen only when the undesired signal
overlaps the receiver's local-oscillator frequency, 44 MHz above the
center of the channel to which the DTV receiver is tuned. Our initial
hypothesis for the cause of the N+7 peak in the previous D/U plots was
that the undesired signal was acting as a noise-like local
oscillator---beating with the desired signal and creating a mixer
product that falls within the IF frequency of the TV. Such a mechanism
would not result in the narrow sensitivity spike observed here. Rather,
the interference mechanism apparently involves interaction between the
DTV receiver's local oscillator and the incoming undesired signal when
the spectrum of the incoming signal overlaps the local oscillator
frequency.

## Desired Signal Source: SFU Versus ATSC997

Test results described in Chapter 5, in the section entitled "Effect of
Desired Signal Source", demonstrate that, with no undesired signals
present, DTV receivers could operate at a lower desired signal level
when the desired signal was supplied by a newer, higher-quality 8-VSB
signal source (the Rohde and Schwarz SFU acquired by the FCC late in
this measurement program) than when it was supplied by the Sencore
ATSC997, the source that supplied the desired signal for most of the
measurements presented in this report (and the only 8-VSB signal source
available at the Laboratory during most of the channel-30 test period).
That section of Chapter 5 also presents the results of signal quality
tests, such as modulation error ratio, on each of the two sources.

The tests presented here look at the effect of the desired signal source
on susceptibility to interference. Specifically, interference rejection
measurements were performed with a desired signal level of -68 dBm on
channel 30 supplied by each of the two signal generators.

Table 7-2 shows the D/U ratios measured with the SFU as the desired
signal source relative to the baseline measurements made with the
ATSC997 as the source. The table also includes means and standard
deviations calculated across channel offsets (statistics computed on
five measurements) for each DTV receiver, across DTV receivers except
for receiver G5 (statistics computed on seven measurements), and across
both the channel offsets and receivers (statistics computed on 35
measurements).

[]{#__RefHeading___Toc163024572 .anchor}Table 7‑14. D/U Ratio With SFU
as Desired Signal Source Relative to That With Baseline Generator
(ATSC997)

  ------------ ------------- ------------- ------------- ------------- ------------- ------------- ------------- ------------- ------------- ------------
  **Channel    **D/U Ratio                                                                                                     **Mean (dB)** **Standard
  Offset**     Relative to                                                                                                     (Excluding    Deviation
               Baseline                                                                                                        G4)           (dB)**
               (dB)**                                                                                                                        (Excluding
                                                                                                                                             G4)

               **A3**        **D3**        **I1**        **J1**        **M1**        **N1**        **O1**        **G4**                      

  N-6          -1.37         -0.01         -1.54         -1.42         -1.39         -1.96         -1.29         -6.29         ***-1.28***   ***0.60***

  N-4          -1.15         -0.11         -1.00         -1.44         -1.16         -1.51         -1.03         -5.16         ***-1.06***   ***0.46***

  N-3          -1.03         -0.88         -0.98         -0.57         -1.10         -1.50         -1.06         -5.70         ***-1.02***   ***0.28***

  N-2          -1.21         -0.56         -0.96         -1.63         -1.14         -1.42         -0.90         -4.82         ***-1.12***   ***0.35***

  N+2          -1.28         -1.50         -1.27         -1.44         -0.75         -1.30         -1.12         -4.49         ***-1.24***   ***0.25***

  ***Mean***   ***-1.21***   ***-0.61***   ***-1.15***   ***-1.30***   ***-1.11***   ***-1.54***   ***-1.08***   ***-5.29***   ***-1.14***   

  ***Std       ***0.13***    ***0.61***    ***0.25***    ***0.42***    ***0.23***    ***0.25***    ***0.14***    ***0.72***                  ***0.40***
  Dev***                                                                                                                                     
  ------------ ------------- ------------- ------------- ------------- ------------- ------------- ------------- ------------- ------------- ------------

*Note:*

*The overall means and standard deviations (lower right corner of the
chart) omitted data for receiver G4 for reasons discussed in the text.*

Overall, the SFU measurements differed from the baseline measurements by
an average of about -1.1 dB (excluding receiver G4), indicating that the
receivers were slightly less susceptible to out-of-channel interference
when looking at a desired signal from the SFU as opposed to the ATSC997.
This difference reduces to -1.0 dB if the newer "repeat baseline" mean
is subtracted. A difference of 1 dB in an individual measurement having
a 0.4 dB standard deviation is large enough to suggest a statistically
significant difference. If the measurement differences were deemed
independent of one another, the standard deviation of the mean would be
reduced by a factor of square-root of 35 (*i.e.*, 5.9) to less than 0.1
dB. The size of the 1-dB mean difference relative to this computed
standard deviation provides strong evidence that this is a real
difference rather than a statistical artifact. Other measurements,
presented in Chapter 5, support the notion that there is a real
difference between the signal sources that influences the performance of
DTV receivers.

Except for the tests with receiver G4, there appears to be no major
trend across the receivers or the channel offsets.

The measurements for receiver G4 were dramatically different from those
for the other receivers. The change in signal sources *appeared* to have
a 5 dB effect on D/U ratios for that receiver; however, when the "repeat
baseline tests" were performed (the next section of this chapter), the
measurements on receiver G4 were performed twice with results differing
by as much as 6 dB for one of the channel offsets. Furthermore, when
receiver threshold without interference (D~MIN~) had been measured as
part of the D~MIN~+3 dB measurements presented in Chapter 5, D~MIN~
measurements on consecutive days yielded results differing by 5.4 dB.
Later, in measuring intermodulation effects with pairs of undesired
signals of unequal power, another discrepancy of about 6 dB arose for
that receiver. No other receiver exhibited such variations. Although
receiver G4 is the best-performing receiver tested (in terms of
interference rejection capabilities), there appears to be something
intermittent or variable in its performance. Consequently, results for
G4 were omitted from the overall mean and standard deviation data
presented in this chapter.

The results suggest that degraded signal quality from the ATSC997
reduces the receiver's available margin to handle interference. Signal
quality measurements presented in Chapter 5 did show that the signal
from the ATSC997 is inferior to that from the ATSC997, but we are unable
to identify a signal quality measurement low enough to explain the
performance differences of the TV receivers.

## Repeat Baseline Test

We wanted to determine whether the 1-dB change in D/U ratio discussed in
the previous section was actually related to the change in signal
sources or whether it might have been caused by some aspect of the test
setup. A different spectrum analyzer was used for the comparative tests
than for the baseline tests. Also, the baseline tests had been performed
about four months earlier than the comparative tests, so it was
plausible that some other unintended change in the equipment setup or
performance might have contributed to the observed change.

To rule out such equipment and test-setup issues the baseline tests were
repeated. Table 7-3 shows the results. The repeat test produced results
that, on average, differed from the original measurements by only about
0.1 dB. The standard deviation of those differences was 0.33 dB. This
agreement between the four-month old baseline data and new measurements
is considered quite good.

[]{#__RefHeading___Toc163024573 .anchor}Table 7‑15. D/U Ratio for Repeat
of Baseline Test Relative to Baseline

  ------------ ------------- ------------- ------------ ------------ ------------- ------------- ------------ ------------- ------------ ------------ ------------
  **Channel    **D/U Ratio                                                                                                               **Mean       **Standard
  Offset**     Relative to                                                                                                               (dB)**       Deviation
               Baseline                                                                                                                  (Excluding   (dB)**
               (dB)**                                                                                                                    G4)          (Excluding
                                                                                                                                                      G4)

               **A3**        **D3**        **I1**       **J1**       **M1**        **N1**        **O1**       **G4**        ***G4**                   
                                                                                                                            again*                    

  N-6          -0.73         0.01          0.00         0.02         -0.48         -0.27         -0.11        -6.23         *-0.23*      **-0.22**    **0.29**

  N-4          -0.69         0.11          0.50         0.13         -0.36         -0.22         -0.01        -3.37         *-0.09*      **-0.08**    **0.39**

  N-3          -0.47         -0.68         0.15         0.06         -0.26         -0.44         0.10         0.14          *0.63*       **-0.22**    **0.33**

  N-2          -0.31         -0.21         0.33         0.00         -0.04         -0.15         0.12         0.68          *0.19*       **-0.04**    **0.22**

  N+2          0.06          -0.90         -0.03        0.15         0.44          -0.01         0.13         -0.28         *0.36*       **-0.02**    **0.42**

  ***Mean***   ***-0.43***   ***-0.33***   ***0.19***   ***0.07***   ***-0.14***   ***-0.22***   ***0.05***   ***-1.81***   ***0.17***   **-0.12**    

  ***Std       ***0.32***    ***0.44***    ***0.22***   ***0.07***   ***0.36***    ***0.16***    ***0.10***   ***2.93***    ***0.34***                **0.33**
  Dev***                                                                                                                                              
  ------------ ------------- ------------- ------------ ------------ ------------- ------------- ------------ ------------- ------------ ------------ ------------

*Note:*

*The overall means and standard deviations (lower right corner of the
chart) omitted data for receiver G4 for reasons discussed in the section
of this chapter entitled, "Desired Signal Source: SFU Versus ATSC997".*

Results for receiver G4 were omitted from the statistics presented in
the previous paragraph for reasons described in the previous section.
The measurements shown in the "G4" column were made on a Friday. G4 was
measured again ("G4 again" column) on the following Monday with
significantly different results.

## Undesired Signal Type: 8-VSB Versus Bandlimited Gaussian Noise {#undesired-signal-type-8-vsb-versus-bandlimited-gaussian-noise .unnumbered}

Table 7-4 shows the effect of using an 8-VSB signal instead of
bandlimited white Gaussian noise as the *undesired* signal. On average,
the TVs are 1.3 dB less susceptible to interference from a DTV 8-VSB
signal than from white Gaussian noise bandlimited to the same 3-dB
bandwidth. The difference reduces to 1.2 dB when the newer baseline
measurements are used as the reference. Given that the standard
deviation of the mean is expected to be much less than the 0.68 dB value
for individual measurements (by a factor of 5.9, if individual
differences were statistically independent), the observed difference
appears to be real, rather than a statistical artifact.

The reason for the difference could be related to the amplitude
statistics of the respective waveforms. An 8-VSB waveform is likely to
exhibit fewer and smaller amplitude extremes (*i.e.*, less time spent at
levels far above the average power) than a Gaussian noise signal. For
linear interference mechanisms, the interference signal (within the TV)
is linearly related to the incoming undesired signal, and the
interference power (within the TV) is related to the mean-square of that
signal (*i.e.*, the second-order moment). For a third-order interference
mechanism on the other hand, the interference signal in the TV is
related to the cube of the incoming undesired signal, and the
interference power in the TV is related to the 6^th^-order moment of the
undesired signal. We consider it likely that the high order moments of
an 8-VSB signal are lower than those for a Gaussian noise signal (or for
an OFDM signal) of the same power.

[]{#__RefHeading___Toc163024574 .anchor}Table 7‑16. D/U Ratio With 8-VSB
as Undesired Signal Relative to That with Bandlimited Gaussian Noise

  ------------ ------------- ------------- ------------- ------------- ------------- ------------- ------------- ------------- ------------ ------------
  **Channel    **D/U Ratio                                                                                                     **Mean       **Standard
  Offset**     Relative to                                                                                                     (dB)**       Deviation
               Baseline                                                                                                        (Excluding   (dB)**
               (dB)**                                                                                                          G4)          (Excluding
                                                                                                                                            G4)

               **A3**        **D3**        **I1**        **J1**        **M1**        **N1**        **O1**        **G4**                     

  N-6          -1.32         -1.25         -1.61         -0.73         -1.85         -0.87         -1.76         -3.72         **-1.34**    **0.43**

  N-4          -1.31         -1.43         -0.92         -1.07         -1.66         -1.07         -0.87         -1.94         **-1.19**    **0.29**

  N-3          -0.79         -1.85         -2.23         -1.73         -1.50         -2.38         -1.47         -0.26         **-1.71**    **0.53**

  N-2          -0.76         -1.94         -2.31         -0.53         -1.31         -0.91         -0.71         -0.89         **-1.21**    **0.68**

  N+2          0.02          -2.99         -1.94         -0.48         -0.04         -0.67         -0.40         0.50          **-0.93**    **1.12**

  ***Mean***   ***-0.83***   ***-1.89***   ***-1.80***   ***-0.91***   ***-1.27***   ***-1.18***   ***-1.04***   ***-1.26***   **-1.28**    

  ***Std       ***0.55***    ***0.68***    ***0.56***    ***0.51***    ***0.72***    ***0.69***    ***0.56***    ***1.64***                 **0.68**
  Dev***                                                                                                                                    
  ------------ ------------- ------------- ------------- ------------- ------------- ------------- ------------- ------------- ------------ ------------

*Note:*

*The overall means and standard deviations (lower right corner of the
chart) omitted data for receiver G4 for reasons discussed in the section
of this chapter entitled, "Desired Signal Source: SFU Versus ATSC997".*

The variability among these measured differences in D/U ratios for the
change in undesired signal type is somewhat larger than that associated
with the change in the desired signal source. There may be patterns in
the data. For example, the undesired signal type appears to have a
greater effect at N-3 than at N+2. Whether these differences are
associated with the order of the associated interference mechanisms-in
conjunction with moments of the undesired signals (as discussed in the
previous paragraph) is uncertain because the order of the interference
mechanisms is often masked by AGC operation---a topic to be addressed in
subsequent chapters.

## Undesired Signal Type: DVB-H OFDM Versus Bandlimited Gaussian Noise

Tests were performed with an OFDM undesired signal and compared to the
tests with bandlimited Gaussian noise. The OFDM signal was produced by
an Agilent E4438C vector signal generator using Agilent Signal Studio
for DVB software. The signal type was selected as DVB-H, an OFDM signal
format designed for mobile video application. The waveform parameters
were as follows:

1.  Size 2k

2.  Modulation 64 QAM

3.  Channel width 5 MHz

4.  Guard interval 1/8

Plots of the signal spectrum were shown in Figures 2-1 and 2-2. The
bandwidth measurements were shown in Table 2-1.

Table 7-5 shows the D/U ratio measurements made with the DVB-H source as
the undesired signal relative to those for the bandlimited Gaussian
noise baseline. The table includes one point that is greatly
inconsistent with the others (by about 5 dB). That measurement, for
receiver N1 with the undesired signal on channel N-3, indicates that the
receiver was significantly less susceptible to the DVB-H interference
than to the bandlimited Gaussian noise signal.

[]{#__RefHeading___Toc163024575 .anchor}Table 7‑17. D/U Ratio With DVB-H
as Undesired Signal Relative to That with Bandlimited Gaussian Noise

  ------------ ------------- ------------- ------------ ------------- ------------- ------------- ------------- ------------- ------------ ------------
  **Channel    **D/U Ratio                                                                                                    **Mean       **Standard
  Offset**     Relative to                                                                                                    (dB)**       Deviation
               Baseline                                                                                                       (Excluding   (dB)**
               (dB)**                                                                                                         G4)          (Excluding
                                                                                                                                           G4)

               **A3**        **D3**        **I1**       **J1**        **M1**        **N1**        **O1**        **G4**                     

  N-6          -0.87         -0.08         0.24         0.17          -0.78         -0.23         -0.54         -1.47         **-0.30**    **0.44**

  N-4          -0.94         -0.1          1.92         0.04          -0.74         -0.43         -0.54         -0.87         **-0.11**    **0.96**

  N-3          -0.53         -0.53         0.09         -1.13         -0.52         ***-5.44***   -0.53         0.49          **-1.23**    **1.89**

  N-2          -0.54         -0.15         0.2          -0.09         -0.05         -0.08         0.00          -0.08         **-0.10**    **0.22**

  N+2          0.12          -2.37         -0.57        0.26          0.43          0.11          0.24          -1.53         **-0.25**    **0.99**

  ***Mean***   ***-0.55***   ***-0.65***   ***0.38***   ***-0.15***   ***-0.33***   ***-1.21***   ***-0.27***   ***-0.69***   **-0.40      
                                                                                                                              (‑0.25)**    

  ***Std       ***0.42***    ***0.98***    ***0.92***   ***0.56***    ***0.52***    ***2.37***    ***0.37***    ***0.88***                 **1.09
  Dev***                                                                                                                                   (0.66)**
  ------------ ------------- ------------- ------------ ------------- ------------- ------------- ------------- ------------- ------------ ------------

*Note:*

*The overall means and standard deviations (lower right corner of the
chart) exclude data for receiver G4 for reasons discussed in the section
of this chapter entitled, "Desired Signal Source: SFU Versus ATSC997".
The means and standard deviations shown in parentheses also exclude the
value associated with receiver N1 at N-3 **boxed bold italics** for
reasons discussed below.*

Since the 4.8 MHz width of the DVB-H waveform, combined with its
extremely steep spectrum rolloff on each side, left a gap of about 0.6
MHz between each side of the waveform's spectrum and the channel edges,
we wondered whether receiver N1 might have a narrowband interference
susceptibility within channel N-4 that falls outside of the DVB-H
waveform bandwidth. To test this theory, the measurement was repeated
twice, once with the waveform shifted 0.5 MHz downward and once with the
waveform shifted 0.5 MHz upward. The measured D/U ratios relative to the
baseline were as follows:

1.  Frequency shift = -0.5 MHz D/U relative to baseline = -5.97 dB

2.  Frequency shift = +0.5 MHz D/U relative to baseline = +1.95 dB

The results suggest that this receiver had a narrowband susceptibility
between the upper edge of the DVB-H waveform, when it was centered on
the channel, and the upper edge of the channel. The tests conducted with
a 1-MHz wide interferer (Figure 7-1) happen to have been performed with
the same receiver. Those tests do reveal a rapidly increasing
susceptibility to interference as the undesired signal approaches the
upper band edge for channel N-3.

The mean and standard deviation shown in the table were computed in the
same manner those for the other comparison tests in this chapter. In
addition, a second computation was performed omitting the measurement
associated with N-4 for receiver N1 because the reduced width of the
OFDM signal had apparently caused a narrowband susceptibility to be
missed.

Except for the one aberrant point caused by placement of the DVB-H
waveform spectrum, there is no obvious trend in the data.

Using the parenthetical value of mean from the table (-0.25 dB) and
subtracting the mean for the "repeat baseline" test shows a mean
difference of -0.1 dB between the OFDM results and the Gaussian results.
The interference effect of the DVB-H waveform appears to be essentially
identical to that of bandlimited Gaussian noise.

![](media/image36.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024443 .anchor}Figure 7‑36. D/U With 1-MHz
Undesired Signal Bandwidth

#  THEORETICAL FRAMEWORK FOR OUT-OF-CHANNEL INTERFERENCE

Before presenting more measurement results, we devote a chapter to
establishing a theoretical framework that will be used for interpreting
or extending the measurement results in most of the remaining chapters.
We apply this theoretical basis to some of the common interference
mechanisms that apply to TV reception. A more detailed derivation is
included in Appendix B.

When a DTV receiver operates in the presence of white Gaussian
*[co-channel]{.underline}* interference, the threshold of visibility
(TOV) of picture degradation occurs when the desired signal power D
exceeds the co-channel interference by about 15 dB.[^60] This number may
vary somewhat for noise having other statistical properties, and may be
much lower if the noise is heavily concentrated at a band edge where
filtering in the DTV provides additional rejection; nonetheless, one
expects that, as signal power D varies, the undesired signal power at
threshold will vary linearly with it---resulting a constant D/U ratio as
D or U are varied. This relationship holds whenever the co-channel
interference is high enough that the effect of internal noise in the
receiver becomes insignificant.

For most *[out-of-channel]{.underline}* interference mechanisms, the DTV
receiver unintentionally converts a small portion of the out-of-channel
power into co-channel power. If one knows the amount of conversion into
co-channel interference, one can treat the problem as a co-channel
interference problem, which is relatively well understood, as described
above. In this formulation of the problem, measuring the desired signal
power D at the TOV provides an indirect method of measuring the
co-channel power created internal to the receiver, since we know that
the co-channel power will be about 15 dB below the measured value of D.

The conversion process by the DTV receiver from out-of-channel
interference to co-channel interference may be linear or nonlinear. If
it is linear, then the internally-created co-channel interference will
vary linearly with the out-of-channel interference power U causing the
value of the desired signal power D at threshold to vary linearly with
U. The result will be that threshold D/U ratio will be constant as D or
U is varied. If the conversion process is nonlinear, then the
relationship between D and U will be nonlinear and the D/U ratio will
vary with D and U.

## Interference Mechanisms and Order

We will assume that the *[co-channel]{.underline}* interference power
created by the DTV receiver in response to an
*[out-of-channel]{.underline}* undesired signal power U will be
proportional to D^L^U^M^, where L and M are integer constants that
define the ***[order]{.underline}*** of the interference mechanism. For
most interference mechanisms, L will be zero, so only the U^M^ term
exists. The following are among the interference mechanisms that can be
modeled by this formulation.

1.  Linear interference: L=0, M=1. Creates co-channel interference
    proportional to U.

    1.  Example: mixer image. The mixer in a TV receiver converts the
        spectrum of the intended channel of the received signal to an
        intermediate frequency (IF) where it can be filtered more
        precisely to pass the desired channel while rejecting the
        undesired frequencies. Unfortunately, in single-conversion
        tuners a second a 6-MHz wide portion of the input spectrum
        centered 88 MHz above the desired channel is also converted to
        that same IF. Filtering prior to the mixer strongly
        diminishes---but doesn't fully extinguish---this unintended
        signal.

    2.  Example: leakage of the adjacent channel signal through the
        channel selection filter of the DTV receiver would also
        constitute a linear interference mechanism.

2.  Second-order interference: L=0, M=2. Creates co-channel interference
    proportional to U^2^.

    1.  Example: "half-IF" taboo. The second harmonic of an undesired
        signal 22 MHz above the desired signal beats with the second
        harmonic of the receiver's local oscillator, creating a
        difference frequency that falls within the IF band of the
        receiver.

3.  Third-order interference: L=0, M=3. Creates co-channel interference
    proportional to U^3^.

    1.  Example: third-order intermodulation (IM3) of a single,
        adjacent-channel undesired signal. IM3 creates spectral
        components that spill into each adjacent channel.

    2.  Example: third-order intermodulation (IM3) of a pair of
        undesired channels placed at channels N+K and N+2K where N is
        the desired channel. In this case, the interference power
        created in channel N is proportional to U~N+K~^2^U~N+2K~. The
        result is a process that is second-order in terms of U~N+K~ and
        linear in terms of U~N+2K~; however, if the two undesired
        signals are set to equal powers and varied in amplitude
        together, the resulting interference is third order.

4.  Cross-modulation: L=1, M=2. Creates co-channel interference
    proportional to DU^2^.

    1.  Cross-modulation is essentially a third-order effect, but the
        co-channel interference created is proportional to D and to
        U^2^. As a result, increasing the desired signal power does not
        improve the signal-to-interference ratio.

## Threshold of Visibility of Picture Degradation Due to Interference

As stated earlier, the TOV for a DTV receiver occurs when the ratio of
the desired signal to the co-channel interference-plus-noise exceeds the
required signal-to-noise ratio **SNR~R~** for the DTV receiver. We will
assume that the co-channel interference-plus-noise power includes two
components: receiver noise power **N~R~** and the co-channel
interference that was created by linear or nonlinear interference
mechanisms operating on the out-of-channel undesired signal (**c
D^L^U^M^**, where **c** is a constant). Note that the both the
co-channel receiver noise and the co-channel interference power are
generated *within* the DTV receiver. The levels we refer to here are
expressed in terms of equivalent *input* power levels to the TV.

Thus we can say

D / (c D^L^U^M^ + N~R~) = SNR~R~

For 8-VSB DTV receivers the SNR~R~ is about 33.9 (*i.e.*, 15.3 dB
converted to a linear power ratio) if the noise and interference have
white spectra and Gaussian statistics. Note that, while the receiver
noise is likely to be white and Gaussian, the interference may not
be---in which case a different SNR would apply to it, but we will
neglect that difference for the discussion here.

We note that the threshold desired signal power in the absence of
interference (D~MIN~) is given by

D~MIN~ = SNR~R~ N~R~

Thus we can write,

D = SNR~R~ c D^L^U^M^ + D~MIN~

## Slopes of Log-Log Plots of D, U, and D/U 

We first consider the case in which the desired signal at threshold is
much larger than D~MIN~. We can then write,

D ≈ SNR~R~ c D^L^U^M^

Depending on the values of L and M, a plot of D versus U (in power
units, such as microwatts) may be linear or nonlinear; however, a plot
of log(D) versus log(U) will always be linear. Thus, plots of D versus U
in units of dBm will be straight lines, since decibels are a logarithmic
unit. The slope of such a log-log plot indicates the order of the
interference mechanism. For example, for a third-order interference
mechanism (L=0, M=3), the slope of log-D versus log-U will be 3 dB/dB
and the log-U versus log-D will be 0.333 dB/dB; similarly, a plot of D/U
versus D on a log-log scale will have a slope of 0.667 dB/dB. The
expected slopes of log-log plots for various interference mechanisms are
summarized in Table 8-1. The final row of the table will be explained in
the next section.

[]{#__RefHeading___Toc163024576 .anchor}Table 8‑18. Slopes of Log-Log
Plots of D, U, and D/U for Various Interference Mechanisms

+-------------------------+---------+---------+---------+-------------+
| **Interference          | **Slope | **Slope | **Slope | **Charact   |
| Mechanism**             | of\     | of\     | of\     | erization** |
|                         | Log (D) | Log (U) | Log     |             |
|                         | Versus\ | V       | (D/U)   |             |
|                         | Log     | ersus** | V       |             |
|                         | (U)\    |         | ersus** |             |
|                         | in      | **Log   |         |             |
|                         | dB/dB** | (D)\    | **Log   |             |
|                         |         | in      | (D)\    |             |
|                         |         | dB/dB** | in      |             |
|                         |         |         | dB/dB** |             |
+-------------------------+---------+---------+---------+-------------+
| Linear (M = 1)          | 1       | 1       | 0       | Constant    |
|                         |         |         |         | D/U         |
+-------------------------+---------+---------+---------+-------------+
| Second order (M = 2)    | 2       | 0.5     | 0.5     |             |
+-------------------------+---------+---------+---------+-------------+
| Third order (including  | 3       | 0.333   | 0.667   |             |
| third-order             |         |         |         |             |
| intermodulation of a    |         |         |         |             |
| pair of equal-power     |         |         |         |             |
| interferers) (M = 3)    |         |         |         |             |
+-------------------------+---------+---------+---------+-------------+
| Cross modulation (M =   | I       | 0       | 1       | Constant U  |
| 2, L = 1)               | nfinite |         |         |             |
+-------------------------+---------+---------+---------+-------------+
| AGC-Stabilized          | 1       | 1       | 0       | Constant    |
| Nonlinear^1^            |         |         |         | D/U         |
+-------------------------+---------+---------+---------+-------------+

*Notes:*

^1^ *See next section ("Effect of AGC")*

## Effect of AGC

Television receivers incorporate an automatic gain control (AGC)
function that adjusts the gain of one or more stages in the tuner in
order to maintain acceptable signal levels. The gain may be constant (at
its maximum) when signal levels are low. As signal levels rise, a point
is reached at which the AGC begins to reduce the gain to avoid
overdriving the tuner circuitry. The AGC control function may be based
on the level of the desired signal, or on the combined power of the
desired and undesired signals at some point in the tuner (typically the
mixer), or both.[^61] Typically, the AGC will act to reduce the gain of
both RF and IF amplifier stages, but not necessarily at the same signal
levels. As input signal levels increase, the AGC may act to reduce IF
gain first---waiting for higher signal levels before reducing RF
amplifier gain (delayed AGC).

If we consider an interference mechanism that is caused by a
nonlinearity at a given point in the tuner, the expected nonlinear
behavior described in the previous section will exist only for signal
levels up to the point at which AGC begins to reduce gain *prior to the
point of the nonlinearity*. For example, if a given interference
mechanism is caused by nonlinearity in the receiver's mixer, AGC gain
reductions in the IF amplifier will not affect it, but gain reductions
in the RF amplifier will.

Under the assumption that AGC operation tends to adjust gain so as to
maintain either the desired signal or the undesired signal at a constant
level[^62] at the point of nonlinearity, then the interference begins to
behave as if it were linear (with the possible exception of
cross-modulation when AGC operates on undesired signal power).[^63] That
is, further increases in D result in corresponding increases in
threshold U, so D/U remains constant. This occurs because the amplitudes
at the nonlinearity remain constant in spite of further increases in
input signal levels at the receiver's antenna input terminal. The
results are derived in Appendix B.

This suggests that we may see interference that behaves like third-order
interference, for example, at low signal levels, but switches to linear
behavior when a certain signal threshold associated with the AGC is
exceeded. The last row of Table 8-1 refers this effect.

## Weak Signals

As stated above, both the linear and the nonlinear interference
mechanisms will plot as straight lines on a log-log plot (*e.g.*,
plotting U, D, and D/U in decibels). However, this relationship is true
only at desired input signal levels high enough to make the receiver's
own internal noise an insignificant contributor to performance.

As signal level approaches the threshold for the receiver in absence of
interference, the receiver becomes increasingly more susceptible to
interference than such straight-line projections would predict.

Referring to the earlier equation defining the interference threshold,
we had

D = SNR~R~ c D^L^U^M^ + D~MIN~

The presence of the quantity D~MIN~ causes the log-log plots to deviate
from straight-line behavior as D approaches D~MIN~. Figures 8-1 through
8-4 depict the deviation of threshold U versus D from a straight line on
a log-log plot for linear, second-order, third-order, and
cross-modulation interference, respectively. It can be seen that for the
first three cases, the distance in the D direction from the straight
line projection is 3 dB and 6.9 dB when D = D~MIN~ + 3 dB and D~MIN~ + 1
dB, respectively. Distances in the U direction vary with slope of the
line as shown in the illustrations and in Table 8-2. Thus, for example,
when desired signal level drops to a point 1 dB above the receiver's
threshold (D~MIN~), the DTV receiver will be sensitive to interference
from undesired signals that are lower than a straight-line projection
would predict, by amounts ranging from 2.3 to 6.9 dB, depending on the
order of the interference mechanism.

In terms of deviation from the straight-line projection, the effect of
AGC varies according to whether the AGC is driven primarily by desired
signal power or by undesired signal power. In the former case, the
deviation from a straight-line projection matches that of the underlying
interference mechanism. In the latter, the deviation matches that of a
linear process.

[]{#__RefHeading___Toc163024577 .anchor}Table 8‑19. Deviation in
Threshold U from Straight-Line Projection as D approaches D~MIN~

+------------------------------+----------+--------+---------+--------+
|                              | **D      |        |         |        |
|                              | eviation |        |         |        |
|                              | in       |        |         |        |
|                              | T        |        |         |        |
|                              | hreshold |        |         |        |
|                              | U**      |        |         |        |
|                              |          |        |         |        |
|                              | **from   |        |         |        |
|                              | Strai    |        |         |        |
|                              | ght-Line |        |         |        |
|                              | Pr       |        |         |        |
|                              | ojection |        |         |        |
|                              | (dB)**   |        |         |        |
+------------------------------+----------+--------+---------+--------+
| **Interference Mechanism**   | **D/D~   | **D/D  | **D/    | **D/D  |
|                              | MIN~^1^\ | ~MIN~\ | D~MIN~\ | ~MIN~\ |
|                              | = 16     | = 3    | = 1     | = 0    |
|                              | dBm**    | dB**   | dB**    | dB**   |
+------------------------------+----------+--------+---------+--------+
| Linear (M = 1)               | -0.1     | -3.0   | -6.9    | In     |
|                              |          |        |         | finite |
+------------------------------+----------+--------+---------+--------+
| Second order (M = 2)         |          | -1.5   | -3.4    | In     |
|                              |          |        |         | finite |
+------------------------------+----------+--------+---------+--------+
| Third order (including       |          | -1.0   | -2.3    | In     |
| third-order intermodulation  |          |        |         | finite |
| of a pair of equal-power     |          |        |         |        |
| interferers) (M = 3)         |          |        |         |        |
+------------------------------+----------+--------+---------+--------+
| Cross modulation (M = 2, L = |          | -1.5   | -3.4    | In     |
| 1)                           |          |        |         | finite |
+------------------------------+----------+--------+---------+--------+
| AGC-Stabilized Nonlinear w/U | -0.1     | -3.0   | -6.9    | In     |
| driving AGC^2^               |          |        |         | finite |
+------------------------------+----------+--------+---------+--------+

> *Note:*
>
> *^1^ For the nominal D~MIN~ value of -84 dBm, D/D~MIN~ = 16 dB when D
> = -68 dBm*
>
> *^2^ With desired signal driving AGC, deviation from straight-line
> projection matches that of the original nonlinear process, except in
> the case of cross-modulation, which was not completely solved.*

## IM3 With Paired Signals

When the interference is caused by a pair of signals located at channels
N+K and N+2K, the receiver creates third-order intermodulation (IM3)
products in the desired channel N.

In this case, Appendix B shows that the interference equation becomes:

D = (SNR~R~ / IP3^2^) U~N+K~^2^U~N+2K~ + D~MIN~.

We will use the term IP3 / SNR~R~^1/2^ to quantify the IM3 properties of
the receiver by computing it from measurements of D and U at threshold
with D \>\> D~MIN~ and U = U~N+K~ = U~N+2K~.

IP3 / SNR~R~^1/2^ = (U^3^ / D)^1/2^

or, in decibel units

(IP3 / SNR~R~^1/2^)\|~dB~ = 1.5 U\|~dB~ - 0.5 D\|~dB~

where \|~dB~ means conversion to decibels:

X\|~dB~ = 10 log(X)

To compute interference susceptibilities knowing (IP3 /
SNR~R~^1/2^)\|~dB~, we will use the following.

U~N+K~\|~dB~ = (IP3 / SNR~R~^1/2^)\|~dB~ + (D\|~dB~ - U~N+2K~\|~dB~)/2

or,

U~N+2K~\|~dB~ = 2(IP3 / SNR~R~^1/2^)\|~dB~ + D\|~dB~ - 2 U~N+K~\|~dB~\]

See Appendix B for details the derivation.

![](media/image37.wmf){width="6.497916666666667in"
height="4.4430555555555555in"}

[]{#__RefHeading___Toc163024444 .anchor}Figure 8‑37. Deviation of Log-U
Versus Log-D From Straight Line For Linear Interference

![](media/image38.wmf){width="6.497916666666667in"
height="4.4430555555555555in"}

[]{#__RefHeading___Toc163024445 .anchor}Figure 8‑38. Deviation of Log-U
Versus Log-D From Straight Line For 2^nd^-Order Interference

![](media/image39.wmf){width="6.497916666666667in"
height="4.4430555555555555in"}

[]{#__RefHeading___Toc163024446 .anchor}Figure 8‑39. Deviation of Log-U
Versus Log-D From Straight Line For 3^rd^-Order Interference

![](media/image40.wmf){width="6.497916666666667in"
height="4.4430555555555555in"}

[]{#__RefHeading___Toc163024447 .anchor}Figure 8‑40. Deviation of Log-U
Versus Log-D From Straight Line For Cross-Modulation

#  THIRD-ORDER INTERMODULATION WITH PAIRED EQUAL-POWER INTERFERERS

Rhodes and Sgrignoli have raised the issue of ***third-order
intermodulation (IM3***) distortion occurring within a TV receiver
between pairs of undesired input signals as a potentially significant
interference mechanism for DTV reception.[^64] [^65] [^66] This chapter
presents the results of interference rejection measurements performed
using pairs of undesired signals spaced so as to place IM3 products into
the desired channel. Thus, signal pairs were placed on channels N+K and
N+2K, where K is a positive or negative integer. For this chapter the
two undesired sources were maintained at equal power levels. Additional
test results with paired signals are contained in Chapters 10 (unequal
sources) and 11 (detailed measurements on one TV).

In all tests, the undesired signal placed farthest from the desired
channel (*i.e.*, at N+2K) was a white Gaussian noise signal bandlimited
to match the 3-dB width of an 8-VSB signal. For tests with the desired
channel N = 51, the closer undesired signal (at N+K) to the desired
channel N was an 8-VSB signal. For tests with the desired channel N =
30, the closer undesired signal was 8-VSB only if it was on a
first-adjacent channel (N-1 or N+1); otherwise, the bandlimited Gaussian
noise signal was used as the closer undesired signal source. The reason
for the use of bandlimited Gaussian noise instead of 8-VSB was that,
throughout most of the test period, only one 8-VSB source was available
and it was needed as a desired signal source. Tests involving first
adjacent channels were postponed until the procurement of another 8‑VSB
generator because the edge-of-band rolloff of the Gaussian source was
not sufficient to support rejection tests on first adjacent channels.

Table 9-1 summarizes the test parameters. Only the test results from the
first three rows of the chart are presented in this chapter. The fourth
row describes tests at unequal undesired signal levels, which are
presented in Chapter 10. The last row of the table identifies very
detailed tests of the variation of D/U with desired signal level, which
are presented in Chapter 11.

The purpose of these tests was to determine the extent to which pairs of
undesired signals create an interference effect---through IM3 occurring
within a TV receiver---that exceeds the effects of the individual
signals.

## Spectra of Third-Order Intermodulation Distortion

IM3 creates signal components at frequencies that were not present in
the input spectrum, but are in the same general frequency range as the
input signals. The IM3 of interest in this chapter is created within the
tuners of consumer DTV receivers. Since test points are not available
within consumer receivers to show the actual signal effects that occur,
spectra of IM3 components created by a laboratory instrumentation
amplifier were measured to illustrate the concepts.[^67]

[]{#__RefHeading___Toc163024578 .anchor}Table 9‑20. Parameters for
Paired-Interferer Tests (N+K/N+2K)

  ------------- ----------- ----------- ---------- ------------- ------------- ------------ -----------
  **Chapter**   **Desired   **Desired   **K**      **Undesired   **Undesired   **Relative   **Number of
                Channel N** Signal                 Signal at     Signal at     Power of     DTV
                            Power**                N+K**         N+2K**        U~N+K~ and   Receivers
                                                                               U~N+2K~**    Tested**

  9             30          -68 dBm,    1, -1      8-VSB         WGN^1^        Equal        8
                            ‑53 dBm,                                                        
                            ‑28 dBm                                                         

  9             30          -68 dBm,    2 through  WGN^1^        WGN^1^        Equal        8
                            ‑53 dBm     5\                                                  
                                        and\                                                
                                        -2 through                                          
                                        ‑5                                                  

  9             51          -68 dBm,    1 through  8-VSB         WGN^1^        Equal        7^2^
                            ‑53 dBm,    8                                                   
                            ‑28 dBm                                                         

  10            30          D~MIN~+3    2 or 3     WGN^1^        WGN^1^        Variable     2
                            dB,\                                                            
                            -68 dBm,\                                                       
                            -53 dBm                                                         

  11            51          D~MIN~+1    1 through  8-VSB         WGN^1^        Equal        1
                            dB,         4                                                   
                            D~MIN~+3                                                        
                            dB, ‑78 to                                                      
                            ‑8 dBm in                                                       
                            5‑dB steps                                                      
  ------------- ----------- ----------- ---------- ------------- ------------- ------------ -----------

*Notes:*

*^1^ WGN = white Gaussian noise signal bandlimited to match the 3-dB
width of an 8-VSB signal.*

*^2^ For one of the seven TVs tested at channel 51, the complete set of
measurements was performed only for D = -68 dBm; for the other two
levels, only N+1/N+2 tests were performed.*

Figure 9-1(a) shows the spectrum of an 8-VSB signal on channel 34 after
passing through the amplifier at a level 12 dB below the maximum rated
output power of the amplifier. The "shoulders" that can be seen emerging
from the sides of the 8-VSB spectrum about 33‑dB below the main signal
spectrum level are IM3 products. It can be seen that they extend through
most of the width of each adjacent channel (channels 33 and 35), but not
beyond. Thus, IM3 generated with a DTV tuner in response to an undesired
signal on a single TV channel could influence reception of a desired
signal on a *first-adjacent* channel. Put another way, if the TV is
tuned to channel N, its reception there could be adversely impacted by
IM3 caused by an undesired signal on channel N-1 or on channel N+1.

Figure 9-1(b) shows the effect of adding a signal of equal power on a
second channel---in this case channel 38. The addition of the second
signal causes the shoulders around the first signal to increase. A
similar pair of shoulders is also created around the second signal. The
spectral shoulders occupy channels 33, 35, 37, and 39---the channels
adjacent to each of the input signals. In addition to the shoulders
around each input signal, the presence of the second signal causes two
other bumps in the spectrum to occur. One is centered on channel 30 and
the other on channel 42, but they also spill over into the channels
adjacent to those two channels. Thus, intermodulation products can now
be found in channels 29, 30, 31, 33, 35, 37, 39, 41, 42, and 43.

If one imagines that a TV is attempting to receive a signal on channel
30 in the presence of the two undesired signals creating (within the TV
tuner) intermodulation distortion shown in Figure 9-1(b), we would have
the case of interference to channel N from an undesired signal pair,
N+4/N+8. This is one of the cases examined in this chapter, as is the
case of N-4/N-8, which would occur if the receiver were tuned to channel
42. (In test results shown in this chapter, the TV was always tuned to
either channel 30 or channel 51, and the undesired signal channels were
shifted appropriately.)

Figure 9-2(a) shows the effect of changing the amplitudes of both
signals by 5 dB. The IM3 products change by 15 dB, as is expected since
this is a third order process. From this we can conclude that if the
undesired signal levels should rise, the interference effects created
within the TV will rise even faster---at three times the rate of the
rise in input signal level.

If only one of the two signals changes in amplitude, the results are
somewhat more complex. Figure 9‑2(b) shows the effect of a 5-dB change
in amplitude of the signal at channel 34, while the one at channel 38
remains constant. The result is a 10‑dB change in the amplitude of the
IM3 bump closest the changed signal (*i.e.*, the bump at channel 30) and
a 5-dB change in amplitude of the IM3 bump closest to the unchanged
signal (*i.e.*, the bump at channel 42).

The tests in this chapter are configured so that undesired signals are
placed on channels N+K and N+2K and the TV is tuned to channel N. Thus,
channel N is centered on one of the outer spectral bumps. Figure 9-2(b)
confirms the prediction shown in Chapter 8 that the interference power
created at channel N is proportional to U~N+K~^2^ U~N+2K~, where
U~N+K~ and U~N+2K~ represent the respective power levels of the
undesired signals. Thus, the interference created at channel N is a
second order function of U~N+K~ and a linear function of U~N+2K~.

## Channel-30 Results at Three Desired Signal Levels

### "Weak" Desired Signal (D = -68 dBm)

Figure 9-3 shows measured D/U ratios at TOV for eight DTV receivers for
pairs of equal-level undesired signals on channel pairs N+K/N+2K for K =
-5, -4, -3, -2, -1, 1, 2, 3, 4, and 5 and a desired signal power of -68
dBm. The measurements were made with the TVs tuned to channel 30 as the
desired channel N. The desired signal power was set to ‑68 dBm. In
computing the D/U ratio, U was taken as the power of each signal in the
signal pair rather than the combined power of the two signals; thus,

U = U~N+K~ = U~N+2K~

The shaded area at the bottom of the plot represents the measurement
limitations imposed by the test setup---as described in Chapter 4. None
of these measurements were limited by the measurement system.

Though the ATSC A/74 has no recommended performance limits related to
interference by a pair of signals, the red dashed curve labeled "A/74
Max of Pair" is provided as a reference based on single-channel ATSC
interference rejection guidelines. For each point, N+K/N+2K, the value
is equal to the higher (least restrictive) of the ATSC-recommended
DTV-into-DTV interference rejection thresholds for single-channel DTV
interferers. All of the TVs exhibited higher D/U ratios (poorer
performance) at most points than is indicated by this A/74-based curve.

Figure 9-4 summarizes the measurements that were shown in Figure 9-3.
The solid curve shows the median performance of the eight receivers.
Error bars show the best and worst performance among the receivers at
each channel offset. A dashed curve shows the performance of the second
worst performing receiver at each channel offset.

Since the IF filter in a receiver is expected to greatly reduce signal
levels available for creation of intermodulation products *after* the
filter, one would expect that intermodulation between pairs of
out-of-channel interferers would occur prior to the IF filter---probably
in the mixer. Prior to the mixer, a typical single-conversion TV
receiver would include a "tracking filter" that passes the desired
channel but provides a gradually increasing attenuation to signals in
other channels based on separation from the desired channel. The filter
is expected to provide substantial attenuation at N+14 and N+15 in order
to reduce the mixer image response. One would expect that such a
tracking filter---if placed before the point of nonlinearity that
created the intermodulation products---would cause interference effects
of a N+K/N+2K signal pair to diminish as \|K\| increases. Such a trend
is evident in some, but not all of the receivers, based on the measured
data, which extends to \|K\| = 5.

### "Moderate" Desired Signal (D = -53 dBm)

Figure 9-5 shows D/U-ratio measurements at TOV for the same eight
receivers at a higher desired signal level of -53 dBm. Figure 9-6 shows
the median and range of the measurements, as well as the second worst
performance among the eight receivers.

The expected rolloff with increasing \|K\| is even less evident than in
the signal measurements that were made with a desired signal power of
-68 dBm. In some cases, the influence of AGC operation on the N+1/N+2
and N-1/N-2 data may be partly responsible for the lack of increase at
low absolute values of K. This topic is discussed more in Chapter 11.

### "Strong" Desired Signal (D = -28 dBm)

Figure 9-7 shows the D/U measurements for a desired signal level of -28
dBm. At this signal level, the measurements were performed for only two
channel pairs---N‑1/N‑2 and N+1/N+2. The maximum signal levels that
could be generated by the test setup (about ‑7 dBm for each channel for
adjacent-channel tests) were not high enough to create picture errors
for most of the receivers. As a result, threshold measurements were
possible on only three of the receivers for N‑1/N‑2 and only two of the
receivers for N+1/N+2. The other measured points are shown at the
measurement-limit line.

Figure 9-8 presents information regarding the best, median, second
worst, and worst performance for each of the two channel pairs measured.
Since there were only two points per curve, the data is presented in
tabular form. The table shows the threshold values for the worst and
second worst performers. The median and best performing values are shown
only as "\< \[value\]" because most of the data points were beyond the
measurement limit of the test setup.

### Combined Results With Single-Channel Reference Values

The plots shown in the previous three subsections provide no indication
of whether the DTV picture errors are caused by IM3 interactions between
the pair of undesired signals or whether they are caused by each signal
independently.

To determine whether IM3 is the cause, it would be useful to show the
interference thresholds for the individual undesired signals as well.
Thus, we could plot the interference threshold for N+K/N+2K as well as
the interference threshold for N+K alone and that for N+2K alone. An
even better reference would be one that combined the effects of N+K
interference and N+2K interference under the assumption that the
interference mechanisms are independent and not the result of
intermodulation. We attempt to take the latter approach---partly to
reduce the number of curves that must be plotted so that results can be
combined into a manageable number of graphs for this report.

The approach taken is to recognize that the observed interference
phenomena are the result of mechanisms at work within the TV that
convert out-of-channel undesired signals into co-channel interference at
some point within the TV. The desired signal at threshold is then---in
essence---a measure of the power level of that internal co-channel
interference level, since the desired signal at threshold is expected to
be about 15 dB above the co-channel interference. This concept was
discussed in Chapter 8.

We will define D~N+K~ as the desired signal at threshold resulting from
interferer U~N+K~, and D~N+2K~ as the desired signal at threshold
resulting from interferer U~N+2K~. If we were to take measurements of
D~N+K~ and D~N+2K~ at equal *undesired* signal levels
(U~N+K~=U~N+2K~=U), then D~N+K~ + D~N+2K~ would be the expected desired
signal level threshold if both undesired signals were applied
simultaneously ***[and]{.underline}*** there were no interaction between
them. (Summing D~N+K~ and D~N+2K~ is equivalent to summing the
co-channel interference powers created within the receiver from each of
the two undesired signals individually.) If the undesired signal powers
are equal, this is equivalent to summing the D/U ratios:

(D/U)\|~N+K/N+2K~ = (D~N+K~+D~N+2K~)/U = (D/U)\|~N+K~ + (D/U)\|~N+2K~ ,
***if there is no interaction between the two undesired signals***.

This provides a reference point for determining whether the
paired-signal D/U is caused by the combined individual effects of the
two undesired signals or a by nonlinear interaction between them
(*i.e.*, IM3). Summing the D/U ratios to provide this reference point is
strictly valid only if the measurements were performed at equal
*undesired* signal levels (and if the AGC state of the tuner is the same
for each measurement). Our measurements were performed with equal D
values rather than equal U values; however, it would still be valid to
apply this technique if D/U for the individual interferers were constant
with variations in D. This is true of some cases but not for others.
Even when it is not true, very little error is made in summing the D/U
ratios if the interference effect (D/U ratio) for one interferer is much
higher for the other, since, in that case the sum is approximately equal
the D/U of the dominant interferer.

Based on the above we will plot the summed D/U ratio of the individual
interferers along with the measured D/U ratio for the pair of
interferers to provide an indication of whether IM3 effects are at work.
(Note that the summing is performed on the direct power ratios, not on
their values in decibels.)

Figures 9-9 through 9-16 show the measured D/U ratios for the paired
interferers along with the summed D/U ratios for the corresponding
individual interferers. Each graph presents the measurements for one DTV
receiver. The two solid lines on each graph show the paired-signal D/U
ratios measured at desired signal levels of -68 dBm and -53 dBm. The
dashed lines show the summed D/U's for those signal levels. Note that if
one or both of the individual D/U's was beyond the measurement limit of
the test setup, then the sum was computed using the measurement limit;
this fact may cause a summed D/U to exceed the paired-signal D/U if one
element of the sum was at the measurement limit and the other was near
the limit.

Where the solid lines are closely matched by the dashed summed-D/U
lines, the interference effect of the pair of equal-powered undesired
signals is primarily due to one of the individual signals---or to the
combined effect of both---rather than to an IM3 interaction between the
two interferers. Where a solid line is significantly higher than a
dashed line, there is a significant IM3 effect from the pair of signals.

Notably, most of the receivers exhibit very little evidence of IM3
interaction from the N-1/N-2 and N+1/N+2 pairs. For a desired signal
level of -68 dBm, the paired-signal D/U's exceed the summed signal D/U's
by no more than 1.2 dB (and in most cases less than 0.5 dB) with one
exception. For receiver G4 the difference is 4 dB at N-1/N-2. This
indicates that, for equal-power paired undesired signals, any IM3
effects resulting from a signal pair on the first-adjacent channels
(N-1/N-2 and N+1/N+2) of most receivers are insignificant relative to
the interference sensitivities associated with the individual channels,
at least for a desired signal power of -68 dBm. The one exception to
this---one case out of 16 (8 receivers, upper and lower channel
pairs)---yields a 4-dB increase in susceptibility as a result of IM3. At
a desired signal power of -53 dBm, three of the 16 combinations exhibit
an IM3 effect that is about 2 dB above the summed D/U's and one exceeds
the summed D/U's by 3.6 dB.

Even at N-2/N-4 and N+2/N+4 about half of the receivers exhibit little
or no evidence of an IM3 effect for paired equal-power undesired
signals. Among the other half, some exhibit very pronounced IM3 effects
up to 11 dB above the summed D/U's.

At larger channel spacings, there is evidence of IM3 from the signal
pairs significantly exceeding the interference effect of the individual
interferers---by amounts up to at least 17 dB. (In cases where summed
D/U's are computed from measurements that were at the limit of the
measurement setup, the actual summed D/U's are lower than those shown,
so the true amount of the excess is greater than that shown.)

An unexpected and seemingly impossible behavior can be seen for receiver
D3 (Figure 9-10) at N‑2/N-4 for a desired signal level D = -53 dBm. The
D/U for the pair of interferers operating together is actually
significantly lower than the summed D/U's for the individual
interferers. Examination of the single-channel data shows that the
receiver is far more sensitive to interference at N-4 (D/U = -32.3) than
at N-2 (D/U = ‑49.0 dB); however, the D/U ratio for the pair of signals
(with U referring to the undesired power on *each* of the two channels)
is only ‑38.8 dB, 6.5 dB less than the D/U for N-4 alone. Put another
way, an undesired signal level of ‑20.8 dBm on channel N-4 causes
picture errors on the TV, but if a *[second]{.underline}* undesired
signal is placed on channel N‑2, the TV can tolerate a higher
interference level of -14.3 dBm on each of the channels simultaneously!

This result is highly counter-intuitive until one examines detailed test
results for that TV---presented in the Chapter 11. Though those
measurements are limited to cases with interferers on higher channel
numbers than the desired signal (N+K/N+2K with positive values of K),
the data suggests that the presence of an undesired signal on channel
N+2 any higher than approximately ‑35 dBm causes the DTV receiver's AGC
to reduce the RF gain, whereas an undesired signal at N+4 causes no such
gain reduction (or, if it does, the reduction occurs at a higher signal
level). In the case described above, the TV is very susceptible to
interference from an undesired signal placed at N-4, probably due to a
nonlinearity in the tuner; but, adding in an undesired signal at N-2
probably causes the AGC to reduce the RF gain of the tuner (as was the
case at N+2), which reduces the signal levels at the point of the
nonlinearity. A theoretical basis for understanding the effect of AGC on
interference phenomena was presented in Chapter 8 (with more details in
Appendix B). More discussion about the effect of AGC will be presented
in Chapter 11 on the basis of detailed measurement data for Receiver D3.

Table 9-2 shows statistics for the difference (in dB) between the
paired-signal D/U's and the summed D/U's for the eight TV receivers that
were tested. Looking across all of the data, we see that a pair of
appropriately-spaced equal-power undesired signals can create an
intermodulation effect that enhances the interference potential of the
signals. The combined signals can cause TV picture degradation (or loss)
at signal levels at least as much as 17 dB lower than the levels that
would be required to cause picture degradation based on the combined
individual effects of each signal, *i.e.*, without intermodulation
between the pair. (The actual difference may have been much larger. See
the note in table.) At the other extreme, paired signals applied to some
TV receivers on some N+K/N+2K channel pairs cause no increase in
interference effect above the summed effects of the individual signals,
and in one case (discussed in the preceding paragraph), AGC action
causes the paired signal combination to have less of an interference
effect than that of one of the individual signals.

## Channel-51 Results at Three Desired Signal Levels

In this section we present the results of paired-signal rejection
measurements made with the TVs tuned to channel 51 as the desired
channel N. The two undesired signals were placed on N+K and N+2K for K =
1 through 8. The reason for limiting these tests to positive values of K
is that the focus was on potential for interference to upper UHF
channels from other radio services that are expected to operate in
channels 52 through 69 after completion of the DTV transition.

For these tests, the undesired signal on channel N+K was an 8-VSB DTV
signal. The undesired signal on channel N+2K was a white Gaussian noise
source bandlimited to match the 3-dB width of an 8-VSB DTV signal.

[]{#__RefHeading___Toc163024579 .anchor}Table 9‑21. Statistics of
Paired-Signal D/U's Relative to Summed D/U's for 8 Receivers on Channel
30

  -------------- --------------- ---------- ------------ ---------- ---------- ----------- ------------- ------------
  **Undesired    **Excess of                                                                             
  Channel Pair** Paired-Signal                                                                           
                 D/U Above                                                                               
                 Summed D/U's                                                                            
                 (dB)**                                                                                  

                 **D = -68 dBm**                                    **D = -53                            
                                                                    dBm**                                

                 **Min**         **Mean**   **Median**   **Max**    **Min**    ***Lower    ***Lower      ***Lower
                                                                               Bound on*   Bound on*     Bound on\
                                                                               Mean^1^**   Median^1^**   *Max^1^**

  **N-5/N-10**   1.8             9.8        9.8          15.7       3.4        *11.7*      *11.7*        *16.9*

  **N-4/N-8**    0.4             5.7        5.1          12.2       3.4        *9.5*       *9.8*         *16.3*

  **N-3/N-6**    -1.2            5.2        3.1          15.1       -0.2       5.9         6.4           11.3

  **N-2/N-4**    -1.9            -0.2       -0.6         3.0        -6.6       0.5         0.2           5.6

  **N-1/N-2**    -0.3            0.7        0.2          4.0        -0.3       0.7         0.1           3.6

  **N+1/N+2**    -1.5            0.0        0.3          0.6        -1.3       0.6         0.5           2.3

  **N+2/N+4**    -1.5            2.7        0.1          11.3       -1.2       4.0         3.9           11.4

  **N+3/N+6**    -0.2            7.2        6.8          14.1       2.1        *9.8*       *9.9*         *14.7*

  **N+4/N+8**    1.5             8.2        7.0          16.4       0.7        *8.7*       *8.9*         *13.8*

  **N+5/N+10**   0.0             7.9        9.1          12.8       -0.3       *7.1*       *7.3*         *13.7*

                 **-1.9**        **4.7**    **4.1**      **16.4**   **-6.6**   ***5.9***   ***6.8***     ***16.9***
  -------------- --------------- ---------- ------------ ---------- ---------- ----------- ------------- ------------

*Note*

*^1^ For D = -53 dBm, the actual means, medians, and maxima for channels
N+3/N+6 and beyond on the positive side and N-4/N-8 and beyond on the
negative side are underestimated because most of the individual
measurements on which the summed D/U's are based were for measurement
conditions in which TOV for the receivers was not reached due to
limitations on maximum signal that the test setup could generate;
consequently, the values shown in red italics should be viewed as lower
bounds on the actual values.*

### "Weak" Desired Signal (D = -68 dBm)

Figure 9-17 shows measured values of D/U ratios at TOV for seven DTV
receivers for pairs of equal-level undesired signals with the desired
signal power was set to -68 dBm. The seven receivers are a subset of the
eight that were tested for the previous major section of this chapter.
The reader is referred to the channel-30 section of this chapter for
more information on the plot format.

Figure 9-18 summarizes the measurements that were shown in Figure 9-17.
The solid curve shows the median performance of the eight receivers.
Error bars show the best and worst performance among the receivers at
each channel offset. A dashed curve shows the performance of the second
worst performing receiver at each channel offset.

For the most part the D/U ratios exhibit an expected drop (indicating
less susceptibility to interference) as the channel spacing from the
desired channel increases. There are some exceptions. The increase in
D/U for receiver D3 as the undesired signal pair is moved from N+1/N+2
to N+2/N+4 is believed to be the result of an AGC gain reduction
occurring when the undesired signal is placed on N+1. This will be
discussed further in Chapter 11. The peak exhibited by some TVs at
N+7/N+14 is the result of single-channel effects at N+7 (the local
oscillator frequency) or N+14 (mixer image frequency).

### "Moderate" Desired Signal (D = -53 dBm)

Figure 9-19 shows D/U-ratio measurements at TOV for the same seven
receivers at a higher desired signal level of -53 dBm. We note that only
one measurement was performed on receiver N1 at this desired signal
level---at N+1/N+2.[^68] Figure 9-20 shows the median and range of the
measurements, as well as the second worst performance among the
receivers; except for N+1/N+2, the data are for only six of the
receivers.

The expected rolloff with increasing \|K\| is less evident than in the
"weak"-signal measurements. In some cases, the influence of AGC
operation on the N+1/N+2 and N-1/N-2 data may be partly responsible.

### "Strong" Desired Signal (D = -28 dBm)

Figure 9-21 and 9-22 show corresponding plots of D/U measurements of
seven receivers for a desired signal level of ‑28 dBm. As in the case of
-53 dBm, one of the receivers was measured only at N+1/N+2. Most of the
D/U ratios fall outside the measurement range of the test setup.

### Combined Results With Single-Channel Reference Values

Figures 9-23 through 9-29 show the measured D/U ratios for the paired
interferers along with the summed D/U ratios for the corresponding
individual interferers. Each graph presents the measurements for one DTV
receiver. The solid colored lines on each graph show the paired-signal
D/U ratios measured at desired signal levels of -68 dBm, -53 dBm, and
‑28 dBm.

The dashed lines on each graph show the summed D/U's for each of the
three desired signal levels. The summed D/U's represent the summed
interference effects of the two undesired signals in the absence of any
intermodulation products generated by nonlinear interactions of one
signal with the other. Note that if one or both of the individual D/U's
was beyond the measurement limit of the test setup, then the sum was
computed using the measurement limit. This occurred for many of the
summed D/U values for D = ‑68 dBm and most of those for D = -53 dBm and
D = -28 dBm. Where it occurred, the actual TOV levels for the individual
undesired signals are unknown, and the actual differences between the
paired-signal D/U's and the summed D/U's are greater than those shown in
the charts. Because of the number of data points affected by this
limitation, the channel-51 data were not tabulated as the channel-30
data were. We also note that the use of measurement limit values
sometimes caused a summed D/U value on the plots to artificially exceed
the paired-signal D/U when one element of the sum was at the measurement
limit and the other was near the limit---a condition that occurred for
most of the measurements for D = -28 dBm.

Where the solid lines are closely matched by the dashed "summed D/U"
lines, the interference effect of the pair of interferers is primarily
due to one of the individual interferers---or the combined effect of
both---rather than an IM3 interaction between the two interferers. Where
the solid lines significantly exceed the dashed lines, there is a
significant IM3 effect from the pair of signals.

## Estimating 3^rd^ Order Intercept Point (IP3)

The measurements presented in this chapter can be used to determine the
DTV receiver's third-order intercept point (IP3)---a property that
quantifies the nonlinearity of the receiver and allows computation of
IM3 interference effects from undesired signal amplitudes that differ
from the levels actually tested. Our use of the term IP3 here, while
similar to its traditional use in characterizing amplifiers, differs
from the traditionally defined IP3 in two ways:

1.  The measurements here were made with broadband, noise or noise-like
    signals rather than with the CW (continuous wave) sinusoids usually
    used for IP3 measurements; since the process is a third-order one,
    one would expect the effective interference power to be related to
    the sixth-order moments of the input signals; those moments are
    expected to be higher for the noise-like waveforms than for a
    sinusoid of the same input power;

2.  As Figure 9-2 showed, the IM3 power in each side "bump" of the
    spectrum is split across three TV channels, of which only the center
    one (where most of the power is concentrated) is "measured" by the
    TV in our tests; thus, a portion of the IM3 power is excluded from
    the measurement.

There are three limitations on such IP3-based assessment of DTV
interference:

\(1\) IP3 can be quantified from the paired-signal measurements only if
the observed interference is primarily due to IM3 between the signal
pair;

\(2\) While IP3 is usually treated as a constant for a given amplifier,
it will, in fact, vary with AGC operation; and,

\(3\) IP3 computation depends on a knowledge of the signal-to-noise
ratio necessary for the receiver to reach TOV because we are not
measuring IM3 effects directly, but rather are inferring them from
measurements of U and D at TOV.

Regarding the first limitation, we will compute IP3 only when the D/U
ratio for the pair of signals exceeds the summed D/U ratios of the
individual signals (plotted as reference curves in Figures 9-9 through
9-16 and 9-23 to 9-29) by at least 4 dB.

Regarding the second limitation, we will recognize that IP3 will be
constant only when desired and undesired signal levels are low enough
not to cause AGC gain reductions prior to the point of the nonlinearity
that causes the IM3. We will attempt to use changes in measured IP3 to
determine whether or not the AGC is active in the vicinity of a
paired-signal measurement.

Regarding the third limitation, we could choose to substitute a value
such as 33.9 (*i.e.*, 15.3 dB converted to a linear power ratio) for the
required signal-to-noise ratio (SNR~R~) since all of the receivers have
required signal-to-noise ratios close to this value (according to
measurements presented in the SHVERA Study[^69]); however, that value
was measured using white Gaussian noise as the interferer, and, strictly
speaking, the SNR required to overcome IM3 interference may differ from
that of white Gaussian noise due to differing spectral shape or perhaps
statistical properties. Consequently, we choose to incorporate the
SNR~R~ term into the quantity calculated to quantify the receiver's
nonlinearity.

Thus, instead of computing IP3, we choose to compute the quantity, IP3 /
SNR~R~^1/2^, which was shown in Chapter 8 to be related to desired and
undesired signal powers at threshold for paired-signal IM3 interference.
In linear power units, the quantity can be computed by

IP3 / SNR~R~^1/2^ = (U^3^ / D)^1/2^

In decibel units, it is given by

(IP3 / SNR~R~^1/2^)\|~dB~ = 1.5 U\|~dB~ - 0.5 D\|~dB~

The values of IP3 / SNR~R~^1/2^ computed here will be applied to the
case of unequal undesired signal levels in the next chapter.

### Channel 30

Table 9-3 and Figures 9-30 and 9-31 present computed values of IP3 /
SNR~R~^1/2^ (in dB) based on the channel-30 measurements of rejection
ratios for paired signals. Values were computed only when the
paired-signal D/U ratio exceeded the summed single-signal D/U ratios by
at least 4 dB, as stated above. The blank cells represent measurements
that did not meet this condition. See the note at the bottom of the
table for conversion to IP3.

[]{#__RefHeading___Toc163024580 .anchor}Table 9‑22. IP3/SNR~R~^1/2^
Based on Paired-Signal Rejection Measurements at Channel-30

  -------------- --------- ------------- ------------ ------------- -------- -------- -------- ------------- ------------ ------------ ------------
                           **IP3 /                                                                                                     
                           SNR~R~^1/2^                                                                                                 
                           (dB)**                                                                                                      

                 **K**    **-5**        **-4**       **-3**        **-2**   **-1**   **1**    **2**         **3**        **4**        **5**

  **Receiver**   **D       **N-5/ N-10** **N-4/ N-8** **N-3/ N-6**  **N-2/   **N-1/   **N+1/   **N+2/ N+4**  **N+3/ N+6** **N+4/ N+8** **N+5/
                 (dBm)**                                            N-4**    N-2**    N+2**                                            N+10**

  A3             -68                                                                                         ***0.7***    ***3.9***    ***6.8***

  D3             -68       -5.5          -9.4         ***-13.9***                              ***-24.7***   -17.1                     

  G4             -68       ***-1.3***    ***-0.1***   -3.4                                     ***-10.4***   ***-7.1***   ***-4.8***   ***-1.3***

  I1             -68       ***-12.2***                                                                                    ***5.2***    ***3.7***

  J1             -68       ***-3.9***                                                                        ***-6.4***   ***-4.3***   ***2.0***

  M1             -68       ***-5.4***    ***-5.0***   ***-5.5***                               ***-5.2***    ***-6.1***   ***0.6***    ***5.1***

  N1             -68       ***6.7***                                                                                      ***7.6***    

  O1             -68       ***-5.2***    ***-7.1***   -5.4                                                                ***8.2***    ***7.7***

  A3             -53       ***5.4***     2.2          -2.8          0.5                        -0.8          ***-0.5***   ***2.7***    ***5.6***

  D3             -53                                  ***-14.9***                              ***-21.7***                             

  G4             -53       ***1.8***     ***-0.7***   7.6           5.7                        -5.8          ***-8.2***   ***-1.7***   3.2

  I1             -53       -4.3          0.4                                                                 6.0          ***5.4***    ***3.8***

  J1             -53       ***-1.4***    -3.3                                                                ***-3.1***   ***-1.3***   ***-1.5***

  M1             -53       ***-4.7***    ***-4.3***   0.9                                      1.9           ***-3.2***   ***-2.5***   ***4.7***

  N1             -53       ***1.5***     4.7          5.2                                                    7.0          ***6.8***    

  O1             -53       ***-3.9***    -1.6         12.4                                                   9.3          ***8.8***    ***7.8***
  -------------- --------- ------------- ------------ ------------- -------- -------- -------- ------------- ------------ ------------ ------------

*Notes:*

1.  *Outlines represent receivers and channel offsets subjected to
    further measurement in the next chapter.*

2.  *IP3 can be estimated by adding SNR~R~\|~dB~/2 (nominally 15.3 / 2 =
    7.6 dB) to the values of (IP3 / SNR~R~^1/2^)\|~dB~ shown.*

In the table, bold italics with shading indicates values that are
believed to correspond to full gain operation of the receiver through
the mixer (*i.e.*, no RF AGC operation); this judgment was made on the
basis of the change in computed IP3 as desired signal level changed from
-68 dBm to -53 dBm. (Note the lack of shading does not necessarily
indicate that AGC *did* operate in a given region; rather, it may
indicate that the measurements were insufficient to make a judgment.) If
the AGC was *inactive* throughout the range, one would expect a constant
IP3 value. If the AGC *operated* throughout the range to maintain
constant signal levels at the point of nonlinearity, one would expect
IP3 to increase by 15 dB (same change as D). The observed IP3 changes
from D = -68 dBm to D = -53 dBm within the same receiver ranged from -5
to +18 dB. AGC was judged to have operated throughout the range if the
IP3 change was greater than 10 dB; in that case, corresponding cells for
both -68 dBm and -53 dBm are marked as having been influenced by AGC.
Pairs with lower IP3 changes were judged to have had AGC operation
through no more than part of the range, so the low end of the range (D =
-68 dBm) was judged not to have been influenced by AGC. Where IP3 change
was less than 3.5 dB, we judged that both ends of the range were free of
AGC operation.

Measurable IM3 effects were not observed on the first-adjacent channel
cases (N+1/N+2 and N-1/N-2) and many of the second-adjacent channel
cases (N+2/N+4 and N-2/N-4). This is believed to be a result of two
factors: (1) AGC-induced gain reductions in each receiver's front end
reduced the amplitudes of IM3 effects for those channel offsets; and (2)
those channel offsets exhibited higher single-channel interference
effects that would have tended to mask the IM3 effects.

In Figure 9-30, which presents IP3 / SNR~R~^1/2^ values for D = -68 dBm,
the expected increase in IP3 with increasing offset from channel N due
to filtering in the receiver front end is clearly evident for most
receivers on the right half of the graph where there are more data
points. Such a tendency is seen at D = ‑53 dBm (Figure 9-31) for fewer
receivers.

### Channel 51

Table 9-4 and Figures 9-32 and 9-33 present computed values of IP3 /
SNR~R~^1/2^ (in dB) based on the channel-51 measurements of rejection
ratios for paired signals. As with the channel-30 measurements, values
were computed only when the paired-signal D/U ratio exceeded the summed
single-signal D/U ratios by at least 4 dB. The blank cells represent
measurements that did not meet this condition. The reader is referred to
the discussion in the previous section (for channel 30) for information
regarding the shading in the table. See the note at the bottom of the
table for conversion to IP3.

For D = -68 dBm (Figure 9-32) most receivers exhibit an increase in IP3
with increased spacing between the undesired channels and the desired
channel. Such a trend is not clear for D = -53 dBm (Figure 9-33); in
fact, receiver I1 exhibits a very flat IP3.

[]{#__RefHeading___Toc163024581 .anchor}Table 9‑23. IP3/SNR~R~^1/2^
Based on Paired-Signal Rejection Measurements at Channel-51

  -------------- --------- ------------- ------------- ------------ ------------ ----------- ----------- --------- -----------
                           **IP3 /                                                                                 
                           SNR~R~^1/2^                                                                             
                           (dB)**                                                                                  

                 **K**    **1**         **2**         **3**        **4**        **5**       **6**       **7**     **8**

  **Receiver**   **D       **N+1/ N+2**  **N+2/ N+4**  **N+3/ N+6** **N+4/ N+8** **N+5/      **N+6/      **N+7     **N+8/
                 (dBm)**                                                         N+10**      N+12**      /N+14**   N+16**

  A3             -68                                   ***-2.5***   ***1.7***    ***5.3***   8.8                   

  D3             -68                     ***-25.6***   -17.8                                                       

  I1             -68                                                ***4.8***    ***4.7***   ***4.0***             ***4.1***

  J1             -68                                   ***-3.6***   ***-3.5***   ***2.7***   ***6.1***   7.9       9.2

  M1             -68                     ***-3.4***    ***-2.0***   ***3.0***    8.2         13.4                  

  N1             -68                                   4.9          0.2          0.4         3.1                   5.0

  O1             -68                                                             8.7         7.9                   7.8

  A3             -53                     1.1           ***-2.5***   ***1.8***    ***5.3***                         

  D3             -53                     -18.7                                                                     

  I1             -53                                   5.8          ***5.4***    ***4.8***   ***4.6***   4.3       ***5.3***

  J1             -53                                   4.5          ***-1.1***   ***0.2***   ***3.6***             

  M1             -53                     1.0           ***0.2***    ***2.8***                                      

  N1             -53                     NM            NM           NM           NM          NM          NM        NM

  O1             -53                                                                                               
  -------------- --------- ------------- ------------- ------------ ------------ ----------- ----------- --------- -----------

> *Notes:*

3.  ***Bold italics with shading** indicates probable operation at
    signal level low enough to avoid AGC operation; that assessment is
    based on the observed change in IP3 / SNR~R~^1/2^ as desired signal
    level changes from -68 dBm to -53 dBm. (See text for details.)*

4.  *NM (for receiver N1) indicates that no measurements of
    paired-signal D/U ratio were made due to equipment failure. The lack
    of measurements for receiver N1 at D = -53 dBm precluded the
    opportunity to estimate AGC operation; consequently, none of the N1
    measurements at D = ‑68 dBm could be judged to be free of AGC gain
    changes.*

5.  *IP3 can be estimated by adding SNR~R~\|~dB~/2 (nominally 15.3 / 2 =
    7.6 dB) to the values of (IP3 / SNR~R~^1/2^)\|~dB~ shown.*

### Comparison of Channels 30 and 51

Figure 9-34 combines the IP3 / SNR~R~^1/2^ data measured on channels 30
and 51 for a desired signal power of -68 dBm. The measurements include
up to four channel pairs in common. For most of the TV receivers, there
is a close match between the measurements in the overlap region.

## Summary Data

The IP3 data tables are incompletely filled because of our restriction
that we computed the IP3 parameter only when the paired-signal D/U ratio
exceeded the summed single-signal D/U ratios by at least 4 dB. Thus,
data could be missing because the IM3 effects are small, because the
interference effects of the corresponding single-channel undesired
signals are high, or because some single-channel measurements on which
the summed D/U's are based are at the measurement limit of the test
setup. This makes it harder (and in many cases, impossible) to determine
worst-case, second-worst, and median values from the existing
measurements without introducing biases.

We carefully examined both the paired-signal D/U measurements and the
corresponding single-channel D/U measurements including combinations in
which IP3 is not reported due to the paired-signal D/U ratio not meeting
the threshold requirement described above. This evaluation was used to
determine, where possible, the values for median, second-worst, and
worst (lowest) IP3 values among the channel pairs. The results are shown
in Table 9-5 for both channels 30 and 51. The final three columns
combine the data from the two desired channels---by averaging when
measurements exist on both channels---to provide a larger view of the
IP3 variation with channel-pair spacing.

[]{#__RefHeading___Toc163024582 .anchor}Table 9‑24. IP3/SNR~R~^1/2^
Statistics

  -------------- ------------- --------- ------------ ----------- --------- ------------ -------------- ---------- ------------
                 **IP3 /                                                                                           
                 SNR~R~^1/2^                                                                                       
                 (dB)**                                                                                            

                 **Channel                            **Channel                          **Combined**              
                 30**                                 51**                                                         

                 **Worst**     **2nd     **Median**   **Worst**   **2nd     **Median**   **Worst**      **2nd      **Median**
                               Worst**                            Worst**                               Worst**    

  **N-5/N-10**   -12.2         -5.5      -4.5                                            **-12.2**      **-5.5**   **-4.5**

  **N-4/N-8**    -9.4          -7.1      -5.0                                            **-9.4**       **-7.1**   **-5.0**

  **N-3/N-6**                                                                                                      

  **N-2/N-4**                                                                                                      

  **N-1/N-2**                                                                                                      

  **N+1/N+2**                                                                                                      

  **N+2/N+4**                                                                                                      

  **N+3/N+6**    -17.1         -7.1      -2.7         -17.8       -3.6      -2.0         **-17.5**      **-5.3**   **-2.4**

  **N+4/N+8**    -4.8          -4.3      2.2                                1.7          **-4.8**       **-4.3**   **1.9**

  **N+5/N+10**   -1.3          2.0       4.4          0.4         2.7       4.7          **-0.5**       **2.3**    **4.5**

  **N+6/N+12**                                        3.1         4.0       6.1          **3.1**        **4.0**    **6.1**

  **N+7/N+14**                                                                                                     

  **N+8/N+16**                                        4.1         5.0       9.2          **4.1**        **5.0**    **9.2**
  -------------- ------------- --------- ------------ ----------- --------- ------------ -------------- ---------- ------------

The results can be used to compute threshold values of undesired signal
power U and D/U ratio when the two undesired signals have equal power:

U\|~dB~ = (1/3) \[2 (IP3 / SNR~R~^1/2^)\|~dB~ + (D -- D~MIN~)\|~dB~\]

where (D -- D~MIN~)\|~dB~ is computed by converting the desired power
levels to linear power units (*e.g.*, mW), performing the subtraction,
and then converting back to dB.

The calculation has been performed for desired signal levels of -68 dBm
and D~MIN~ + 3 dB, under the assumption that D~MIN~ = -84 dBm. The
results are shown in Tables 9-6 and 9-7.

We note that the absence of data for channel pairs N-3/N-6, N-2/N-4,
N+2/N+4 and N+7/N+14 in these tables does not indicate that IM3 was
immeasurable on all of the receivers. It means, rather, that conclusions
regarding the worst, second-worst, and median values could not be
reached from the receivers that were measurable. On the other hand, the
absence of data in the tables for the first-adjacent pairs (N-1/N-2 and
N+1/N+2) was due to the fact that IM3 effects did not exceed
single-channel effects on any of the receivers by a sufficient amount to
support measurement of IM3 effects.

[]{#__RefHeading___Toc163024583 .anchor}Table 9‑25. Computed Threshold U
Due to IM3 for Equal Paired Signals

  -------------- ------------- --------- ------------ ----------- --------- ------------ ----------- --------- ------------
                 **Threshold U                                                                                 
                 for Paired                                                                                    
                 Signals With                                                                                  
                 U~N+K~ =                                                                                      
                 U~N+2K~ = U                                                                                   
                 (dB)**                                                                                        

                 **D = -68                            **D =                              **D =                 
                 dBm**                                D~MIN~ + 3                         D~MIN~ + 1            
                                                      dB**                               dB**                  

  ** **          **Worst**     **2nd     **Median**   **Worst**   **2nd     **Median**   **Worst**   **2nd     **Median**
                               Worst**                            Worst**                            Worst**   

  **N-5/N-10**   -30.8         -26.3     -25.7        -36.1       -31.7     -31.0        -38.1       -33.6     -33.0

  **N-4/N-8**    -29.0         -27.4     -26.0        -34.3       -32.7     -31.4        -36.2       -34.7     -33.3

  **N-3/N-6**                                                                                                   

  **N-2/N-4**                                                                                                   

  **N-1/N-2**                                                                                                   

  **N+1/N+2**                                                                                                   

  **N+2/N+4**                                                                                                   

  **N+3/N+6**    -34.3         -26.2     -24.3        -39.6       -31.6     -29.6        -41.6       -33.5     -31.5

  **N+4/N+8**    -25.9         -25.6     -21.4        -31.2       -30.9     -26.7        -33.1       -32.8     -28.7

  **N+5/N+10**   -23.0         -21.1     -19.6        -28.3       -26.4     -25.0        -30.3       -28.4     -26.9

  **N+6/N+12**   -20.6         -20.0     -18.6        -25.9       -25.3     -23.9        -27.9       -27.3     -25.9

  **N+7/N+14**                                                                                                  

  **N+8/N+16**   -20.0         -19.3     -16.6        -25.3       -24.7     -21.9        -27.2       -26.6     -23.8
  -------------- ------------- --------- ------------ ----------- --------- ------------ ----------- --------- ------------

*Computation assumes D~MIN~ = -84 dBm*

[]{#__RefHeading___Toc163024584 .anchor}Table 9‑26. Computed Threshold
D/U Due to IM3 for Equal Paired Signals

  -------------- ----------------- --------- ------------ ----------- --------- ------------ ----------- --------- ------------
                 **Paired-Signal                                                                                   
                 D/U for U~N+K~ =                                                                                  
                 U~N+2K~ = U                                                                                       
                 (dB)**                                                                                            

                 **D = -68 dBm**                          **D =                              **D =                 
                                                          D~MIN~ + 3                         D~MIN~ + 1            
                                                          dB**                               dB**                  

                 **Worst**         **2nd     **Median**   **Worst**   **2nd     **Median**   **Worst**   **2nd     **Median**
                                   Worst**                            Worst**                            Worst**   

  **N-5/N-10**   -37.2             -41.7     -42.3        -44.9       -49.3     -50.0        -44.9       -49.4     -50.0

  **N-4/N-8**    -39.1             -40.6     -42.0        -46.7       -48.3     -49.6        -46.8       -48.3     -49.7

  **N-3/N-6**                                                                                                      

  **N-2/N-4**                                                                                                      

  **N-1/N-2**                                                                                                      

  **N+1/N+2**                                                                                                      

  **N+2/N+4**                                                                                                      

  **N+3/N+6**    -33.7             -41.8     -43.7        -41.4       -49.4     -51.4        -41.4       -49.5     -51.5

  **N+4/N+8**    -42.1             -42.4     -46.6        -49.8       -50.1     -54.3        -49.9       -50.2     -54.3

  **N+5/N+10**   -45.0             -46.9     -48.4        -52.7       -54.6     -56.0        -52.7       -54.6     -56.1

  **N+6/N+12**   -47.4             -48.0     -49.4        -55.1       -55.7     -57.1        -55.1       -55.7     -57.1

  **N+7/N+14**                                                                                                     

  **N+8/N+16**   -48.1             -48.7     -51.4        -55.7       -56.3     -59.1        -55.8       -56.4     -59.2
  -------------- ----------------- --------- ------------ ----------- --------- ------------ ----------- --------- ------------

*Computation assumes D~MIN~ = -84 dBm*

![](media/image41.wmf){width="6.497916666666667in"
height="3.091666666666667in"}

*(a) Single 8-VSB Signal*

![](media/image42.wmf){width="6.497916666666667in"
height="3.3583333333333334in"}

*(b) Pair of Equal-Amplitude Signals*

[]{#__RefHeading___Toc163024448 .anchor}Figure 9‑41. Third-Order
Intermodulation Distortion Spectra of Single and Paired Signals

![](media/image43.wmf){width="6.492361111111111in"
height="3.3201388888888888in"}

*(a) Effect of Changing Amplitude of Both Signals*

![](media/image44.wmf){width="6.497916666666667in"
height="3.384027777777778in"}

*(b) Effect of Changing Amplitude of One Signal*

[]{#__RefHeading___Toc163024449 .anchor}Figure 9‑42. Third-Order
Intermodulation Distortion Spectra of Paired Signals Versus Amplitude

![](media/image45.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024450 .anchor}Figure 9‑43. Paired-Signal D/U
of 8 receivers at D = -68 dBm on Channel 30

![](media/image46.wmf){width="6.495138888888889in"
height="4.560416666666667in"}

[]{#__RefHeading___Toc163024451 .anchor}Figure 9‑44. Paired-Signal D/U
Statistics of 8 receivers at D = -68 dBm on Channel 30

![](media/image47.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024452 .anchor}Figure 9‑45. Paired-Signal D/U
of 8 receivers at D = -53 dBm on Channel 30

![](media/image48.wmf){width="6.495138888888889in"
height="4.560416666666667in"}

[]{#__RefHeading___Toc163024453 .anchor}Figure 9‑46. Paired-Signal D/U
Statistics of 8 receivers at D = -53 dBm on Channel 30

![](media/image49.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024454 .anchor}Figure 9‑47. Paired-Signal D/U
of 8 receivers at D = -28 dBm on Channel 30---1st-Adjacent Only

  --------------- --------------------------- ---------------------------
                  **Susceptibility to         
                  Interference (D/U at        
                  Threshold \[dB)\]**         

                  **N-1/N-2**                 **N+1/N+2**

  Worst           -18.1                       -16.4

  2^nd^ Worst     -19.3                       -20.1

  Median          \< -20.7                    \< -20.2

  Best            \< -20.7                    \< -20.2
  --------------- --------------------------- ---------------------------

[]{#__RefHeading___Toc163024455 .anchor}Figure 9‑48. Paired-Signal D/U
of 8 receivers at D = -28 dBm on Channel 30---1st-Adjacent Only

![](media/image50.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024456 .anchor}Figure 9‑49. Paired-Signal D/U
of Receiver A3 on Channel 30 with Summed D/U's as Reference

![](media/image51.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024457 .anchor}Figure 9‑50. Paired-Signal D/U
of Receiver D3 on Channel 30 with Summed D/U's as Reference

![](media/image52.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024458 .anchor}Figure 9‑51. Paired-Signal D/U
of Receiver I1 on Channel 30 with Summed D/U's as Reference

![](media/image53.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024459 .anchor}Figure 9‑52. Paired-Signal D/U
of Receiver J1 on Channel 30 with Summed D/U's as Reference

![](media/image54.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024460 .anchor}Figure 9‑53. Paired-Signal D/U
of Receiver M1 on Channel 30 with Summed D/U's as Reference

![](media/image55.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024461 .anchor}Figure 9‑54. Paired-Signal D/U
of Receiver N1 on Channel 30 with Summed D/U's as Reference

![](media/image56.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024462 .anchor}Figure 9‑55. Paired-Signal D/U
of Receiver O1 on Channel 30 with Summed D/U's as Reference

![](media/image57.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024463 .anchor}Figure 9‑56. Paired-Signal D/U
of Receiver G4 on Channel 30 with Summed D/U's as Reference

![](media/image58.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024464 .anchor}Figure 9‑57. Paired-Signal D/U
of 7 receivers at D = -68 dBm on Channel 51

![](media/image59.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024465 .anchor}Figure 9‑58. Paired-Signal D/U
Statistics of 7 receivers at D = -68 dBm on Channel 51

![](media/image60.wmf){width="6.497916666666667in"
height="4.4430555555555555in"}

[]{#__RefHeading___Toc163024466 .anchor}Figure 9‑59. Paired-Signal D/U
of 7 receivers at D = -53 dBm on Channel 51

![](media/image61.wmf){width="6.497916666666667in"
height="4.4430555555555555in"}

[]{#__RefHeading___Toc163024467 .anchor}Figure 9‑60. Paired-Signal D/U
Statistics of 6 receivers at D = -53 dBm on Channel 51

![](media/image62.wmf){width="6.497916666666667in"
height="4.4430555555555555in"}

[]{#__RefHeading___Toc163024468 .anchor}Figure 9‑61. Paired-Signal D/U
of 7 receivers at D = -28 dBm on Channel 51

![](media/image63.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024469 .anchor}Figure 9‑62. Paired-Signal D/U
Statistics of 6 receivers at D = -28 dBm on Channel 51

![](media/image64.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024470 .anchor}Figure 9‑63. Paired-Signal D/U
of Receiver A3 on Channel 51 with Summed D/U's as Reference

![](media/image65.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024471 .anchor}Figure 9‑64. Paired-Signal D/U
of Receiver D3 on Channel 51 with Summed D/U's as Reference

![](media/image66.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024472 .anchor}Figure 9‑65. Paired-Signal D/U
of Receiver I1 on Channel 51 with Summed D/U's as Reference

![](media/image67.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024473 .anchor}Figure 9‑66. Paired-Signal D/U
of Receiver J1 on Channel 51 with Summed D/U's as Reference

![](media/image68.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024474 .anchor}Figure 9‑67. Paired-Signal D/U
of Receiver M1 on Channel 51 with Summed D/U's as Reference

![](media/image69.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024475 .anchor}Figure 9‑68. Paired-Signal D/U
of Receiver N1 on Channel 51 with Summed D/U's as Reference

![](media/image70.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024476 .anchor}Figure 9‑69. Paired-Signal D/U
of Receiver O1 on Channel 51 with Summed D/U's as Reference

![](media/image71.wmf){width="6.497916666666667in"
height="4.445138888888889in"}

[]{#__RefHeading___Toc163024477 .anchor}Figure 9‑70. Third-Order
Intercept Point Parameter with Desired Signal = ‑68 dBm on Channel 30

![](media/image72.wmf){width="6.497916666666667in"
height="4.4430555555555555in"}

[]{#__RefHeading___Toc163024478 .anchor}Figure 9‑71. Third-Order
Intercept Point Parameter with Desired Signal = ‑53 dBm on Channel 30

![](media/image73.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024479 .anchor}Figure 9‑72. Third-Order
Intercept Point Parameter with Desired Signal = -68 dBm on Channel 51

![](media/image74.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024480 .anchor}Figure 9‑73. Third-Order
Intercept Point Parameter with Desired Signal = -53 dBm on Channel 51

![](media/image75.wmf){width="9.478472222222223in"
height="6.278472222222222in"}

[]{#__RefHeading___Toc163024481 .anchor}Figure 9‑74. Third-Order
Intercept Point Parameter---Channel 30/51 Comparison

#  IM3 WITH PAIRED SIGNALS OF UNEQUAL AMPLITUDES

The previous chapter showed the results of D/U measurements on eight
receivers for pairs of undesired signals that were equal in power. In
this chapter, we select two receivers and one channel offset pair for
each for additional measurements with unequal undesired input signals. A
model of the results is presented to allow measurements from the
previous chapter to be to be extended to unequal signal levels on the
other receivers. It will be seen that the model performs best at low
desired signal levels.

## Measurements on Two Receivers

The tests for this chapter were performed on receiver G4 with an
undesired signal pair at N+2/N+4 and receiver M1 with an undesired
signal pair at N+3/N+6. The selections of these receivers and channel
offsets were based on their relatively high (though not the highest)
differences between paired-signal D/U and summed D/U measurements, as
presented in Chapter 9. This selection criterion ensured that the tests
would be performed on receivers that exhibited easily measurable IM3
effects---at least for paired signals of equal levels. Plots of
paired-signal D/U's and summed D/U's for these receivers were shown in
Figures 9-16 and 9-13, respectively, in Chapter 9.

Figure 10-1 shows measurements of threshold signal levels for a pair of
undesired signals on N+2 and N+4 for receiver G4. The three curves
correspond to three desired signal levels: -53 dBm, -68 dBm, and
D~MIN~ + 3 dB. The measurements were performed by attenuating one
undesired signal with respect to the other, and then adjusting an
attenuator that affected both undesired signal levels until TOV for the
DTV receiver was found.[^70] The X-axis shows the signal level of the
undesired signal on channel N+2. The Y-axis shows the level of the
undesired signal on channel N+4. The dashed lines represent a model, to
be discussed in the next section.

If one moves down the chart toward very low signal levels on N+4, each
curve asymptotically approaches the respective threshold level for N+2
alone. Similarly, moving leftward on the chart toward very low levels on
N+2 causes at least one curve (that for D~MIN~ + 3 dB) to asymptotically
approach the threshold value for N+4 alone.[^71] In between these two
conditions is the region where IM3 between the pair of signals is the
dominant interference mechanism.

Figure 10-2 shows the same type of measurement performed on receiver M1.
This receiver exhibited very odd behavior when the undesired signal
power on N+3 (U~N+3~) was between -27 and -21 dBm. As U~N+3~ is
increased in this range, the upper two curves exhibit first a dip in
U~N+6~ relative to the previous trajectory, then a sharp increase, and
finally a return back down to the previous trajectory. The lower curve
exhibits the dip, but the threshold value of U~N+3~ is reached before
subsequent behavior had an opportunity to occur.

Figure 10-3 isolates the curve corresponding to a desired signal power
of -68 dBm and adds a shading effect to illustrate the bizarreness of
the behavior. Consider moving along the solid diagonal line,
representing equal values of undesired signals, while the desired signal
level remains at -68 dBm. Beginning at the lower left and moving
rightward, DTV reception is visually flawless. When each of the
undesired signals reaches a level of -26.6 dBm, the TV picture begins to
exhibit visual errors. As the level of the undesired signal pair
increases about another dB, the picture is lost entirely. However, a
further increase causes the picture to come back, and, with a little
additional increase, to again become error free. But the new error-free
condition exists only over a very narrow range of undesired signal
levels before picture errors---followed by complete picture
failure---occur again as the undesired signal levels rise further.

This behavior---of first losing the picture, then regaining it, and then
losing it again with increases in undesired signal levels---was observed
at D = -68 dBm for increases in both undesired signals at equal levels,
as well as for both D = -68 dBm and D = -53 dBm when U~N+6~ was fixed in
power (at an appropriate level) and U~N+3~ was varied. We have no
explanation for the observed behavior, but we suspect that AGC
operation---driven by the signal level on N+3---is involved.

## Modeling and Extrapolation

Appendix B demonstrated that a pair of undesired signals at N+K and N+2K
can create an IM3-based interference effect that is proportional to
U~N+K~^2^ and to U~N+2K~. The resulting relationship between the
threshold values of D, U~N+K~, and U~N+2K~ is given in Chapter 8 as

D = (SNR~R~ / IP3^2^) U~N+K~^2^U~N+2K~ + D~MIN~.

where SNR~R~ / IP3^2^ quantifies the IM3 characteristics of the receiver
for the specified channel offsets (N+K and N+2K) and AGC gain state. It
is clear from the equation that, for a fixed desired signal power,
increasing the power of one of the undesired signals must result in a
reduction of threshold power of the other if AGC gain remains constant
with the variations. Furthermore, because the U~N+K~ term is squared and
the U~N+2K~ term is not, a change in U~N+K~ must be countered with a
larger, but opposite, change in U~N+2K~, in order to remain at
threshold. For example, a 3 dB increase in U~N+K~ results in the
threshold value of U~N+2K~ dropping by 6 dB.

Chapter 8 shows that one can compute the threshold of one undesired
signal given the level of the other by means of the following equations:

U~N+K~\|~dB~ = (IP3 / SNR~R~^1/2^)\|~dB~ + (D\|~dB~ - U~N+2K~\|~dB~)/2

U~N+2K~\|~dB~ = 2(IP3 / SNR~R~^1/2^)\|~dB~ + D\|~dB~ - 2 U~N+K~\|~dB~

If there are no AGC-induced changes in tuner gain prior to the point of
the nonlinearity that causes IM3 in a given situation, then the value of
(IP3 / SNR~R~^1/2^)\|~dB~ is a constant, which can be computed from a
measurement of threshold made with equal levels of undesired signals on
the two channels (*i.e.*, U = U~N+K~ = U~N+2K~).

(IP3 / SNR~R~^1/2^)\|~dB~ = (3 U\|~dB~ - D\|~dB~ )/2

Values of IP3 / SNR~R~^1/2^ computed in this way for eight receivers
were shown in Tables 9‑3 through 9-5 and Figures 9-30 through 9-34 of
Chapter 9. (Note that for values of D approaching D~MIN~, the quantity
D\|~dB~ should be replaced by (D -- D~MIN~)\|~dB~ where the subtraction
is performed in linear power units, before conversion to dB.)

Figures 10-1 and 10-2 included dashed line representing modeled
performance in three regions:

1.  A horizontal line represents the threshold value of U~N+2K~ in the
    absence of an undesired signal at N+K; this portion of the model is
    based on direct measurement of the threshold under that condition;

2.  A vertical line represents the threshold value of U~N+K~ in the
    absence of an undesired signal at N+2K; this portion of the model is
    based on direct measurement of the threshold under that condition;

3.  A diagonal line with a slope of -2 dB/dB represents the IM3
    contribution to interference based on the formulas above; the
    required value of IP3 / SNR~R~^1/2^ was computed by measurement of
    threshold with U~N+K~ = U~N+2K~.

Thus, three measurements (indicated by the black circles) were required
to create each modeled performance curve. Given that those same three
measurements exist for each of the eight receivers at various channel
offsets, we can apply the modeling technique to the other receivers and
other channel offsets. We choose to do this only at the lower signal
levels (D = ‑68 dBm and below) since the model appears to be a better
fit to measurements at such levels. (At higher levels, AGC is more
likely to influence the results.)

We note that, even if the AGC did not engage to reduce gain prior to the
IM3-generating nonlinearity during measurement of the threshold for
equal-powered undesired signals, it is still possible that it might
engage under some non-equal undesired signal conditions. This is more
likely to occur on the basis of U~N+K~, since it is likely to be
subjected to less attenuation by the tuner's tracking filter than is
U~N+2K~. If the AGC does engage on U~N+K~, the IM3 segment of the model
curve will switch at that point from being a diagonal line to a
horizontal line extending rightward from the AGC engagement point (per
Appendix B). ***Since we haven't attempted to determine AGC thresholds
for each case, the reader should recognize that the curves shown in the
models presented in this chapter will be invalid to the right of such an
AGC engagement point, if one occurs.*** In Chapter 14, we identify one
such case.

### Models for D = -68 dBm

Figures 10-4 through 10-10 show paired-signal IM3 models for the eight
DTV receivers at a desired signal level of ‑68 dBm. Each graph
represents one channel-offset pair---*e.g.*, N-5/N-10 for the first.
Each graph contains one curve for each DTV receiver for which an
IP3 / SNR~R~^1/2^ was determined in Table 9-3.

No plots are shown for the first-adjacent channel cases (N-1/N-2 and
N+1/N+2) because measurements presented in Chapter 9 were not adequate
to ensure that a paired-signal IM3 effect was measured for those
channels (as opposed to individual-channel effects). Chapter 11 will
show, in detail, that the paired-signal IM3 on N+1/N+2 is limited to
certain regions of the amplitude range for receiver D3 (at least for
equal amplitude undesired signals).

Each curve shows that the presence of one undesired signal can affect
the TV receiver's susceptibility to the other. As an example, we examine
the curve corresponding to receiver D3 in Figure 10-5, where K is ‑4
(*i.e.*, the channel pair is N-4/N-8). Starting at the top left end of
that curve, we see that the TV is susceptible to interference from an
undesired signal at -13 dBm on channel N+2K (y-axis). Moving to the
right, we see that, if an undesired signal is also present on channel
N+K at a level exceeding -37 dBm, the susceptibility of the receiver to
interference on channel N+2K will increase (*i.e.*, the receiver will be
affected by smaller undesired signals on that channel). As the level of
the undesired signal on channel N+K increases, the signal level on
channel N+2K necessary to cause interference drops by 2 dB for each 1‑dB
increase in power on channel N+K---eventually reaching -45 dBm when the
undesired signal on channel N+K reaches -21 dB. Similarly, we can view
the undesired signal on channel N+2K as causing the TV to be more
susceptible to interference from channel N+K.

This example could be applied to the case in which a desired
signal---broadcast from a DTV station on channel N---is received at a
level of -68 dBm at the input to a DTV receiver and another DTV
broadcast on channel N-4 is the first undesired signal. The analysis
described above could be used to predict the vulnerability of the DTV
receiver to emissions from a white-space device or another DTV station
operating on channel N-8, as a function of the undesired signal level on
channel N-4 at the input to the receiver.

Table 10-1 summarizes the information in the model plots. Note that the
statistics provided here apply to the subset of combinations of channel
offsets and TVs for which a measurement of IP3 / SNR~R~^1/2^ was
obtained. In general, the greatest susceptibility to interference is
predicted to be on channel N+2K when a large signal is present on N+K.
If no undesired signal is present on channel N+K, the receivers can
tolerate undesired signal levels as high as -27 to -1 dBm on N+2K. With
an undesired signal on N+2K, the receivers are predicted to be
susceptible to undesired signal powers as low as -79 to ‑28 dBm---an
increase in susceptibility ranging from 23 to 63 dBm. The signal level
on N+K necessary to cause such an increase in interference
susceptibility can range from -28 to -3 dBm, but the susceptibility
increase begins at levels of -45 to -24 dBm on channel N+2K.

If one were interested in determining what undesired signal level could
cause interference to DTV reception, one might consider two different
approaches with respect to IM3 from paired signals:

\(1\) Identify a level that could cause interference
***[if]{.underline}*** a similar signal level happens to occur at
another channel offset that would place IM3 products in the desired
channel;

\(2\) Identify levels that will cause interference given a specific
knowledge of signal levels that already exist on other channels that
might combine with the signal of interest to cause IM3.

In case (1) analysis could be performed based on the equal-power
paired-signal test results from Chapter 9 (or summary charts presented
in Chapter 15 of this report). In case (2), the modeled results in this
chapter could provide a basis for analysis.

[]{#__RefHeading___Toc163024585 .anchor}Table 10‑27. Range of Impact of
IM3 from Pairs of Undesired Signals When D = -68 dBm

+-------------------------------------+----+------+-----+----+-------+
|                                     | ** |      |     |    |       |
|                                     | St |      |     |    |       |
|                                     | at |      |     |    |       |
|                                     | is |      |     |    |       |
|                                     | ti |      |     |    |       |
|                                     | cs |      |     |    |       |
|                                     | of |      |     |    |       |
|                                     | U  |      |     |    |       |
|                                     | nd |      |     |    |       |
|                                     | es |      |     |    |       |
|                                     | ir |      |     |    |       |
|                                     | ed |      |     |    |       |
|                                     | Si |      |     |    |       |
|                                     | gn |      |     |    |       |
|                                     | al |      |     |    |       |
|                                     | Le |      |     |    |       |
|                                     | ve |      |     |    |       |
|                                     | ls |      |     |    |       |
|                                     | (  |      |     |    |       |
|                                     | dB |      |     |    |       |
|                                     | m) |      |     |    |       |
|                                     | ** |      |     |    |       |
+-------------------------------------+----+------+-----+----+-------+
|                                     | ** | **   | **  | ** | **Sta |
|                                     | Mi | Medi | Mea | Ma | ndard |
|                                     | n. | an** | n** | x. | D     |
|                                     | ** |      |     | ** | eviat |
|                                     |    |      |     |    | ion** |
+-------------------------------------+----+------+-----+----+-------+
| **Susceptibility increase on N+K    |    |      |     |    |       |
| due to N+2K:**                      |    |      |     |    |       |
+-------------------------------------+----+------+-----+----+-------+
| > Susceptibility to N+K begins      | -  | -    | -4  | -  | 11.9  |
| > increasing at U~N+2K~=            | 79 | 46.6 | 7.7 | 28 |       |
|                                     | .4 |      |     | .0 |       |
+-------------------------------------+----+------+-----+----+-------+
| > Susceptibility to N+K reaches     | -  | -5.2 | -   | -1 | 5.4   |
| > max. at U~N+2K~=                  | 27 |      | 6.9 | .4 |       |
|                                     | .0 |      |     |    |       |
+-------------------------------------+----+------+-----+----+-------+
| > U~N+K~ threshold before increase  | -  | -    | -1  | -2 | 5.7   |
| > in susceptibility                 | 28 | 12.5 | 3.3 | .6 |       |
|                                     | .2 |      |     |    |       |
+-------------------------------------+----+------+-----+----+-------+
| > U~N+K~ threshold after increase   | -  | -    | -3  | -  | 5.4   |
| > in susceptibility                 | 45 | 34.2 | 3.7 | 24 |       |
|                                     | .2 |      |     | .2 |       |
+-------------------------------------+----+------+-----+----+-------+
| > Net increase in susceptibility    | 11 | 19.4 | 2   | 31 | 5.1   |
| > caused by U~N+2K~                 | .7 |      | 0.4 | .6 |       |
+-------------------------------------+----+------+-----+----+-------+
| **Susceptibility increase on N+2K   |    |      |     |    |       |
| due to N+K:**                       |    |      |     |    |       |
+-------------------------------------+----+------+-----+----+-------+
| > Susceptibility to N+2K begins     | -  | -    | -3  | -  | 5.4   |
| > increasing at U~N+K~=             | 45 | 34.2 | 3.7 | 24 |       |
|                                     | .2 |      |     | .2 |       |
+-------------------------------------+----+------+-----+----+-------+
| > Susceptibility to N+2K reaches    | -  | -    | -1  | -2 | 5.7   |
| > max. at U~N+K~=                   | 28 | 12.5 | 3.3 | .6 |       |
|                                     | .2 |      |     |    |       |
+-------------------------------------+----+------+-----+----+-------+
| > U~N+2K~ threshold before increase | -  | -5.2 | -   | -1 | 5.4   |
| > in susceptibility                 | 27 |      | 6.9 | .4 |       |
|                                     | .0 |      |     |    |       |
+-------------------------------------+----+------+-----+----+-------+
| > U~N+2K~ threshold after increase  | -  | -    | -4  | -  | 11.9  |
| > in susceptibility                 | 79 | 46.6 | 7.7 | 28 |       |
|                                     | .4 |      |     | .0 |       |
+-------------------------------------+----+------+-----+----+-------+
| > Net increase in susceptibility    | 23 | 38.8 | 4   | 63 | 10.1  |
| > caused by U~N+K~                  | .5 |      | 0.8 | .1 |       |
+-------------------------------------+----+------+-----+----+-------+

### Models for D = D~MIN~ + 3 dB

Figures 10-11 through 10-17 show plots of models corresponding to a
desired signal level that is 3 dB above the D~MIN~ value that was
measured for each receiver. Since we made no measurement of
paired-signal thresholds at D~MIN~ + 3 dB (except for those shown in
Figures 10-1 and 10-2, which were not used in Figures 10-11 through
10-17), the plots are based on an assumption that IP3 / SNR~R~^1/2^ is
the same at this low desired signal level as it was at D = -68 dBm. To
help ensure the validity of this assumption, models are shown only for
DTVs and channel offsets for which Table 9-3 indicates that -68 dBm was
likely to be low enough to avoid AGC operation (based on the change in
IP3 / SNR~R~^1/2^ as desired the signal decreased from -53 dBm to
‑68 dBm). Nonetheless, this extrapolation to lower signal levels
constitutes an additional potential source of error in these plots that
was not present in the Figures 10-4 to 10-10.

Comparing the modeled curve for receiver M1 in Figure 10-15 to the
measurements for that receiver at D = D~MIN~ + 3 dB in Figure 10-2, we
see that the modeled threshold along the equal-power line is about
‑32 dBm, whereas the measured threshold is about ‑30 dBm. This 2 dB
error can be attributed to the anomalous behavior of the receiver for D
= -68 dBm in the vicinity of the equal power line (Figure 10-2). In
fact, if the model had been computed from the IP3 / SNR~R~^1/2^ value
for D = -53 dBm, it would match the measurement within 0.3 dB.

Table 10-2 summarizes the information in the model plots. Note that the
statistics provided here apply to the subset of combinations of channel
offsets and TVs for which a measurement of IP3 / SNR~R~^1/2^ was
obtained and for which AGC was judged to be inactive at -68 dBm (for
tuner stages prior to the nonlinearity that causes the observed IM3) so
that IP3 could be assumed constant below that level. In most cases, the
greatest susceptibility to interference is predicted to occur on channel
N+2K, where the susceptibility may increase by amounts ranging from 6 to
59 dB when a large signal is present on N+K.

[]{#__RefHeading___Toc163024586 .anchor}Table 10‑28. Range of Impact of
IM3 from Pairs of Undesired Signals When D =D~MIN~ + 3 dB

+------------------------------------+----+------+-----+----+--------+
|                                    | ** |      |     |    |        |
|                                    | St |      |     |    |        |
|                                    | at |      |     |    |        |
|                                    | is |      |     |    |        |
|                                    | ti |      |     |    |        |
|                                    | cs |      |     |    |        |
|                                    | of |      |     |    |        |
|                                    | U  |      |     |    |        |
|                                    | nd |      |     |    |        |
|                                    | es |      |     |    |        |
|                                    | ir |      |     |    |        |
|                                    | ed |      |     |    |        |
|                                    | Si |      |     |    |        |
|                                    | gn |      |     |    |        |
|                                    | al |      |     |    |        |
|                                    | Le |      |     |    |        |
|                                    | ve |      |     |    |        |
|                                    | ls |      |     |    |        |
|                                    | (  |      |     |    |        |
|                                    | dB |      |     |    |        |
|                                    | m) |      |     |    |        |
|                                    | ** |      |     |    |        |
+------------------------------------+----+------+-----+----+--------+
|                                    | ** | **   | **  | ** | **St   |
|                                    | Mi | Medi | Mea | Ma | andard |
|                                    | n. | an** | n** | x. | Devia  |
|                                    | ** |      |     | ** | tion** |
+------------------------------------+----+------+-----+----+--------+
| **Susceptibility increase on N+K   |    |      |     |    |        |
| due to N+2K:**                     |    |      |     |    |        |
+------------------------------------+----+------+-----+----+--------+
| > Susceptibility to N+K begins     | -  | -    | -4  | -  | 14.4   |
| > increasing at U~N+2K~=           | 68 | 39.5 | 1.3 | 12 |        |
|                                    | .7 |      |     | .4 |        |
+------------------------------------+----+------+-----+----+--------+
| > Susceptibility to N+K reaches    | -  | -9.0 | -1  | -2 | 6.7    |
| > max. at U~N+2K~=                 | 32 |      | 1.1 | .9 |        |
|                                    | .3 |      |     |    |        |
+------------------------------------+----+------+-----+----+--------+
| > U~N+K~ threshold before increase | -  | -    | -2  | -  | 6.4    |
| > in susceptibility                | 38 | 23.9 | 3.7 | 12 |        |
|                                    | .5 |      |     | .3 |        |
+------------------------------------+----+------+-----+----+--------+
| > U~N+K~ threshold after increase  | -  | -    | -3  | -  | 5.2    |
| > in susceptibility                | 50 | 39.4 | 8.9 | 30 |        |
|                                    | .0 |      |     | .7 |        |
+------------------------------------+----+------+-----+----+--------+
| > Net increase in susceptibility   | 3  | 15.4 | 1   | 29 | 7.2    |
| > caused by U~N+2K~                | .2 |      | 5.1 | .6 |        |
+------------------------------------+----+------+-----+----+--------+
| **Susceptibility increase on N+2K  |    |      |     |    |        |
| due to N+K:**                      |    |      |     |    |        |
+------------------------------------+----+------+-----+----+--------+
| > Susceptibility to N+2K begins    | -  | -    | -3  | -  | 5.2    |
| > increasing at U~N+K~=            | 50 | 39.4 | 8.9 | 30 |        |
|                                    | .0 |      |     | .7 |        |
+------------------------------------+----+------+-----+----+--------+
| > Susceptibility to N+2K reaches   | -  | -    | -2  | -  | 6.4    |
| > max. at U~N+K~=                  | 38 | 23.9 | 3.7 | 12 |        |
|                                    | .5 |      |     | .3 |        |
+------------------------------------+----+------+-----+----+--------+
| > U~N+2K~ threshold before         | -  | -9.0 | -1  | -2 | 6.7    |
| > increase in susceptibility       | 32 |      | 1.1 | .9 |        |
|                                    | .3 |      |     |    |        |
+------------------------------------+----+------+-----+----+--------+
| > U~N+2K~ threshold after increase | -  | -    | -4  | -  | 14.4   |
| > in susceptibility                | 68 | 39.5 | 1.3 | 12 |        |
|                                    | .7 |      |     | .4 |        |
+------------------------------------+----+------+-----+----+--------+
| > Net increase in susceptibility   | 6  | 30.8 | 3   | 59 | 14.3   |
| > caused by U~N+K~                 | .4 |      | 0.2 | .3 |        |
+------------------------------------+----+------+-----+----+--------+

![](media/image76.wmf){width="4.997222222222222in"
height="4.4430555555555555in"}

[]{#__RefHeading___Toc163024482 .anchor}Figure 10‑75. Threshold U for
Paired, Unequal Undesired Signals on Receiver G4

![](media/image77.wmf){width="4.398611111111111in"
height="4.4430555555555555in"}

[]{#__RefHeading___Toc163024483 .anchor}Figure 10‑76. Threshold U for
Paired, Unequal Undesired Signals on Receiver M1

![](media/image78.wmf){width="4.902083333333334in"
height="4.4430555555555555in"}

[]{#__RefHeading___Toc163024484 .anchor}Figure 10‑77. Threshold U for
Paired, Unequal Undesired Signals on Receiver M1 at D = -68 dBm

![](media/image79.wmf){width="4.397916666666666in"
height="4.427083333333333in"}

[]{#__RefHeading___Toc163024485 .anchor}Figure 10‑78. Modeled Thresholds
for N-5/N-10 with D = -68 dBm

![](media/image80.wmf){width="4.397916666666666in"
height="4.427083333333333in"}

[]{#__RefHeading___Toc163024486 .anchor}Figure 10‑79. Modeled Thresholds
for N-4/N-8 with D = -68 dBm

![](media/image81.wmf){width="4.397916666666666in"
height="4.427083333333333in"}

[]{#__RefHeading___Toc163024487 .anchor}Figure 10‑80. Modeled Thresholds
for N-3/N-6 with D = -68 dBm

![](media/image82.wmf){width="4.397916666666666in"
height="4.427083333333333in"}

[]{#__RefHeading___Toc163024488 .anchor}Figure 10‑81. Modeled Thresholds
for N+2/N+4 with D = -68 dBm

![](media/image83.wmf){width="4.397916666666666in"
height="4.427083333333333in"}

[]{#__RefHeading___Toc163024489 .anchor}Figure 10‑82. Modeled Thresholds
for N+3/N+6 with D = -68 dBm

![](media/image84.wmf){width="4.397916666666666in"
height="4.427083333333333in"}

[]{#__RefHeading___Toc163024490 .anchor}Figure 10‑83. Modeled Thresholds
for N+4/N+8 with D = -68 dBm

![](media/image85.wmf){width="4.397916666666666in"
height="4.427083333333333in"}

[]{#__RefHeading___Toc163024491 .anchor}Figure 10‑84. Modeled Thresholds
for N+5/N+10 with D = -68 dBm

![](media/image86.wmf){width="4.397916666666666in"
height="4.427083333333333in"}

[]{#__RefHeading___Toc163024492 .anchor}Figure 10‑85. Modeled Thresholds
for N-5/N-10 with D = D~MIN~ + 3 dB

![](media/image87.wmf){width="4.397916666666666in"
height="4.427083333333333in"}

[]{#__RefHeading___Toc163024493 .anchor}Figure 10‑86. Modeled Thresholds
for N-4/N-8 with D = D~MIN~ + 3 dB

![](media/image88.wmf){width="4.397916666666666in"
height="4.427083333333333in"}

[]{#__RefHeading___Toc163024494 .anchor}Figure 10‑87. Modeled Thresholds
for N-3/N-6 with D = D~MIN~ + 3 dB

![](media/image89.wmf){width="4.397916666666666in"
height="4.427083333333333in"}

[]{#__RefHeading___Toc163024495 .anchor}Figure 10‑88. Modeled Thresholds
for N+2/N+4 with D = D~MIN~ + 3 dB

![](media/image90.wmf){width="4.397916666666666in"
height="4.427083333333333in"}

[]{#__RefHeading___Toc163024496 .anchor}Figure 10‑89. Modeled Thresholds
for N+3/N+6 with D = D~MIN~ + 3 dB

![](media/image91.wmf){width="4.397916666666666in"
height="4.427083333333333in"}

[]{#__RefHeading___Toc163024497 .anchor}Figure 10‑90. Modeled Thresholds
for N+4/N+8 with D = D~MIN~ + 3 dB

![](media/image92.wmf){width="4.397916666666666in"
height="4.427083333333333in"}

[]{#__RefHeading___Toc163024498 .anchor}Figure 10‑91. Modeled Thresholds
for N+5/N+10 with D = D~MIN~ + 3 dB

#  SINGLE AND PAIRED REJECTION RATIOS VERSUS DESIRED SIGNAL LEVEL---A DETAILED EXAMPLE

This chapter presents measurements of D/U ratio and of U at threshold as
functions of desired signal level D based on a detailed set of
measurements for one DTV receiver, D3. The tests included single
interferers as well as paired interferers spaced to place IM3 products
in the desired signal channel. The amount of effort involved in making
these measurements precluded such an evaluation of other receivers;
however, the results from this one set of measurements provide some
insight into the behavior of interference susceptibilities that will aid
in developing an understanding of test results for other DTV receivers.

Figure 11-1 shows measurements of D/U versus D for receiver
D3---measured for the desired channel N = 51. Chronologically, this was
the first rejection performance work done under this test program apart
from a crude set of measurements used to select the TV for this test.
The test was performed to provide some insight into the variation of
certain interference effects with desired signal level prior to testing
at fixed desired signal levels.[^72]

The *dashed* curves on the plot represent measurements using pairs of
equal-level undesired signals at N+1/N+2, N+2/N+4, N+3/N+6, and N+4/N+8.
The solid lines represent measurements with single undesired signals on
channels N+1 through N+7, N+14, and N+15. Curves labeled "N+1 (No
Filter)" and "N+1/N+2 (No Filter)" are measurements performed with the
filter removed from the test setup; this allowed the test setup to
create higher interfering signal levels.[^73]

Though the number of curves on each plot makes it difficult to identify
individual results, the curves are all combined on one graph to
illustrate both the diversity and the commonality in the behavior of the
various interference phenomena. The data will be dissected into separate
charts later in the chapter.

The first point on each curve is a measurement with the desired signal
at approximately 1 dB above the minimum signal D~MIN~ for the TV.
(D~MIN~ is the desired signal level corresponding to the threshold of
visibility (TOV) of picture degradation in the absence of interference.)
The second point is 3 dB above D~MIN~. The third point is at D~MIN~ + 5
dB, and all subsequent points are at 5-dB intervals.

Note the following reference levels on the graph.

1.  Diamonds (![](media/image93.png){width="0.12430555555555556in"
    height="0.1284722222222222in"}) on the X-axis mark the following
    desired signal levels.

    1.  -84 dBm is the received level of a DTV signal at the edge of
        coverage of a broadcast station (per OET-69); this is also
        marked by a black vertical dashed line.

    2.  -68 dBm, -53 dBm, and -28 dBm are the desired signal levels that
        the ATSC designated as "weak", "moderate", and "strong",
        respectively; most D/U measurements shown elsewhere in this
        report were made at these three levels.

    3.  Not shown (off scale to the right) is -8 dBm, the largest
        expected DTV signal.

2.  A diagonal dashed line corresponds to an undesired signal level of
    -8 dBm---equal to the maximum DTV signal that is expected at the
    input to a TV receiver.

Figure 11-2 shows the same measurement data as Figure 11-1, but it is
presented as undesired signal level at threshold rather than as D/U
ratios. Thus, in Figure 11-2, high points on the graph represent high
rejection performance rather than high susceptibility to interference.

Figures 11-3 and 11-4 are plots of slope of log-D versus log-U and of
log-U versus log-D, respectively. The slope information will aid in
evaluating order of the interference mechanisms represented by the
curves. The slope of log-D versus log-U directly indicates order of the
interference mechanism (except where AGC affects the results and at
desired signal levels near D~MIN~); thus, an interference mechanism that
is third-order in terms of the undesired signal level should have a
slope of 3 in Figure 11-3. Figure 11-4 is included because the
interference effect of certain interference mechanisms such as
cross-modulation is directly proportional to desired signal as well as
being dependent on the undesired signal level; the result is predicted
to be an infinite slope in Figure 11-3 or a zero slope in Figure 11-4.
Slopes were computed from adjacent pairs of measurement points from
Figures 11-1 and 11-2 and are plotted at the midpoint of the pair. Thus,
for example, the slope that was computed based on measurements at
desired signal levels of -68 dBm and ‑63‑dBm was plotted at ‑65.5 dBm.

## General Observations

Returning to Figure 11-1, we make some general observations regarding
the interference rejection results.

First, in examining the left portion of the graph---for desired signals
less than about -60 dBm---we note the following.

1.  Some of the curves are---for the most part---horizontal lines,
    indicating constant D/U ratio as desired signal is varied. This
    result is true for interference at N+14 and N+15 because
    interference effects on these channels result from the receiver's
    mixer image---a linear interference mechanism. Less expected is that
    the curves for N+1 and N+2 are flat, a topic that will be discussed
    later. Totally unexpected is the fact that interference from a pair
    of undesired signals at N+1/N+2 also exhibits a flat D/U and that
    the D/U is nearly identical to that for N+1 alone, over part of the
    curve. N+1/N+2 is expected to generate IM3---a third order nonlinear
    process (third order when the amplitudes of both undesired signals
    are adjusted together).

2.  Some of the curves exhibit upward slopes of log(D/U) versus log-D.
    Many of the slopes appear to be identical, but others---such as
    those for N+3 and for N+7---are steeper.

3.  While most of the curves appear to be nearly straight lines, all
    bend upward at their left-hand ends, where the desired signal level
    approaches D~MIN~.

Next, looking at the middle to right hand portions of the graph, we note
the following.

1.  Most of the curves that are upward-sloped on the left exhibit an
    abrupt bend---becoming approximately horizontal. The D/U's, which
    were increasing as straight lines (on the dB versus dB scale),[^74]
    dip down gradually after the bend, but then eventually begin to
    increase again. The bend is believed to be associated with AGC
    action in the receiver for reasons discussed in Chapter 8.

2.  The abrupt bend in most of the curves occurs at the same desired
    signal level of approximately ‑53 dBm. We believe that the receiver
    AGC begins reducing RF gain at this desired signal level.

3.  One curve, that for interference at N+2/N+4, exhibits its bend at a
    lower desired signal level---approximately -58 dBm. In this case, it
    is considered likely that AGC action is initiated---not based on the
    desired signal level alone, but rather based on the total power
    reaching an AGC sensing point in the receiver. In this case, the
    approximately -37 dBm undesired power on channel N+2 (see
    Figure 11‑2) is sufficient that---after filtering within the
    tuner---it combines with the desired signal power to engage the AGC.

4.  The curves for N+1 and for the N+1/N+2 pair gradually shift from
    their horizontal slope on the left of the graph to upward slopes on
    the right half of the plot. The flat portions at the left side of
    both curves is believed to be due to AGC action similar to that
    discussed in the previous bullet; in this case, AGC action based on
    the level of the undesired signal at N+1 exceeding a threshold on
    the order of -40 dB or lower results in the curves being flat in the
    left hand region. In the upward-sloped region, the D/U of the
    N+1/N+2 curve tracks that of the N+1 curve, but at a D/U ratio that
    is about 3‑dB higher than that for N+1. This portion of both of the
    curves is likely to be the result of IM3 occurring either at an
    early RF amplifier stage that is not controlled by the AGC, or at
    the same point as the other IM3 examples (probably the mixer), but
    after the AGC's gain reduction capability for those stages has
    reached its limit.

## IM3 With Paired Undesired Signals

We start by assessing the paired-signal results, because those results
enable us to understand the N+1 results. To provide a simpler view,
Figure 11-5 was created to show D/U for the four tested pairs (the
dashed lines) and for the single interferers associated with them (solid
lines). All other data has been removed from the plot.

### N+2/N+4, N+3/N+6, and N+4/N+8

We first examine the paired signal test results that did not involve the
first adjacent channel. We note that the D/U curves for N+2/N+4,
N+3/N+6, and N+4/N+8 (Figure 11-5) have two distinctive regions: an
up-sloped region on the left and more horizontal, but dish-shaped region
to the right. The dish-shaped region slopes downward initially, but then
begins to trend upward (on two of the three curves) on the far right.
The two regions are separated by an abrupt bend in each curve, occurring
at a desired signal level of either -53 dBm or -58 dBm.

Looking at the sloped portions of the curves to the left of D = -58 dBm,
we see that the D/U ratios (and thus the interference effects) of the
paired signals (dashed curves) are higher than those of the
corresponding single signals.[^75] For example, the D/U ratios for
N+2/N+4 (the top curve) are significantly higher than those for N+2 and
N+4 individually. This implies that the pair of undesired signals
combines synergistically so as to create an interference effect larger
than the sum of the interference effects of the individual signals. This
synergism is the result of third-order intermodulation (IM3) distortion
occurring somewhere in the DTV receiver---most likely in the mixer.

Looking at the slope of log-D versus log-U (Figure 11-3), we see that
the slope measurements of the paired signal curves in this region fall
between 3 and 4 dB/dB. The expected slope for an IM3 process with both
undesired signals varied in amplitude together is 3 dB/dB. We take this
as further confirmation of IM3 as the primary cause of the paired signal
interference.

While we had expected the paired-signal IM3 to be significant only at
high signal levels, it is interesting to note in Figure 11-1 that IM3
for the N+2/N+4 pair causes higher interference susceptibility than any
single-channel interferer---including the first-adjacent channel---all
the way down to a desired signal level only 1 dB above the lowest signal
level at which the receiver can operate (D~MIN~). Similarly,
susceptibility to interference from an undesired signal pair at N+3/N+6
is greater---even at signal levels down to D~MIN~ + 1 dB---than from any
single channel except the first adjacent channel, and it exceeds even
that except when the desired signal drops to D~MIN~ + 3 dB or below.
Even on N+4/N+8, interference susceptibility exceeds that of any single
channel, except the first adjacent one, down to 2 dB above D~MIN~; mixer
image interference at N+15 barely surpasses N+4/N+8 interference effects
only at D~MIN~ + 1 dB.

We also note in Figure 11-5 that D/U ratios of the N+K/N+2K pairs fall
gradually as K increases. The fact that IM3 is observed even for N+4/N+8
suggests that it occurs at a place in tuner at which undesired signals
all the way out to N+8 (for the N+4/N+8 pair) are still present. The
gradual fall with increasing K suggests that the nonlinearity causing
these IM3 effects is after the tracking filter in the RF section. We
surmise that the IM3 effects observed on this part of each of the three
paired-signal curves being discussed in this section is caused by
nonlinearity at the mixer.

We now note the abrupt bend in each of the three curves (for N+2/N+4,
N+3/N+6, and N+4/N+8), representing a change in character of the
interference effect. Based on discussions in the Chapter 8, we attribute
that bend and subsequent leveling of the D/U plots to AGC action in the
tuner. Specifically, we conclude that, beginning at this bend, the AGC
adjusts gain downward with further increases in signal level and that
this gain adjustment occurs in the RF amplifier stage since the
nonlinearity that is affected is probably at the mixer.

We further note that the curves for N+3/N+6 and N+4/N+8 exhibit this AGC
bend at identical levels of desired signal, D = -53 dBm. Four of the
single-interferer curves in Figure 11-1 exhibit this same bend point. We
conclude that the RF AGC engages whenever the desired signal exceeds -53
dBm.

#### N+2/N+4---A Different AGC Point {#n2n4a-different-agc-point .unnumbered}

On the other hand, the N+2/N+4 curve exhibits its AGC bend when D = -58
dBm. This suggests an AGC action that is influenced by the *undesired*
signal level. The bend occurs when the undesired signal level applied to
both N+2 and N+4 reaches -36.5 dBm (Figure 11-2). The
desired-signal-driven AGC thresholds for the other curves occur when
undesired signals on channel N+3 or beyond are at signal levels ranging
from -31 to -17 dBm (Figure 11-2); these levels apparently do not result
in AGC action since all bends occurred at the same *desired* signal
level. In particular, the bend in the N+4 curve at D = ‑53 dBm and U =
-25 dBm suggests that the early bend in the N+2/N+4 curve is entirely
due to N+2 as opposed to N+4.

Hence, it is clear that the RF gain reduction in at least this one
case---and maybe in all---is triggered by total signal level (desired
plus undesired) at a point in the tuner where total power from each
channel is influenced by filtering. Assuming both AGC mechanisms are the
same, the fact that AGC action begins at a desired signal level of -53
dBm for most cases, but begins at a desired signal of -58 dBm in the
case at hand implies that the undesired signal is making up the
difference---at total of about -54.7 dBm referred to the input[^76] to
get to the apparent AGC threshold of -53 dBm referred to the input.
(This suggests that, had the desired signal level been much smaller, the
threshold at which N+2 would engage the AGC would be 1.7 dB higher than
that observed---*i.e.*, at U = -36.5 dBm + 1.7 dB = -34.8 dBm). Since
the undesired input level on channel N+2 at the point of RF AGC action
occurred at an input level of -36.5 dBm, it appears that the total power
in the N+2 channel is attenuated by filtering by about 18.2 dB (*i.e.*,
‑36.5 dBm ‑ \[‑54.7 dBm\]) relative to the desired channel.

We examine the N+2 curve (Figure 11-2) to see whether it exhibits
evidence of RF AGC action beginning at an undesired signal level in the
region of -34.8 to -36.5 dBm. There are no obvious AGC bends in the
curve; however, the undesired signal level for points on the curve
ranges from -34.1 to -11.7 dBm. Thus it is likely that the AGC
reductions of RF gain began just prior to the left-most point on the N+2
curve and continued throughout the curve.

#### Deviation From Straight Line Near Receiver Threshold {#deviation-from-straight-line-near-receiver-threshold .unnumbered}

The portion of each of the three D/U curves (N+2/N+4, N+3/N+6, and
N+4/N+8 in Figure 11-5) to the left of the AGC bend exhibits a primarily
straight-line appearance with a slope consistent with a third-order
interference process; however, there is an upward deviation from the
straight line at the left end of each curve. Chapter 8 predicted that
such deviations will occur as the desired signal level approaches D~MIN~
for the receiver. Specifically, Table 11‑2 predicts that, for a
third-order interference process, the undesired signal at threshold will
deviate from a straight-line projection by 1.0 dB when D = D~MIN~ + 3 dB
and by 2.3 dB when D = D~MIN~ + 1 dB.

By using these predicted deviations together with the theoretical slope
for a third-order process (Table 11‑1) and a single measurement at D =
-68 dBm (15 dB above D~MIN~), one can predict the actual measured
threshold values of undesired signal at D~MIN~ + 3 dB and D~MIN~ + 1 dB
with errors not exceeding 0.6 dB for the former prediction and 1.2 dB
for the latter in this particular case.

### N+1/N+2

Following the trend that was observed in the sub-section titled,
"N+2/N+4, N+3/N+6, and N+4/N+8", one might expect that the curve for
N+1/N+2 would look just like those for the other three paired signals
except that it would be positioned above those curves on the D/U chart
(Figure 11‑5)---indicating that the TV is more susceptible to
interference from the adjacent-channel pair than from the pairs that are
further away from the desired channel. The measurements dash this
expectation. Not only is the N+1/N+2 curve below the other three for
most of its trajectory, but its shape is completely different---flat
where the others are sloped and sloped where the others are essentially
flat.

Also unexpected is that the N+1 curve overlays the N+1/N+2 curve for
desired signals ranging from ‑73 dBm to -68 dBm. Apparently in this
region, adding an undesired signal at N+2 to an existing one at N+1
causes no additional interference effect. Clearly, in this region, the
IM3 contribution from the pair is negligible compared to the
interference effect of N+1 alone, and the overall interference effect is
*[less than]{.underline}* that of the other pairs.

We can take a clue as to the reason for the unexpected behavior from the
observations about AGC in the previous section. We note that a signal
level exceeding -34.8 dBm on channel N+2 is able to cause the AGC to
reduce the RF amplifier. (The observed threshold of -36.5 dBm was
slightly less because the desired signal was also contributing to the
energy seen by the AGC sampling point.) Given that RF AGC operation
begins at a level of -53 dBm on channel N, at -34.8 dBm on channel N+2,
and a higher, but unknown level on channels N+3 and beyond, we would
expect that an undesired signal on channel N+1 would activate the RF AGC
at a level somewhere between the channel N and channel N+1
values---*i.e.*, between -53 and ‑34.8 dBm. Furthermore, a typical
bandpass filter at channel N would take a much bigger bite out of a
signal at N+2 than out of a signal at N+1, so we might expect the AGC
threshold for N+1 to be closer to that at N than to that at N+2. This
suggests that the AGC threshold for N+2 is somewhere between that for N
and the midpoint between those for N and N+2; hence, we would expect a
threshold between -44 and -53 dBm. Looking at the U versus D plot in
Figure 11-2, we see that only the left-most point on the N+1/N+2 curve
has a U value within this range; all other points are above the
range---suggesting that the RF AGC is active throughout the plotted
curve, with the possible exception of the left-most point.

RF AGC operation throughout the curve provides a reason for the
different behavior of N+1/N+2 interference relative to the other pairs.
At all measured threshold points for N+1/N+2 (except possibly
D~MIN~ + 1 dB) the RF gain is reduced, reducing the IM3 at the
mixer---apparently to a level below the N+1 interference mechanism that
is at work.

The N+1/N+2 D/U ratio matches that for N+1 virtually exactly for desired
signal levels of -73 to -68 dBm or so. Outside of this range, the paired
signal shows more interference effect than N+1 alone. Since N+2 has a
relatively low D/U ratio, the fact that interference susceptibility for
the pair significantly exceeds that of N+1 indicates that the IM3 of the
pair becomes significant outside of this narrow range. Why?

#### Desired Signal Levels Above -58 dBm  {#desired-signal-levels-above--58-dbm .unnumbered}

At desired signal levels above -58 dBm, both the N+1/N+2 and N+1 plots
of D/U (Figure 11-5) become upward sloped. In this region it is assumed
that the interference mechanism for both single adjacent-channel case
(N+1) and the paired signal case (N+1/N+2) is IM3. (Recall that IM3
creates shoulders around a single undesired signal that spill into the
adjacent channel. Thus, for the first-adjacent-channel case, a pair of
signals is not needed to create IM3 in the desired channel.) The slope
of log-D versus log-U (Figure 11-3) goes to about three---consistent
with IM3. The D/U of N+1/N+2 exceeds that of N+1 alone by about 3
dB---consistent with the expectation that more IM3 will be generated in
the paired-signal case than in the single-signal case.

The fact that more IM3 occurs with N+1/N+2 than with N+1 in the
right-hand part of the curves suggests that the interference is being
generated by a nonlinearity occurring before the IF filter; so, again,
it appears that the relevant nonlinearity is likely to be at the mixer
or an earlier point in the tuner. The upturn of the D/U curves at a
desired signal level around -63 dBm indicates that either the
interference is being generated by a nonlinearity at an RF amplifier
stage that is not controlled by the AGC or the interference is being
generated by nonlinearity at the mixer *and* the AGC range for the RF
amplifier has run out---*i.e.*, the RF amplifier is at its minimum gain.
As a result, the D/U ratio rises with further increases in signal level.
In Figure 11-5 the beginnings of a similar trend can be seen at the
right-hand end of the curve for N+2/N+4, where D/U begins rising, but
does so at a level *below* the D/U of N+1/N+2, indicating that N+2/N+4
generates less IM3 than does N+1/N+2 due to rolloff of the tracking
filter in the RF stage.

#### Desired Signal Levels Below -73 dBm {#desired-signal-levels-below--73-dbm .unnumbered}

The upturn of D/U for N+1/N+2 relative to N+1 below -73 dBm was
unexpected. Measurements were repeated to confirm the behavior; the
result was the same.

In general all of the D/U curves exhibit an upturn from their
straight-line projections as one moves leftward on the plot---toward
D~MIN~. Such an upturn is predicted in Chapter 8 (Table 8-2). The
increase in D/U for N+1/N+2 above that of N+1, while D/U for N+2 remains
low, suggests that IM3 for the signal pair becomes dominant again at low
signal levels near the receiver's threshold. In fact, by the time
desired signal drops to -82 dBm, D/U at N+1/N+2 has returned to its
"rightful place" above the D/U for the other signal pairs. Thus, the
adjacent undesired signal pair (N+1/N+2) finally exhibits a greater
interference effect than that of the more distant signal pairs, an
expectation which was foiled by AGC gain reductions in the RF stage at
most other points along the curve. Apparently, the AGC-induced RF-gain
reductions are gone or nearly gone by this point on the graph.

## Single Undesired Signals

To facilitate the discussions below, Figure 11-6 and 11-7 were created
to show the D/U ratio and threshold U, respectively, for single
undesired signals (excluding the paired signal data that are included in
Figures 11‑1 and 11-2). For the most part the plots exhibit a
near-straight-line character (in the log-log plots due to units of dB)
in a region from about D = -78 dBm to D = -58 or -53 dBm.

To the left of this region, all D/U curves exhibit upturns from their
straight line projections. Those upturns are attributed to the effect of
receiver noise as the minimum signal threshold for the DTV receiver is
approached.

Moving to the right, five of the plots (like three of the paired-signal
plots) exhibit an abrupt downward bend in D/U to a relatively constant
D/U ratio beginning at what we have termed the "AGC bend" at D =
‑53 dBm. The bend is caused by a stabilization of nonlinear interference
mechanisms by AGC operation.

### N+1

The case of N+1 interference is discussed extensively in the previous
section. The observed behavior differs among three regions of the curve.

In the middle section, from D = -78 dBm to D = -58 dBm, the D/U is
constant, as would be expected for a linear interference process.
However, we showed, in the "N+1/N+2" section of this chapter, that the
AGC is actively adjusting RF gain throughout this section, so the
constant D/U could be due to a linear interference mechanism or a
non-linear one whose effect has been stabilized by the AGC. The
"N+1/N+2" section also argued that the interference in this region
occurs at a point beyond the first IF filter stage. It could be due to a
nonlinearity in an IF amplifier stage or due to a linear process, such
as inadequate IF selectivity allowing the edge of the N+1 signal to leak
into the demodulator.

In the right-hand section, beyond D = -53 dBm, interference was shown to
be the likely result of IM3 in the mixer after the AGC has reached the
limit of its ability to reduce gain of the RF amplifier.

In the left-hand section, to the left of D = -73 dBm, there is a rise in
the left-most two points on the curve that is attributable to the
influence of receiver noise as the receiver threshold is approached. The
fact that the rise is somewhat smaller than expected, coupled with a
possible slight dip in D/U to the left of D = ‑73 dBm may suggest a
diminishment of the interference mechanism that was dominant in the
middle section of the curve. Such a diminishment could occur if that
interference mechanism were nonlinear and if the AGC action ends as one
moves leftward on the curve through that region. An alternative
hypothesis is that the AGC-induced gain reductions might have increased
the noise figure of the tuner and that the additional noise diminishes
as one moves to the left on the curve and the AGC causes the RF gain to
increase. (Cowley and Hanrahan state that noise figure "increases at 1
dB per dB of gain backoff...with some AGC architectures."[^77])

### N+2

The D/U ratio for N+2 is shown in the bottom-most horizontal curve in
Figure 11-6.

In the "N+2/N+4" section of this chapter, we showed that the AGC begins
to reduce RF gain when the undesired signal level on N+2 exceeds a
threshold of -34.8 dBm (or lower if the desired signal level approaches
-53 dBm). Figure 11-7 shows that the undesired signal level throughout
the N+2 curve exceeds this AGC threshold; thus, it appears that the AGC
was controlling the RF gain throughout this curve.

The constant D/U ratio versus D throughout most of the plot is
consistent with either a linear interference mechanism or an
AGC-stabilized nonlinear one. The upturn at the left of the D/U plot
(Figure 11‑6) as D approaches D~MIN~ is caused by the effect of receiver
noise.

### N+3

The D/U curve for N+3 exhibits a steeper slope than the IM3-driven
curves (Figure 1-1). On the plot of threshold U versus D, one can see
that, for desired signal levels between -73 dBm and -53 dBm, the
threshold U is almost constant---increasing only by only 1.1 dB in a
span of 20 dB change in desired signal level. A constant value of U
would be expected for interference caused by a cross-modulation
mechanism. The slope of log-U versus log-D for such a mechanism would be
nominally zero, a value approached in this case, as can be seen in
Figure 11-4.

We suspect cross modulation in the mixer (a likely candidate for N+2
interference as well). We attribute the abrupt bend in U (downward bend
in D/U) toward a more constant D/U ratio at D = -53 dBm to AGC gain
reductions in the RF amplifier driven by the desired signal level.

### N+4

For desired signal levels below D = -63 dBm, the log-D versus log-U
curve for N+4 approaches 3---consistent with third-order interference
mechanism (Figure 11-3). We are unable to propose such a mechanism in
this case. The so-called the "half IF" taboo channel for analog TV was
based on the second harmonic of an undesired signal beating with the
second harmonic of the local oscillator frequency. Such an effect would
create a susceptibility to interference that is centered 22 MHz
(3 ^2^/~3~ channels) above the desired channel---placing it
predominantly at N+4. However, we anticipate that such an effect would
be second-order in terms of the undesired signal level, and thus would
exhibit a log-D versus log-U slope of two.

Between D = -63 dBm and D = -53 dBm, the slope increases
significantly---possibly indicating a shift toward cross-modulation as
the dominant interference mechanism.

As with many of the other curves, the D/U for N+4 flattens when D
exceeds -53 dBm, due to AGC action in the RF amplifier.

### N+5

The slope of the N+5 curve to the left of the AGC bend at D = -53 dBm
appears to be consistent with a third-order process. We are unable to
propose a likely mechanism.

### N+6

Oddly, the *slope* of log-D versus log-U for N+6 appears to linearly
increase with desired signal level until the AGC bend point, as can be
seen in Figure 11-3. Mathematically, this would suggest that log-D is
linearly related to U. Indeed, when desired signal level in dB is
plotted against the threshold undesired signal level in linear power
units (Figure 11-8), the result is strikingly linear to the left of the
AGC bend. Whether there is a physical reason for this behavior or it is
just a fluke is not known; however, we note that N+6 is one of the
smaller interference vulnerabilities for this receiver, so no additional
assessment has been performed.

### N+7

As was noted in Chapter 5 of this report, most of the DTV receivers
tested for this program exhibited an increased susceptibility to
interference at N+7 relative to the surrounding channels. The
interference threshold at N+7 was found to be nearly constant in terms
of undesired signal level as desired signal level was varied over a wide
range up to ‑53 dBm. (See for example even numbered Figures 5-12 through
5-16.) The behavior can be seen here in Figure 11-7.

Initially, we attributed the interference phenomenon to the "IF beat"
mechanism, which was one reason for the N+7 analog taboo.[^78] "IF beat"
interference is caused by an undesired signal on channel N+7 or N-7
beating with the desired signal---creating interference that can pass
through the IF filter of the receiver. The lack of a corresponding
susceptibility at N-7 (based on tests presented in Chapter 5) suggests
that another mechanism may be at work. Furthermore, tests with a
narrower-bandwidth interferer, presented in Chapter 7, suggest that the
interference occurs only when the undesired signal spectrum overlaps the
local oscillator frequency of the receiver. (Located 44 MHz above the
center of the desired channel, the local oscillator falls within channel
N+7.) This suggests some sort of direct interaction between the
undesired signal and the local oscillator, although we have not
identified a specific mechanism.

### N+14 and N+15

The mixer image band for a single-conversion TV tuner with a 44 MHz IF
overlaps parts of channels N+14 and N+15. In Figure 11-6, the D/U ratio
on these channels is seen to be essentially constant except when D
approaches D~MIN~. This is consistent with the fact that the mixer image
interference mechanism is linear.

## Summary

The detailed assessment of one receiver's out-of-channel interference
rejection performance provides a basis for understanding the less
detailed measurements for the other receivers. In particular, we note
the following.

1.  Paired-signal IM3 can be one of the more dominant interference
    mechanisms, even at low signal levels.

2.  The expected increase in D/U ratio with increasing signal levels for
    nonlinear interference mechanisms is flattened above levels at which
    the AGC engages to stabilize the nonlinearity.

3.  AGC flattening of D/U ratios may begin at lower signal levels for
    close-in interference (*e.g.*, N+1) than for interferers spaced
    further from the desired channel. This can cause the unexpected
    result that, at some signal levels, a TV may be more tolerant of
    interference on the first-adjacent channels than on some other
    channels.

4.  As signal levels continue to increase, the flatting of D/U ratios by
    AGC may end, allowing D/U ratios to, again, increase with increasing
    signal levels.

![](media/image94.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024499 .anchor}Figure 11‑92. D/U Versus D for
Receiver D3 (Desired Signal on Channel 51)

![](media/image95.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024500 .anchor}Figure 11‑93. Threshold U Versus
D for Receiver D3 (Desired Signal on Channel 51)

![](media/image96.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024501 .anchor}Figure 11‑94. Slope of Log-D
versus Log-U for Receiver D3 (Desired Signal on Channel 51)

![](media/image97.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024502 .anchor}Figure 11‑95. Slope of Log-U
versus Log-D for Receiver D3 (Desired Signal on Channel 51)

![](media/image98.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024503 .anchor}Figure 11‑96. D/U Versus D for
Receiver D3---Paired Signals And Their Constituents

![](media/image99.wmf){width="6.497916666666667in"
height="4.4430555555555555in"}

[]{#__RefHeading___Toc163024504 .anchor}Figure 11‑97. D/U Versus D for
Receiver D3---Single Undesired Signals

![](media/image100.wmf){width="6.497916666666667in"
height="4.4430555555555555in"}

[]{#__RefHeading___Toc163024505 .anchor}Figure 11‑98. Threshold U Versus
D for Receiver D3---Single Undesired Signals

![](media/image101.wmf){width="6.497916666666667in"
height="4.4430555555555555in"}

[]{#__RefHeading___Toc163024506 .anchor}Figure 11‑99. Linear Undesired
Power Versus Log-Desired Signal Power for N+6

#  EXTENDING THE RESULTS TO LOWER SIGNAL LEVELS

This chapter extrapolates the channel-30, single-channel interference
rejection measurements from Chapter 5 of this report to a lower desired
signal level, D~MIN~ + 1 dB. It also employs measured data from Chapter
11 to evaluate the extrapolation method. The motivation for the
extrapolation was explained in Chapter 2.

## Order of Interference Processes and Effect of AGC

Chapter 8 presented a theoretical framework for understanding DTV
interference susceptibilities. Table 12-1 summarizes the effects of the
order of an interference mechanism and the state of the tuner's AGC on
plots of threshold undesired versus desired signal power at the input to
a TV according to that framework.

[]{#__RefHeading___Toc163024587 .anchor}Table 12‑29. Characteristics of
Log-Log Plots of Undesired Versus Desired Signal Power At TOV

+----------------+--------------------------+--------------------------+
|                | **Characteristics of     |                          |
|                | Log-Log Plot of U Versus |                          |
|                | D**                      |                          |
+----------------+--------------------------+--------------------------+
| **Tuner AGC    | **Fixed gain** (or AGC   | **AGC operating to       |
| State**       | operating to adjust gain | adjust gain of a tuner   |
|                | of a tuner stage         | stage prior to relevant  |
| and            | *[after]{.underline}*    | nonlinearity^1^**        |
|                | the relevant             |                          |
| **Input        | nonlinearity^1^)         |                          |
| Condition↓**   |                          |                          |
+----------------+--------------------------+--------------------------+
| **D \>\>       | Straight line with slope | Straight line with unity |
| D~MIN~**       | determined by the order  | slope---matching that of |
|                | of the interference      | a linear interference    |
|                | mechanism. Slope is      | mechanism                |
|                | unity for linear         |                          |
|                | interference.            |                          |
+----------------+--------------------------+--------------------------+
| **D            | Deviation from           | Deviation from           |
| approaching    | straight-line determined | straight-line:           |
| D~MIN~**       | by order of interference |                          |
|                | mechanism                | 1.  matches linear       |
|                |                          |     process if AGC is    |
|                |                          |     driven by U;         |
|                |                          |                          |
|                |                          | 2.  determined by order  |
|                |                          |     of interference      |
|                |                          |     mechanism if AGC is  |
|                |                          |     driven by D          |
+----------------+--------------------------+--------------------------+

*^1^ Relevant nonlinearity refers to the nonlinearity responsible for a
given observed interference effect.*

*Slopes are listed in Table 8-1 and deviations from straight line are
listed in Table 8-2 of Chapter 8.*

### Behavior for Desired Signal Levels From -68 dBm to -53 dBm

Over the desired signal range from -68 dBm to -53 dBm, the desired
signal power is far enough above D~MIN~ that the model predicts
essentially straight-line behavior for log-U versus log-D, assuming that
the interference mechanisms and AGC state remain the same throughout the
region.

Figure 12-1 shows the slopes of threshold U vs D in dB units over this
signal range for each of the receivers and channel offsets for which
threshold measurements were successful (*i.e.*, the rejection
performance was not beyond the measurement limit imposed by the test
setup) at N = channel 30. The graph also includes horizontal reference
lines corresponding to the slopes for the various interference
mechanisms discussed in this report.

We note that some points clearly fit the expectations for a category of
interference. For example, most of the receivers exhibit linear-like
interference behavior when the undesired signal is on channels N-4
through N+2. It is considered likely that the actual interference
mechanisms in those cases are nonlinear and that the linear-like
behavior is caused by AGC operation. Interference to receiver D3 from
undesired signals on channels N-15 through N-4 clearly fits the pattern
of cross-modulation---a fact that was also discussed in Chapter 5 in the
section entitled, "Taboo Effects and Other Observations", based on other
evidence. The susceptibility of most receivers at N+7 also matches the
slope expected for cross-modulation, although we suspect that the actual
mechanism is different from those that have been postulated here based
on the discussion in Chapter 7.

Some of the points fall in-between categories, possibly as a result of
changes in the dominant interference mechanisms over the 15 dB range of
desired signal amplitudes, or due to changes in AGC operation over that
range.

### Behavior for Desired Signal Levels From D~MIN~ + 3 dB to -68 dBm

As the desired signal drops to a point 3-dB above D~MIN~, the deviation
from straight-line behavior is expected to become significant---ranging
from 1 to 3 dB (Table 8-2 of Chapter 8).

Because of this deviation, we have chosen to estimate the slope of the
straight-line portion of the log-undesired versus log-desired signal
curves in the region between D~MIN~ + 3 dB and -68 dBm by what we will
call the ***[adjusted slope]{.underline}***. The slope will be estimated
by first shifting the left-hand point of the range (D = D~MIN~ + 3 dB)
by 3 dB to the left (to D = D~MIN~). Figures 8-1 through 8-4 (Chapter 8)
showed that, in cases that are not stabilized by AGC operation, such a
shift returns that point to the straight-line whose slope we are trying
to predict, in all cases except the cross-modulation case. With AGC
operation driven by the undesired signal level, the same will be true.
Slope estimated in this way will deviate from that of the straight-line
portion we would like to estimate in cases involving cross-modulation or
involving AGC operation driven by the desired signal level. Neglecting
these cases, the expected slopes of log-U versus log-D for linear (or
AGC-stabilized nonlinear), second order, and third order interference
processes are 1, 1/2, and 1/3 dB/dB, respectively, and the expected
slopes of log-D versus log-U are 1, 2, and 3 dB/dB.

For the cross-modulation case, Figure 8-4 showed that the straight-line
projection should have a slope of zero for log-U versus log-D or an
infinite slope for log-D versus log-U. The shift of the left hand point
of the range by 3 dB (for a log-U versus log-D plot) does not return
that point to the straight line in this case. Rather, in the nominal
case, where D~MIN~ = -84 dBm, we are measuring the slope of a line
connecting the points (D = -68 dBm, U = U~T~) and (D = -84 dBm, U =
U~T~ - 1.5 dB), where U~T~ is the constant threshold value of U along
the straight line. The expected slope, then, is 0.09 for log-U versus
log-D or 10.7 for log-D versus log-U, though small measurement errors
could cause the latter number to vary widely.

Similarly, for the case of nonlinear interference stabilized by AGC
operation driven by desired signal level, the adjusted slope of log-U
versus log-D will be somewhat less than the unity slope of the
straight-line portion of the curve, and the slope of the log-D versus
log-U curve will exceed unity.

Figure 12-2 shows the "adjusted slope" of log-log curves of U versus D
computed by the above method for D from D~MIN~ + 3 dB to -68 dBm. Figure
12-3 shows the adjusted slope of log-log curves of D versus U---the
reciprocal of the slopes shown in Figure 12-2. For reasons discussed
above, the slopes of the cross-modulation case generally fall above zero
on the first plot and below infinity for the second. Similarly, some of
the AGC-stabilized cases fall below unity slope of the first plot and
above unity on the second.

## Extrapolation to D = D~MIN~ + 1 dB

The extrapolations to D = D~MIN~ + 1 dB will be based on measurements at
D = D~MIN~ + 3 dB---an extrapolation distance (in terms of desired
signal level) of only 2 dB. Though the extrapolation distance is short,
it should be recognized that threshold undesired signal levels are
expected to change rapidly as D~MIN~ is approached, as was illustrated
in Figures 8-1 through 8-4. Consequently, both measurements and
extrapolations can be subject to greater errors as D approaches D~MIN~,
due to high sensitivity to the D/D~MIN~ ratio. As an example, when
D/D~MIN~ is expected to be 1 dB, misjudging the D/D~MIN~ ratio by 0.25
dB could cause the threshold undesired signal level to change by amounts
ranging from 0.3 to 1.1 dB, depending on the direction of the error and
the order of the interference process.

The extrapolation will consist of two parts:

1.  a straight-line projection part based on the slopes identified in
    Table 8-1 for each of the interference categories;

2.  an estimate of the deviation from straight-line projection based on
    the deviations listed in Table 8-2; more specifically, we will use
    the difference between the straight line deviation for D/D~MIN~ = 1
    dB and that for D/D~MIN~ = 3 dB.

The first part will require that we categorize each interference case
(each channel offset for each receiver) into one of four categories: (1)
linear or AGC-stabilized; (2) second order; (3) third order; (4)
cross-modulation. The second part will require additional categorization
within the linear or AGC-stabilized category.

The category of each interference process will be estimated from the
*adjusted slope* of the log-D versus log-U data from D = -68 dBm to D =
D~MIN~ + 3 dB, computed as described in the previous section. The
boundary between third-order interference and cross-modulation will be
set at an adjusted slope of 5. The categories will serve as the basis
for defining the slope of the straight-line portion of the extrapolation
(Table 8-1), as well as for estimating the deviation from the
straight-line projection. The measurement data at D = D~MIN~ + 3 dB will
serve as the anchor point for the extrapolation.

The deviation from straight-line behavior will create a need to adjust
the threshold undesired signal downward from the straight-line
projection by an amount equal to the difference between the deviation
for D~MIN~ + 1 dB and that for D~MIN~ + 3 dB, as determined by Table 8-2
(Chapter 8). Those differences range from ‑1.3 to ‑3.8 dB[^79]---a span
of 2.5 dB.

But selection of the correct values from Table 8-2 will, in some cases,
require more knowledge than we have. For cases that appear to be
nonlinear (order higher than 1) based on the above, the appropriate
values from Table 8-2 can be used directly; however, for channel offsets
that appear to exhibit linear behavior based on the above, Table 8-2
shows that the expected offset depends on whether the underlying
interference mechanism was truly linear or was made to appear linear by
AGC action. We will assume that the underlying mechanism is linear only
for N+14 and N+15, the mixer image frequencies. For the other cases, the
correction depends both on the order of the nonlinearity and on whether
the AGC action was driven primarily by *desired* signal level or
primarily by the *undesired* signal level. In the former case the
deviation matches that for the underlying nonlinear process, which we
don't know; in the latter, the deviation will be the same as for a
linear process.

Though we have enough information to resolve some of these questions for
receiver D3, on which detailed tests were performed, the limited
measurements performed on the other receivers are inadequate for such
resolution. Consequently, we take the following approach to computing
the deviation from a straight-line projection for all receivers:

1.  If the interference behavior appears nonlinear, use the values from
    Table 8-2 for the estimated order of the interference;

2.  For N+14 and N+15, use the values from Table 8-2 for linear
    processes;

3.  For all other cases that appear linear, select a deviation from
    straight line behavior as the midpoint between the two extremes that
    could be occur---*i.e.*, nonlinear with U driving the AGC (‑3.8 dB
    adjustment) and third-order with D driving the AGC (-1.3 dB); we
    will accept the error of up to 1.3 dB in either direction that could
    result from adjustments based on the midpoint (-2.6 dB).

Table 12-2 summarizes the entire extrapolation process.

[]{#__RefHeading___Toc163024588 .anchor}Table 12‑30. Process for
Extrapolation from D = D~MIN~+3dB to D~MIN~+1dB

  ------------- ------------- -------------- ----------------- ------------- -----------
  **Undesired   **Adjusted    **Assumed      **Extrapolation                 
  Channel**     Slope of\     Interference   of Threshold U                  
                Log-D Versus  Mechanism**    From\                           
                Log-U\                       D = D~MIN~+3dB to               
                (dB/dB)**                    D~MIN~+1dB (dB)**               

                                             **Straight-Line   **Deviation   **Total**
                                             Projection**      From Straight 
                                                               Line**        

  **N+14 or                   Linear         -2.0              -3.8          **-5.8**
  N+15**                                                                     

  **All         **\< 1.5**    AGC Stabilized -2.0              -2.6          **-4.6**
  others**                    Nonlinear                                      

  **All         **1.5 to      2^nd^ Order    -1.0              -1.9          **-2.9**
  others**      2.5**                                                        

  **All         **2.5 to 5**  3^rd^ Order    -0.7              -1.3          **-1.9**
  others**                                                                   

  **All         **Magnitude   Cross          0                 -1.9          **-1.9**
  others**      \>5**         Modulation                                     
  ------------- ------------- -------------- ----------------- ------------- -----------

### Extrapolation Test

In Table 12-3 we have applied this extrapolation process to data from
the detailed measurements that were made on receiver D3 on channel 51
(Chapter 11). Values of threshold U at D = D~MIN~ + 1 dB extrapolated
from measurements at D = D~MIN~ + 3 dB and -68 dBm are compared to
measurements at D = D~MIN~ + 1 dB. The extrapolation errors were less
than 1 dB in each case.

### Extrapolation of Channel-30 Measurements on All Eight Receivers

Extrapolations of threshold undesired signal level to a desired signal
level of D~MIN~ + 1 dB were performed for all channel-30 measurements of
single-channel rejection performance for the eight fifth-generation DTV
receivers.

Figure 12-4 shows D/U ratios for the eight receivers based on the
extrapolation. Note that the plot includes data for a given receiver at
a given channel offset only if a valid measurement was obtained at
D~MIN~ + 3 dB, from which to extrapolate, and if the slope could be
estimated. Slope estimation requires a valid measurement at D = -68 dBm,
except in the cases of N+14 and N+15, where the interference process was
assumed to be linear.

The plot also includes the ATSC performance guidelines corresponding to
a desired signal level of -68 dBm. (ATSC does not specify rejection
performance at a lower desired signal level.)

The extrapolated data are combined with measured data in graphs in
Chapter 13 and tabulations in Appendix A.

[]{#__RefHeading___Toc163024589 .anchor}Table 12‑31. Error Test for
Extrapolation From D = D~MIN~ + 3 dB to D~MIN~ + 1 dB

  ----------- ---------- ------------------ --------------- ------------ ------- ---------- ---------------
              Adjusted   Modeled            Change in U as                                  Extrapolation
              Slope of   Interference       D goes from                                     Error\
              Log-D      Mechanism          D~MIN~+3dB to                                   (dB)
              Versus                        D~MIN~+1dB (dB)                                 
              Log-U                                                                         
              (dB/dB)                                                                       

                                            Extrapolated                         Measured   
                                            Change In U                          Change in  
                                                                                 U          

                                            Straight-Line   Deviation    Total              
                                            Portion of      From                            
                                            Projection      Straight                        
                                                            Line                            

  ***N+1***   1.3        AGC-Stabilized     -2.0            ***-2.6***   -4.6    -4.2       0.4
                         Nonlinear                                                          

  ***N+2***   1.2        AGC-Stabilized     -2.0            ***-2.6***   -4.6    -4.7       -0.2
                         Nonlinear                                                          

  N+3         5.5        Cross-Modulation   0.0             -1.9         -1.9    -1.7       0.2

  N+4         3.0        3^rd^ Order        -0.7            -1.3         -1.9    -1.8       0.1

  N+5         3.2        3^rd^ Order        -0.7            -1.3         -1.9    -1.6       0.3

  N+6         4.5        3^rd^ Order        -0.7            -1.3         -1.9    -1.2       0.8

  N+7         6.3        Cross-Modulation   0.0             -1.9         -1.9    -2.4       -0.4

  N+14        1.1        Linear             -2.0            -3.8         -5.8    -5.0       0.8

  N+15        1.1        Linear             -2.0            -3.8         -5.8    -5.6       0.3

  ***N+1/     1.1        AGC-Stabilized     -2.0            ***-2.6***   -4.6    -5.2       -0.6
  N+2***                 Nonlinear                                                          

  N+2/ N+4    3.4        3^rd^ Order        -0.7            -1.3         -1.9    -1.4       0.6

  N+3/ N+6    3.3        3^rd^ Order        -0.7            -1.3         -1.9    -2.1       -0.1

  N+4/ N+8    3.4        3^rd^ Order        -0.7            -1.3         -1.9    -2.4       -0.5
  ----------- ---------- ------------------ --------------- ------------ ------- ---------- ---------------

> *Notes*
>
> *^1^ For cases shown in bold italics, the apparent linearity is
> assumed to be a possible result of AGC action and deviation from
> straight line is calculated as described in text.*
>
> *Rounding to 0.1 dB after calculations are performed may cause some
> apparent discrepancies of up to 0.1 dB.*

![](media/image102.wmf){width="6.497916666666667in"
height="4.4430555555555555in"}

[]{#__RefHeading___Toc163024507 .anchor}Figure 12‑100. Slope of
Threshold U Versus D from D = -68 dBm to -53 dBm

![](media/image103.wmf){width="6.497916666666667in"
height="4.4430555555555555in"}

[]{#__RefHeading___Toc163024508 .anchor}Figure 12‑101. Slope of
Threshold U Versus D from D =D~MIN~+3dB to -68 dBm

![](media/image104.wmf){width="6.497916666666667in"
height="4.4430555555555555in"}

[]{#__RefHeading___Toc163024509 .anchor}Figure 12‑102. Slope of
Threshold D Versus U from D =D~MIN~+3dB to -68 dBm

![](media/image105.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024510 .anchor}Figure 12‑103. D/U of 8
Receivers at D = D~MIN~ + 1 dB on Channel 30 (Extrapolation)

#  COMBINING MEASURED AND EXTRAPOLATED RESULTS

This chapter shows single-channel rejection performance for eight DTV
receivers for a desired signal on channel 30. The results shown combine
the measurements of Chapter 5 (D = -28 dBm, -53 dBm, ‑68 dBm, and
D~MIN~ + 3 dB) with the extrapolations of Chapter 12 (D = D~MIN~ + 1
dB).

Figure 13-1 shows D/U ratios for receiver A3. Figure 13-2 shows the same
information as Figure 13-1, but shows it as the threshold value for
undesired signal power. The first graph will be useful for those who
prefer to work in terms of D/U ratios and for identifying channel
offsets that behave in a linear manner (constant D/U ratio as D changes)
either because the interference mechanism is linear (N+14 and N+15) or
due to AGC action. The second is useful for identifying the absolute
signal levels that cause interference effects and for identifying
channel offsets where thresholds tend to be constant in terms of
absolute power of the undesired signal (*e.g.*, N+7).

Figures 13-3 to 13-16 are the same pair of plot formats for each of the
remaining seven receivers.

We note that the D/U plots (odd-numbered Figures 13-1 through 13-15)
show four measurement limit curves. From top to bottom, these correspond
to limits at D = -28 dBm, -53 dBm, -68 dBm, and D~MIN~ + 3 dB,
respectively. In the top two curves, all points are determined by the
maximum undesired signal power that the test setup could deliver to the
input of a TV receiver. The third curve, for D = -68 dBm, has two
sources of measurement limits: at N-1 and N+1, the measurement
limitation is based on leakage of the undesired signal into the desired
channel; at all other channel offsets, the measurements are limited by
maximum undesired signal level. For D = D~MIN~ + 3 dB, the measurement
limitation (shown by the bottom, shaded region of the graph) is caused
by leakage of the undesired signal into the desired channel; since this
is a soft limit, values below the limit are shown, but their accuracies
are influenced by the leakage. In the case of data extrapolated to
D~MIN~ + 1 dB, data points are shown only if the measurements on which
they were based were not subject to measurement limits.

The undesired signal threshold plots (even-numbered Figures 13-2 through
13-16) show only one measurement limit curve---the curve associated with
the maximum undesired signal power that the test setup could inject into
the receiver. The N-1 and N+1 offsets for D = -68 dBm and all of the
offsets for D = D~MIN~ + 3 dB are subject to an additional limitation,
shown only in the D/U plots, based on leakage of the undesired signal
into the desired channel.

We note in particular the case of receiver D3 in Figures 13-3 and 13-4.
In Chapter 5 we stated that the smooth rise in D/U (or corresponding
smooth fall in threshold U) as one moves from N-15 to N-4 is suggestive
of a particular broadband interference mechanism---cross-modulation.
Chapter 8 showed that cross-modulation is expected to exhibit a constant
threshold U with changes in desired signal level except as the desired
signal level approaches D~MIN~ or if the AGC begins to reduce gain prior
to the tuner nonlinearity at which the cross-modulation is occurring. We
see in Figure 13-4 that the curves corresponding to D = -53 dBm and D =
-68 dBm are essentially identical from N-15 to N-4 (except for a small
bump associated with a single-channel interference susceptibility at
N-11. Interference susceptibility increases by a few dB as one moves
past the curve for D = D~MIN~ + 3 dB to the curve corresponding to D =
D~MIN~ + 1 dB; the increased susceptibility is an expected result of
receiver noise becoming significant at lower signal levels. All four of
the curves appear to be the result of cross-modulation.

At N-3 things change. The D/U ratio, which had been smoothly increasing
as the undesired channel moved toward the desired channel, takes an
abrupt drop---indicating that the receiver's AGC has acted to decrease
the RF gain prior to the mixer---the likely point of the nonlinearity
that caused the cross-modulation. Since each curve corresponds to fixed
desired signal level, it is clear that the AGC must have been engaged by
the undesired signal, which is likely to be larger in amplitude at the
AGC sampling point when the undesired signal is on N-3 than when it was
on N-4 and beyond because of the tuner's RF tracking filter response.
The smaller change in the D~MIN~ + 3 dB curve as compared to the -68 dBm
curve suggests that the AGC gain reduction was relatively small in the
former case (where U is about -22 dBm). Thus, it is clear that the AGC
engages on an undesired signal level somewhat lower than -22 dBm on
N+3---a factor that will become important in some analysis in the next
chapter.

Chapter 15 includes composite charts for median, second-worst, and worst
performance among the receivers.

![](media/image106.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024511 .anchor}Figure 13‑104. D/U of Receiver
A3 at Five Desired Signal Levels on Channel 30

![](media/image107.wmf){width="6.497916666666667in"
height="4.4430555555555555in"}

[]{#__RefHeading___Toc163024512 .anchor}Figure 13‑105. Threshold U of
Receiver A3 at Five Desired Signal Levels on Channel 30

![](media/image108.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024513 .anchor}Figure 13‑106. D/U of Receiver
D3 at Five Desired Signal Levels on Channel 30

![](media/image109.wmf){width="6.497916666666667in"
height="4.4430555555555555in"}

[]{#__RefHeading___Toc163024514 .anchor}Figure 13‑107. Threshold U of
Receiver D3 at Five Desired Signal Levels on Channel 30

![](media/image110.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024515 .anchor}Figure 13‑108. D/U of Receiver
I1 at Five Desired Signal Levels on Channel 30

![](media/image111.wmf){width="6.497916666666667in"
height="4.4430555555555555in"}

[]{#__RefHeading___Toc163024516 .anchor}Figure 13‑109. Threshold U of
Receiver I1 at Five Desired Signal Levels on Channel 30

![](media/image112.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024517 .anchor}Figure 13‑110. D/U of Receiver
J1 at Five Desired Signal Levels on Channel 30

![](media/image113.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024518 .anchor}Figure 13‑111. Threshold U of
Receiver J1 at Five Desired Signal Levels on Channel 30

![](media/image114.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024519 .anchor}Figure 13‑112. D/U of Receiver
M1 at Five Desired Signal Levels on Channel 30

![](media/image115.wmf){width="6.497916666666667in"
height="4.4430555555555555in"}

[]{#__RefHeading___Toc163024520 .anchor}Figure 13‑113. Threshold U of
Receiver M1 at Five Desired Signal Levels on Channel 30

![](media/image116.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024521 .anchor}Figure 13‑114. D/U of Receiver
N1 at Five Desired Signal Levels on Channel 30

![](media/image117.wmf){width="6.497916666666667in"
height="4.4430555555555555in"}

[]{#__RefHeading___Toc163024522 .anchor}Figure 13‑115. Threshold U of
Receiver N1 at Five Desired Signal Levels on Channel 30

![](media/image118.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024523 .anchor}Figure 13‑116. D/U of Receiver
O1 at Five Desired Signal Levels on Channel 30

![](media/image119.wmf){width="6.497916666666667in"
height="4.4430555555555555in"}

[]{#__RefHeading___Toc163024524 .anchor}Figure 13‑117. Threshold U of
Receiver O1 at Five Desired Signal Levels on Channel 30

![](media/image120.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024525 .anchor}Figure 13‑118. D/U of Receiver
G4 at Five Desired Signal Levels on Channel 30

![](media/image121.wmf){width="6.497916666666667in"
height="4.4430555555555555in"}

[]{#__RefHeading___Toc163024526 .anchor}Figure 13‑119. Threshold U of
Receiver G4 at Five Desired Signal Levels on Channel 30

#  VERIFICATION TESTS USING ALTERNATIVE METHODS

This chapter presents the results of tests and analyses performed to
validate the test methodology and test setup used for the measurements
in this report. Readers primarily interested in DTV receiver test
results may prefer to skip ahead to Chapter 15 or to the "Summary"
section of this chapter.

Most of tests described in this section of the report were intended to
eliminate various artifacts that might be associated with the primary
test setup used for measurements throughout this report, and then to
retest a TV to see whether the interference rejection results change.
One test was designed to directly measure the effect of one such
artifact---the noise plateau around the desired channel caused by using
a band-reject filter to "clean up" the output spectrum of the undesired
signal.

The other reason for the validation tests was to confirm unexpected
results of the interference rejection tests---most notably, the peak in
interference susceptibility that was observed to varying degrees at
channel N+7 for nine out of ten receivers that was tested.

The verification tests were performed only for channel 30.

## Alternative Test Setup With Bandpass Filter on Undesired Signal

The primary test setup for measurements presented in this report used a
band-***reject*** filter to limit leakage of the *undesired* signal into
the *desired* channel, as described in Chapter 4. This differs from the
more conventional approach of placing a band-***pass*** filter around
the *undesired* signal (or signals). The band-reject approach leaves a
plateau in the out-of-band spectrum of the undesired signals---a plateau
which is filtered out only in the desired channel and its immediate
vicinity. (See, for example, Figures 4‑1 and 4-2 of Chapter 4.)

For the measurements described in this section of the report, the test
approach was changed to a more conventional one. Instead of subjecting
the undesired signal to a band-*[reject]{.underline}* filter designed to
limit leakage *into the desired channel* (channel 30), a
band*[pass]{.underline}* filter was employed to limit leakage into *any
channel outside of the undesired channel*. The bandpass filter used for
this test was an existing seven-section cavity filter (Micro
Communications, Inc, Type \"N\" IDBP Filter, Part \# 220035 C/N) for TV
broadcast channel 29. Filter response was down 0.7 to 0.8 dB at the
channel-29 band edges (0.4 dB at the DTV pilot frequency) and more than
73 dB beyond the first-adjacent channels. Measured frequency response is
shown in Figure 14-1.

The use of the fixed bandpass filter for the undesired signal as opposed
to a band-reject filter at the desired channel required a change in test
approach. The undesired signal was fixed at channel 29 and the desired
channel, along with the TV tuner, were switched among channels 14, 15,
21 to 28, and 30 to 37---creating test cases corresponding to N+15,
N+14, N+8 through N+1, and N-1 through N-8. (Note that we were changing
N rather than the undesired channel to achieve these offsets.)

Though the main purpose of testing in this way was to eliminate the
noise shoulders that appeared around the desired channel in the primary
test setup, several other changes were made in the test setup in order
to rule out the influence of other possible artifacts. Specifically, the
test setup (Figure 4-1 of Chapter 4) was modified as described below and
as shown in Figure 14-2.

1.  The Rohde and Schwarz SFU 8-VSB signal generator was used as the
    undesired signal source for all of these measurements. This was
    intended to eliminate the effects of any generator-specific
    artifacts that might be produced by the Agilent E4437B signal
    generator that was configured to produce bandlimited Gaussian noise
    as the undesired signal source for much of the testing described in
    this report.

2.  All amplifiers and step attenuators, as well as some fixed
    attenuator pads, were eliminated to simplify the test setup and to
    reduce the maximum signal levels that existed within the test setup
    in order to reduce the possibility of unintended coupling of signals
    (*e.g.*, by radiation).

Rejection ratio measurements were performed on one DTV (receiver J1)
using the alternative test setup. Figure 14-3 compares the results with
the previous measurements using the primary test setup. All measurements
matched within 1.5 dB. The measurements differed on N-1 and N+1 by only
0.4 and 0.8 dB, respectively. On the other channels, the D/U ratios with
the alternative test setup averaged 0.7 dB lower than those with the
primary test setup. Since the alternative test setup used an 8-VSB
signal rather than bandlimited Gaussian noise as the interferer,[^80]
the alternative test setup was expected to exhibit lower D/U ratios than
the primary one by about 1.2 dB based on the difference in signal type
(Chapter 7).

The match between test results is quite close, especially given that the
different test approaches forced testing to be performed on different TV
channels (mostly channels 21 through 37 for the alternative test setup
and channel 30 for the primary one).

## Broadband Notched Noise

Since the primary test setup left a plateau of noise surrounding the
desired channel, a decision was made to test each TV receiver to
determine the effect of that plateau by itself (*i.e.*, without the
undesired signal). The signal generator used as an undesired signal
source for non-adjacent tests on channel 30 had a noise floor that was
56 to 59 dB below the undesired signal power when measured in a 6-MHz
bandwidth beyond the first adjacent channels. The primary test setup
subjected the undesired signal to a band-reject filter that further
attenuated this noise floor within the desired channel. The result was a
signal spectrum that included the main undesired signal spectrum, plus a
noise plateau 56 to 59 dB below it, but with a valley cut into the noise
plateau at channel N, as shown in Figure 4-2.

### Measurements

The "broadband notched noise" tests were performed by replacing the
undesired signal source with a white Gaussian noise generator having a
spectrum that extended from about 40 to 850 MHz---*i.e.*, covering the
entire broadcast television spectrum and beyond. The noise signal
spectrum was "notched" by the same band-reject filter that had been used
to filter the undesired signal in all of the non-adjacent tests at
channel 30 (*i.e.*, all tests except at N-1 and N+1). Figure 14-4 shows
a portion of the resulting spectrum. Essentially, the undesired signal
for these tests consisted of white noise filling the entire TV spectrum
and beyond, but with a 43-dB deep hole cut in it at channel 30 (N), and
with some filter rolloff through the first-adjacent channels.[^81]

The interference rejection performance of the eight DTV receivers were
then measured using this broadband notched noise source. Tests were
performed for desired signal levels of -68 and -53 dBm. D/U ratios were
computed with U being the undesired power per TV channel averaged across
channels N-4 through N-2 and N+2 through N+4.

The results are shown in the first two data columns of Table 14-1. At a
desired signal power of -68 dBm, the interference thresholds occurred at
a D/U ratio ranging from -27.1 to -23.0 dB, where U is measured on a per
TV channel basis, as described above. The corresponding D/U range when D
= -53 dBm was slightly higher at -25.9 to -20.6 dB.

[]{#__RefHeading___Toc163024590 .anchor}Table 14‑32. Broadband Notched
Noise D/U Ratios at Threshold

  -------------- ----------------- -------------- ---------------- --------------
                 **D/(U/channel)                  **D/U Caused by  
                 For Notched Noise                Noise Plateau If 
                 Only (dB)**                      Single-Channel U 
                                                  Were 56 dB Above 
                                                  the Noise        
                                                  Plateau (dB)**   

  **Receiver**   **D = -68 dBm**   **D = -53      **D = -68 dBm**  **D = -53
                                   dBm**                           dBm**

  A3             -26.9             -25.9          -82.9            -81.9

  D3             -25.5             -22.9          -81.5            -78.9

  I1             -25.4             -23.6          -81.4            -79.6

  J1             -23.0             -20.6          -79.0            -76.6

  M1             -27.1             -25.6          -83.1            -81.6

  M2             -23.1             -22.0          -79.1            -78.0

  N1             -26.1             -22.2          -82.1            -78.2

  G4             -23.4             -23.7          -79.4            -79.7

  **Max**        **-23.0**         **-20.6**      **-79.0**        **-76.6**

  **Min**        **-27.1**         **-25.9**      **-83.1**        **-81.9**
  -------------- ----------------- -------------- ---------------- --------------

Thus, all of the TVs could operate with the noise plateau 23 dB or more
above the desired channel, on a noise-power-per-channel basis when D =
-68 dBm and 20.6 dB or more above the desired channel when D = -53 dBm.
Since the actual undesired noise source power used in the tests was 56
dB above its noise plateau, one would expect that the effect of the
noise plateau by itself would limit D/U measurements to about -79 dB at
D = -68 dBm and about -77 dB at D = -53 dBm. If we want to maintain at
least 10 dB margin between measured D/U's and the failure point due to
the plateau, these numbers increase to -69 and -67 dB, respectively.

In reality, D/U ratio measurements were limited by the maximum undesired
signal level that the test setup could generate to values of about -52
dB at D = -53 dBm and -66 dB at D = -68 dBm; consequently, plateau noise
*[alone]{.underline}* would not have affected the measurements, even for
the most vulnerable TV.

### IM3 Analysis

We saw in Chapter 10 that a high level signal on a channel N+K can cause
a receiver to be susceptible to interference from very low level signals
on channel N+2K. We could consider the intended undesired signal to be
on N+K and the plateau noise to contain a signal at N+2K at a level 56
dB below the intended undesired signal. (Note that, for N+/-2 and
beyond, the plateau noise ranges from 56 to 59 dB below the undesired
signal power, so this is a worst-case assumption.) The same could be
considered with the roles of N+K and N+2K reversed.

To test whether IM3 between the undesired signal and the plateau could
have been responsible for any of the measured single-channel D/U ratios,
lines corresponding to the cases of U~N+K~/U~N+2K~ = 56 dB
U~N+K~/U~N+2K~ = -56 dB were overlaid on the modeled IM3 charts from
Figures 10-4 to 10-17. The intersections of those overlaid lines with
the modeled curve for each channel offset, each TV, and each of two
desired signal levels (-68 dBm and D~MIN~ + 3 dB) were then examined.

In all of the 67 cases available on the plots, the U~N+K~/U~N+2K~ = -56
dB line crossed the horizontal segment of the model plot, indicating
that the measured U~N+2K~ threshold was reached before the plateau-based
IM3 threshold would have been reached. In 63 out of the 67 cases
available on the plots, the U~N+K~/U~N+2K~ = 56 dB line crossed the
vertical segment of the model plot, indicating that the measured U~N+K~
threshold was reached before the plateau-based IM3 threshold would have
been reached. These results indicate that IM3 between the undesired
signal and the plateau was not a factor in these cases.

In three cases, the U~N+K~/U~N+2K~ = 56 dB line crossed model plot near
the intersection of the vertical segment and the diagonal IM3 segment.
This suggests that, in those cases, the "single-channel" threshold that
was measured and reported in Chapter 5 may have actually been caused by
IM3 between the undesired signal and the plateau. The model plots for
those cases are shown in Figures 14-5 to 14-7. The three cases are
summarized in the following bullets.

1.  Receiver D3 at D = -68 dBm, N+2 threshold occurred at U = -20.5 dBm,
    D/U = -47.5 dB.

2.  Receiver G4 at D = -68 dBm, N-5 threshold occurred at U = -5.4 dBm,
    D/U = -62.7 dB;

3.  Receiver G4 at D = D~MIN~ + 3 dB, N+4 threshold occurred at , D/U =
    -13.5 dB,U = -69.6 dBm;

The two cases involving receiver G4 correspond to D/U ratios below (more
negative than) -60 dB. If IM3 between the undesired signal and the
plateau caused measurement limitations at those levels, the measurement
limitations occurred beyond the planned measurement range of the test
setup and in a region that represents very good rejection performance by
the DTV receivers; consequently, the cases are not considered important.
The remaining case, involving receiver D3, corresponds to the second
best rejection ratio among the eight receivers at N+2 for a desired
signal level of -68 dBm. If the results were influenced by IM3, it would
mean that the actual performance was even better and falls only 0.8 dB
short of the best performance among the eight receivers.

In one other case (Figure 14-8), the U~N+K~/U~N+2K~ = 56 dB line crossed
a model plot on the diagonal IM3 segment at a U~N+K~ value about 5 dB
below the single-channel threshold that had been measured for that case
(receiver D3 at D = -68 dBm, N-3 threshold occurring at U = -8.2 dBm,
D/U = -59.8 dB). This is expected to be an impossible situation in that
the IM3 effect is predicted to occur at a lower desired signal level
than the actual -8.2 dBm threshold that was measured for the
single-channel interferer. Theoretically, IM3 should have caused an
artificially low reading of about -13 dBm at threshold.

Our use of worst-case assumptions regarding the undesired
signal-to-plateau ratio (56 dB, whereas the range was 56 to 59 dB) is
not enough to account for the difference; however, Figures 13-3 and 13-4
and the related discussion in Chapter 13 offer some insight into what is
happening. The text in Chapter 13 argues that the receiver's AGC
activates to reduce the tuner gain prior to the mixer when the undesired
signal level on channel N-3 exceeds a level somewhat below -22 dBm.
Referring to Figure 14-8, we see that the AGC would engage beginning at
a point above and to the left of U~N+K~ = -22 dBm and U~N+2K~ = -52 dB.
The Appendix B shows that, when AGC engages on U~N+K~, the threshold
value of U~N+2K~ becomes constant with further increases in U~N+K~. This
means that the sloped IM3 portion of the model for receiver D3 in Figure
14-8 should end its downward trajectory and switch to a horizontal
trajectory when the AGC engages. The horizontal trajectory would
continue until the curve intersects the vertical segment corresponding
to the measured single-channel threshold for U~N+K~. An examination of
the plot shows that, with this new trajectory, the dashed line
representing U~N+K~/U~N+2K~ = 56 dB would not intersect the IM3 segment
of the line. The apparent contradiction was actually caused by a failure
to show the AGC engagement effect in the model for that receiver.
Chapter 10, the origin of the modeled results cautions that the model
becomes invalid beyond the signal levels at which the AGC engages to
reduce gain prior to the nonlinearity that causes the IM3 (usually the
mixer).

Thus we conclude that the only cases in which we have identified a
*potential* for IM3 between the undesired signal and the plateau to have
influenced the test results are cases in which measured rejection
performance of a receiver was *very* good. If the unintended IM3 did
actually influence those measurements, then the actual receiver
performance was even better than the measurement indicated---a result
that would not change any conclusions of this report.

## Screen-Room Test

We are unaware of other reports of DTV receivers exhibiting an N+7
interference vulnerability, such as was observed on nine of ten
receivers tested for this report. In an effort to rule out test
environment anomalies as the cause, receiver D3 was placed in a closed
screen room. No equipment inside the screen room, other than the TV, was
powered on. The rejection performance test equipment was placed outside
of the screen room about 18 feet from the TV. Rejection performance was
measured with a desired signal of -68 dBm on channel 30 and the white
Gaussian noise source (bandlimited to match the 3-dB width of an 8-VSB
signal) was placed on channel N+7 and was adjusted to determine TOV. The
resulting D/U ratio was -42.1 dB. The measurement one month earlier
using the primary test setup without the screen room was -41.6 dB. The
difference of only 0.5 dB provides further evidence that the observed
N+7 sensitivity is not an anomaly of the test environment.

## Summary

A single screen-room measurement confirmed that the N+7 susceptibility
is not caused by direct pickup involving the TV receiver.

The noise plateau discussed in this report was about 56 dB or more below
the undesired signal power when measured on a per-channel basis. Tests
were performed using an alternative test setup that (1) employed a
bandpass filter approach to attenuate the noise plateau globally rather
than just within the desired channel and (2) eliminated amplifiers and
attenuators to create a simpler (and more limited) configuration that
maintained lower signal levels in the test setup to minimize potential
for unintended signal coupling. The test results closely matched those
obtained with the primary test setup used in this report.

Tests of each of the eight receivers against notched plateau noise
demonstrated that the rejection performance tests were not influenced by
the presence of the noise plateau *by itself*.

Analysis was performed to determine whether IM3 effects between the
undesired signal and a portion of the undesired signal plateau 56 or
more dB lower could have affected the measured results for
single-channel rejection performance. Since IM3 properties vary among
the individual receivers as well as with channel offset and desired
signal amplitude, a global answer is not feasible. Measurements of IM3
effects performed with equal-powered paired signals (Chapter 9) were
used to develop models for paired-signal IM3 for 67 combinations of TV
receivers, channel offsets, and desired power levels (Chapter 10). Each
of these 67 was examined to determine whether IM3 could have influenced
the single channel measurements in either of two cases (undesired signal
at N+K and undesired signal at N+2K)---a total of 134 cases of
single-channel rejection measurements. The evaluation suggested that
three of the 134 measurements *might* have been affected by IM3 with the
noise plateau. All three involved very good rejection performance (two
with D/U's beyond -60 dB and one only -48 dB, but the second best
performance among eight receivers); *if* IM3 influenced the
measurements, the actual rejection performance was even better than that
measured---a result that would not change any conclusions of this
report.

![](media/image122.wmf){width="6.497916666666667in"
height="4.4430555555555555in"}

[]{#__RefHeading___Toc163024527 .anchor}Figure 14‑120. Frequency
Response of Channel-29 Bandpass Filter

![](media/image123.wmf){width="6.115277777777778in"
height="2.6256944444444446in"}

[]{#__RefHeading___Toc163024528 .anchor}Figure 14‑121. Alternative Test
Configuration With Bandpass Filter on Undesired Signal

![](media/image124.wmf){width="6.497916666666667in"
height="4.4430555555555555in"}

[]{#__RefHeading___Toc163024529 .anchor}Figure 14‑122. D/U Measurements
on Receiver J1 with Primary Versus Alternative Test Setup

![](media/image125.wmf){width="6.497916666666667in"
height="4.4430555555555555in"}

[]{#__RefHeading___Toc163024530 .anchor}Figure 14‑123. Spectrum of
Undesired Signal for Broadband Notched Noise Test

![](media/image126.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024531 .anchor}Figure 14‑124. Model Plot for
"Plateau IM3" On Receiver G4 at D = -68 dBm with N-5/N-10

![](media/image127.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024532 .anchor}Figure 14‑125. Model Plot for
"Plateau IM3" On Receiver D3 at D = -68 dBm with N+2/N+4

![](media/image128.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024533 .anchor}Figure 14‑126. Model Plot for
"Plateau IM3" On Receiver G4 at D = D~MIN~+3dB with N+4/N+8

![](media/image129.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024534 .anchor}Figure 14‑127. Model Plot for
"Plateau IM3" On Receiver G4 at D =-68 dBm with N-3/N-6

#  SUMMARY AND CONCLUSIONS

We now summarize the main findings of the measurement program.

This report presented the following:

1.  Tests of 30 consumer DTV receivers to determine tuner type (*e.g.*,
    single conversion or double conversion);

2.  Measurements of out-of-channel interference rejection performance of
    eight DTV receivers tuned to channel 30;

3.  Measurements of out-of-channel interference rejection performance of
    seven DTV receivers (a subset of the eight) tuned to channel 51;

4.  A theoretical framework for understanding the results;

5.  Extrapolation of the measurement results to a desired signal level 1
    dB above the minimum signal threshold for each receiver.

The out-of-channel interference tests included single-channel
interferers and pairs of interferers at channel spacings that could
place third-order intermodulation distortion products in the desired TV
channel. Most of the tests used undesired (*i.e.*, interfering) signals
that occupied most of the 6-MHz width of a DTV channel assignment. An
8-VSB DTV signal was used as the undesired signal for all tests on
first-adjacent channels. For other channel spacings, the source was
either an 8-VSB source (for the channel-51 tests) or a Gaussian noise
source bandlimited to match the 3-dB width of an 8-VSB signal (for the
channel-30 tests). For paired-signal tests, the second undesired signal
was always a Gaussian source. A limited number of tests were performed
to measure the relative interference effects of 8-VSB, Gaussian noise,
and OFDM signals. One TV was tested to determine the effects of a
narrower-band undesired signal---a Gaussian noise source bandlimited to
a 3-dB width of 1 MHz.

The out-of-channel interference rejection performance measurements are
presented in this report in terms of desired and undesired signal power
levels at the RF input (*i.e.*, antenna terminal) of each DTV receiver.
While the test results are intended to be useful in assessing
interference potential and developing protection criteria to prevent
interference, the results do not translate directly into such criteria.
Assessing existing protection criteria or developing new criteria will
require steps that are beyond the scope of this report, such as
definition of the scenarios on which protection is to be based, modeling
of propagation from the undesired signal source to the DTV antenna,
modeling of antenna gain and of losses from the TV antenna to the DTV
receiver, and policy decisions regarding the DTV receiver performance
and signal margins to be assumed in developing the protection criteria.

We have attempted to provide receiver interference rejection performance
data over a parameter range sufficient to support the broad needs of the
Commission and the technical community. While we note that the rejection
performance measurements in this report were performed on only a small
sample of consumer DTV receivers and thus do not provide a robust
statistical basis for identifying the overall range of performance of
consumer DTV receivers, they do provide a more representative sample of
the performance of currently available products than did the earlier
tests of the prototype receiver.

In forming conclusions from the measurements, we focus primarily on the
measurement results at channel 30, since that channel is more central to
the UHF band and thus is likely to be more representative of performance
across the band. Results from channel 51 are used for comparative
purposes, and to fill in gaps in the measurements at channel 30.

## DTV Tuner Type

Tuner type is of significance because the "taboos" that limited local
analog TV channel allotments at certain channel spacings were based
primarily on interference susceptibilities that were unique to
single-conversion tuners having a 44-MHz intermediate frequency (IF).
The reduced vulnerability of the prototype ATSC DTV receiver---relative
to analog TV---was achieved by a combination of the more robust ATSC
digital transmission system that is inherently less susceptible to noise
and interference than the NTSC analog system and the use of a
double-conversion tuner in the prototype receiver.

Tests of 30 consumer DTV receivers demonstrated that all 30 have
single-conversion tuners with 44-MHz IF. (28 were identified as single
conversion by means of a small but detectable leakage of the tuner's
local oscillator frequency from its antenna port. The remaining two were
identified by means of interference vulnerabilities that we expect to be
unique to single-conversion tuners with 44-MHz IF.)

## Effect of Undesired Signal Type

Tests were performed to determine the relative interference effects of
the following types of signals:

7.  White Gaussian noise bandlimited to the 3-dB width of an 8-VSB
    signals;

8.  8-VSB DTV signal;

9.  DVB-H---an orthogonal frequency division multiplexing (OFDM)
    signal---set for a 5-MHz channel width; and

10. White Gaussian noise bandlimited to a 3-dB width of 1 MHz.

The first three signal types were tested on eight DTV receivers at the
five non-first-adjacent channel offsets that exhibited the most
interference potential among the receivers at low signal levels (N+2,
N-2, N-3, N-4, and N-6). (Channels N-1 and N+1 were not tested because
the Gaussian source did not have adequate band-edge rolloff to permit
testing on first-adjacent channels.)

The interference effects of the OFDM signal and of the Gaussian noise
signal averaged 1.0 and 1.2 dB, respectively, greater than the
interference effects of the 8-VSB signal. That is, the signal level of
an OFDM signal or of a Gaussian noise signal that is required to
interfere with DTV reception is about 1 dB lower than the level of an
8-VSB signal that would cause interference at the same channel offset.

Tests with the reduced-bandwidth interferer (1 MHz wide) were performed
on only one receiver. The results generally tracked those of the wider
Gaussian noise interferer except where narrowband interference
susceptibilities existed, such as at N+7, where reception was
susceptible to interference when the undesired signal spectrum
overlapped the TV's local oscillator frequency.

## Cliff Effect

The ATSC digital television broadcast system can achieve flawless
picture reception under interference conditions that would produce an
unusable picture for analog broadcast TV;[^82] however, once an
undesired signal reaches a level at which picture impairments become
visible on a DTV receiver, the picture degrades extremely rapidly with
further increases in undesired signal level. The rapid degradation from
flawless picture to no picture at all is known as the cliff effect.

The interference rejection test results in this report are presented as
signal levels at the threshold of visibility (TOV) of picture
degradation---*i.e.*, the point at which picture degradation (in the
form of pixilation, image freezes, or dropouts) becomes visible.
Increases in interfering signal level above this point result in further
degradation---and ultimately complete loss---of the TV picture.

Though the "hardness" of the thresholds was not one of the measurement
parameters for this study, a strong "cliff effect" was observed during
the tests. For example, in most cases, increasing interference level
about 1 dB above TOV caused complete loss of picture. In some cases
picture loss didn't occur until the undesired signal level rose as much
as much as 3 dB and in one case, 5 dB (though picture errors occurred
continuously in that case after only a 1.5 dB increase). In a few cases
picture loss occurred concurrently with appearance of errors or with
only an additional 0.1 dB increase in interference---an extremely abrupt
cliff! By contrast, interference to analog TV occurs much more
gradually. An 8-dB increase in signal level of an interferer from the
TOV level for analog TV may cause the interference effect to grow to the
"slightly-annoying" level, from the TV viewer's point of view.[^83] A
total increase of 20 to 30 dB may be required to make the analog picture
unusable.[^84]

## Interference from a Single Undesired Signal

The interference tests with a desired signal on channel 30 were
performed using an 8-VSB undesired signal for first-adjacent channels
(N-1 and N+1) and a white Gaussian noise signal bandlimited to match the
3-dB width of an 8-VSB signal for all other channels.

Measurements of interference rejection performance are specified in
terms of desired signal power D and undesired (*i.e.*, interfering)
signal power U at the RF input of the DTV receiver. We have chosen to
present the interference rejection performance measurements in two ways:
as D/U ratios and as threshold values for the undesired signal level U.
Each has its own application. D/U ratios might be preferable for all
analytical work if they were constant with desired signal power;
however, nonlinearity of interference mechanisms and the effects of
receiver noise at low desired signal levels cause D/U ratios to be
variable. Nonetheless, D/U ratios can be convenient to use in
applications like DTV-into-DTV interference assessment because
estimation of D/U ratios may be easier and more accurate that estimation
of absolute levels where long-distance propagation is
involved---especially if the broadcast stations are co-sited. Use of
absolute signal level thresholds may be more appropriate for assessing
shorter distance interference from low-power devices because the effects
of TV antenna height and placement on the undesired signal are likely to
be very different from their effects on the desired signal.

No receiver appeared to fully achieve the ATSC recommended guidelines
for interference rejection performance. After taking into account
differences between the Gaussian-noise interferer used for most of the
tests and the 8-VSB interferer specified by the ATSC, the
best-performing receiver appears to fail the guidelines at only one
channel offset, and there by only 1 dB. A second receiver failed to meet
the voluntary guidelines by 1 to 2 dB at two channel offsets. The
remaining five receivers failed to meet the guidelines at two to 16
channel offsets; the worst failure for each of those receivers ranged
from 8 to 24 dB.

The single-channel rejection performance measurements performed for this
report are best summarized by Figures 15-1 through 15‑6. The first graph
presents the rejection performance in terms of D/U ratios and the second
in terms of the undesired signal power at TOV. The first pair of graphs
presents the *median* rejection performance across the eight DTV
receivers at each of the tested channel offsets (from N-16 to
N+16---omitting the co-channel case). The second pair presents the
*second-worst* performance across the eight receivers. The third pair
presents the *worst* performance.

Each graph shows the interference thresholds at five desired signal
levels: -28 dBm, ‑53 dBm, ‑68 dBm, D~MIN~ + 3 dB, and D~MIN~ + 1 dB,
where D~MIN~ is the desired signal level corresponding to the TOV for
the receiver in the absence of interference. For measurements at
D~MIN~ + 3 dB, each TV was tested by first measuring its minimum signal
threshold D~MIN~, then setting the desired signal power 3 dB higher that
threshold for the interference rejection tests. Thus the desired signal
level was different for each DTV receiver. The results at D~MIN~ + 1 dB
were extrapolated from the measured values at D~MIN~ + 3 dB by means of
a model developed in Chapters 8 and 12.

Each graph shows measurement limitations imposed by the test setup---in
the form of solid black lines and a shaded region. The D/U plots
(Figures 15-1, 15-3, and 15-5) show four measurement limit curves that
correspond, from top to bottom, to limits at D = -28 dBm, -53 dBm, -68
dBm, and D~MIN~ + 3 dB, respectively. In the case of data extrapolated
to D~MIN~ + 1 dB, data points are shown only if the measurements on
which they were based were not subject to measurement limits. The
undesired signal threshold plots (even-numbered Figures 15-2, 15-4, and
15-6) show only one measurement limit curve---the curve associated with
the maximum undesired signal power that the test setup could inject into
the receiver; the N-1 and N+1 offsets for D = -68 dBm and all of the
offsets for D = D~MIN~ + 3 dB are subject to an additional
limitation---shown only in the D/U plots---that is caused by leakage of
the undesired signal into the desired channel.

We make the following observations regarding the results.

5.  In terms of absolute signal levels that can cause interference, the
    TVs are at their most vulnerable when operating at low desired
    signal levels.

6.  At low desired signal levels the TV receivers are *as* susceptible
    to interference from the second-adjacent channels (N-2 and N+2) as
    from first-adjacent channels (N-1 and N+1) in terms of median
    performance of the receivers. In terms of worst and second-worst
    performance, the receivers are *more* susceptible to interference
    from second-adjacent channels than from first-adjacent channels.
    (This contradicts the assumptions of OET-69 and the receiver
    performance guidelines of ATSC Document A/74.)

7.  The receivers tend to be more susceptible to interference from N+2,
    N+1, N-1, N-2, N-3, N-4, and sometimes N-6 than from the mixer image
    channel offsets of N+14 and N+15.

8.  At moderate desired signal levels, the receivers exhibit relatively
    high susceptibility to interference from channel N+7. This
    interference threshold is nearly constant in terms of absolute power
    of the undesired signal necessary to cause interference at different
    levels of desired signals. At lower desired signal levels, other
    channel offsets become more vulnerable.

## Interference From IM3-Generating Pairs of Undesired Signals

Pairs of undesired signals placed on channels N+K and N+2K, where K is a
positive or negative integer, create an opportunity for third-order
intermodulation (IM3) occurring in the DTV tuner to create spectral
products that fall in the desired channel N. We had anticipated
paired-signal IM3 effects would be significant only at high signal
levels; however, detailed measurements on one DTV receiver (Chapter 11)
demonstrated that such effects can constitute a dominant interference
susceptibility even at desired signal levels very near the minimum
signal threshold for the TV, when such signal pairs exist.

Measurements of interference thresholds were performed with
equal-powered undesired signals on N+K/N+2K combinations for eight DTVs
on channel 30 and seven of those DTVs on channel 51. Tests were
performed for K = -5 to 5 when N was 30 and for K = 1 to 8 when N was
51. In both cases, desired signal levels were set to -68 dBm and -53
dBm. Not all measured cases produced interference effects that were
sufficiently higher than the single-channel interference effects to
allow measurement of the IM3 effects. For those that were, a third-order
intercept point (IP3) was computed.

The data was carefully examined to identify cases for which median,
second-worst, and worst IP3 across the eight receivers could be
determined. In cases in which corresponding values (*e.g.*,
"second-worst") were obtained from both the channel 30 measurements and
the channel 51 measurements, the results were averaged across the two
channels; in cases where only one channel yielded a value, that value
was used. IP3's computed from that data were used to extend the results,
by calculation, to desired power levels of D~MIN~ + 3 dB and D~MIN~ + 1
dB. For simplicity, that calculation assumed that D~MIN~ = ‑84 dBm for
each receiver.

Figure 15-7 shows the *[median]{.underline}* D/U ratios across the eight
tested receivers for a desired signal level of *‑68 dBm*. The "Single
Signal" curve is a duplicate of the corresponding curve from Figure
15-1. Paired signal combinations for which IM3 effects were measurable
across a sufficient set of receivers to allow the median IP3 to be
computed are shown as pairs of large red dots connected by straight
lines. The horizontal pairs represent rejection thresholds for
equal-level undesired signals. For example, the connected pair of dots
at N+3 and N+6 indicates that the median D/U ratio for a signal pair at
N+3 and N+6 is --43.7 dB when the desired signal level is -68 dBm. (For
equal-powered undesired signals, the "U" in the D/U ratio is U = U~N+K~
= U~N+2K~.)

The right-most signal pair (N+8/N+16) was plotted in three ways---as an
equal-power signal pair (horizontal line) and as two sets of unequal
pairs. Unequal pairs were created by raising and lowering the N+8 point
by 10 dB, which results in a +/-20 dB change in the threshold for N+16.
The example illustrates behavior that would be exhibited by any of the
signal pairs for unequal signals with such a signal level deviation.
That is, if U~N+K~ were to change by X dB from the equal-level threshold
value, the U~N+2K~ threshold would change by -2X dB. Thus, the presence
of a signal stronger than the equal-power threshold on one channel in a
pair, makes the other channel susceptible to weaker undesired signals.
In the example, increasing the undesired signal power at channel N+8 by
10 dB from the equal-power threshold (resulting in a 10 dB *decrease* in
D/U at N+8) causes the threshold D/U ratio at N+16 to increase from its
equal power value of ‑51.4 dB to -31.4 dBm. The result is that the
susceptibility of the TV to interference on channel N+16 is now greater
than its susceptibility to interference on the first adjacent channels
(N-1 or N+1). Charts and tables in Chapter 10 illustrate the range of
thresholds that can result.

We note that the behavior of unequal signal pairs as described in the
previous paragraph and quantified in the charts and tables of Chapter 10
is valid only over signal level regions for which the receiver's
automatic gain control (AGC) does not act to reduce tuner gain prior to
the nonlinearity that causes the IM3 effects (usually in the mixer). In
some cases (including one identified in Chapter 14), a large increase in
U~N+K~ for small K values may cause such AGC gain reductions. When that
happens, the model predicts that the sensitivity of the receiver to
interference on N+2K will freeze---exhibiting no further increases in
interference susceptibility with further increases in U~N+K~.

Regarding signal pairs that are missing from Figure 15-7 (and from the
subsequent plots that will be introduced), we note the following.

1.  In the case of the first-adjacent pairs (N-1/N-2 and N+1/N+2) the
    values are missing because the measurements of paired-signal
    thresholds for those channel pairs did not exceed single-channel
    effects on any of the receivers by a sufficient amount to support
    measurement of IM3 effects. (We note that equal undesired signal
    powers levels are not necessarily optimal for detecting IP3 effects,
    so it is not known whether IM3 estimates could have been obtained
    from measurements at unequal levels.)

2.  In the case of channel pairs N-3/N-6, N-2/N-4, N+2/N+4 and N+7/N+14,
    IM3 effects were successfully measured for some of the receivers,
    but the receivers that did *not* support such measurement created
    uncertainty in trying to determine worst, second-worst, and median
    values of the IP3 parameter; consequently, those values are missing
    from the graphs.

3.  No signal pair measurements were performed beyond N-5/N-10 in on the
    left side of the plots.

It can be seen on the right side of the plot, where measurements are
more plentiful, that the paired-signal interference effects gradually
decrease with separation from the desired channel.

If one were interested in determining general undesired signal levels at
which IM3 can interfere with TV reception, the "Equal Signal Pairs"
plots in Figure 15‑7 (and in subsequent charts to be described next)
could be used to identify a level that could cause interference
***[if]{.underline}*** a similar signal level happens to occur at
another channel offset that would place IM3 products in the desired
channel. If, on the other hand, one wanted to determine case-specific
interference vulnerabilities that take into account *existing* undesired
sources (*e.g.*, a nearby DTV broadcast station when the receiver is
tuned to a more distant station), one could use the data from Chapter 10
to determine the signal level associated, for example, with a new non-TV
service that would cause interference under specific reception
conditions. Such analysis using signal levels from existing channel
allotments could reveal greater interference susceptibilities than those
based on equal signal pairs.

Figure 15-8 presents the same data as Figure 15-7, but shows it as the
threshold value of undesired signal power U rather than as a D/U ratio.

The previous two plots corresponded to *median* receiver performance
with a desired signal level of ‑68 dBm. The subsequent two pairs of
charts show similar data for the second-worst and worst performing
receivers. That six-chart sequence is followed by six charts
corresponding to a desired signal level of D~MIN~ + 3 dB and six more
charts corresponding to a desired signal of D~MIN~ + 1 dB.

The plots show that IM3 between paired signals can be the dominant
source of interference at many channel offsets, when undesired signals
exist at IM3-generating spacings (N+K/N+2K). IM3 interference effects
from paired signals on the first-adjacent channel pair (N+1/N+2 or
N-1/N-2) appear to be less important than the single-channel
interference effects for first adjacent channels; the same is sometimes,
but not always, true for the second adjacent pair (N+2/N+4 or N-2/N-4).
At other channel spacings the paired signal IM3 effects dominate when
the desired signal level is -68 dBm.

As desired signal level drops, IM3 effects diminish more rapidly than
first- and second-adjacent single-channel interference effects. This can
be seen by comparing, for example, Figures 15-7 and 15-19. Nonetheless,
paired-signal IM3 appears to be the dominant interference vulnerability
for channel offsets from about N+4 to N+16 (with the exception of the
mixer image at N+14 and N+15) and from about N-5 to N-10, even at
desired signal levels near D~MIN~ and even if the paired signals are
assumed to be equal in level. No paired signal measurements were
performed beyond N+16 and N-10, so it is not know how far out the effect
continues; however, the effect is seen to diminish with increasing
channel offset from the desired channel.

Paired signals at IM3-generating spacings have the potential to create
even greater interference susceptibilities if an existing undesired
signal on one of the IM3-generating channels (*e.g.*, a nearby DTV
broadcast station when the receiver is tuned to a more distant station)
exceeds the measured equal-power-level threshold for paired signals. In
such a case, the presence of that signal can greatly increase
susceptibility to interference on the other channel of the
IM3-generating pair. This situation generally creates the greatest
vulnerabilities when the stronger undesired signal is on channel N+K and
it exceeds the equal-power paired-signal threshold; in that case, the
receiver susceptibility to interference on the N+2K channel increases by
twice the N+K signal excess above the equal power threshold.

The ATSC Receiver Guidelines document (A/74) provides no recommended
performance levels for rejection of paired-signal interference.

![](media/image130.wmf){width="6.497916666666667in"
height="4.4430555555555555in"}

[]{#__RefHeading___Toc163024535 .anchor}Figure 15‑128. Median D/U of 8
Receivers at Five Signal Levels on Channel 30

![](media/image131.wmf){width="6.497916666666667in"
height="4.4430555555555555in"}

[]{#__RefHeading___Toc163024536 .anchor}Figure 15‑129. Median Threshold
U of 8 Receivers at Five Signal Levels on Channel 30

![](media/image132.wmf){width="6.497916666666667in"
height="4.4430555555555555in"}

[]{#__RefHeading___Toc163024537 .anchor}Figure 15‑130. 2^nd^ Worst D/U
of 8 Receivers at Five Signal Levels on Channel 30

![](media/image133.wmf){width="6.497916666666667in"
height="4.4430555555555555in"}

[]{#__RefHeading___Toc163024538 .anchor}Figure 15‑131. 2^nd^ Worst
Threshold U of 8 Receivers at Five Signal Levels on Channel 30

![](media/image134.wmf){width="6.497916666666667in"
height="4.4430555555555555in"}

[]{#__RefHeading___Toc163024539 .anchor}Figure 15‑132. Worst D/U of 8
Receivers at Five Signal Levels on Channel 30

![](media/image135.wmf){width="6.497916666666667in"
height="4.4430555555555555in"}

[]{#__RefHeading___Toc163024540 .anchor}Figure 15‑133. Worst Threshold U
of 8 Receivers at Five Signal Levels on Channel 30

![](media/image136.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024541 .anchor}Figure 15‑134. Median D/U of 8
Receivers at D = -68 dBm With IM3 Signal Pairs

![](media/image137.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024542 .anchor}Figure 15‑135. Median Threshold
U of 8 Receivers at D = -68 dBm With IM3 Signal Pairs

![](media/image138.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024543 .anchor}Figure 15‑136. 2^nd^ Worst D/U
of 8 Receivers at D = -68 dBm With IM3 Signal Pairs

![](media/image139.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024544 .anchor}Figure 15‑137. 2^nd^ Worst
Threshold U of 8 Receivers at D = -68 dBm With IM3 Signal Pairs

![](media/image140.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024545 .anchor}Figure 15‑138. Worst D/U of 8
Receivers at D = -68 dBm With IM3 Signal Pairs

![](media/image141.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024546 .anchor}Figure 15‑139. Worst Threshold U
of 8 Receivers at D = -68 dBm With IM3 Signal Pairs

![](media/image142.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024547 .anchor}Figure 15‑140. Median D/U of 8
Receivers at D = D~MIN~+3dB With IM3 Signal Pairs

![](media/image143.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024548 .anchor}Figure 15‑141. Median Threshold
U of 8 Receivers at D = D~MIN~+3dB With IM3 Signal Pairs

![](media/image144.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024549 .anchor}Figure 15‑142. 2^nd^ Worst D/U
of 8 Receivers at D = D~MIN~+3dB With IM3 Signal Pairs

![](media/image145.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024550 .anchor}Figure 15‑143. 2^nd^ Worst
Threshold U of 8 Receivers at D = D~MIN~+3dB With IM3 Signal Pairs

![](media/image146.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024551 .anchor}Figure 15‑144. Worst D/U of 8
Receivers at D = D~MIN~+3dB With IM3 Signal Pairs

![](media/image147.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024552 .anchor}Figure 15‑145. Worst Threshold U
of 8 Receivers at D = D~MIN~+3dB With IM3 Signal Pairs

![](media/image148.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024553 .anchor}Figure 15‑146. Median D/U of 8
Receivers at D = D~MIN~+1dB With IM3 Signal Pairs

![](media/image149.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024554 .anchor}Figure 15‑147. Median Threshold
U of 8 Receivers at D = D~MIN~+1dB With IM3 Signal Pairs

![](media/image150.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024555 .anchor}Figure 15‑148. 2^nd^ Worst D/U
of 8 Receivers at D = D~MIN~+1dB With IM3 Signal Pairs

![](media/image151.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024556 .anchor}Figure 15‑149. 2^nd^ Worst
Threshold U of 8 Receivers at D = D~MIN~+1dB With IM3 Signal Pairs

![](media/image152.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024557 .anchor}Figure 15‑150. Worst D/U of 8
Receivers at D = D~MIN~+1dB With IM3 Signal Pairs

![](media/image153.wmf){width="6.492361111111111in"
height="4.433333333333334in"}

[]{#__RefHeading___Toc163024558 .anchor}Figure 15‑151. Worst Threshold U
of 8 Receivers at D = D~MIN~+1dB With IM3 Signal Pairs

#######  TABULATED REJECTION PERFORMANCE RESULTS

This appendix includes tabulations of statistical data from the
interference rejection performance measurements of eight DTV receivers
on tuned to channel 30. The data are presented as D/U ratios and as
threshold levels of the undesired signal U in separate major sections of
this appendix.

Within each major section, a separate table is provided for rejection
performance data at each of five desired signal levels:

1.  D~MIN~ + 1 dB

2.  D~MIN~ + 3 dB

3.  -68 dBm

4.  -53 dBm

5.  -28 dBm

The rejection performance results for the four higher levels were
obtained by direct measurement. For that data, "\>" or "\<" symbols
appear when the statistical parameter shown depends on a value that was
at the measurement limit of the test setup. For example, if the "Best U"
value is listed as \>-6.6 dBm, that means that a valid measurement of
rejection performance of the best performing receiver was not obtained
due to measurement system limitations. Specifically, at that channel
offset, the maximum undesired signal power that the test setup was
capable of supplying to the DTV input was -6.6 dBm and the TV picture
was still flawless at that level; thus we know only that the threshold
undesired signal power of the best receiver was greater than -6.6 dBm.
If only the best receiver measurement was so limited, values will be
listed for the median, 2^nd^ worst, and worst performance, but not for
the mean or standard deviation, because those values can be computed
only if all of the measurement values were valid.

The rejection results for D~MIN~ + 1 dB were extrapolated from
measurements at D = -68 dBm and D = D~MIN~ + 3 dB, but only if valid
measurements were available at both of those levels. Otherwise the
corresponding cell in the table is left blank.

In the case of the measurements at D = D~MIN~ + 3 dB or extrapolations
for D = D~MIN~ + 3 dB, the desired signal level was different for each
receiver, based on separately measured D~MIN~ values for the receivers.
Table A-1 shows statistics for the D~MIN~ values.

[]{#__RefHeading___Toc163024591 .anchor}Table A‑1. Statistics of D~MIN~
for 8 Receivers on Channel 30

  -------------------------- ------------------- -------------------------
  ** **                      **D~MIN~**          **D~MIN~+3dB**

  **Minimum (dBm)**          -86.2               -83.2

  **Median (dBm)**           -84.0               -81.0

  **Mean (dBm)**             -83.9               -80.9

  **Maximum (dBm)**          -81.8               -78.8

  **Standard Deviation       1.3                 1.3
  (dB)**                                         
  -------------------------- ------------------- -------------------------

######## Threshold D/U Statistics for 8 Fifth-Generation DTV Receivers

######### Desired Signal = DMIN + 1 dB (Extrapolated from Measurements at DMIN + 3 dB)

[]{#__RefHeading___Toc163024592 .anchor}Table A‑2. D/U Statistics for 8
Receivers at D = D~MIN~ + 1 dB on Channel 30

  ------------- -------- ---------- --------- -------- --------- ------------
  **Undesired   **Best   **Median   **Mean    **2nd    **Worst   **Standard
  Channel**     D/U      D/U (dB)** D/U       Worst    D/U       Deviation
                (dB)**              (dB)**    D/U      (dB)**    (dB)**
                                              (dB)**             

  N-16                                                            

  N-15                                                            

  N-14                                                            

  N-13                   -73.0                -64.4    -64.2     

  N-12                   -72.3                -62.7    -60.9     

  N-11                   -70.6                -61.0    -59.0     

  N-10                   -68.2                -59.3    -57.0     

  N-9                    -66.8                -56.5    -55.0     

  N-8           -72.6    -62.7      -60.3     -52.5    -45.1     8.9

  N-7           -71.7    -62.1      -58.7     -50.0    -44.6     8.8

  N-6           -72.9    -53.0      -51.6     -43.2    -26.6     13.9

  N-5           -71.0    -53.3      -54.0     -47.2    -40.6     8.9

  N-4           -65.6    -45.4      -47.9     -41.8    -36.2     9.5

  N-3           -57.5    -45.5      -46.5     -40.4    -36.9     7.1

  N-2           -49.1    -36.0      -36.5     -29.3    -23.2     8.4

  N-1           -38.2    -35.4      -35.4     -33.0    -32.8     2.0

  N+1           -38.9    -36.7      -36.2     -33.9    -32.2     2.3

  N+2           -50.7    -37.5      -37.8     -30.3    -23.5     9.2

  N+3           -61.9    -50.2      -50.6     -44.3    -43.5     5.8

  N+4           -69.8    -55.3      -56.1     -50.9    -47.7     6.7

  N+5           -67.3    -61.6      -61.0     -59.6    -50.2     5.0

  N+6                                                             

  N+7           -72.1    -64.4      -64.0     -57.8    -52.8     7.1

  N+8                                                             

  N+9                                                             

  N+10                                                            

  N+11                                                            

  N+12                                                            

  N+13                                                            

  N+14                   -54.4                -48.1    -47.7      

  N+15                    -48.8               -44.9    -42.9      

  N+16                                                            
  ------------- -------- ---------- --------- -------- --------- ------------

######### Desired Signal = D~MIN~ + 3 dB

[]{#__RefHeading___Toc163024593 .anchor}Table A‑3. D/U Statistics for 8
Receivers at D = D~MIN~ + 3 dB on Channel 30

  ------------- -------- ---------- ---------- --------- ---------- ------------
  **Undesired   **Best   **Median   **Mean D/U **2nd     **Worst    **Standard
  Channel**     D/U      D/U (dB)** (dB)**     Worst D/U D/U (dB)** Deviation
                (dB)**                         (dB)**               (dB)**

  N-16          \< -76.0 -73.2      \< -72.3   -67.8     -67.8      \> 3.4

  N-15          \< -76.0 -71.4      \< -72.1   -69.2     -69.0      \> 2.8

  N-14          \< -75.3 -72.7      \< -71.8   -67.6     -67.1      \> 3.4

  N-13          \< -74.8 -72.9      \< -71.4   -66.7     -65.3      \> 3.9

  N-12          \< -74.8 -72.3      \< -70.7   -65.2     -63.5      \> 4.5

  N-11          \< -74.6 -70.5      \< -68.9   -63.5     -61.6      \> 4.8

  N-10          \< -74.7 -68.7      \< -67.8   -61.8     -59.6      \> 5.0

  N-9           \< -74.1 -67.2      \< -65.3   -59.1     -57.5      \> 5.9

  N-8           -72.5    -64.1      -61.8      -55.1     -47.7      7.9

  N-7           -71.7    -63.0      -60.2      -52.6     -47.1      7.9

  N-6           -72.9    -55.5      -53.5      -45.7     -29.2      13.1

  N-5           -71.0    -55.9      -56.0      -49.7     -43.2      8.0

  N-4           -66.6    -47.9      -50.0      -44.3     -38.8      8.8

  N-3           -60.1    -48.1      -49.1      -42.9     -39.5      7.1

  N-2           -51.7    -38.5      -39.1      -31.9     -25.7      8.4

  N-1           -40.7    -38.0      -38.0      -35.6     -35.3      2.0

  N+1           -41.5    -39.3      -38.7      -36.4     -34.7      2.3

  N+2           -51.5    -40.1      -40.1      -32.9     -26.1      8.9

  N+3           -62.8    -52.8      -52.6      -46.8     -46.0      5.5

  N+4           -69.6    -57.1      -57.6      -53.5     -47.6      6.4

  N+5           -67.2    -63.2      -62.0      -61.8     -50.1      5.1

  N+6           -73.7    -72.1      -70.0      -66.7     -61.3      4.2

  N+7           -72.0    -64.4      -63.9      -57.8     -52.7      7.1

  N+8           \< -77.1 \<-74.6    \< -74.5   -73.2     -72.1      \> 1.5

  N+9           \< -78.4 \<-75.2    \< -75.5   \<-74.8   -73.3      \> 1.5

  N+10          \< -77.9 \<-74.7    \< -75.0   -73.1     -72.8      \> 1.9

  N+11          \< -78.3 \<-75.8    \< -75.8   \<-75.0   -73.2      \> 1.5

  N+12          \< -79.3 \<-75.8    \< -76.3   \<-75.1   -73.1      \> 2.0

  N+13          \< -79.1 \<-76.0    \< -76.4   \<-75.0   -73.2      \> 1.9

  N+14          \< -78.8 -58.2      \< -61.5   -51.9     -51.6      \> 9.9

  N+15          \< -78.3 -52.6      \< -56.5   -48.7     -46.8      \> 10.2

  N+16          \< -77.7 \<-75.7    \< -75.8   \<-74.9   -73.2      \> 1.4
  ------------- -------- ---------- ---------- --------- ---------- ------------

#########  Desired Signal = -68 dBm

[]{#__RefHeading___Toc163024594 .anchor}Table A‑4. D/U Statistics for 8
Receivers at D = -68 dBm on Channel 30

  ------------- -------- ---------- -------- -------- --------- ------------ -------------
  **Undesired   **Best   **Median   **Mean   **2nd    **Worst   **Standard   **ATSC
  Channel**     D/U      D/U (dB)** D/U      Worst    D/U       Deviation    Performance
                (dB)**              (dB)**   D/U      (dB)**    (dB)**       Guideline
                                             (dB)**                          (dB)**

  N-16          \< -66.9 -64.2      \< -63.9 -62.2    -59.2     \> 2.7        

  N-15          \< -67.0 -64.1      \< -64.0 -61.8    -59.7     \> 2.7       -50.0

  N-14          \< -67.2 -64.1      \< -63.8 -61.6    -59.3     \> 2.8       -50.0

  N-13          -67.0    -64.1      -63.6    -61.4    -58.8     2.8          -57.0

  N-12          -66.1    -62.7      -63.0    -61.3    -58.3     2.7          -57.0

  N-11          -65.9    -62.0      -62.1    -60.8    -56.7     2.8          -57.0

  N-10          -66.0    -63.5      -62.4    -59.6    -57.1     3.0          -57.0

  N-9           -65.0    -60.9      -60.9    -58.1    -56.0     3.1          -57.0

  N-8           -64.2    -58.0      -58.3    -55.0    -50.7     4.5          -57.0

  N-7           -64.2    -58.2      -57.2    -53.5    -48.4     5.1          -57.0

  N-6           -62.5    -52.9      -52.0    -48.3    -31.8     9.7          -57.0

  N-5           -62.6    -55.5      -54.3    -49.7    -44.5     5.7          -56.0

  N-4           -61.9    -47.4      -49.3    -45.8    -40.7     6.3          -52.0

  N-3           -59.8    -49.6      -50.1    -44.3    -41.9     6.2          -48.0

  N-2           -49.7    -40.9      -40.1    -32.0    -28.1     7.4          -44.0

  N-1           -40.1    -39.3      -39.1    -38.0    -37.9     0.8          -33.0

  N+1           -42.1    -39.7      -39.7    -38.3    -37.9     1.4          -33.0

  N+2           -48.3    -42.3      -41.1    -34.3    -29.8     6.9          -44.0

  N+3           -57.0    -54.6      -51.9    -48.3    -39.8     5.8          -48.0

  N+4           -60.0    -56.6      -54.9    -54.4    -41.1     5.9          -52.0

  N+5           -65.4    -58.4      -56.9    -53.6    -42.6     7.1          -56.0

  N+6           \< -66.3 -63.1      \< -61.6 -56.3    -52.9     \> 4.6       -57.0

  N+7           -60.3    -53.3      -51.9    -45.0    -41.6     6.8          -57.0

  N+8           \< -66.6 -65.0      \< -64.5 -63.1    -60.9     \> 2.0       -57.0

  N+9           \< -66.6 -65.9      \< -65.2 -63.4    -62.1     \> 1.6       -57.0

  N+10          \< -66.5 -65.0      \< -65.0 -63.1    -62.9     \> 1.4       -57.0

  N+11          \< -66.2 \<-65.9    \< -65.2 -63.2    -63.2     \> 1.3       -57.0

  N+12          \< -66.0 \<-65.7    \< -65.0 -62.9    -62.9     \> 1.3       -57.0

  N+13          \< -65.9 \<-65.5    \< -64.9 -63.3    -63.2     \> 1.1       -57.0

  N+14          \< -65.3 -60.3      \< -59.2 -52.9    -51.2     \> 5.3       -50.0

  N+15          \< -64.8 -55.0      \< -56.0 -50.1    -48.7     \> 5.7       -50.0

  N+16          \< -64.5 \<-64.2    \< -64.1 -63.6    -63.4     \> 0.4        

  N-5/N-10      -49.8    -42.3      -43.6    -41.7    -37.2     4.2          

  N-4/N-8       -46.3    -41.9      -42.4    -39.1    -38.2     3.1          

  N-3/N-6       -45.2    -41.7      -40.6    -36.0    -33.0     4.1          

  N-2/N-4       -51.4    -40.7      -39.3    -30.7    -29.5     7.0          

  N-1/N-2       -39.2    -35.7      -34.8    -29.9    -27.3     4.1          

  N+1/N+2       -39.7    -36.5      -36.1    -34.9    -29.0     3.3          

  N+2/N+4       -42.3    -38.0      -37.2    -31.0    -28.9     5.1          

  N+3/N+6       -51.1    -43.5      -44.0    -40.6    -33.9     5.8          

  N+4/N+8       -50.8    -46.8      -46.0    -42.1    -39.6     4.2          

  N+5/N+10      -52.5    -48.3      -47.9    -44.4    -42.5     3.3          
  ------------- -------- ---------- -------- -------- --------- ------------ -------------

######### Desired Signal = -53 dBm

[]{#__RefHeading___Toc163024595 .anchor}Table A‑5. D/U Statistics for 8
Receivers at D = -53 dBm on Channel 30

  ------------- -------- ---------- -------- --------- --------- ------------ -------------
  **Undesired   **Best   **Median   **Mean   **2nd     **Worst   **Standard   **ATSC
  Channel**     D/U      D/U (dB)** D/U      Worst D/U D/U       Deviation    Performance
                (dB)**              (dB)**   (dB)**    (dB)**    (dB)**       Guideline
                                                                              (dB)**

  N-16          \< -52.2 -51.4      \< -50.5 -49.2     -45.7     \> 2.2        

  N-15          \< -52.4 \<-52.0    \< -50.6 -49.0     -45.1     \> 2.5       -45.0

  N-14          \< -52.6 \<-52.2    \< -50.6 -48.8     -44.5     \> 2.8       -45.0

  N-13          \< -52.8 -52.0      \< -50.5 -48.8     -44.3     \> 2.9       -45.0

  N-12          \< -52.9 -50.8      \< -50.1 -48.6     -43.7     \> 3.1       -45.0

  N-11          \< -52.9 -50.9      \< -49.8 -46.8     -42.9     \> 3.5       -45.0

  N-10          \< -52.9 -52.3      \< -50.5 -48.2     -42.3     \> 3.6       -45.0

  N-9           \< -52.7 -52.2      \< -50.2 -48.1     -41.4     \> 3.9       -45.0

  N-8           \< -52.6 -51.4      \< -49.5 -47.1     -40.2     \> 4.3       -45.0

  N-7           \< -52.3 -50.5      \< -48.9 -45.7     -38.8     \> 4.7       -45.0

  N-6           \< -52.1 -47.7      \< -45.7 -36.9     -32.4     \> 7.3       -45.0

  N-5           \< -51.9 -51.6      \< -48.4 -43.8     -34.7     \> 6.2       -42.0

  N-4           \< -51.9 -47.0      \< -45.7 -39.9     -32.3     \> 6.6       -40.0

  N-3           \< -51.8 -49.1      \< -48.2 -45.2     -41.9     \> 3.3       -40.0

  N-2           -49.0    -41.5      -39.8    -31.8     -27.4     7.1          -40.0

  N-1           -40.0    -39.0      -38.5    -37.7     -34.4     1.8          -33.0

  N+1           -41.9    -39.4      -39.4    -38.3     -36.0     1.8          -33.0

  N+2           -46.8    -42.2      -40.6    -34.5     -30.3     6.3          -40.0

  N+3           \< -50.9 -49.8      \< -46.8 -48.1     -25.1     \> 8.8       -40.0

  N+4           \< -51.0 -50.1      \< -46.6 -45.1     -29.1     \> 7.5       -40.0

  N+5           \< -51.2 -49.0      \< -46.7 -44.5     -31.9     \> 6.5       -42.0

  N+6           \< -51.4 -50.8      \< -48.9 -46.3     -39.8     \> 4.1       -45.0

  N+7           -51.2    -38.7      -38.8    -32.6     -26.9     8.0          -45.0

  N+8           \< -51.7 \<-51.4    \< -50.9 -49.6     -48.7     \> 1.1       -45.0

  N+9           \< -51.6 \<-51.3    \< -51.1 \<-51.2   -49.2     \> 0.8       -45.0

  N+10          \< -51.5 \<-51.2    \< -51.1 \<-51.1   -49.8     \> 0.5       -45.0

  N+11          \< -51.2 \<-51.0    \< -51.0 \<-50.9   -50.4     \> 0.3       -45.0

  N+12          \< -51.2 \<-50.8    \< -50.8 \<-50.7   -50.4     \> 0.3       -45.0

  N+13          \< -50.9 \<-50.6    \< -50.6 \<-50.4   \<-50.4   \> 0.2       -45.0

  N+14          \< -50.5 \<-50.1    \< -50.2 \<-50.0   -50.0     \> 0.2       -45.0

  N+15          \< -50.0 \<-49.7    \< -49.5 \<-49.6   -47.6     \> 0.8       -45.0

  N+16          \< -49.5 \<-49.3    \< -49.3 \<-49.2   \<-49.2   \> 0.1        

  N-5/N-10      -39.0    -33.6      -34.3    -32.2     -30.6     2.8          

  N-4/N-8       -38.4    -34.6      -34.2    -32.5     -28.2     3.1          

  N-3/N-6       -43.6    -37.4      -36.4    -32.5     -25.4     5.8          

  N-2/N-4       -41.9    -38.2      -36.4    -28.6     -28.6     5.2          

  N-1/N-2       -39.0    -36.0      -34.4    -27.4     -26.3     4.9          

  N+1/N+2       -38.7    -35.4      -35.2    -33.3     -30.1     2.6          

  N+2/N+4       -38.9    -35.1      -33.4    -31.4     -20.8     5.7          

  N+3/N+6       -41.6    -34.1      -34.4    -29.9     -22.9     6.1          

  N+4/N+8       -41.2    -35.8      -36.0    -33.6     -28.4     4.2          

  N+5/N+10      -41.6    -38.2      -37.7    -34.3     -32.2     3.1          
  ------------- -------- ---------- -------- --------- --------- ------------ -------------

######### Desired Signal = -28 dBm

[]{#__RefHeading___Toc163024596 .anchor}Table A‑6. D/U Statistics for 8
Receivers at D = -28 dBm on Channel 30

  ------------- -------- ---------- -------- --------- --------- ------------ -------------
  **Undesired   **Best   **Median   **Mean   **2nd     **Worst   **Standard   **ATSC
  Channel**     D/U      D/U (dB)** D/U      Worst D/U D/U       Deviation    Performance
                (dB)**              (dB)**   (dB)**    (dB)**    (dB)**       Guideline
                                                                              (dB)**

  N-16          \< -27.3 \<-27.2    \< -27.1 \<-26.9   \<-26.8   \> 0.2        

  N-15          \< -27.4 \<-27.3    \< -27.2 \<-27.0   \<-26.9   \> 0.2       -20.0

  N-14          \< -27.6 \<-27.5    \< -27.4 \<-27.2   \<-27.1   \> 0.2       -20.0

  N-13          \< -27.8 \<-27.7    \< -27.6 \<-27.3   \<-27.3   \> 0.2       -20.0

  N-12          \< -27.9 \<-27.8    \< -27.7 \<-27.5   \<-27.4   \> 0.2       -20.0

  N-11          \< -28.0 \<-27.8    \< -27.7 \<-27.5   \<-27.4   \> 0.2       -20.0

  N-10          \< -27.9 \<-27.8    \< -27.7 \<-27.5   \<-27.4   \> 0.2       -20.0

  N-9           \< -27.8 \<-27.7    \< -27.6 \<-27.3   \<-27.3   \> 0.2       -20.0

  N-8           \< -27.6 \<-27.5    \< -27.4 \<-27.2   \<-27.1   \> 0.2       -20.0

  N-7           \< -27.4 \<-27.3    \< -27.2 \<-27.1   \<-27.0   \> 0.1       -20.0

  N-6           \< -27.2 \<-27.1    \< -27.0 \<-26.9   \<-26.7   \> 0.2       -20.0

  N-5           \< -27.0 \<-26.9    \< -26.9 \<-26.9   \<-26.7   \> 0.1       -20.0

  N-4           \< -26.9 \<-26.9    \< -26.9 \<-26.8   \<-26.7   \> 0.1       -20.0

  N-3           \< -26.9 \<-26.8    \< -26.8 \<-26.7   \<-26.6   \> 0.1       -20.0

  N-2           \< -26.6 \<-26.5    \< -26.5 \<-26.5   \<-26.4   \> 0.1       -20.0

  N-1           \< -20.9 \<-20.8    \< -20.8 \<-20.7   -20.7     \> 0.1       -20.0

  N+1           \< -20.3 \<-20.2    \< -20.2 \<-20.2   -19.8     \> 0.1       -20.0

  N+2           \< -26.2 \<-26.0    \< -26.0 \<-26.0   \<-26.0   \> 0.1       -20.0

  N+3           \< -26.0 \<-25.8    \< -25.8 \<-25.8   -25.3     \> 0.2       -20.0

  N+4           \< -26.0 \<-25.8    \< -25.8 \<-25.8   \<-25.7   \> 0.1       -20.0

  N+5           \< -26.2 \<-26.0    \< -26.0 \<-26.0   \<-25.9   \> 0.1       -20.0

  N+6           \< -26.5 \<-26.3    \< -26.3 \<-26.2   \<-26.1   \> 0.1       -20.0

  N+7           \< -26.6 \<-26.4    \< -25.3 -23.9     -20.0     \> 2.3       -20.0

  N+8           \< -26.7 \<-26.4    \< -26.4 \<-26.3   \<-26.2   \> 0.1       -20.0

  N+9           \< -26.6 \<-26.3    \< -26.3 \<-26.2   \<-26.1   \> 0.2       -20.0

  N+10          \< -26.5 \<-26.2    \< -26.2 \<-26.1   \<-26.0   \> 0.2       -20.0

  N+11          \< -26.3 \<-26.0    \< -26.0 \<-25.9   \<-25.8   \> 0.2       -20.0

  N+12          \< -26.1 \<-25.8    \< -25.8 \<-25.7   \<-25.6   \> 0.2       -20.0

  N+13          \< -25.9 \<-25.6    \< -25.6 \<-25.4   \<-25.4   \> 0.2       -20.0

  N+14          \< -25.5 \<-25.2    \< -25.2 \<-25.1   \<-25.0   \> 0.2       -20.0

  N+15          \< -25.1 \<-24.8    \< -24.8 \<-24.7   \<-24.6   \> 0.2       -20.0

  N+16          \< -24.5 \<-24.3    \< -24.3 \<-24.2   \<-24.1   \> 0.2        

  N-5/N-10      NA       NA         NA       NA        NA        NA           

  N-4/N-8       NA       NA         NA       NA        NA        NA           

  N-3/N-6       NA       NA         NA       NA        NA        NA           

  N-2/N-4       NA       NA         NA       NA        NA        NA           

  N-1/N-2       \< -20.9 \<-20.8    \< -20.3 -19.3     -18.1     \> 1.0       

  N+1/N+2       \< -20.3 \<-20.2    \< -19.7 -20.1     -16.4     \> 1.4       

  N+2/N+4       NA       NA         NA       NA        NA        NA           

  N+3/N+6       NA       NA         NA       NA        NA        NA           

  N+4/N+8       NA       NA         NA       NA        NA        NA           

  N+5/N+10      NA       NA         NA       NA        NA        NA           
  ------------- -------- ---------- -------- --------- --------- ------------ -------------

######## Threshold U Statistics for 8 Fifth-Generation DTV Receivers

######### Desired Signal = D~MIN~ + 1 dB (Extrapolated from Measurements at D~MIN~ + 3 dB)

[]{#__RefHeading___Toc163024597 .anchor}Table A‑7. Threshold U
Statistics for 8 Receivers at D = D~MIN~ + 1 dB on Channel 30

  ------------- --------- ----------- --------- --------- --------- ------------
  **Undesired   **Best U  **Median U  **Mean U  **2nd     **Worst U **Standard
  Channel**     (dBm)**   (dBm)**     (dBm)**   Worst U   (dBm)**   Deviation
                                                (dBm)**             (dB)**

  N-16                                                               

  N-15                                                               

  N-14                                                               

  N-13                    -11.0                 -18.8     -19.3     

  N-12                    -11.4                 -20.3     -22.8     

  N-11                    -12.5                 -22.0     -24.7     

  N-10                    -14.4                 -23.7     -26.7     

  N-9                     -15.8                 -26.5     -28.8     

  N-8           -12.7     -18.8       -22.5     -31.2     -37.9     8.8

  N-7           -13.5     -20.6       -24.2     -33.7     -38.5     8.8

  N-6           -12.4     -29.6       -31.3     -39.2     -56.4     13.5

  N-5           -14.3     -29.4       -28.9     -35.8     -43.1     8.6

  N-4           -19.6     -37.3       -34.9     -41.3     -47.5     9.1

  N-3           -26.7     -37.1       -36.4     -42.6     -46.8     7.1

  N-2           -36.2     -47.0       -46.4     -53.7     -57.6     7.7

  N-1           -44.8     -47.0       -47.4     -49.9     -50.9     2.2

  N+1           -43.2     -46.0       -46.6     -49.1     -51.5     2.7

  N+2           -34.6     -45.9       -45.1     -52.7     -57.3     8.6

  N+3           -23.3     -32.5       -32.3     -38.8     -40.2     5.5

  N+4           -15.5     -27.7       -26.8     -32.2     -34.3     6.3

  N+5           -17.2     -21.1       -21.9     -23.5     -31.8     4.6

  N+6                                                                

  N+7           -12.4     -17.1       -18.9     -25.3     -29.2     6.4

  N+8                                                                

  N+9                                                                

  N+10                                                               

  N+11                                                               

  N+12                                                               

  N+13                                                               

  N+14                                28.3      33.9      36.0       

  N+15                                33.3      37.1      40.8       

  N+16                                                               
  ------------- --------- ----------- --------- --------- --------- ------------

######### Desired Signal = D~MIN~ + 3 dB

[]{#__RefHeading___Toc163024598 .anchor}Table A‑8. Threshold U
Statistics for 8 Receivers at D = D~MIN~ + 3 dB on Channel 30

  ------------- --------- ----------- --------- --------- --------- ------------
  **Undesired   **Best U  **Median U  **Mean U  **2nd     **Worst U **Standard
  Channel**     (dBm)**   (dBm)**     (dBm)**   Worst U   (dBm)**   Deviation
                                                (dBm)**             (dB)**

  N-16          \> -4.2   -8.2        \> -8.6   -12.3     -13.9     \> 3.5

  N-15          \> -4.2   -9.7        \> -8.8   -11.7     -12.8     \> 3.2

  N-14          \> -4.2   -8.6        \> -9.1   -13.3     -14.7     \> 3.7

  N-13          \> -4.6   -9.1        \> -9.5   -14.2     -16.4     \> 4.2

  N-12          \> -4.3   -9.4        \> -10.2  -15.7     -18.3     \> 4.8

  N-11          \> -5.9   -10.5       \> -12.0  -17.4     -20.1     \> 5.0

  N-10          -7.1      -11.9       \> -13.1  -19.2     -22.1     \> 5.2

  N-9           -9.2      -13.4       \> -15.6  -21.9     -24.2     \> 6.0

  N-8           -10.8     -15.3       -19.1     -26.7     -33.4     7.8

  N-7           -11.6     -16.8       -20.7     -29.1     -33.9     7.8

  N-6           -10.4     -25.0       -27.4     -34.6     -51.8     12.7

  N-5           -12.3     -24.8       -25.0     -31.3     -38.5     7.8

  N-4           -16.7     -32.7       -30.9     -36.7     -43.0     8.3

  N-3           -22.1     -32.5       -31.8     -38.1     -42.2     7.1

  N-2           -31.6     -42.5       -41.8     -49.1     -53.1     7.7

  N-1           -40.2     -42.4       -42.8     -45.4     -46.3     2.2

  N+1           -38.6     -41.4       -42.1     -44.5     -46.9     2.7

  N+2           -31.6     -41.3       -40.8     -48.1     -52.7     8.4

  N+3           -20.4     -28.3       -28.3     -34.3     -35.7     5.3

  N+4           -13.5     -23.5       -23.3     -27.6     -32.3     5.9

  N+5           -15.2     -17.8       -18.9     -19.0     -29.9     4.6

  N+6           \> -6.7   -8.9        -10.9     -14.4     -18.6     4.3

  N+7           -10.5     -15.2       -17.0     -23.4     -27.2     6.4

  N+8           \> -3.2   \>-6.4      \> -6.4   -8.5      -9.4      \> 2.3

  N+9           \> -1.8   \>-5.3      \> -5.4   -8.4      -8.4      \> 2.4

  N+10          \> -2.9   \>-6.4      \> -5.9   -7.8      -8.7      \> 2.1

  N+11          \> -1.9   \>-5.4      \> -5.1   -7.8      -8.5      \> 2.5

  N+12          \> -1.8   \>-4.3      \> -4.6   -7.7      -8.6      \> 2.8

  N+13          \> -2.0   \>-4.1      \> -4.5   -7.4      -8.5      \> 2.7

  N+14          \> -2.3   -22.4       \> -19.4  -28.1     -30.2     \> 9.5

  N+15          \> -2.8   -27.4       \> -24.3  -31.3     -34.9     \> 9.9

  N+16          \> -3.3   \>-4.6      \> -5.1   -7.1      -8.5      \> 2.0
  ------------- --------- ----------- --------- --------- --------- ------------

######### Desired Signal = -68 dBm

[]{#__RefHeading___Toc163024599 .anchor}Table A‑9. Threshold U
Statistics for 8 Receivers at D = -68 dBm on Channel 30

  ------------- --------- ----------- --------- --------- --------- ------------
  **Undesired   **Best U  **Median U  **Mean U  **2nd     **Worst U **Standard
  Channel**     (dBm)**   (dBm)**     (dBm)**   Worst U   (dBm)**   Deviation
                                                (dBm)**             (dB)**

  N-16          \> -1.1   -3.9        \> -4.1   -5.9      -8.8      \> 2.7

  N-15          \> -1.0   -3.9        \> -4.0   -6.3      -8.3      \> 2.7

  N-14          \> -0.8   -3.9        \> -4.2   -6.4      -8.7      \> 2.8

  N-13          -1.0      -3.9        -4.4      -6.7      -9.2      2.8

  N-12          -1.9      -5.3        -5.0      -6.7      -9.7      2.7

  N-11          -2.1      -6.1        -5.9      -7.2      -11.2     2.8

  N-10          -2.1      -4.5        -5.6      -8.4      -10.9     2.9

  N-9           -3.1      -7.1        -7.1      -9.9      -11.9     3.1

  N-8           -3.8      -10.0       -9.7      -13.0     -17.4     4.5

  N-7           -3.8      -9.8        -10.8     -14.5     -19.6     5.1

  N-6           -5.5      -15.1       -16.0     -19.7     -36.2     9.7

  N-5           -5.4      -12.5       -13.7     -18.3     -23.5     5.7

  N-4           -6.1      -20.6       -18.7     -22.2     -27.3     6.3

  N-3           -8.2      -18.4       -17.9     -23.7     -26.2     6.3

  N-2           -18.3     -27.2       -27.9     -36.0     -40.0     7.4

  N-1           -28.0     -28.7       -28.9     -30.0     -30.1     0.8

  N+1           -25.9     -28.3       -28.3     -29.6     -30.2     1.4

  N+2           -19.7     -25.7       -26.9     -33.7     -38.2     6.9

  N+3           -11.1     -13.3       -16.1     -19.7     -28.2     5.8

  N+4           -8.1      -11.4       -13.1     -13.6     -27.0     5.9

  N+5           -2.6      -9.6        -11.1     -14.5     -25.5     7.1

  N+6           \> -1.7   -4.9        \> -6.4   -11.8     -15.2     \> 4.6

  N+7           -7.7      -14.8       -16.0     -23.0     -26.4     6.8

  N+8           \> -1.4   -3.0        \> -3.4   -4.8      -7.1      \> 2.0

  N+9           \> -1.4   -2.2        \> -2.8   -4.5      -5.9      \> 1.6

  N+10          \> -1.5   -3.0        \> -3.0   -4.9      -5.2      \> 1.4

  N+11          \> -1.8   \>-2.2      \> -2.8   -4.8      -4.9      \> 1.3

  N+12          \> -2.0   \>-2.3      \> -3.0   -5.0      -5.1      \> 1.3

  N+13          \> -2.1   \>-2.5      \> -3.0   -4.6      -4.8      \> 1.1

  N+14          \> -2.7   -7.7        \> -8.8   -15.1     -16.8     \> 5.2

  N+15          \> -3.1   -12.9       \> -12.0  -18.0     -19.3     \> 5.7

  N+16          \> -3.5   \>-3.8      \> -3.9   -4.5      -4.6      \> 0.4

  N-5/N-10      -18.2     -25.7       -24.4     -26.3     -30.8     4.2

  N-4/N-8       -21.7     -26.1       -25.6     -28.9     -29.8     3.1

  N-3/N-6       -22.8     -26.3       -27.4     -32.0     -35.0     4.1

  N-2/N-4       -16.7     -27.3       -28.7     -37.3     -38.5     6.9

  N-1/N-2       -28.8     -32.3       -33.2     -38.1     -40.7     4.1

  N+1/N+2       -28.3     -31.5       -31.9     -33.1     -39.0     3.4

  N+2/N+4       -25.7     -30.0       -30.8     -37.1     -39.1     5.1

  N+3/N+6       -17.0     -24.5       -24.0     -27.4     -34.1     5.8

  N+4/N+8       -17.2     -21.2       -22.0     -25.8     -28.4     4.2

  N+5/N+10      -15.6     -19.7       -20.1     -23.6     -25.5     3.2
  ------------- --------- ----------- --------- --------- --------- ------------

######### Desired Signal = -53 dBm

[]{#__RefHeading___Toc163024600 .anchor}Table A‑10. Threshold U
Statistics for 8 Receivers at D = -53 dBm on Channel 30

  ------------- --------- ----------- --------- --------- --------- ------------
  **Undesired   **Best U  **Median U  **Mean U  **2nd     **Worst U **Standard
  Channel**     (dBm)**   (dBm)**     (dBm)**   Worst U   (dBm)**   Deviation
                                                (dBm)**             (dB)**

  N-16          \> -0.8   -1.6        \> -2.5   -3.7      -7.3      \> 2.2

  N-15          \> -0.6   \>-1.1      \> -2.4   -4.0      -7.9      \> 2.5

  N-14          \> -0.3   \>-0.9      \> -2.4   -4.2      -8.5      \> 2.8

  N-13          \> -0.1   -1.1        \> -2.5   -4.1      -8.8      \> 2.9

  N-12          \> -0.1   -2.2        \> -2.9   -4.4      -9.4      \> 3.1

  N-11          \> -0.1   -2.0        \> -3.2   -6.3      -10.1     \> 3.5

  N-10          \> -0.1   -0.7        \> -2.5   -4.8      -10.7     \> 3.7

  N-9           \> -0.2   -0.8        \> -2.8   -4.9      -11.6     \> 3.9

  N-8           \> -0.4   -1.6        \> -3.5   -5.8      -12.8     \> 4.3

  N-7           \> -0.6   -2.5        \> -4.1   -7.3      -14.2     \> 4.7

  N-6           \> -0.9   -5.3        \> -7.3   -16.2     -20.5     \> 7.3

  N-5           \> -1.0   -1.4        \> -4.6   -9.2      -18.3     \> 6.2

  N-4           \> -1.1   -6.0        \> -7.3   -13.0     -20.8     \> 6.6

  N-3           \> -1.2   -3.8        \> -4.9   -7.8      -11.1     \> 3.3

  N-2           -4.0      -11.5       -13.2     -21.2     -25.7     7.1

  N-1           -13.1     -14.0       -14.6     -15.4     -18.6     1.8

  N+1           -11.0     -13.6       -13.6     -14.7     -17.1     1.9

  N+2           -6.2      -10.9       -12.4     -18.5     -22.7     6.3

  N+3           \> -2.1   -3.2        \> -6.2   -4.9      -27.9     \> 8.8

  N+4           \> -2.1   -2.9        \> -6.4   -7.9      -23.9     \> 7.4

  N+5           \> -1.8   -4.0        \> -6.3   -8.5      -21.1     \> 6.5

  N+6           \> -1.6   -2.2        \> -4.1   -6.7      -13.2     \> 4.1

  N+7           -1.8      -14.3       -14.2     -20.4     -26.1     8.0

  N+8           \> -1.4   \>-1.6      \> -2.1   -3.4      -4.3      \> 1.1

  N+9           \> -1.5   \>-1.7      \> -1.9   \>-1.8    -3.8      \> 0.8

  N+10          \> -1.6   \>-1.8      \> -1.9   \>-1.9    -3.2      \> 0.5

  N+11          \> -1.8   \>-2.0      \> -2.1   \>-2.1    -2.7      \> 0.3

  N+12          \> -1.8   \>-2.2      \> -2.2   \>-2.3    -2.6      \> 0.3

  N+13          \> -2.2   \>-2.5      \> -2.4   \>-2.6    \>-2.6    \> 0.2

  N+14          \> -2.6   \>-2.9      \> -2.8   \>-3.0    -3.1      \> 0.2

  N+15          \> -3.0   \>-3.3      \> -3.5   \>-3.4    -5.4      \> 0.8

  N+16          \> -3.5   \>-3.7      \> -3.7   \>-3.8    \>-3.8    \> 0.1

  N-5/N-10      -14.1     -19.4       -18.7     -20.8     -22.4     2.8

  N-4/N-8       -14.5     -18.5       -18.8     -20.5     -24.8     3.1

  N-3/N-6       -9.4      -15.6       -16.6     -20.5     -27.6     5.8

  N-2/N-4       -11.1     -14.8       -16.6     -24.4     -24.4     5.1

  N-1/N-2       -14.0     -17.1       -18.6     -25.6     -26.7     4.9

  N+1/N+2       -14.3     -17.6       -17.9     -19.7     -23.0     2.6

  N+2/N+4       -14.1     -17.8       -19.6     -21.6     -32.2     5.7

  N+3/N+6       -11.5     -18.8       -18.6     -23.1     -30.0     6.1

  N+4/N+8       -11.8     -17.2       -17.0     -19.4     -24.5     4.1

  N+5/N+10      -11.4     -14.8       -15.3     -18.7     -20.8     3.1
  ------------- --------- ----------- --------- --------- --------- ------------

######### Desired Signal = -28 dBm

[]{#__RefHeading___Toc163024601 .anchor}Table A‑11. Threshold U
Statistics for 8 Receivers at D = -28 dBm on Channel 30

  ------------- --------- ----------- --------- --------- --------- ------------
  **Undesired   **Best U  **Median U  **Mean U  **2nd     **Worst U **Standard
  Channel**     (dBm)**   (dBm)**     (dBm)**   Worst U   (dBm)**   Deviation
                                                (dBm)**             (dB)**

  N-16          \> -0.7   \>-0.8      \> -0.9   \>-1.1    \>-1.2    \> 0.2

  N-15          \> -0.6   \>-0.7      \> -0.8   \>-1.0    \>-1.1    \> 0.2

  N-14          \> -0.4   \>-0.5      \> -0.6   \>-0.8    \>-0.9    \> 0.2

  N-13          \> -0.2   \>-0.2      \> -0.4   \>-0.6    \>-0.6    \> 0.2

  N-12          \> -0.1   \>-0.2      \> -0.3   \>-0.6    \>-0.6    \> 0.2

  N-11          \> -0.1   \>-0.2      \> -0.3   \>-0.5    \>-0.6    \> 0.2

  N-10          \> -0.1   \>-0.2      \> -0.3   \>-0.6    \>-0.6    \> 0.2

  N-9           \> -0.3   \>-0.3      \> -0.4   \>-0.7    \>-0.7    \> 0.2

  N-8           \> -0.4   \>-0.5      \> -0.6   \>-0.8    \>-0.8    \> 0.2

  N-7           \> -0.6   \>-0.7      \> -0.8   \>-0.9    \>-1.0    \> 0.1

  N-6           \> -0.8   \>-0.9      \> -1.0   \>-1.1    \>-1.2    \> 0.1

  N-5           \> -0.9   \>-1.1      \> -1.1   \>-1.2    \>-1.3    \> 0.1

  N-4           \> -1.1   \>-1.1      \> -1.1   \>-1.2    \>-1.3    \> 0.1

  N-3           \> -1.2   \>-1.2      \> -1.2   \>-1.3    \>-1.4    \> 0.1

  N-2           \> -1.4   \>-1.5      \> -1.5   \>-1.5    \>-1.6    \> 0.1

  N-1           \> -7.2   \>-7.2      \> -7.2   \>-7.3    -7.3      \> 0.0

  N+1           \> -7.7   \>-7.8      \> -7.8   \>-7.8    -8.2      \> 0.1

  N+2           \> -1.9   \>-2.0      \> -2.0   \>-2.0    \>-2.0    \> 0.1

  N+3           \> -2.0   \>-2.1      \> -2.2   \>-2.2    -2.7      \> 0.2

  N+4           \> -2.0   \>-2.2      \> -2.2   \>-2.2    \>-2.2    \> 0.1

  N+5           \> -1.8   \>-2.0      \> -2.0   \>-2.0    \>-2.1    \> 0.1

  N+6           \> -1.5   \>-1.7      \> -1.7   \>-1.8    \>-1.8    \> 0.1

  N+7           \> -1.5   \>-1.6      \> -2.7   -4.1      -8.0      \> 2.3

  N+8           \> -1.4   \>-1.6      \> -1.6   \>-1.7    \>-1.7    \> 0.1

  N+9           \> -1.4   \>-1.7      \> -1.7   \>-1.8    \>-1.9    \> 0.2

  N+10          \> -1.5   \>-1.8      \> -1.8   \>-1.9    \>-2.0    \> 0.2

  N+11          \> -1.7   \>-2.1      \> -2.0   \>-2.1    \>-2.2    \> 0.2

  N+12          \> -1.9   \>-2.2      \> -2.2   \>-2.3    \>-2.4    \> 0.2

  N+13          \> -2.1   \>-2.5      \> -2.4   \>-2.6    \>-2.6    \> 0.2

  N+14          \> -2.5   \>-2.8      \> -2.8   \>-2.9    \>-3.0    \> 0.2

  N+15          \> -2.9   \>-3.3      \> -3.2   \>-3.4    \>-3.4    \> 0.2

  N+16          \> -3.5   \>-3.7      \> -3.7   \>-3.9    \>-3.9    \> 0.1

  N-5/N-10      NA        NA          NA        NA        NA        NA

  N-4/N-8       NA        NA          NA        NA        NA        NA

  N-3/N-6       NA        NA          NA        NA        NA        NA

  N-2/N-4       NA        NA          NA        NA        NA        NA

  N-1/N-2       \> -7.1   \>-7.2      \> -7.7   -8.7      -9.9      \> 1.0

  N+1/N+2       \> -7.7   \>-7.8      \> -8.3   -7.9      -11.7     \> 1.4

  N+2/N+4       NA        NA          NA        NA        NA        NA

  N+3/N+6       NA        NA          NA        NA        NA        NA

  N+4/N+8       NA        NA          NA        NA        NA        NA

  N+5/N+10      NA        NA          NA        NA        NA        NA
  ------------- --------- ----------- --------- --------- --------- ------------

#######  THEORETICAL BASIS FOR OUT-OF-CHANNEL INTERFERENCE

When a DTV receiver operates in the presence of white Gaussian
*[co-channel]{.underline}* interference, the threshold of visibility
(TOV) of picture degradation occurs when the desired signal power D
exceeds the co-channel interference by about 15 dB.[^85] This number may
vary somewhat for noise having other statistical properties, and may be
much lower if the noise is heavily concentrated at a band edge where
filtering in the DTV provides additional rejection; nonetheless, one
expects that, as signal power D varies, the undesired signal power at
threshold will vary linearly with it---resulting a constant D/U ratio as
D or U are varied. This relationship holds whenever the co-channel
interference is high enough that the effect of internal noise in the
receiver becomes insignificant.

For most *[out-of-channel]{.underline}* interference mechanisms, the DTV
receiver unintentionally converts a small portion of the out-of-channel
power into co-channel power. If one knows the amount of conversion into
co-channel interference, one can treat the problem as a co-channel
interference problem, which is relatively well understood, as described
above. In this formulation of the problem, measuring the desired signal
power D at the TOV provides an indirect method of measuring the
co-channel power created internal to the receiver, since we know that
the co-channel power will be about 15 dB below the measured value of D.

The conversion process by the DTV from out-of-channel interference to
co-channel interference may be linear or nonlinear. If it is linear,
then the internally-created co-channel interference will vary linearly
with the out-of-channel interference power U causing the value of the
desired signal power D at threshold to vary linearly with U. The result
will be that threshold D/U ratio will be constant as D or U is varied.
If the conversion process is nonlinear, then the relationship between D
and U will be nonlinear and the D/U ratio will vary with D and U.

We will assume that the *[co-channel]{.underline}* interference power
created by the DTV receiver in response to an
*[out-of-channel]{.underline}* undesired signal power U will be
proportional to D^L^U^M^, where L and M are integer constants that
define the ***[order]{.underline}*** of the interference mechanism. For
most interference mechanisms, L will be zero, so only the U^M^ term
exists. The following are among the interference mechanisms that can be
modeled by this formulation.

5.  Linear interference: L=0, M=1. Creates co-channel interference
    proportional to U.

    1.  Example: mixer image. The mixer in a TV receiver converts the
        spectrum of the intended channel of the received signal to an
        intermediate frequency (IF) where it can be filtered more
        precisely to pass the desired channel while rejecting the
        undesired frequencies. Unfortunately, in single-conversion
        tuners a second a 6-MHz wide portion of the input spectrum
        centered 88 MHz above the desired channel is also converted to
        that same IF. Filtering prior to the mixer strongly
        diminishes---but doesn't fully extinguish---this unintended
        signal.

    2.  Example: leakage of the adjacent channel signal through the
        channel selection filter of the DTV would also constitute a
        linear interference mechanism.

6.  Second-order interference: L=0, M=2. Creates co-channel interference
    proportional to U^2^.

    1.  Example: "half-IF" taboo. The second harmonic of an undesired
        signal 22 MHz above the desired signal beats with the second
        harmonic of the receiver's local oscillator, creating a
        difference frequency that falls within the IF band of the
        receiver.

7.  Third-order interference: L=0, M=3. Creates co-channel interference
    proportional to U^3^.

    1.  Example: third-order intermodulation (IM3) of a single,
        adjacent-channel undesired signal. IM3 creates spectral
        components that spill into each adjacent channel.

    2.  Example: third-order intermodulation (IM3) of a pair of
        undesired channels placed at channels N+K and N+2K where N is
        the desired channel. In this case, the interference power
        created in channel N is proportional to U~N+K~^2^U~N+2K~. The
        result is a process that is second-order in terms of U~N+K~ and
        linear in terms of U~N+2K~; however, if the two undesired
        signals are set to equal powers and varied in amplitude
        together, the resulting interference is third order.

8.  Cross-modulation: L=1, M=2. Creates co-channel interference
    proportional to DU^2^.

    1.  Cross-modulation is essentially a third-order effect, but the
        co-channel interference created is proportional to D and to
        U^2^. As a result, increasing the desired signal power does not
        improve the signal-to-interference ratio.

We define the following:

D = Power of desired signal on channel N at input to TV

U~N+K~ = Power of interferer on channel N+K at input to TV

U~N+2K~ = Power of interferer on channel N+2K at input to TV

where D, U~N+K~, and U~N+2K~ refer to signal level combinations that
place the TV at TOV

R = Required SNR of the TV receiver at TOV

D~MIN~ = D at TOV in absence of interference or external noise

N~R~ = Receiver noise referred to the input of the TV

Thus,

R = D~MIN~/N~R~

N~R~ = D~MIN~/R

Consequently, N~R~ can be inferred from measurements of D~MIN~ and R

Let

P~CC~ = Total power of co-channel noise and interference affecting the
demodulation of the DTV signal by the TV, referenced to the input. P~CC~
includes co-channel interference created by non-linear effects in the
TV.

We will consider two cases. That of a single interferer with power U,
where

P~CC~ = N~R~ + c U^M^ D^L^

And that of third-order intermodulation (IM) between a pair of signals
U~N+K~, and U~N+2K~

P~CC~ = N~R~ + c~IM3~ U~K~^2^ U~2K~

The "c" terms are constants related to the nonlinear process in the
receiver. The 1st term in each equation is receiver noise. The second is
the interference term created by distortion in the TV tuner. The terms M
and L define the order of the nonlinear interference process with
respect to the undesired and desired signals, respectively.

We start with the case of a single interferer.

######## Single Interferer

We have

P~CC~ = N~R~ + c U^M^ D^L^

We will generally be interested in three cases:

1.  Linear interference mechanisms: M = 1; L = 0

2.  2^nd^-order interference mechanisms: M = 2; L = 0

3.  3^rd^-order interference mechanisms: M = 3; L = 0

4.  Cross-modulation: M = 2; L = 1

At TOV the desired signal must exceed P~CC~ by a factor equal to the
required signal-to-noise ratio R. (We assume that the same value of R
applies for both receiver noise and noise created by an undesired
signal.) Thus

D/P~CC~ = R, or, equivalently,

D = R P~CC~

Substituting, we have

D = R (N~R~ + c U^M^ D^L^)

Substituting N~R~ = D~MIN~/R, we have

D = R c D^L^U^M^ + D~MIN~

U^M^ = (D - D~MIN~) / (R c D^L^)

And, finally,

U = \[(D - D~MIN~) / (R c D^L^)\]^1/M^

We will also find it useful to write this as

U = D^(1-L)/M^ \[(1 - D~MIN~/D) / (R c)\]^1/M^

######### High Signal Levels (D \>\> DMIN)

When D \>\> D~MIN~, the equation simplifies to

U ≈ \[D^1-L^ / (R c)\]^1/M^

U ≈ D^(1-L)\ /\ M^ / (R c)^1/M^

Similarly, D/U at threshold is given by

D/U ≈ D/\[ D^(1-L)\ /\ M^ / (R c)^1/M^\]

D/U ≈ (R c)^1/M^ D^(M\ --\ 1\ +\ L)/M^

Now we wish to view U and D in log-based units, such as decibels.

log(U) ≈ log\[D^(1-L)\ /\ M^ / (R c)^1/M^\] = \[(1 -- L)/M\] log(D) --
(1/M) log(R c)

log(D/U) ≈ log\[(R c)^1/M^ D^(M\ --\ 1\ +\ L)/M^\] = \[(M -- 1 + L)/M\]
log(D) + (1/M) log(R c)

Thus a log-log plot of U versus D will be a straight line, with slope (1
-- L) / M. Similarly, the slope of log-D versus log-U will be M / (1 --
L), and the slope of log(D/U) versus log-D is given by

\[(M -- 1 + L)/M\].

Table A-1 summarizes this slope information for the interference
mechanisms of interest.

[]{#__RefHeading___Toc163024602 .anchor}Table B‑12. Slopes of Log-Log
Plots of D, U, and D/U for Various Interference Mechanisms

+------------------------------+------------+------------+------------+
| **Interference Mechanism**   | **Slope    | **Slope    | **Slope    |
|                              | of\        | of\        | of\        |
|                              | Log (D)    | Log (U)    | Log (D/U)  |
|                              | Versus**   | Versus**   | Versus**   |
|                              |            |            |            |
|                              | **Log (U)\ | **Log (D)\ | **Log (D)\ |
|                              | in dB/dB** | in dB/dB** | in dB/dB** |
+------------------------------+------------+------------+------------+
| Linear (M = 1, L = 0)        | 1          | 1          | 0          |
+------------------------------+------------+------------+------------+
| Second order (M = 2, L = 0)  | 2          | 0.5        | 0.5        |
+------------------------------+------------+------------+------------+
| Third order (including       | 3          | 0.333      | 0.667      |
| third-order intermodulation  |            |            |            |
| of a pair of equal-power     |            |            |            |
| interferers) (M = 3, L = 0)  |            |            |            |
+------------------------------+------------+------------+------------+
| Cross modulation (M = 2, L = | Infinite   | 0          | 1          |
| 1)                           |            |            |            |
+------------------------------+------------+------------+------------+

######### Low Signal Levels

The interference mechanisms described above are expected to result in
linear relationships between log-U and log-D at threshold when the
desired signal level is high enough that receiver noise is
insignificant. Now we consider the case of smaller signal levels. Recall
that

U = \[(D - D~MIN~) / (R c D^L^)\]^1/M^

Note that the presence of receiver noise (causing D~MIN~ to be non-zero
and the log-U versus log-D relationship to deviate from a straight line)
results in U changing by a factor of

\[(D - D~MIN~) / D\]^1/M^

Consider the case where D is X dB above D~MIN~. Then U is Y dB above the
value it would have had based on a straight-line log-log projection from
the results at a high desired signal level.

X = 10 log(D / D~MIN~)

Y = 10 log{(D - D~MIN~) / D\]^1/M^ }

Y = (1/M) 10 log\[1 -- 10^-X/10^\] dB

Table B-2 summarizes these results for three values of X.

[]{#__RefHeading___Toc163024603 .anchor}Table B‑13. Deviation in
Threshold U from Straight-Line Projection as D Approaches D~MIN~

+------------------------------+----------+--------+---------+--------+
|                              | **D      |        |         |        |
|                              | eviation |        |         |        |
|                              | in       |        |         |        |
|                              | T        |        |         |        |
|                              | hreshold |        |         |        |
|                              | U**      |        |         |        |
|                              |          |        |         |        |
|                              | **from   |        |         |        |
|                              | Strai    |        |         |        |
|                              | ght-Line |        |         |        |
|                              | Pr       |        |         |        |
|                              | ojection |        |         |        |
|                              | (dB)**   |        |         |        |
+------------------------------+----------+--------+---------+--------+
| **Interference Mechanism**   | **D/D~   | **D/D  | **D/    | **D/D  |
|                              | MIN~^1^\ | ~MIN~\ | D~MIN~\ | ~MIN~\ |
|                              | = 16     | = 3    | = 1     | = 0    |
|                              | dBm**    | dB**   | dB**    | dB**   |
+------------------------------+----------+--------+---------+--------+
| Linear (M = 1)               | -0.11    | -3.02  | -6.87   | In     |
|                              |          |        |         | finite |
+------------------------------+----------+--------+---------+--------+
| Second order (M = 2)         | -0.06    | -1.51  | -3.43   | In     |
|                              |          |        |         | finite |
+------------------------------+----------+--------+---------+--------+
| Third order (including       | -0.04    | -1.01  | -2.29   | In     |
| third-order intermodulation  |          |        |         | finite |
| of a pair of equal-power     |          |        |         |        |
| interferers) (M = 3)         |          |        |         |        |
+------------------------------+----------+--------+---------+--------+
| Cross modulation (M = 2, L = | -0.06    | -1.51  | -3.43   | In     |
| 1)                           |          |        |         | finite |
+------------------------------+----------+--------+---------+--------+

> *Note:*
>
> *^1^ For the nominal D~MIN~ value of -84 dBm, D/D~MIN~ = 16 dB when D
> = -68 dBm*

######### Effect of AGC

The above relationships are expected to hold when automatic-gain-control
(AGC) does not cause changes in gain between the TV antenna port and the
point in the TV tuner at which the ***[relevant
nonlinearity]{.underline}*** occurs (*i.e.*, the location of the
nonlinearity that causes the observed interference, assuming it is
caused by a nonlinearity).

When either the desired signal power (D) or an undesired signal (U)
rises sufficiently that AGC causes gain reductions *prior to the point
of a relevant nonlinearity*, the relationships change.

We define the following terms:

G = power gain from the antenna input terminal of the TV to the point of
a relevant nonlinearity;

G~MAX~ = the value of G when both D and U are low enough that AGC does
not reduce the gain of any tuner stages prior to the nonlinearity;

In a television, AGC operation may be invoked based on increasing levels
of either the desired signal D on channel N or of some filtered
combination of desired and undesired signals.[^86] In modeling AGC, we
will assume that, if the AGC reduces gain of a tuner stage prior to the
point of the relevant nonlinearity, it will do so in such a way as to
achieve a constant power level with changes input signal level.
Specifically, the power which is maintained constant by AGC action will
be either the desired signal or the total power of some filtered
combination of desired and undesired signals (as in the case of
"broadband AGC"). We will consider two bounding cases:

1.  AGC driven by D. AGC adjusts gain in such a way that the level of
    the *desired* signal at the point of the nonlinearity remains
    constant;

2.  AGC driven by U~N+K~. AGC is controlled by a filtered combination of
    desired and undesired signals, but with undesired signal at the AGC
    sensing point being much larger than the desired signal, so that the
    AGC adjusts gain to, in effect, maintain a constant *undesired*
    signal power at the point of the relevant nonlinearity.

For each of these two cases, we define a signal level threshold above
which the AGC reduces the gain of tuner stages prior to the point of the
relevant nonlinearity:

D~AGCthresh~ = the desired signal power at the TV input, above which AGC
begins reducing G;

U~N-K,AGCthresh~ = the undesired signal power on channel N+K, above
which AGC begins reducing G.

Thus, in the first case, we will assume that the AGC reduces gain by 1
dB for each 1-dB increase in D above D~AGCthresh~. In the second case we
assume that AGC reduces gain by 1 dB for each 1-dB increase in U beyond
U~N-K,AGCthresh~.

In the single-interferer case, recall that the total co-channel noise
plus interference that seen by the receiver, referenced to input levels,
is

P~CC~ = N~R~ + c U~N+K~^M^ D^L^

We note that this formula applies when gain prior to the relevant point
of nonlinearity is at its maximum (G = G~MAX~)---*i.e.*, the AGC hasn't
caused any gain reductions. Thus, the formula is valid only when D \<
D~AGCthresh~ and U~K~ \< U~K-AGCthresh~. If either AGC threshold is
exceed, G is reduced and the formula is no longer valid. We include the
N+K subscript on U to emphasize that the AGC threshold will be different
for different channel offsets because of filtering in the receiver.

It should be recognized that the terms U~N+K~^M^ and D^L^ describe
nonlinear behavior at some point in the TV tuner---perhaps at the mixer,
or at the output of the IF amplifier. Thus, we could more correctly
describe the nonlinearity in terms of signal levels at this point in the
TV tuner. If we use bold italicized terms to represent desired signal
power, undesired signal power, and receiver noise referred to the point
of nonlinearity in the tuner, we can rewrite the equation as follows:

***P~CC~*** = ***N~R~*** + ***c~1~*** ***U~N+K~***^M^ ***D***^L^ when G
= G~MAX~

where

***P~CC~*** = G P~CC~

***N~R~*** = G N~R~

***c~1~*** = a new constant describing the nonlinearity in terms of
levels at the point of nonlinearity, instead of at referenced to the
input

***U~N+K~*** = G U~N+K~

***D*** = G D

Performing substitutions, we have

G P~CC~ = G N~R~ + ***c~1~*** (G U~N+K~)^M^ (G D)^L^

G P~CC~ = G N~R~ + ***c~1~*** G^M+L^ U~N+K~^M^ D^L^

P~CC~ = N~R~ + ***c~1~*** G^M+L-1^ U~N+K~^M^ D^L^

P~CC~ = N~R~ + ***c~1~*** G~MAX~^M+L-1^ (G/G~MAX~)^M+L-1^ U~N+K~^M^ D^L^

When G = G~MAX~, this formula must be equivalent to the previous
version:

P~CC~ = N~R~ + c U~N+K~^M^ D^L^ when G = G~MAX~

Thus, it is clear that the relationship between the nonlinearity
constant defined referenced to the input and that defined referenced to
the point of the nonlinearity is

c = ***c~1~*** G~MAX~^M+L-1^

Consequently, we will rewrite the new formula as follows:

P~CC~ = N~R~ + c (G/G~MAX~)^M+L-1^ U~N+K~^M^ D^L^

At threshold, P~CC~ = D/R; also R N~R~ = D~MIN~. So we have

D = R \[N~R~ + c (G/G~MAX~)^M+L-1^ U~N+K~^M^ D^L^

D = D~MIN~ + R c (G/G~MAX~)^M+L-1^ U~N+K~^M^ D^L^

[AGC Driven By D]{.underline}

We first consider the case in which the *[desired]{.underline}* signal
reaches a sufficient level to cause AGC gain reductions before the point
of the relevant nonlinearity. We assume that

G/G~MAX~ = 1, when D ≤ D~AGCthresh~, and

= D~AGCthresh~/D, when D \> D~AGCthresh~

Thus, for the case of D \> D~AGCthresh~, we have

D = D~MIN~ + R c (D~AGCthresh~/D)^M+L-1^ U^M^ D^L^\]

D - D~MIN~ = R c D~AGCthresh~^M+L-1^ U^M^ D^-M+1^\]

U^M^ = (D - D~MIN~) D^M-1^ /(R c D~AGCthresh~^M+L-1^)

U = \[(D - D~MIN~) D^M-1^ /(R c D~AGCthresh~^M+L-1^)\]^1/M^

U = \[(D - D~MIN~) D^M^ /(R c D D~AGCthresh~^M+L-1^)\]^1/M^

U = D \[(D - D~MIN~) /(R c D D~AGCthresh~^M+L-1^)\]^1/M^

U = D \[(1 - D~MIN~/D) /(R c D~AGCthresh~^M+L-1^)\]^1/M^

We recall and rearrange the original formula that applies when there are
no AGC gain reductions,

U = \[(D - D~MIN~) / (R c D^L^)\]^1/M^

U = D^(1-L)/M^ \[(1 - D~MIN~/D) / (R c)\]^1/M^

We now combine this with the case of no AGC gain changes.

+-----------------------------------------------------------------------+
| With AGC operation driven by desired signal level,                    |
|                                                                       |
| U = D \[(1 - D~MIN~/D) /(R c D~AGCthresh~^M+L-1^)\]^1/M^, when D \>   |
| D~AGCthresh~ (*i.e.*, AGC operating)                                  |
|                                                                       |
| D^(1-L)/M^ \[(1 - D~MIN~/D\] / (R c)\]^1/M^, when D ≤ D~AGCthresh~    |
| (*i.e.*, no AGC operation)                                            |
+-----------------------------------------------------------------------+

Consider the case when D \>\> D~MIN~. The formula becomes,

U ≈ D \[1 / (R c D~AGCthresh~^M+L-1^)\]^1/M^, when D \> D~AGCthresh~
(*i.e.*, AGC operating)

D^(1-L)/M^ / (R c)^1/M^, when D ≤ D~AGCthresh~ (*i.e.*, no AGC
operation)

Notice that the first formula (for use when the AGC is operating) is
linear in D. *I.e.*, the threshold undesired signal is directly
proportional to the desired signal level. This means that, at signal
levels D \>\> D~MIN~, the interference behaves as if it is linear, even
though the underlying mechanism is nonlinear. ***For D \>\> D~MIN~, once
D exceeds the AGC threshold for gain adjustments prior to the point of
the relevant nonlinearity, D/U ratio remains constant with further
increases in D. Beyond this AGC threshold, the interference behaves as
if it derives from a linear mechanism, even though the actual
interference mechanism may be nonlinear**.*

The above statement applies to D \>\> D~MIN~. We now examine further the
case of small signal levels.

U = D \[(1 - D~MIN~/D) /(R c D~AGCthresh~^M+L-1^)\]^1/M^, when D \>
D~AGCthresh~ (*i.e.*, AGC operating)

Or

U = D (1 - D~MIN~/D)^1/M^ / (R c D~AGCthresh~^M+L-1^)^1/M^, when D \>
D~AGCthresh~ (*i.e.*, AGC operating)

We can see that the presence of receiver noise (causing non-zero D~MIN~)
causes the undesired signal threshold U to change by a factor of

(1 - D~MIN~/D)^1/M^, when D \> D~AGCthresh~ (*i.e.*, AGC operating)

***The effect of receiver noise on threshold U is the same result that
was obtained when D was below the AGC threshold.***

[AGC Driven by U]{.underline}

Now consider the case in which the *[undesired]{.underline}* signal
reaches a sufficient level to cause AGC gain reductions before the point
of the relevant nonlinearity. We assume that

G/G~MAX~ = 1, when U~N+K~ ≤ U~N+K-AGCthresh~, and

= U~N+K,AGCthresh~/U~N+K~, when U~N+K~ \> U~N+K-AGCthresh~

Thus, for the case U~N+K~ \> U~N+K,AGCthresh~, we have

D = D~MIN~ + R c (G/G~MAX~)^M+L-1^ U~N+K~^M^ D^L^

Substituting for G/G~MAX~,

D = D~MIN~ + R c (U~N+K,AGCthresh~/U~N+K~)^M+L-1^ U~N+K~^M^ D^L^

Rearranging,

D - D~MIN~ = R c U~N+K,AGCthresh~^M+L-1^ U~N+K~^1-L^ D^L^

U~N+K~^1-L^ = (D - D~MIN~) / \[R c U~N+K,AGCthresh~^M+L-1^ D^L^\]

There is no solution when L = 1, the cross-modulation case. For other
cases, where L = 0,

U~N+K~ = (D - D~MIN~) / \[R c U~N+K,AGCthresh~^M-1^\]

We now combine this with the case of no AGC gain changes.

+-----------------------------------------------------------------------+
| With AGC operation driven by the undesired signal level,              |
|                                                                       |
| U~N+K~ = (D - D~MIN~) / (R c U~N+K,AGCthresh~^M-1^), when U~N+K~ \>   |
| U~N+K,AGCthresh~, (*i.e.*, AGC operating), L = 0;                     |
|                                                                       |
| D^(1-L)/M^ \[(1 - D~MIN~/D\] / (R c)\]^1/M^, when U~N+K~ ≤            |
| U~N+K,AGCthresh~ (*i.e.*, no AGC operation)                           |
+-----------------------------------------------------------------------+

By requiring that L = 0, we are excluding the case of cross-modulation
from the solution when the AGC is operating on undesired signal level.
Recall that, for large desired signal levels well above D~MIN~, the
solution to the no-AGC cross-modulation case is a fixed value of U,
independent of D, because the co-channel interference power created by
the TV tuner is directly proportional to D; a 1-dB increase in D causes
a 1-dB increase in co-channel interference power, so changing D doesn't
get you closer to, or take you further from, the TOV. If we consider the
case with AGC driven by undesired signal, our hypothesis is that the AGC
acts to keep the power of the *undesired* signal at a fixed level at the
point of the nonlinearity by driving down the gain as the undesired
signal at the input increases. The net effect, then, of a 1-dB increase
in undesired signal at the input will be that the undesired signal power
at the point of nonlinearity remains constant, but the power of the
desired signal at that point decreases. As we described above, such a
change does not move the operating point either closer to, or further
from, the TOV. Rather, whether the TV operates error free will depend
only on whether the AGC threshold is above or below the TOV threshold
for U that results from the cross-modulation process.

Note that, in the formula that applies when AGC is operating, we find
that U is directly proportional to D if D \>\> D~MIN~. Thus, the AGC
operation causes the interference to act as if it were linear, even if
the underlying mechanism is nonlinear.

At low signal levels, the effect of receiver noise is identical to that
for a linear process.

***Except in the case of cross-modulation, AGC operation that is driven
by [undesired]{.underline} signal level causes the interference to
behave as if it were created by a linear process. This conclusion
applies both to the slope of log-U versus log-D at high signal levels,
and to the deviation from that straight-line log-log curve at low signal
levels.***

######## IM3 With Paired Signals {#im3-with-paired-signals-1 .unnumbered}

When a pair of undesired signals placed on channels N+K and N+2K,
nonlinearities in the receiver can create third-order intermodulation
products in the desired channel N.

If the undesired signals are set to equal amplitudes (U = U~N+K~ =
U~N+2K~), then the results are identical to the third-order interference
case described above. More generally, we substitute U~N+K~^2^ U~N+2K~
for U^3^ in those formulas.

D = R (N~R~ + c U~N+K~^2^ U~N+2K~)

D = D~MIN~ + R c U~N+K~^2^ U~N+2K~

If the two undesired signals have equal power (U = U~N+K~ = U~N+2K~) and
D \>\> D~MIN~ so that receiver noise is insignificant, the equation
simplifies to

D = R c U^3^

Or,

D/R = c U^3^ = IM3 power referred to the input of the TV receiver.

Rhodes and Sgrignoli point out that IM3 is often computed in terms of
the third-order intercept power (IP3) for an amplifier or receiver.[^87]
In decibel units, this is written as

IM3\|~dB~ = 3 U\|~dB~ -- 2 IP3\|~dB~

In linear power units, the equation can be rewritten as

IM3 = U^3^ / IP3^2^

Using this in our equation,[^88]

D/R = c U^3^ = IM3 = U^3^ / IP3^2^

In this form we see that our constant c is equal to 1/ IP3^2^ and our
original equation (when receiver noise is insignificant) becomes

D = (R / IP3^2^) U~N+K~^2^ U~N+2K~

Given measurements at threshold for D and U, along with knowledge of the
required SNR of the DTV receiver (R), we could compute IP3 as follows
(when the two undesired signals are equal):

IP3 = (R U^3^ / D)^1/2^

Rather than do this, we will group the IP3 and R terms.

IP3 / R^1/2^ = (U^3^ / D)^1/2^

+-----------------------------------------------------------------------+
| IP3 / R^1/2^ = (U^3^ / D)^1/2^                                        |
|                                                                       |
| or, in decibel units,                                                 |
|                                                                       |
| (IP3 / R^1/2^)\|~dB~ = 1.5 U\|~dB~ - 0.5 D\|~dB~                      |
+-----------------------------------------------------------------------+

Once we know IP3 / R^1/2^, we can use it in our original, more general
equation.

D = D~MIN~ + R c U~N+K~^2^ U~N+2K~

D = D~MIN~ + U~N+K~^2^ U~N+2K~ / (IP3 / R^1/2^)^2^

If we know one of the two undesired signals, we can determine the
threshold value of the other from:

U~N+K~^2^ U~N+2K~ = (IP3 / R^1/2^)^2^ (D - D~MIN~)

+-----------------------------------------------------------------------+
| U~N+K~ = (IP3 / R^1/2^) (D - D~MIN~)^1/2^ / U~N+2K~^1/2^              |
|                                                                       |
| U~N+2K~ = (IP3 / R^1/2^)^2^ (D - D~MIN~) / U~N+K~^2^                  |
+-----------------------------------------------------------------------+

If D \>\> D~MIN~, then the equations can be converted to dB as follows:

+-----------------------------------------------------------------------+
| U~N+K~\|~dB~ = (IP3 / R^1/2^)\|~dB~ + (D\|~dB~ - U~N+2K~\|~dB~) / 2   |
|                                                                       |
| U~N+2K~\|~dB~ = 2 (IP3 / R^1/2^)\|~dB~ + D\|~dB~ - 2 U~N+K~\|~dB~     |
+-----------------------------------------------------------------------+

######### AGC With Paired-Signal IM3

We consider the case of AGC operating in such a way as to maintain one
of the two undesired signals at a constant power level at the point of
the nonlinearity that causes the observed IP3.

We begin with AGC operation based on the power of the first of the two
undesired signals. We assume that

G/G~MAX~ = 1, when U~N+K~ ≤ U~N+K-AGCthresh~, and

= U~N+K,AGCthresh~/U~N+K~, when U~N+K~ \> U~N+K-AGCthresh~

Thus, for the case U~N+K~ \> U~N+K,AGCthresh~, we have

D = D~MIN~ + (G/G~MAX~)^2^ U~N+K~^2^ U~N+2K~ / (IP3 / R^1/2^)^2^

Substituting for G/G~MAX~,

D = D~MIN~ + (U~N+K,AGCthresh~/U~N+K~)^2^ U~N+K~^2^ U~N+2K~ / (IP3 /
R^1/2^)^2^

Rearranging,

D - D~MIN~ = (U~N+K,AGCthresh~)^2^ U~N+2K~ / (IP3 / R^1/2^)^2^

***Thus when the AGC is driven by the power of U~N+K~, the desired
signal power at threshold is linearly related to the power of the second
undesired signal U~N+2K~ and independent of the power of first undesired
signal power U~N+K~. At a constant desired signal power, the threshold
of U~N+2K~ is constant---independent of U~N+K~.***

Now we consider the case of AGC operation based on the power of the
second undesired signal. We assume that

G/G~MAX~ = 1, when U~N+2K~ ≤ U~N+2K-AGCthresh~, and

= U~N+2K,AGCthresh~/U~N+2K~, when U~N+2K~ \> U~N+2K-AGCthresh~

Thus, for the case U~N+2K~ \> U~N+2K,AGCthresh~, we have

D = D~MIN~ + (G/G~MAX~)^2^ U~N+K~^2^ U~N+2K~ / (IP3 / R^1/2^)^2^

Substituting for G/G~MAX~,

D = D~MIN~ + (U~N+2K,AGCthresh~/U~N+2K~)^2^ U~N+K~^2^ U~N+2K~ / (IP3 /
R^1/2^)^2^

Rearranging,

D - D~MIN~ = (U~N+2K,AGCthresh~)^2^ (U~N+K~^2^ / U~N+2K~) / (IP3 /
R^1/2^)^2^

***Recall that, for values below the AGC threshold, each 1-dB increase
in the power of U~N+2K~ causes a 0.5 dB decrease in the undesired signal
power that can be tolerated on U~N+K~ for a given desired signal power.
When the AGC is driven by the power of U~N+2K~, this trend reverses
above the AGC threshold. At constant a desired signal power, each 1 dB
increase in U~N+2K~ above the AGC threshold causes a 0.5‑dB increase in
the undesired signal power that can be tolerated on channel N+K.***

######## Summary

######### Single Undesired Signals

Interference creating by linear or non-linear effects within a TV
receiver acting on incoming signals has been modeled as a conversion of
the incoming signals into co-channel interference with a power
proportional to D^L^ U^M^, where D and U represent the desired and
undesired signal powers, respectively, at the input to the TV receiver.
The model has been developed for the following types of interference
mechanisms:

1.  Linear (M = 1; L = 0)

2.  Second-order (M = 2; L = 0)

3.  Third-order (M = 3; L = 0)

4.  Cross-modulation (M = 2; L = 1)

The model includes the effects of receiver noise at low signal levels.

The basic model applies to the case in which no AGC-induced gain changes
occur between the input of the receiver and the point in the tuner at
which the interference mechanism is created (usually a nonlinearity).
The model is then extended to include the changed behavior that occurs
when AGC acts to reduce gain prior to the point at which the
interference is created. The AGC model assumes that, for signal levels
above a certain threshold, the gain will be adjusted in such a way as to
maintain a constant signal level at the point at which the interference
is created. In practice, that constant signal level assumption may apply
to the desired signal power D or to a filtered sum of desired and
undesired signal powers. The AGC model considers two bounding cases of
such operation:

3.  AGC driven by *desired* signal power. AGC adjusts gain in such a way
    that the level of the desired signal at the point of the
    nonlinearity remains constant;

4.  AGC driven by undesired signal power. Here we assumed that the AGC
    is controlled by a filtered combination of desired and undesired
    signals, but with undesired signal at the AGC-sensing point being
    much larger than the desired signal, so that the AGC adjusts gain
    to, in effect, maintain a constant *undesired* signal power at the
    point of the relevant nonlinearity.

Relevant formulas for undesired signal power at TOV are:

U~N+K~ = D^(1-L)/M^ \[(1 - D~MIN~/D) / (R c)\]^1/M^, when D ≤
D~AGCthresh~ and U~N+K~ ≤ U~N+K,AGCthresh~ (*i.e.*, no AGC operation)

U~N+K~ = D \[(1 - D~MIN~/D) /(R c D~AGCthresh~^M+L-1^)\]^1/M^, when D \>
D~AGCthresh~ (*i.e.*, AGC operating to keep desired signal constant at
the point in the receiver at which the interference is created)

U~N+K~ = (D - D~MIN~) / (R c U~N+K,AGCthresh~^M-1^), when U~N+K~ \>
U~N+K,AGCthresh~ (*i.e.*, AGC operating to keep the undesired signal
power constant at the point in the receiver at which the interference is
created) and L = 0 (*i.e.*, the formula does not apply to
cross-modulation).

where,

D = Power of desired signal on channel N at input to TV

U = Power of the undesired, out-of-channel signal at channel N+K at
input to TV

(D and U refer to signal level combinations that place the TV at TOV)

R = Required SNR by TV at TOV

D~MIN~ = Desired signal at TOV in absence of interference or external
noise

c = a constant describing the interference mechanism

When operating well above the minimum desired signal level that a TV can
demodulate (in the absence of interference), the interference model
predicts that a log-log plot of undesired signal power (U) versus
desired signal power (D) or a log-log plot of D/U ratio versus desired
signal power (D) (*i.e.*, plots in units of decibels) will be linear,
with a slope determined by the interference mechanism and the AGC
operation. The slopes are summarized in Table B-4.

[]{#__RefHeading___Toc163024604 .anchor}Table B‑14. Slopes of Log-Log
Plots of D, U, and D/U for Various Interference Mechanisms

+-------------------------+---------+---------+---------+-------------+
| **Interference          | **Slope | **Slope | **Slope | **Charact   |
| Mechanism**             | of\     | of\     | of\     | erization** |
|                         | Log     | Log (U) | Log     |             |
|                         | (D)**   | V       | (D/U)   |             |
|                         |         | ersus** | V       |             |
|                         | **V     |         | ersus** |             |
|                         | ersus** | **Log   |         |             |
|                         |         | (D)\    | **Log   |             |
|                         | **Log   | in      | (D)\    |             |
|                         | (U)\    | dB/dB** | in      |             |
|                         | in      |         | dB/dB** |             |
|                         | dB/dB** |         |         |             |
+-------------------------+---------+---------+---------+-------------+
| Linear (M = 1)          | 1       | 1       | 0       | Constant    |
|                         |         |         |         | D/U         |
+-------------------------+---------+---------+---------+-------------+
| Second order (M = 2)    | 2       | 0.5     | 0.5     |             |
+-------------------------+---------+---------+---------+-------------+
| Third order (including  | 3       | 0.333   | 0.667   |             |
| third-order             |         |         |         |             |
| intermodulation of a    |         |         |         |             |
| pair of equal-power     |         |         |         |             |
| interferers) (M = 3)    |         |         |         |             |
+-------------------------+---------+---------+---------+-------------+
| Cross modulation (M =   | I       | 0       | 1       | Constant U  |
| 2, L = 1)               | nfinite |         |         |             |
+-------------------------+---------+---------+---------+-------------+
| AGC-Stabilized          | 1       | 1       | 0       | Constant    |
| Nonlinear               |         |         |         | D/U         |
+-------------------------+---------+---------+---------+-------------+

As desired signal power approaches D~MIN~, the threshold of the receiver
in the absence of interference, the undesired signal deviates from the
log-log straight line by amounts shown in Table B-4.

[]{#__RefHeading___Toc163024605 .anchor}Table B‑15. Deviation in
Threshold U from Straight-Line Projection as D approaches D~MIN~

+------------------------------+----------+--------+---------+--------+
|                              | **D      |        |         |        |
|                              | eviation |        |         |        |
|                              | in       |        |         |        |
|                              | T        |        |         |        |
|                              | hreshold |        |         |        |
|                              | U**      |        |         |        |
|                              |          |        |         |        |
|                              | **from   |        |         |        |
|                              | Strai    |        |         |        |
|                              | ght-Line |        |         |        |
|                              | Pr       |        |         |        |
|                              | ojection |        |         |        |
|                              | (dB)**   |        |         |        |
+------------------------------+----------+--------+---------+--------+
| **Interference Mechanism**   | **D/D~   | **D/D  | **D/    | **D/D  |
|                              | MIN~^1^\ | ~MIN~\ | D~MIN~\ | ~MIN~\ |
|                              | = 16     | = 3    | = 1     | = 0    |
|                              | dBm**    | dB**   | dB**    | dB**   |
+------------------------------+----------+--------+---------+--------+
| Linear (M = 1)               | -0.1     | -3.0   | -6.9    | In     |
|                              |          |        |         | finite |
+------------------------------+----------+--------+---------+--------+
| Second order (M = 2)         |          | -1.5   | -3.4    | In     |
|                              |          |        |         | finite |
+------------------------------+----------+--------+---------+--------+
| Third order (including       |          | -1.0   | -2.3    | In     |
| third-order intermodulation  |          |        |         | finite |
| of a pair of equal-power     |          |        |         |        |
| interferers) (M = 3)         |          |        |         |        |
+------------------------------+----------+--------+---------+--------+
| Cross modulation (M = 2, L = |          | -1.5   | -3.4    | In     |
| 1)                           |          |        |         | finite |
+------------------------------+----------+--------+---------+--------+
| AGC-Stabilized Nonlinear w/U | -0.1     | -3.0   | -6.9    | In     |
| driving AGC^2^               |          |        |         | finite |
+------------------------------+----------+--------+---------+--------+

> *Note:*
>
> *^1^ For the nominal D~MIN~ value of -84 dBm, D/D~MIN~ = 16 dB when D
> = -68 dBm*
>
> *^2^ With [desired]{.underline} signal driving AGC, deviation from
> straight-line projection matches that of the original nonlinear
> process, except in the case of cross-modulation, which is not
> addressed.*

######### Third-Order Intermodulation With Paired Signals at N+K and N+2K

Third-order intermodulation between paired signals at N+K and N+2K was
modeled as follows.

D = Power of desired signal on channel N at input to TV

U~N+K~ = Power of interferer on channel N+K at input to TV

U~N+2K~ = Power of interferer on channel N+2K at input to TV

where D, U~N+K~, and U~N+2K~ refer to signal level combinations that
place the TV at TOV.

R = Required SNR of TV at TOV

D~MIN~ = Desired signal at TOV in absence of interference or external
noise

IP3 = Third-order intercept point of the receiver under the current AGC
conditions

We define the interference performance in terms of a parameter that
combines IP3 with the required SNR of the DTV receiver (nominally 15.3
dB, or 33.9). The parameter is computed from measurements of threshold
values of undesired and desired signals when the two undesired signals
have equal power (U = U~N+K~ = U~N+2K~).

+-----------------------------------------------------------------------+
| IP3 / R^1/2^ = (U^3^ / D)^1/2^                                        |
|                                                                       |
| or, in decibel units,                                                 |
|                                                                       |
| (IP3 / R^1/2^)\|~dB~ = 1.5 U\|~dB~ - 0.5 D\|~dB~                      |
+-----------------------------------------------------------------------+

Once we know IP3 / R^1/2^, we can use it in one of the following
equations to determine the threshold for one undesired signal in terms
of the other undesired signal power.

+-----------------------------------------------------------------------+
| U~N+K~ = (IP3 / R^1/2^) (D - D~MIN~)^1/2^ / U~N+2K~^1/2^              |
|                                                                       |
| U~N+2K~ = (IP3 / R^1/2^)^2^ (D - D~MIN~) / U~N+K~^2^                  |
+-----------------------------------------------------------------------+

If D \>\> D~MIN~, then the equations can be converted to dB as follows:

+-----------------------------------------------------------------------+
| U~N+K~\|~dB~ = (IP3 / R^1/2^)\|~dB~ + (D\|~dB~ - U~N+2K~\|~dB~) / 2   |
|                                                                       |
| U~N+2K~\|~dB~ = 2 (IP3 / R^1/2^)\|~dB~ + D\|~dB~ - 2 U~N+K~\|~dB~     |
+-----------------------------------------------------------------------+

[AGC With Paired-Signal IM3]{.underline}

When gain is constant, each 1-dB increase in the power of U~N+K~ causes
a 2‑dB decrease in the undesired signal power that can be tolerated on
U~N+2K~ at a constant desired signal power. Conversely, each 1-dB
increase in the power of U~N+2K~ causes a 0.5‑dB decrease in the
undesired signal power that can be tolerated on U~N+K~.

If the AGC acts to keep the power of U~N+K~ constant at the point of the
nonlinearity that creates the observed IM3, the threshold of U~N+2K~
becomes a linear function of desired signal power and is independent of
U~N+K~.

If the AGC acts to keep the power of U~N+2K~ constant at the point of
the nonlinearity that creates the observed IM3, the fixed-gain trend
reverses. At constant a desired signal power, each 1 dB increase in
U~N+2K~ above the AGC threshold causes a 0.5‑dB ***increase*** in the
undesired signal power that can be tolerated on channel N+K.

**BIBLIOGRAPHY**

\_\_\_\_, Code of Federal Regulations (CFR) Title 47,
Telecommunications, Section 73.

\_\_\_\_, "Longley-Rice Methodology for Evaluating TV Coverage and
Interference", Office of Engineering and Technology (OET) Bulletin No.
69, ***\<OET-69\>***, Federal Communications Commission, 6 February
2004.

Advanced Television Systems Committee (ATSC), "ATSC Recommended
Practice: Receiver Performance Guidelines", ***\<ATSC Receiver
Guidelines\>***, ATSC Doc. A/74, 17 June 2004.

Advanced Television Systems Committee (ATSC), "ATSC Standard: Digital
Television Standard (A/53), Revision C Including Amendment No. 1", Doc.
A/53C, 13 July 2004.

Advanced Television Systems Committee, "Recommended Practice: Guide to
the Use of the ATSC Digital Television Standard", ATSC Doc. A/54A, 4
December 2003.

Advanced Television Systems Committee, "Transmission Measurement and
Compliance for Digital Television", ATSC Standard Doc. A/64 Rev A, 30
May 2000.

Bendov, Oded and C. B. Patel, "Television Receiver Optimization in the
Presence of Adjacent Channel Interference", IEEE Transactions On
Broadcasting, Vol. 51, No. 1, March 2005, p.38-39.

Bendov, Oded and others, "Planning Factors for Fixed and Portable DTTV
Reception", IEEE Transactions On Broadcasting, Vol. 50, No. 3, September
2004.

Bretl, Wayne and Gary Sgrignoli, "Summary of the Grand Alliance VSB
Transmission System Laboratory Tests", IEEE Transactions on Consumer
Electronics, Vol 42, No. 3, June 1996.

Bretl, Wayne and others, "VSB Modem Subsystem Design for Grand Alliance
Digital Television Receivers", IEEE Transactions on Consumer
Electronics. Vol. 41, No. 3, August 1995, p.773.

Chong, Young-Jun and others, "The Design And Implementation Of TV Tuner
For Digital Terrestrial Broadcasting", International Conference on
Consumer Electronics (ICCE), 2000 Digest of Technical Papers, 13-15 June
2000, p40 -- 41.

Cowley, Wayne and Robert Hanrahan, "ATSC Compliance and Tuner Design
Implications", Electronic Engineering Times, May 1, 2006.
(http://www.eetasia.com/ART_8800416208_480700_f6d4765f200605.HTM)

Egli, J., "Radiowave propagation above 40 Mc over irregular terrain",
Proceedings of the IRE, Vol. 45, Oct. 1957, pp.1383-1391.

Eilers, Carl and Gary Sgrignoli, "Digital Television Transmission
Parameters---Analysis and Discussion", IEEE Transactions on
Broadcasting, Vol. 45, No. 4, Dec 1999, p.368.

Federal Communications Commission Advisory Committee on Advanced
Television Service, "Final Technical Report", Oct 31, 1995, p.19.

Henderson, John and others, "ATSC DTV Receiver Implementation",
Proceedings of the IEEE, Vol. 94, No. 1, January 2006, p.125.

Martin, Stephen R., "Tests of ATSC 8-VSB Reception Performance of
Consumer Digital Television Receivers Available in 2005", Report FCC/OET
TR 05-1017, ***\<SHVERA Study\>***, November 2, 2005.
(www.fcc.gov/oet/info/documents/reports/TR-05-1017-ATSC-reception-testing.pdf)

Rhodes, Charles W. and Gary J. Sgrignoli, "Interference Mitigation for
Improved DTV Reception", IEEE Transactions on Consumer Electronics, Vol.
51, No. 2, May 2005, p. 463-470.

Rhodes, Charles W., "DTV interference could be mitigated by receivers,"
TV Technology Magazine, Vol. 22, No. 17, p.21-23, Aug. 18, 2004.

Rhodes, Charles W., "Interference Between Television Signals due to
Intermodulation in Receiver Front-Ends", IEEE Transactions On
Broadcasting, Vol. 51, No. 1, March 2005, p.36.

Rhodes, Charles W., "The Challenge of Channel Election, TV
Technology.com, January 19, 2005.
(http://www.tvtechnology.com/features/digital_tv/Features_Rhodes-01.19.05.shtml)

Scheinberg, N. and others, "A GaAs Up Converter Integrated Circuit for a
Double Conversion Cable TV 'Set-Top' Tuner", IEEE Journal of Solid-State
Circuits, Vol. 29, No. 6, June 1994, p.688.

Wu, Yiyan, "Performance Comparison of ATSC 8-VSB and DVB-T COFDM
Transmission Systems for Digital Television Terrestrial Broadcasting",
IEEE Transactions on Consumer Electronics, Vol. 45, No.3, August 1999,
p. 922.

[^1]: Advanced Television Systems Committee, "ATSC Recommended Practice:
    Receiver Performance Guidelines", ***\<ATSC Receiver
    Guidelines\>***, ATSC Doc. A/74, 17 June 2004.

[^2]: In this context, a protection scenario refers to a set of
    conditions that may be part of the analytic process of setting
    protection limits. The conditions might include such factors as the
    distance from the interfering device to the antenna of the DTV
    receiver and the attenuation of any intervening walls.

[^3]: 8-level Vestigial Side Band (8-VSB) is the over-the-air digital
    television (DTV) transmission format specified by the Advanced
    Television Systems Committee's (ATSC) Digital Television Standard
    (A/53) and adopted by the FCC as the U.S. standard for terrestrial
    DTV broadcasting.

[^4]: An 8-VSB signal was used for the first tests performed under this
    program (those on channel 51) because it nearly filled the 6-MHz
    width of a TV channel and it exhibited steep rolloff at the band
    edges---an essential characteristic for adjacent-channel
    interference tests. After failure of that 8-VSB source, tests (on
    channel 30) were performed using the bandlimited Gaussian noise
    source. Because the band-edge rolloff of that signal was not
    sufficiently steep to permit interference measurements on
    first-adjacent channels, those tests were postponed until
    procurement of a new 8-VSB signal source (after repair of the
    previous source was found to be impossible). All tests involving two
    interferers made use of bandlimited Gaussian noise as the second
    source.

[^5]: The ATSC provides recommended guidelines for DTV receiver
    performance in its document, "ATSC Recommended Practice: Receiver
    Performance Guidelines", ATSC Doc. A/74, 17 June 2004.

[^6]: "Longley-Rice Methodology for Evaluating TV Coverage and
    Interference", Office of Engineering and Technology (OET) Bulletin
    No. 69, \<OET-69\>, Federal Communications Commission, 6 February
    2004.

[^7]: Stephen R. Martin, "Tests of ATSC 8-VSB Reception Performance of
    Consumer Digital Television Receivers Available in 2005", Report
    FCC/OET TR 05-1017, ***\<SHVERA Study\>***, November 2, 2005.
    ([www.fcc.gov/oet/info/documents/reports/TR-05-1017-ATSC-reception-testing.pdf](http://www.fcc.gov/oet/info/documents/reports/TR-05-1017-ATSC-reception-testing.pdf))

[^8]: 8-level Vestigial Side Band (8-VSB) is the over-the-air digital
    television (DTV) transmission format specified by the Advanced
    Television Systems Committee's (ATSC) Digital Television Standard
    (A/53) and adopted by the FCC as the U.S. standard for terrestrial
    DTV broadcasting.

[^9]: See 47 C.F.R. section 73.623(d)

[^10]: Charles W. Rhodes, "The Challenge of Channel Election, *TV
    Technology.com*, January 19, 2005.
    (<http://www.tvtechnology.com/features/digital_tv/Features_Rhodes-01.19.05.shtml>)

[^11]: Oded Bendov and others, "Planning Factors for Fixed and Portable
    DTTV Reception", *IEEE Transactions On Broadcasting*, Vol. 50, No.
    3, September 2004.

[^12]: Martin, \<SHVERA Study\>, 2005, chapter 3.

[^13]: Federal Communications Commission Advisory Committee on Advanced
    Television Service, "Final Technical Report", Oct 31, 1995, p.19.

[^14]: Advanced Television Systems Committee, "ATSC Recommended
    Practice: Receiver Performance Guidelines", \<ATSC Receiver
    Guidelines\>, ATSC Doc. A/74, 17 June 2004.

[^15]: In this context, a protection scenario refers to a set of
    conditions that may be part of the analytic process of setting
    protection limits. The conditions might include such factors as the
    distance from the interfering device to the antenna of the DTV
    receiver and the attenuation of any intervening walls.

[^16]: Martin, \<SHVERA Study\>, 2005.

[^17]: The mixer image for a single-conversion TV tuner is centered 88
    MHz above the center frequency of the desired channel. It occupies
    portions of channels N+14 and N+15, where N is the desired channel.

[^18]: The actual pattern of TV desired signals can differ significantly
    from the flat terrain model due to the variability in terrain and
    other geographic features that are present in a local area;
    consequently, terrain-dependent models are normally used for
    coverage area calculations. The simpler model used here is intended
    only to provide some insight regarding signal excess.

[^19]: J. Egli, "Radiowave propagation above 40 Mc over irregular
    terrain", Proceedings of the IRE, Vol. 45, Oct. 1957, pp.1383-1391.

[^20]: We note that these percentages assume that the same TV antenna
    system (*e.g.*, a high gain antenna on a 10-meter mast and a
    downlead having a given loss) is used throughout the coverage area.
    If closer-in TV viewers choose less extensive antenna systems (lower
    gain, shorter mast, or indoor location), those customers may
    experience low signal excess even if far inside the maximum coverage
    range.

[^21]: Martin, \<SHVERA Study\>, 2005, chapter 6.

[^22]: The absence of a set top box among the receivers is consistent
    with the fact that all set top boxes that were identified for
    inclusion in the SHVERA Study had been introduced to the market in
    or before November 2004---a date that was probably too early to have
    included "fifth generation" DTV reception technology.

[^23]: Martin, \<SHVERA Study\>, 2005.

[^24]: We show later in this report that a tuner's automatic gain
    control (AGC) can "stabilize" the effects of nonlinear interference
    mechanisms resulting in a more constant value of D/U at higher
    signal levels.

[^25]: This data was based on a simple, flat-terrain propagation model.
    The results are intended only to illustrate that signal level at the
    input to a TV receiver can vary substantially with changes in
    antenna type and placement.

[^26]: This is more than just a convenience. For fixed desired signal
    levels, one can easily translate data between threshold U values and
    D/U ratios; however, for desired signals levels that are receiver
    dependent (*e.g.*, D~MIN~+3db), the desired signal power necessary
    to convert between the two formats may be lost to the user for
    results that are presented as, for example, median across eight
    receivers or second-worst of eight receivers.

[^27]: The down-conversion also reverses the direction of the frequency
    spectrum because the local oscillator frequency is above the
    frequency of the incoming signal.

[^28]: The diagram omits automatic gain control elements and lumps the
    first IF filter into a single filter located after the first IF
    amplifier; the actual implementation included filters before and
    after the first IF amplifier. A more detailed block diagram is
    available in the following reference:\
    Advanced Television Systems Committee, "Recommended Practice: Guide
    to the Use of the ATSC Digital Television Standard", ATSC Doc.
    A/54A, 4 December 2003, Figure 9.2, p.86.

[^29]: N. Scheinberg and others, "A GaAs Up Converter Integrated Circuit
    for a Double Conversion Cable TV 'Set-Top' Tuner", *IEEE Journal of
    Solid-State Circuits*, Vol. 29, No. 6, June 1994, p.688

[^30]: Wayne Bretl and others, "VSB Modem Subsystem Design for Grand
    Alliance Digital Television Receivers", *IEEE Transactions on
    Consumer Electronics*. Vol. 41, No. 3, August 1995, p.773.

[^31]: Scheinberg and others, 1994, p.688

[^32]: Nick Cowley and Robert Hanrahan, "ATSC Compliance and Tuner
    Design Implications", *Electronic Engineering Times*, May 1, 2006.
    (<http://www.eetasia.com/ART_8800416208_480700_f6d4765f200605.HTM>)

[^33]: Yiyan Wu, "Performance Comparison of ATSC 8-VSB and DVB-T COFDM
    Transmission Systems for Digital Television Terrestrial
    Broadcasting", *IEEE Transactions on Consumer Electronics*, Vol. 45,
    No.3, August 1999, p. 922.

[^34]: Charles W. Rhodes, "Interference Between Television Signals due
    to Intermodulation in Receiver Front-Ends", *IEEE Transactions On
    Broadcasting*, Vol. 51, No. 1, March 2005, p.36.

[^35]: John Henderson and others, "ATSC DTV Receiver Implementation",
    *Proceedings of the IEEE*, Vol. 94, No. 1, January 2006, p.125.

[^36]: Wayne Bretl and others, 1995, p.773.

[^37]: The term "fifth generation" in this report refers to DTV
    receivers that exhibit multipath performance equivalent to that of
    Zenith fifth-generation demodulators. These two TVs exhibited
    multipath performance well below that level.

[^38]: "Longley-Rice Methodology for Evaluating TV Coverage and
    Interference", Office of Engineering and Technology (OET) Bulletin
    No. 69, \<OET-69\>, Federal Communications Commission, 6 February
    2004, p.8.

[^39]: \<ATSC Receiver Guidelines\>, ATSC Doc. A/74, p.13-14.

[^40]: Martin, \<SHVERA Study\>, 2005, chapter 3.

[^41]: The file was provided by Mark Hryszko of the Digital Television
    group of Advanced Micro Devices.

[^42]: The indirect measurement method used in generating the
    spectrum---measuring it without the filter, then adding in an
    in-situ measurement of filter response---would not identify any
    energy coupled by radiation into the test setup at a point after the
    filter or any spectral components created by intermodulation
    distortion occurring after the filter; however, the use of
    double-shielded cables throughout the test setup and the avoidance
    of using any active devices after the filter are expected to
    preclude significant degradation in test setup performance due to
    these factors.

[^43]: DTV allotment planning factors assume that a DTV receiver can
    operate at an input level of -84 dBm on UHF channels. The ATSC
    Receiver Guidelines document recommends that receivers be able to
    operate with signal levels at least as low as -83 dBm. Measurements
    on 28 DTV consumer receivers in the SHVERA Study showed a median
    capability of -83.9 dBm at channel 30.

[^44]: Section 73.622E of the rules (CFR 47) establishes 41 dBuV/m as
    the UHF DTV field strength at the noise-limited edge-of-coverage
    contour. This field strength is derived from a planning model in
    which a -84 dBm signal is delivered to the DTV input at the
    edge-of-coverage in order to enable at TV with a 7-dB noise figure
    and a 15-dB required signal-to-noise ratio to operate.

[^45]: The repeated use of the number 84 is not a typographical error.
    This number appears in three contexts in this discussion: D~MIN~ is
    typically -84 dBm (a value also assumed in the rules); signal excess
    diminishes to 3 dB at 84 percent of the maximum reception range;
    and, 84 percent of the coverage area that can be achieved by a
    nominal receiver (*i.e.* with D~MIN~ of -84 dBm) will exhibit signal
    levels at the TV input that are below the ATSC-specified "weak"
    signal level.

[^46]: These percentages refer to fractions of the coverage area
    possible for a given TV receiver with a given antenna system and
    with flat local terrain.

[^47]: The decision to measure at D~MIN~ + 3 dB and extrapolate to
    D~MIN~ + 1 dB, rather than the other way around, was made because
    measurements become more sensitive to measurement error of the
    desired signal level and of D~MIN~ as the desired signal level
    approaches D~MIN~.

[^48]: Martin, \<SHVERA Study\>, 2005, Chapter 4.

[^49]: \"Control Software for the HP89400 Vector Signal Analyzer for
    Measuring DTV and NTSC Signals\", VSA5.BAS, Version 5.02, by Gary
    Sgrignoli. Note that it was necessary to exit the control software
    to turn the instrument's equalizer ON and OFF.

[^50]: Advanced Television Systems Committee, "Transmission Measurement
    and Compliance for Digital Television", ATSC Standard Doc. A/64 Rev
    A, 30 May 2000, p.5.

[^51]: Carl Eilers and Gary Sgrignoli, "Digital Television Transmission
    Parameters---Analysis and Discussion", IEEE Transactions on
    Broadcasting, Vol. 45, No. 4, Dec 1999, p.368.

[^52]: Both the Wavetech and SFU results were an average of 0.2 dB
    higher than the four-months-earlier SFU results from Table 5-1.

[^53]: Taboos are channel spacings at which analog TV reception is
    vulnerable to interference. The taboos limited the allotment of
    local analog channel assignments.

[^54]: Mixer image for a single-conversion tuner occurs at a separation
    of twice the intermediate frequency (IF) above the center of the
    desired channel. The IF for single-conversion TV receivers is 44
    MHz.

[^55]: Young-Jun Chong, and others, "The design and implementation of TV
    tuner for digital terrestrial broadcasting." Consumer Electronics,
    2000. ICCE. 2000 Digest of Technical Papers. International
    Conference on Consumer Electronics (ICCE), 2000 Digest of Technical
    Papers, 13-15 June 2000, p. 40 -- 41.

[^56]: The susceptibility drops below the measurement floor of the test
    setup.

[^57]: Failure of the 8-VSB source that had served as the undesired
    signal for these tests forced the use of the bandlimited Gaussian
    noise source for subsequent tests on channel 30.

[^58]: Dates are presented to address issues of whether observed
    differences were caused by possible changes in test setup
    performance or equipment. (A different spectrum analyzer was used
    for the comparative signal tests than for the baseline tests.)
    Though the baseline tests were performed about four months before
    the comparative tests, the "repeat baseline" test was performed as
    part of the comparative tests and was performed after the "SFU as D"
    test.

[^59]: The ATSC997 was the desired signal source for all tests except as
    follows. The SFU was a desired source for:

    \(1\) some tests to identify effect of the desired signal source
    (here and in Chapter 5, "Effect of Desired Signal Source"), and (2)
    tests with D = D~MIN~ + 3 dB with non-adjacent interference. The
    Wavetech WS-2100 with an external Drake upconverter served as the
    desired signal source for tests with D = D~MIN~ + 3 dB with the
    undesired signal at N-1 or N+1.

[^60]: The SHVERA Study test results on 28 receivers showed that D must
    exceed U by amounts ranging from 14.9 to 15.8 dB, with a median
    value of 15.3 dB.

[^61]: O. Bendov and C. B. Patel, "Television Receiver Optimization in
    the Presence of Adjacent Channel Interference", IEEE Transactions On
    Broadcasting, Vol. 51, No. 1, March 2005, p.38-39.

[^62]: AGC will generally act on the basis of either desired signal
    power or total power at a point in the tuner. Broadband AGC is an
    example of the latter. If operating on the basis of total power, the
    relative contributions of the desired and undesired signals at the
    AGC control point may differ from their relative levels at the
    receiver input due to filtering within the receiver. In the case of
    AGC operation based on total power, the two bounding cases---desired
    signal being dominant and undesired signal being dominant---were
    considered in the analysis.

[^63]: For the case in which the AGC acts to maintain the *desired*
    signal at a constant power at the point of tuner nonlinearity that
    is responsible for the dominant interference, Appendix B shows the
    math behind the transition to linear behavior for each of the four
    types of interference discussed in this chapter. For the case in
    which the AGC acts to maintain the *undesired* signal at a constant
    level, Appendix B shows the math only for three of the four
    interference categories. The case of cross-modulation with AGC
    acting on undesired signal was not completely solved. When desired
    signal power is much greater than D~MIN~, cross-modulation causes
    TOV to occur at a fixed threshold undesired signal power (U),
    independent of the desired signal power, for cases in which gain is
    constant. If the undesired signal rises to a point at which the AGC
    begins reducing gain prior to the point of nonlinearity, the model
    suggests the following: (1) if that AGC threshold occurs *before*
    the TOV is reached, then the subsequent gain reductions will prevent
    TOV from being reached as U increases further (until the range of
    gain reduction for the AGC is exceeded or another nonlinearity
    becomes significant); (2) if the AGC threshold occurs *after* TOV is
    reached, then the TV will remain in a degraded picture state with
    further increases in undesired signal power.

[^64]: Charles W. Rhodes, "Interference Between Television Signals due
    to Intermodulation in Receiver Front-Ends", IEEE Transactions On
    Broadcasting, Vol. 51, No. 1, March 2005, p.31-37.

[^65]: Charles W. Rhodes, and Gary J. Sgrignoli, "Interference
    Mitigation for Improved DTV Reception", IEEE Transactions on
    Consumer Electronics, Vol. 51, No. 2, May 2005, p. 463-470.

[^66]: Charles W. Rhodes, "DTV interference could be mitigated by
    receivers," TV Technology Magazine, vol. 22, no. 17, p.21-23, Aug.
    18, 2004.

[^67]: An HP8447E amplifier rated for 0.1 watts (20 dBm) output served
    as the IM3 producer. For the first illustration it was driven with a
    signal sufficient to create an output level of 8.1 dBm on each of
    one or two TV channels.

[^68]: This test series was terminated by equipment failure, followed by
    a change in focus of the test program.

[^69]: Martin, \<SHVERA Study\>, 2005, chapter 3.

[^70]: Referring to the block diagram in Figure 4-1, the output level of
    one of the two "AWGN" sources was lowered with respect to the other.
    Step Attenuator-U, which operates on the sum of the two sources, was
    then adjusted to find the TOV point.

[^71]: We note that this is the receiver that exhibited intermittent
    changes in performance of up to 6 dB, as noted in Chapter 7.
    Consequently, there is approximately a 6-dB mismatch between three
    of the threshold shown here and equivalent measurements presented
    elsewhere in this report.

[^72]: Our expectation at the onset of this project was that the primary
    vulnerabilities that would need to be investigated would be the
    first-adjacent channel response, the mixer image response, and
    possibly the effects of third-order intermodulation (IM3) distortion
    for signal pairs. In order to gain an understanding of the nature of
    these interference vulnerabilities, we decided to conduct detailed
    measurements on a TV receiver that exhibited high enough
    interference susceptibilities for those cases to permit measurement
    over a wide range of signal levels. Prior to procurement of custom
    filters for this project, measurements on first-adjacent channels
    were not feasible with the signal generators available at the FCC
    Laboratory; however, crude measurements could be made at other
    channel spacings. Such measurements were performed on eight TVs
    (including three that were used in tests reported in this document)
    with the goal of identifying a TV that exhibited relatively high
    mixer image and third-order intermodulation (IM3) effects. The mixer
    image measurements were performed using a single undesired signal at
    N+15 and a desired signal level of ‑68 dBm; IM3 measurements were
    performed for undesired signal pairs at N+1/N+2 and at N+2/N+4 with
    each undesired signal set for -14 dBm. (It was thought, incorrectly,
    that such high signal levels might be necessary to enable
    observation of IM3 effects.) The selected receiver (D3) had the
    highest IM3 effects and the second highest mixer image response
    among the three tested receivers at these levels.

[^73]: Removal of the filter was possible because the high D/U ratios
    (above -20 dB) for those few measurements reduced the otherwise
    stringent requirement on splatter of the undesired signal into the
    desired channel.

[^74]: Note that linear appearance on a log-log plot (such as these
    plots in decibels) does not necessarily indicate a linear function
    but rather a fixed-order function such as X^M^ where M is a fixed
    exponent. The slope of the plot of D versus U on a log-log scale
    provides the value of the exponent that describes the *order* of the
    interference mechanism. A linear process (M=1) will have a slope of
    one on a log-log plot.

[^75]: Measurements of D/U for N+8 were not performed in this test;
    however, measurements presented in Chapter 6 show that D/U for N+8
    is quite small.

[^76]: This value was obtained by converting -53 dBm and -58 dBm to
    milliwatts, subtracting the two, and then converting back to dBm.

[^77]: Cowley and Hanrahan, 2006.

[^78]: The other reason was the potential for direct radiation of one
    TV's local oscillator to cause interference to another nearby
    receiver tuned seven channels higher.

[^79]: The differences of the rounded numbers is the table, -6.9 -
    (-3.0) is -3.9, however, if the calculation is performed before
    rounding, and the answer is then rounded, the result is -3.8 dB.

[^80]: The undesired signal for all channel offsets except N-1 and N+1
    was Gaussian noise in measurements made with the primary test setup.

[^81]: Total noise power in channel N was 42.8 dB below the average
    power per channel on channels N-4, N-3, N-2, N+2, N+3, and N+4.

[^82]: The co-channel D/U ratio for DTV into DTV interference is 15.3
    dB. Analog TV reaches the point of unusability at a D/U ratio of
    16.1 dB for interference from DTV and requires a significantly
    higher D/U ratio to achieve a high quality picture. Results are
    from:

    Wayne Bretl and Gary Sgrignoli, "Summary of the Grand Alliance VSB
    Transmission System Laboratory Tests", IEEE Transactions on Consumer
    Electronics, Vol 42, No. 3, June 1996, sections 3.7.1 and 3.8.1.

[^83]: Tests of interference rejection thresholds for DTV into analog
    NTSC TV for 8 taboo channels show that D/U ratios differed by an
    average of 8.1 dB between TOV and CCIR Grade 3 ("Slightly Annoying")
    at a weak signal level. These results were obtained by averaging
    data from table in Bretl and Sgrignoli, 1996, section 3.8.3.

[^84]: Tests of lower-adjacent interference rejection thresholds for DTV
    into analog NTSC TV showed a difference of 20.2 dB between D/U ratio
    at TOV and D/U ratio at the point of unusability at a weak signal
    level. Similar tests for co-channel interference showed a difference
    of 32 dB between TOV and the point of unusability (Bretl and
    Sgrignoli, 1996, sections 3.8.1 and 3.8.2.1).

[^85]: SHVERA Study results on 28 receivers showed that D must exceed U
    by amounts ranging from 14.9 to 15.8 dB, with a median value of
    15.3 dB.

[^86]: Bendov and Patel, 2005, p.38-39.

[^87]: For example, see Rhodes and Sgrignoli, 2005, p. 464.

[^88]: We note that IP3 is typically defined in this way for narrowband
    signals. Here we use a definition that, while similar to the
    narrowband case, is not the same because: (1) we are using to model
    IM3 with broadband signals rather than sinusoids, and (2) we are
    interested only in the IM3 power than falls in TV channel N although
    the IM3 signal also extends into channels N-1 and N+1.