NBSIR 73-333 (K)

TEST PROCEDURES HANDBOOK FOR

SURVEILLANCE RECEIVERS BELOW 100 MHz

M.G. Arthur

Electromagnetic Metrology

Information Center

Electromagnetics Division

Institute for Basic Standards

National Bureau of Standards

Boulder, Colorado 80302

October 1973

Prepared for:

U.S. Army Security Test and Evaluation Center

Ft. Huachuca, Arizona
,s)01-UT,o^
NBSIR 73-333

TEST PROCEDURES HANDBOOK FOR

SURVEILLANCE RECEIVERS BELOW 100 MHz

M.G. Arthur

Electromagnetic Metrology

Information Center

Electromagnetics Division

Institute for Basic Standards

National Bureau of Standards

Boulder, Colorado 80302

October 1973

Prepared for:

U.S. Army Security Test and Evaluation Center

Ft. Huachuca, Arizona

U.S. DEPARTMENT OF COMMERCE, Frederick B. Dent, Secretary

NATIONAL BUREAU OF STANDARDS, Richard W Roberts Director
1
CONTENTS

Page

LIST OF FIGURES vii

LIST OF TABLES x ABSTRACT xiii

1.0. INTRODUCTION 1

1.1. PURPOSE 1

1.2. SCOPE AND LIMITATIONS 1

1.3. SOURCES OF INFORMATION 2

2.0 SURVEILLANCE RECEIVERS 6

2.1. GENERAL CHARACTERISTICS 6

2.2. CRITERIA FOR TEST AND CALIBRATION 7 2.3. SPECIFICATIONS OF TYPICAL RECEIVERS 7 3.0. TEST METHODS AND PROCEDURES 11

3.1. GENERAL 11

3.2. STANDARD TEST CONDITIONS 17

3.2.1. AMBIENT CONDITIONS 17

3.2.2. PRIMARY INPUT POWER SUPPLY VOLTAGE 18

3.2.3. ELECTROMAGNETIC COMPATIBILITY CONDITIONS ... 18

3.2.4. RECEIVER PREPARATION 18

3.2.5. TEST INSTRUMENTATION PREPARATION 19

3.2.6. TERMINATIONS 19

3.2.7. TEST FREQUENCIES 20

3.2.8. SIGNAL LEVELS 20

3.2.9. MODULATION 21

3.3. MEASUREMENT ERRORS 2 2 3.3.1. TYPES OF ERRORS 2 2

3.3.2. ORIGINS OF ERRORS 2 2

3.3.3. ERROR EQUATION 2 2 3.3.4. REDUNDANCY 23

3.3.5. POOLING ERRORS 24

3.3.6. OBTAINING MEASUREMENT UNCERTAINTIES 25

iii
CONTENTS (Contd.)

Pa^e

. 0. DETAILED TEST PROCEDURES 26

4.1. SENSITIVITY 26

4.1.1. SENSITIVITY OF A GAIN-LIMITED AM RECEIVER ... 27

4.1.2. 6 dB SN/N SENSITIVITY OF A NOISE-LIMITED AM

RECEIVER 33

4.1.3. 12 dB SINAD SENSITIVITY OF A NOISE-LIMITED AM

RECEIVER 40

4.1.4. QUIETING SENSITIVITY OF AN FM RECEIVER WITH

ONE OR MORE LIMITERS 47

4.1.5. 12 dB SINAD SENSITIVITY OF AN FM RECEIVER WITH

ONE OR MORE LIMITERS 54

4.1.6. NOISE FACTOR 61

4.2. SIGNAL-TO-NOISE RATIO 85

4.3. GAIN 91

4.3.1. POWER GAIN 91

4.3.2. DYNAMIC RANGE 9 8

4.3.3. AUTOMATIC GAIN CONTROL 115

4.4. SELECTIVITY 135

4.4.1. SELECTANCE 136

4.4.2. CW BANDWIDTH 154

4.4.3. SHAPE FACTOR 16 4

4.4.4. MODULATION ACCEPTANCE BANDWIDTH 172

4.4.5. SPURIOUS RESPONSE ATTENUATION .... 177

4.4.6. NOISE BANDWIDTH 191

4.4.7. DESENSITIZATION 196

4.4.8. CROSS MODULATION 204

4.4.9. ADJACENT CHANNEL SELECTIVITY 212

4.4.10. INTERMODULATION DISTORTION 218

4.4.11. IMPULSE BANDWIDTH 2 50

iv
CONTENTS (Contd.)

Pa^e

4.5 INTERFERENCE SUSCEPTIBILITY 258

4.5.1. CONDUCTED INTERFERENCE SUSCEPTIBILITY OF A

NOISE-LIMITED AM RECEIVER 259

4.5.2. CONDUCTED INTERFERENCE SUSCEPTIBILITY OF AN

FM RECEIVER WITH ONE OR MORE LIMITERS .... 267

4.5.3. RADIATED INTERFERENCE SUSCEPTIBILITY OF A

NOISE-LIMITED AM RECEIVER 275

4.5.4. RADIATED INTERFERENCE SUSCEPTIBILITY OF AN

FM RECEIVER WITH ONE OR MORE LIMITERS .... 281

4.6. EMISSION 287

4.6.1. CONDUCTED EMISSION . 2 87

4.6.2. RADIATED EMISSION 295

4.7. TIME DELAY 299

4.8. FREQUENCY STABILITY 309

4.9. FREQUENCY READOUT ERROR 316

4.10. IMPEDANCE 321

4.11. STANDING WAVE RATIO 330

4.12. DETECTORS 336

4.13. AUDIO SECTION 337

4.13.1. AUDIO GAIN 337

4.13.2. AUDIO FREQUENCY RESPONSE 3 42

4.13.3. AUDIO LINEARITY 363

4.13.4. AUDIO DISTORTION 369

4.13.5. HUM AND NOISE 374

4.13.6. NOISE LIMITER THRESHOLD 378

4.13.7. SQUELCH SENSITIVITY 384

4.14. POWER SUPPLY SECTION 39 0

4.14.1. INPUT POWER 390

4.14.. 2. OUTPUT VOLTAGE 398

4.14.3. VOLTAGE REGULATION 401

4.14.4. RIPPLE AND NOISE 415

V
CONTENTS (Contd.)

^ Page

5.0. TEST EQUIPMENT 419

5.1. GENERAL REQUIREMENTS ..... 419

5.2. SPECIAL REQUIREMENTS 419

5.2.1. RF SIGNAL GENERATORS 420

5.2.2. VOLTMETERS 420

5.2.3. IMPEDANCE METERS 421

5.2.4. IMPEDANCE MATCHING NETWORKS 421

5.2.5. ISOLATION NETWORKS 422

5.2.6. COMBINING NETWORKS 422

5.2.7. INSERTION NETWORKS 423

5.2.8. LINE IMPEDANCE NETWORKS 423

5.3. INVENTORY REQUIREMENTS 425

5.3.1. EQUIPMENT IN USASATEC INVENTORY 42 5

5.3.2. EQUIPMENT NOT IN USASATEC INVENTORY 425

5.4. CALIBRATION REQUIREMENTS 433

5.4.1. CALIBRATION SCHEDULE 433

5.4.2. CALIBRATION INFORMATION 4 34

6.0 RECOMMENDATIONS 435

6.1. VERIFICATION OF PROCEDURES 4 35

6.2. PARAMETERS NOT COVERED 435

6.3. IMPROVED PROCEDURES 4 36

7.0 BIBLIOGRAPHY 438

vi
LIST OF FIGURES

Figure Page

4.1.1. Test Set-Up for Gain Limited Sensitivity .... 28

4.1.2. Test Set-Up for 6 dB SN/N Sensitivity 34

4.1.3. Test Set-Up for 12 dB SN/N Sensitivity (AM). . . 42

4.1.4. Test Set-Up for Quieting Sensitivity 48

4.1.5. Test Set-Up for 12 dB SINAD Sensitivity (FM) . . 56

4.1.6.1. Test Set-Up for Noise Factor, ANFM Method ... 63

4.1.6.2. Test Set-Up for Noise Factor, Y-Factor/Power

Meter Method 6 8

4.1.6.3. Test Set-Up for Noise Factor, Y-Factor/Attenuator

Method 7 4 4.1.6.4. Test Set-Up for Noise Factor, 3 dB Method ... 81

4.2. Test Set-Up for Signal- to-Noise Ratio 86

4.3.1. Test Set-Up for Power Gain 9 2

4.3.2.1. Test Set-Up for Dynamic Range, MGC 9 9

4.3.2.2. Test Set-Up for Dynamic Range, AGC 109

4.3.3.1. Test Set-Up for Automatic Gain Control; Gain

vs. AGC Voltage 117

4.3.3.2. Test Set-Up for Automatic Gain Control; Leveling

Effect 123

4.3.3.3. Test Set-Up for Automatic Gain Control; Time

Constants 130

4.4.1.1. Test Set-Up for Selectance, Point-by-Point

Method I 13 8 4.4.1.2. Test Set-Up for Selectance, Point-by-Point

Method II 144

4.4.1.3. Test Set-Up for Selectance, Swept Frequency

Method 149

4.4.2.1. Test Set-Up for Bandwidth, Generator Method . . 155

vii
List of Figures (Contd.)

Figure Page

4.4.2.2. Test Set-Up for Bandwidth, Swept-Frequency

Method 162

4.4.3. Test Set-Up for Shape Factor 165

4.4.4. Test Set-Up for Modulation Acceptance Bandwidth 173

4.4.5.1. Test Set-Up for Spurious Response Attenuation (AM) 180

4.4.5.2. Test Set-Up for Spurious Response Attenuation (FM) 185

4.4.6. Test Set-Up for Noise Bandwidth 192

4.4.7. Test Set-Up for Desensitization 197

4.4.8. Test Set-Up for Cross Modulation 205

4.4.9. Test Set-Up for Adjacent Channel Selectivity . . 214

4.4.10.1. Test Set-Up for Intermodulation Distortion,

Method I 220

4.4.10.2. Test Set-Up for Intermodulation Distortion,

Method II 227

4.4.10.3. Test Set-Up for Intermodulation Distortion,

Method III 236

4.4.10.4. Test Set-Up for Intermodulation Distortion,

Method IV 244

4.4.11.1. Test Set-Up for Impulse Bandwidths 252

4.4.11.2. Impulse Response Pattern 255

4.5.1. Test Set-Up for Conducted Interference

Susceptibility (AM) 261

4.5.2. Test Set-Up for Conducted Interference

Susceptibility (FM) 268

4.5.3. Test Set-Up for Radiated Interference

Susceptibility (AM) 277

4.5.4. Test Set-Up for Radiated Interference

Susceptibility (FM) 283

viii
List of Figures (Contd.)

Figure Page

4.6.1. Test Set-Up for Conducted Emission 290

4.6.2. Test Set-Up for Radiated Emission 297

4.7. Test Set-Up for Time Delay 300

4.8. Test Set-Up for Frequency Stability 311

4.9. Test Set-Up for Frequency Readout Error 317

4.10.1. Test Set-Up for Impedance, Method I 323

4.10.2. Test Set-Up for Impedance, Method II 327

4.11. Test Set-Up for Standing Wave Ratio 332

4.13.1. Test Set-Up for Audio Gain 338

4.13.2.1. Test Set-Up for Audio Frequency Response, Pointby-Point Method I 343

4.13.2.2. Test Set-Up for Audio Frequency Response, Pointby-Point Method II 349

4.13.2.3. Test Set-Up for Audio Frequency Response, Swept

Frequency Method 354

4.13.2.4. Test Set-Up for Audio Frequency Response,

RF Method 357

4.13.3. Test Set-Up for Audio Linearity 364

4.13.4. Test Set-Up for Audio Distortion 371

4.13.5. Test Set-Up for Audio Hum and Noise 375

4.13.6. Test Set-Up for Noise Limiter Threshold 379

4.13.7. Test Set-Up for Squelch Sensitivity 385

4.14.1. Test Set-Up for Input Power 392

4.14.2. Test Set-Up for Output Voltage 399

4.14.3.1. Test Set-Up for Voltage Regulation (Line) .... 402

4.14.3.2. Test Set-Up for Voltage Regulation (Load) .... 410

4.14.4. Test Set-Up for Ripple and Noise 416

5.2.8. Line Impedance Network 424

ix
LIST OF TABLES

Table Page

I Selected Electrical Specifications of Typical

Surveillance Receivers 8

II Test Procedure Summary 13

III Sources of Documented Procedures 16

IV Gain-Limited Sensitivity Initial Control Settings 31

V 6 dB S/N Sensitivity Initial Control Settings . 37

VI 12 dB SINAD Sensitivity (AM) Initial Control

Settings 44

VII Quieting Sensitivity Initial Control Settings . 51

VIII 12 dB SINAD Sensitivity (FM) Initial Control

Settings 58

IX Noise Factor, ANFM Method Initial Control

Settings 65

X Noise Factor, Y-Factor/Power Meter Method

Initial Control Settings 70

XI Noise Factor, Y-Factor/Attenuator Method

Initial Control Settings 76

XII Noise Factor, 3 dB Method Initial Control

Settings 83

XIII Signal-to-Noise Ratio Initial Control Settings . 88

XIV Power Gain Initial Control Settings 94

XV Dynamic Range (MGC) Initial Control Settings . . 102

XVI Dynamic Range (AGC) Initial Control Settings . . Ill

XVII Automatic Gain Control; Gain vs. AGC Voltage

Initial Control Settings 119

XVIII Automatic Gain Control; Leveling Effect

Initial Control Settings 125

XIX Automatic Gain Control; Time Constants

Initial Control Settings 132

XX Selectance, Point-by-Point Method I Initial

Control Settings 140

X
List of Tables (Contd.)

Table Page

XXI Selectance, Swept-Frequency Method Initial

Control Settings 151

XXII CW Bandwidth, Generator Method Initial Control

Settings 158

XXIII Shape Factor Initial Control Settings 16 8

XXIV Desensitization Initial Control Settings .... 200

XXV Cross Modulation Initial Control Settings ... 209

XXVI Intermodulation Distortion, Method I Initial

Control Settings 222

XXVII Band Pass Filter Frequency, . . . 224

XXVIII Intermodulation Distortion, Methods II and III

Initial Control Settings 230

XXIX Frequency f , of Generator No. 2 23 3

XXX Intermodulation Distortion, Method IV Initial

Control Settings 246

XXXI Impulse Bandwidth Initial Control Settings ... 254

XXXII Conducted and Radiated Interference Susceptibility (AM) Initial Control Settings .... 263

XXXIII Conducted and Radiated Interference Susceptibility (FM) Initial Control Settings .... 271

XXXIV Conducted Emission Initial Control Settings . .29 2

XXXV Time Delay Initial Control Settings 30 3

XXXVI Oscilloscope Control Settings 304

XXXVII Frequency Stability Initial Control Settings . . 314

XXXVIII Frequency Readout Error Initial Control Settings 319

XXXIX Impedance, Methods I and II Initial Control

Settings 324

XXXX Standing Wave Ratio Initial Control Settings . . 333

XXXXI Audio Frequency Response, RF Method Initial

Control Settings 360 — xi
List of Tables (Contd.)

Table Page

XXXXII Noise Limiter Threshold Initial Control Settings 382

XXXXIII Squelch Sensitivity Initial Control Settings . . 387

XXXXIV Input Power Initial Control Settings 395

XXXXV Voltage Regulation Initial Control Settings . . 405

XXXXVI Test Equipment Requirements 426

xii
ABSTRACT

This handbook contains test methods and procedures for

radio receivers of advanced design that operate in the

frequency range below 100 MHz. Sixty-one methods are

given for testing forty receiver characteristics such

as sensitivity, selectivity, gain, interference susceptibility, audio characteristics, power supply characteristics

and others. Each receiver characteristic is defined. For

each method, the following information is given: (a) test

equipment required, (b) step by step procedure, (c) data

required, and (d) measurement error computation. The handbook also includes a general discussion of standard test

conditions, suitable test equipment, and measurement errors.

Key Words: Electronic measurements; electronic

test equipment; measurement errors;

radio receivers; receiver characteristics; receiver testing.

1.0. INTRODUCTION

Engineers and measurement specialists have provided a variety of methods, techniques, and procedures for testing

electronic equipment, and for measuring the various performance

parameters that are critical to the proper utilization of

electronic systems. This body of knowledge is scattered in

various documents so that it is not always convenient to produce

upon demand any given procedure that may be needed. Further,

because of incompleteness, differences of purpose or outlook,

and advances in the state of the art, much of this published

measurement knowledge does not satisfy current needs in certain

technical areas

.

This manual is an attempt to improve upon the current

situation by collecting together those procedures that are

useful for testing and measuring the performance of surveillance

receivers

.

1.1. PURPOSE

The specific purpose of this manual is to up-grade the test

procedures used by the U.S. Army Security Test and Evaluation

Center at Ft. Huachuca, Arizona in its test and evaluation of

prototype surveillance receiver equipment in the frequency range

below 100 MHz.

1.2. SCOPE AND LIMITATIONS

The test and measurement procedures given are for surveillance

and similar types of communications receivers. Long-established

procedures are included only if they are still valid. New procedures,

that may not yet be widely adopted, are included when they are

superior and practicable. Requirements that are not now met by
known procedures are identified, and some possible solutions are

offered when known.

The procedures given in this manual are written for the

knowledgeable engineering technician who has had training

and experience in electronic measurements . These are not procedures

that can be correctly performed by elementary-level personnel, nor

are they such as to require advanced training as may be found only

at the primary standards laboratory level.

In some cases, several procedures are given to meet a variety

of needs of accuracy, speed, convenience, or equipment inventory

limitations

.

1.3. SOURCES OF INFORMATION

Principal sources of information are issuances of the IEEE,

EIA, lEC, CCIR, and DoD, listed below. Other sources of

general information are listed in Section 7.0. , Bibliography.

a. IEEE (Institute of Electrical and Electronics Engineers)

1. IEEE Standard Dictionary of Electrical and Electronics

Terms, IEEE Std 100 - 1972, Wiley - Interscience , 1972.

2. IRE Standards on Receivers: Definitions of Terms,

19 52 (52 IRE 17. SI) (IEEE No. 188).

3. IRE Standards on Radio Receivers: Methods of Testing

Amplitude - Modulation Broadcast Receivers, 19 48

(48 IRE 17. SI) ( IEEE No. 186) .

4. IRE Standards on Radio Receivers: Methods of Testing

Frequency - Modulation Broadcast Receivers, 1947

(47 IRE 17. SI) (IEEE No. 185).

2
5. IEEE Test Procedures for Frequency-Modulated Mobile

Communications Receivers, IEEE No. 184, April 1969

(Revision of 49 IRE 26. SI).

6. IEEE Standards for Measurement of Radio Noise Generated

by Motor Vehicles and Affecting Mobile Communications

Receivers in the Frequency Range 25 to lOOO Megacycles

per Second, IEEE No. 263, November 1965.

7. IRE Standards on Audio Techniques: Definitions of

Terms, 1958 (58 IRE 3. SI).

8. IRE Standards on Audio Systems and Components: Methods

of Measurement of Gain, Amplification, Loss Attenuation,

and Amplitude-Frequency-Response, 1956 (56 IRE 3. SI).

EIA (Electronic Industries Association)

1. Minimum Standards for Land-Mobile Communication FM or

PM receivers, EIA RS-204, January 1958.

Also, Standards Proposal No. 1092, a revision of RS-204

October 1970

.

2. Minimum Standards for Land-Mobile Communication Systems

Using FM or PM in tne 25-470 Mc Frequency Spectrum,

EIA RS-237, August i960.

lEC (International Electrotechnical Commission)

1 . Recommended Methods of Measurement on Receivers for

Amplitude-Modulation Broadcast Transmissions,

Publication 69, 1954.
2. Recommended Methods of Measurement on Receivers for

Frequency-Modulation Broadcast Transmissions,

Publication 91, 1958.

3. Recommended Methods of Measurement of Radiation from

Receivers for Amplitude-Modulation, Frequency-Modulation

and Television Broadcast Transmissions, Publication

106, 1959; and Publication 106A, 1962.

CCIR (International Radio Consultative Committee)

1, Noise and Sensitivity of Receivers, Recommendation

331-2, Xllth Plenary Assembly, New Delhi, 1970.

2. Selectivity of Receivers, Recommendation 332-2,

XII th Plenary Assembly, New Delhi, 19 70.

3, Bandwidths and Signal-to-Noise Ratios in Complete

Systems, Recommendation 339-2, Xllth Plenary Assembly

New Delhi, 1 9 70 .

4. Amplitude-Modulation Sound Broadcasting, Objective

Two-Signal Methods of Measurement of Radio-Frequency

Wanted-to-Interfering Signal Ratios, Report 399-1,

Xllth Plenary Assembly, New Delhi, 1970.

DOD (Department of Defense)

1 . Measurement of Radio Frequency Spectrum Characteristics,

MIL-STD-449C, 1 March 1965.

2. Electromagnetic Interference Characteristics,

Requirements for Equipment, MIL-STD-461A

7 February 1969

.
3. Measurement of Electromagnetic Interference

Characteristics, MIL-STD-462, 1 August 1968.

4 . Electromagnetic Interference Test Requirements

and Test Methods, MIL-STD-826, 20 January 1964.

5. Materiel Test Procedure for Receiver-Transmitter,

General, MTP 6-2-242, 1 September 1967.

5
2.0. SURVEILLANCE RECEIVERS

- 2.1. GENERAL CHARACTERISTICS

The modern surveillance receiver is a high-performance

HF and VHF receiver based upon the latest advances in

communications technology. Although its operational features

are similar to its predecessors, its electrical design and

construction bear little resemblance to receivers of a decade

ago. Most notable are the characteristics of all solid-state

design, modular construction, and digitally controlled

heterodyne oscillators. Excellent short- and long-term stability

is achieved through the use of automatic frequency control

referenced to a precision crystal oscillator. Digital frequency

display is common. The small power requirements of solid-state

circuits further contribute to stability as well as to compact

size and moderate weight. The availability of low-noise, linear

transistors results in improved sensitivity and exceptional

dynamic range, while at the same time reducing intermodulation

and distortion products. The small space and power requirements

of modern circuits make feasible the use of independent networks

where multipurpose networks had been used; for example, separate

detectors for CW, AM, FM, USB, LSB , and AGC , separate AF amplifiers for line and speaker outputs, and separate BFO circuits for

CW, USB, and LSB detection.

Modern surveillance receivers are also less susceptible to

electromagnetic interference because of improved filtering,

shielding, and amplifier linearity. They are designed to work

over a wide range of ambient temperature, mechanical shock,

and primary power options.

6
2.2. CRITERIA FOR TEST AND CALIBRATION

The surveillance receiver under test must be in normal

operating condition before making any measurements of its

electrical parameters. For example, all operating discrepancies

must be corrected. All tuned circuits must be aligned and tuned

according to the manufacturer's specified procedures. Any

malfunctions must be repaired. Power supply voltages must be

within the manufacturer's prescribed tolerances.

Although these test procedures can serve to reveal

malfunctions and improper operation of the receiver, they are

not intended for this purpose. Much time may be saved if the

receiver is checked according to the maintenance procedures

provided by the manufacturer before starting these tests.

2.3. SPECIFICATIONS OF TYPICAL RECEIVERS

The electrical specifications of surveillance receivers

will vary according to the frequency range, application, and

operational requirements. Some electrical specifications of

typical receivers are listed in Table I. No single receiver will

necessarily include all of these parameters, nor will the specified

value of a given parameter always fall within the range listed.

The test procedures given in this handbook are designed to

measure these parameters within the ranges listed in Table I.

In addition, procedures for other parameters are also given.

7
TABLE I Selected Electrical Specifications

Of Typical Surveillance Receivers

Parameter

Sensitivity

Noise Factor

Units

Microvolts

Decibels

Range

0.1 to 3 yv

3 to 15 dB

Gain Decibels 10 0 to 150 dB

Dynamic Range Decibels

With AGC

With MGC

Automatic Gain Control

(Levelling Effect)

Automatic Gain Control Seconds

Attack time

Decay time

Bandwidth Hertz

80 to 120 dB

20 to 120 dB

2 to 6 dB levell

for inputs from

1 to 100,000 yV

0.001 to 0.1 sec

0.01 to 5 sec.

100 Hz to 25 kHz

Shape Factor 1.3:1 to 10 :1

8
Table I (Cont'd)

Parameter

9 . Spurious Response

Attenuation

Units

Decibels

Range

40 to 100 dB

10. Desensitization Millivolts 10 to 10 0 0 mV

11. Cross Modulation Millivolts 10 to 1000 mV

12 . Intermodulation

Distortion

Decibels 30 to 100 dB

13. Conducted Interference Millivolts

Susceptibility

1 to 10 00 mV

14. Radiated Interference Volts/meter

Susceptibility

0.01 to 1 v/V

15. Conducted Emission Millivolts 1 mV max.

16. Radiated Emission Millivolts/meter 1 mV/m max,

17. Time Delay Seconds 0.04 to 20 m sec

18. Frequency Stability (after warm-up)

Time Hertz/unit time

Temperature

Supply voltage

Hertz/° Celcius

Hertz/volt

Short: 1 to 5 Hz/10 min,

Long: 5 to 20 0

Hz/8 hr.

1 to 100 Hz/°C

1 to 10 Hz/V

9
Table I (Cont'd)

Parameter Units Range

19 . Readout Error Hertz 100 to 1000 Hz

20 . Impedance

RF/IF

AF

Ohms

50 to 600 Q

3 to 600 Q

21. Standing Wave Ratio 1:1 to 3:1

22. Audio Output Power Watts 0.001 to 10 W

23. Audio Frequency

Response

Within ±3 dB from

100 to 5000 Hz

24. Audio Distortion Percent 1 to 10%

25. Audio Hum & Noise Decibels

(below reference output)

-30 dB max

26. Squelch Sensitivity Microvolts 0.05 to 0.5 yV

27. Input Voltage

AC

DC

Volts

10 0 to 12 5 VAC

20 0 to 250 VAC

40 to 400 Hz

22 to 34 VDC

10
3.0. TEST METHODS AND PROCEDURES

3.1. GENERAL

The test procedures included in this handbook are suimnari zed

in Table II. Detailed procedures, including definitions of the

parameters measured, purpose of the measurement, general method

used, test equipment required, step-by-step procedures, data

required, and a discussion of measurement errors, are given in

Section 4.0. , below.

Table II lists (a) each receiver parameter for which a procedure is given, (b) the sub-section of this handbook in

which it is given, (c) the nominal range over which the parameter

can be measured, (d) the best and typical measurement accuracies

attainable, and (e) the developmental status of the procedure.

The key to the status is as follows

O — Old. The procedure, or one similar to it, or the

basic principal underlying it, has been established

for sufficient time for it to have become known by

people who make receiver measurements

.

N — New. The procedure, to our knowledge, has not formally

appeared in the open literature.

T — Tested. The procedure has been used and found

suitable for the intended measurement.

P — Provisional. The procedure, or one similar to it,

has been used, but it has not yet been fully

tested and verified as suitable for the intended

measurement

.

11
U — Untested. The procedure has been drawn up for this

handbook; and although it is expected to be suitable

for the intended measurement, it has not been

adequately tested and verified.

The reason for the variety of statuses is explained below.

These procedures come from a variety of sources. The principal

sources of documented procedures are those listed in Section 1.3,

above. Table III shows the extent to which these sources have

contributed to this handbook. It can be seen that, although they

represent the technical output of the major standardizing

organizations (except for DoD) in the area of radio measurements,

they fail to provide adequate procedures for a majority of the

listed receiver parameters.

When the principal sources provided inadequate or no procedures

for certain parameters , new procedures were adapted from

information contained in handbooks and textbooks, technical

journals and reports, privately published monographs, and from

individual metrologists . Most of these ancillary sources do not

provide the required detailed information (e.g., step-by-step

procedures, equipment requirements, error analysis, etc.). Such

information has been newly written specifically for this handbook.

Thus, many of the procedures in Section 4,0., below, although

based upon sound principles , have not been tested sufficiently

to validate that they are entirely practical and without

shortcomings in all their particulars . These are identified by

the status symbols "N", "P", and "U" in Table II.

12
^ecuxon Parameter

TABLE II Test Procedure Summary

Range

Accuracy

Best Typical

Dynamic Characteristics

4.4.1.3. Selecrance - Method I 4.4.1.4. Selecrance - Method II 4.4.1.5. Selectance - Method III 4.4.2.3. CVr Bandvridth - Method I 4.4.2.4. Civ Bandwidth - Method II

4.4.3. Shape Factor

4.4.4. Modulation Acceptance

Bandv.'idth

4.4.5.3. Spurious Response

Attenuation (AM)

4.4.5.4. Spurious Response

Attenuation (FM)

<0 .1 ms

.

Decay Time

:

>10 sec.

100 dB max.

100 dB max.

40 dB max. <100 Hz->25 kHz

<100 Hz->25 kHz

-1:1 - 20:1

<2 kHz->25 kHz

0 - 100 dB

0 - 100 dB

6%

6%

6%

8%

3%

10%

6%

10%

8%

8%

8%

12%

6%

12%

10%

15%

40%

40%

40%

40%

25%

40%

40%

50%

0.3 dB 0.4 dB - 1.5 dB

0.3dB 0.4dB-1.5dB

Status

4. 1. 1. Gain-limited Sensitivity (AM) 0. 1 yV min

.

3% 5% - 20% 0 ,T

i 4. 1. 2. 6 dB SlVN Sensitivity (AM) 0. 1 yV rain. 3% 5% - 20% 0 ,T

4

.

1 . 3

.

12 d3 SINAD Sensitivity (AM) 0

.

1 viV m.in. 5% 8% - 30% N ,P

4

,

1. 4

,

Quieting Sensitivity (FM) 0. 1 vV min

.

3% 5% - 20% 0 /T

4

.

1. 5. 12 gB SINAD Sensitivity (FM) 0. 1 vV min

.

5% 8% - 30% 0 ,T

4. 1 . 6 . 3. Xoise Factor - ANFM Method 1 dB - 15 dB 0 .3 dB 0 .5 dB - 1. 5 dB 0 ,T

4

.

1. 6 . 4

.

Noise Factor - Y-Factor/Power Meter 1 dB - 15 dB 0 . 2 dB 0 . 3 dB - 1 dB 0 ,T

4

.

1 . 6 . 5

.

Noise Factor - Y-Fac- or/Attenuator 1 dB - 15 dB 0 . 2 dB 0 .3 dB - 1 dB 0 /T

4

.

1 . 6. 6 . Noise Facror - 3 dB Method 1 dB - 15 d3 0 . 3 dB 0 .5 dB - 1. 5 dB 0 ,T

4

,

2

.

Signal-to-Noise Ratio 0 - 60 dB 0 . 2 dB 0 . 3 dB - 0

.

8 dB 0 ,T

4. 3. 1. Power Gain 0 - 120 dB 0 .3 dB 0 .4 dB - 1. 5 dB 0 ,P

4

.

3 . 2 . 3. Dynamic Range , MGC 120 dB max. 0 .3 dB 0 .4 dB - 3 dB N /U

3. 2 . ^ Dynamic Range , AGC 120 dB max. 0 .4 dB 1 dB - 4 dB N ,u

3. 3. 1. Automatic Gain Control

Gain vs. AGC Voltage

120 dB

10 VDC

max . gain max . AGC6 % 8% - 40 % 0 ,P

4

.

3 . 3 . 2 . Automatic Gain Control

Leveling Effect 120 dB max

.

8 % 10% - 40 % 0 ,P

A 3. 3. 3. Automatic Gain Control Attack Time :

0,P

0,P

0,P

0,T

0,P

0,T

0,P

0,T

0,P

0,P

13
TABLE II (Cont'd)

Section

4.4.6.

4.4.7.

4.4.8. 4.4.9. 4.4.10.3.

4.4.10.4.

4.4.10.5.

4.4.10.6.

4.4.11.

4.5.1.

4.5.2.

4.5.3.

4.5.4.

4.6.1.

4.6.2.

4.7

4.8.

4.9. 4.10.3. 4.10.4

4 .11

4.13.1. 4.13.2.3.

4.13.2.4.

4.13.2.5.

Parameter

Noise Bandwidth

De sensitization

Cross Modulation

Adjacent Channel Selectivity

Intermodulation Distortion

Method I Intermodulation Distortion

Method II Intermodulation Distortion

Method III Intermodulation Distortion

Method IV

Range

<100 Hz->25 kHz

0 - 100 dB

1 V max.

0 - 120 dB

Accuracy

Best Typical

10% 15% - 50%

0.4 dB 0.6 dB - 2 dB

10% 12% - 50%

20 100 dB

1 yV - 1 V

1 yV - 1 V

1 yV - 1 V

0 . 7 dB 0 . 9 dB - 2 . 5 dB

0 . 5 dB 0 . 8 dB - 3 dB

3%

3%

5%

5% - 20%

5% - 20%

8% - 30%

Status

0,T

N,U

0,P

0,T

N,P

0,P

0,P

0,P

Impulse Bandwidth <100 Hz->25 kHz 8% 10% - 30% 0,,p Conducted Interference

Susceptibility (AM) 1

- 1000 mV 5% 8% - 30% ,p Conducted Interference

Susceptibility (FM) 1

- 1000 mV 5% 8% - 30% N ,p Radiated Interference

Susceptibility (AM) < 100 V/m 100% - 1000% 0,f u Radiated Interference

Susceptibility (FM) < 100 V/m 100% - 1000% 0,rU Conducted Emission -130 to 0 dBm 0 ,.3 dB 0 ,. 5 dB - 1.5 dB N,,P Radiated Emission 0 - 1000 yV/m 100% - 1000% 0,rU Time Delay 10 y sec - 100 msec 2% 3% - 10% N,-U Frequency Stability 0.1 - 1000 Hz 0 ,.2 Hz 0.. 2 Hz - 1 Hz N,,P Frequency Readout Error 0 - 10 kHz (Readout resolution) N,,P Impedance - Method I 1 - 1000 n 4% 5% - 20% 0,rT Impedance - Method II 1 - 1000 n 4% 5% - 20% 0,rT Standing Wave Ratio 1:1 - 10 :

1

6% 8% - 20% 0,-T Audio Gain 0 - 6 0 dB 0 ..5 dB 0 ., 7 dB - 2 dB N,,P Audio Frequency Response

Method I 10 Hz - 25 kHz 0 ..5 dB 0.. 7 dB - 2 dB 0,,T Audio Frequency Response

Method II 10 Hz - 25 kHz 0 ..5 dB 0.. 7 dB - 2 dB 0,rT Audio Frequency Response

Method III 10 Hz - 25 kHz 10% - 100% 0,,T

14
TABLE II (Cont'd)

Accuracy

Section Parameter Range Best Typical Status

4..13,,2,.6. Audio Frequency Response

Method IV 10 Hz - 25 kHz 0 ,.5 dB 0 ,. 7 dB - 2 dB 0,,P

4,.13,,3. Audio Linearity 0 - 60 dB 0,.5 dB 0 ,. 7 dB - 2 dB 0,,T

4..13,,4, Audio Distortion 0.1% - 20% 8% 10% - 50% 0,fT

4..13,.5, Hum and Noise -0 dB to -40 dB below P

o

0,.5 dB 0 .. 7 dB - 2 dB 0,,P

4,,13,.6. Noise Limiter Threshold 0 - 10 V 2% 4% - 15% N,,P

4.,13,,7. Squelch Sensitivity 0.01 ViV — 1 yV 5% 8% - 30% 0,,P

4.,14,,1. Input Power (AC/DC) 1 W - 150 W 2% 4% - 15% 0,,T

4.,14,,2. Output Voltage (DC) 0 - > + 300 V 1% 2% - 10% 0,,T

4.,14,.3,.3. Voltage Regulation - Line 0.001% - 10% 2% 4% - 15% 0,,T

4,.14,.3,, 4 . Voltage Regulation - Load 0.001% - 10% 2% 4% - 15% 0,,T

4.,14,.4, Ripple and Noise 1 mv - 10 V 1% 2% - 10% 0,,T

15
TABLE III Sources of Documented Procedures

CDCO CO

0 0 0

IEEE IEEE IEEE

Gain-Limited Sensitivity S L S

6 dB SN/N Sensitivity

12 dB SINAD Sensitivity (AM) Quieting Sensitivity S S 12 dB SINAD Sensitivity (FM) Noise Factor S Signal-to-Noise Ratio U Power Gain Dynamic Range Automatic Gain Control S S L Selectance L s CW Bandwidth L Shape Factor Modulation Acceptance Bandwidth

Spurious Response Attenuation L S Noise Bandwidth L Desensitization S S Cross Modulation

Adjacent Channel Selectivity S Intermodulation Distortion U S L Impulse Bandwidth L Conducted Interference Susceptibility (AM) L Conducted Interference Susceptibility (FM) L Radiated Interference Susceptibility (AM) L L Radiated Interference Susceptibility (FM) L L Conducted Emission L L Radiated Emission * L L Time Delay * Frequency Stability S S Frequency Readout Error * Impedance

Standing Wave Ratio Detectors

Audio Gain , * Audio Frequency Response s S Audio Linearity * * * Audio Distortion U s S Hum and Noise L s s Noise Limiter Threshold * * Squelch Sensitivity S

* Input Power * Output Voltage * Voltage Regulation * Ripple and Noise L *

Key: * — No procedure provided

U — Procedure used as provided

o

7 7 < CO \D c c c in 0 o 0 m as

(N m JJ T T 1 1 0 0

r- u u u

1 i i

+J H 1 S s

H o 1-1 m CO -.0 c/l 0 0 0 0 1 1 Z

r XI 0 u o Cu J cfi ;3 m a; c2 CU Cd. a; ^ s n: r:

s S u

s s u

u

^ s

s S

U S

L L

L L

U S S

S U

S s S S u S S U

u N

S S S S S s S u S

S S s N N SN

s L L S L L

s L L S L L

N s L L

s L N s L L

L s S L L L s L L

L s S L L L s L L

L L L

* * * * * * * *

* * * * *

* S s

* * * L S s N L L L U S

* s

*

S S S S

*

* S L N N * *

* * * * *

s

•k * S * * * * * * * *

* * * * * *

* * *

* * * *

* * * *

S Small Modification

L -- Large Modification

N Procedure not used

16
The procedures in this handbook, therefore, are a mixture

(a) of proven methods and (b) of "unproven" methods that are based

upon either proven principles or upon the adaptation of similar

methods to the requirements at hand. The new, provisional, or

untested procedures should be used v/ith technical prudence, but

may be expected to yield the desired results v/ithout significant

modifications

.

3.2. STANDARD TEST CONDITIONS

Certain test conditions apply to the majority of these

procedures and therefore can be "standardized." Deviations from

these standard conditions occur in specific instances, and these

are made clear in Section 4.0.

These standard test conditions are recommendations only,

and may be modified according to the needs of a particular

measurement situation. IVhen this is done, the prevailing test

conditions should be recorded with the test data so that proper

account can be taken thereof , in the interpretation of the

measurement results

.

3.2.1. AMBIENT CONDITIONS

3.2.1.1. STANDARD TEMPERATURE

Standard temperature shall be +20°C to + 35°C.

3.2.1.2. STANDARD RELATIVE HUMIDITY

Standard relative humidity shall be as f ollov/s :

a. Zero to 90 percent at 20®C to 30°C

b. Zero to 70 uercent at 30°C to 35°C

17
3.2.1.3. STANDARD ATMOSPHERIC PRESSURE

Standard atmospheric pressure shall be the ambient atmospheric

pressure at the time of the test.

, 3.2.2. PRIMARY INPUT POWER SUPPLY VOLTAGE

Standard input power supply voltage shall be within ±5

percent of the mean of the rated operating voltage range of

the receiver, as given in the manufacturer's specifications.

3.2.3. ELECTROMAGNETIC COMPATIBILITY CONDITIONS

These tests shall be conducted, as far as practicable, in

areas that are sufficiently free from electromagnetic interference

fields to allow the measurements to be made without significant

adverse effect on the results. Primary input power sources shall

be sufficiently filtered to accomplish the same end. Test

instrumentation shall be properly shielded, filtered, and

grounded so as to minimize erroneous results caused by

extraneous signals from these or other sources

.

3.2.4. RECEIVER PREPARATION

3.2.4.1. OPERATING CONDITIONS

When important to the test results, the receiver should be

situated so that it closely approximates the physical and

electrical conditions in which it is intended to operate. All

accessories that may affect test results shall be installed

and put into operation.

18
3.2.4.2. RECEIVER CONDITION

Before any raeasurements are performed, the receiver shall

be in proper operating condition as stated in Section 2.2., above.

3.2.4.3. v:ar:-i-up ti:<ie

Sufficient warm-up tine, e.g., from one-half to two hours,

shall be provided before any measurements are performed to insure

adequate stabilization of the receiver paramieters

.

3.2.5. TEST INSTRUI-IENTATION PREPARATION

3.2.5.1. OPERATING CONDITIONS

Test instruments shall be operated according to the

manufacturer's instructions. Check for proper grounding, proper

connections of cables and probes, and proper shielding, filtering,

and isolation as required. Sufficient vrarm-up time shall be

provided to insure stable operation.

3.2.5.2. CALIBRATION

All test equipment must meet the manufacturer's specifications

on accuracy and other performance parameters. Information on

accuracy, frequency response, spectral purity, etc., must be

verified and at hand in order to obtain meaningful results from

these tests

.

3.2.6. TERI^INATIONS

All terminations to receiver terminals (ports) shall be of

the proper impedance and povrer rating, as specified by the

receiver manufacturer. They shall be adequately shielded to

prevent interference to, or from, other parts of the

measurement systemi.

19
3.2.7. TEST FREQUENCIES

No standard test frequencies are specified in this handbook.

Test frequencies are to be determined according to the purposes

of the test.

3.2,8. SIGNAL LEVELS

3.2.8.1. INPUT SIGNAL VOLTAGE

No standard input signal level is specified in this handbook.

When a specific level is required for a particular test, it is

so stated in that test procedure.

R.F. input signal levels are expressed in terms of the open

circuit voltage across the output terminals of the source of the

input signal. If an impedance matching, filter, or attenuating

network is used between the signal generator output terminals

and the receiver input terminals, the input signal level is the

open circuit voltage across the output terminals of the network.

If no such network is used, the input signal is the open circuit

voltage across the output terminals of the generator.

3.2.8.2. AUDIO OUTPUT POWER

Reference audio output power shall be established for the

receiver as one of the following power levels:

a. 50% of manufacturer's rated audio output power

b. Maximum audio output power having a 12 dB SINAD ratio

(6.3% noise and distortion)

c. Manufacturer's rated audio output power

20
d. Some other power level that is determined by the

characteristics of the receiver or the requirements of the test

In this handbook, reference audio output power is taken to be

50% of manufacturer's rated audio output power. Any deviation

from this meaning is identified in the text. When the manufacturer

has not given a rated audio output power for the receiver under

test, establish one using a reasonable criterion, such as the

power level at the 10% distortion point.

In all cases, the basis for the reference output power

level should be stated in the test report.

3.2.9. MODULATION

3.2.9.1. AMPLITUDE MODULATION

Standard amplitude modulation shall be 30% with a 1000

hertz sinusoid voltage.

3.2.9.2. SINGLE SIDEBAND MODULATION

Standard single sideband suppressed carrier modulation

frequencies shall be the two tones of 400 hertz and 2500 hertz.

The amplitudes of these two tones shall be equal.

3.2.9.3. FREQUENCY MODULATION

Standard frequency modulation shall be ±60% of rated system

deviation with a 1000 hertz sinusoid voltage. Rated system

deviation shall be as given by the receiver manufacturer; or,

if this is not specified, it may be taken to be the CW bandwidth

of the receiver. CAUTION: The CW bandwidth may not be suitable

as a basis for determining rated system deviation in some

receivers that are not designed correctly for FM reception.

21
3.3. MEASUREMENT ERRORS

A measurement error is the difference between the true value

and the measured value of a quantity.

3.3.1. TYPES OF ERRORS

Measurement errors are of two types: systematic and random.

A systematic error is the difference between the true value and

the limiting mean of a set of measured values of a quantity. A

random error is the error caused by a random process, as

contrasted with a systematic or deterministic process.

3.3.2. ORIGINS OF ERRORS

Measurement errors result primarily from uncertainties in

the data. They can also result from procedural mistakes; but

this source of error can be removed by using care, repeating

measurements, cross-checking, and a variety of other procedural

methods. Uncertainties in the data come from such sources as

(a) uncertainties in the true value of a meter or dial reading,

(b) uncertainties in the calibration of an instrument, (c)

imprecision in the indicated meter reading due to random

fluctuations or poor resolution, (d) variations in the parameter

being measured during the measurement interval, and (e) variations

caused by human frailties in performing the measurement.

3.3.3. ERROR EQUATION

The total measurement error is obtained by means of an

error equation. The error equation comes from an error analysis

of the measurement process, and contains terms which represent

the individual sources of error.

22
A thorough error analysis of each measurement procedure is

beyond the scope of this handbook. Further, the desired level

of precision for these tests does not warrant a highly exhaustive

treatment. Therefore, only the principal sources of error have

been accounted for in the error equations provided in this

handbook.

The total error of a measiarement normally consists of both

systematic and random errors. In general, the error equation

applies separately to both types of errors. Thus, the error

equation is used twice, once for systematic errors and once

for random errors. The total error is then expressed in two

parts, viz., a systematic part and a random part. In some

cases, one type may predominate over the other, in which case

the total error may be substantially systematic or random.

The error equations given in Section 4.0. are primarily for

use with systematic uncertainties, although they can also be

used with random uncertainties. For proper use of these

equations, refer to Section 3.3.5., below.

3.3.4. REDUNDANCY

Measurements should be made more than once for the following

reasons

a. Gross errors and mistakes may be revealed.

b. The average result usually has a smaller error than

each individual result.

c. The spread of the individual results provides an

estimate of the measurement error.

23
Repeating the measurement many times can reduce the random

error, but it will not reduce the systematic error. Systematic

error is reduced by using test equipment having greater

inherent accuracy.

Random error is expressed in terms of

deviation, s, of the measurement data. It

to take 3s (three standard deviations) as

of the measured value of the parameter.

Standard deviation decreases with the square root of n,

the number of measurement results. Significant improvements

accrue as n increases from one to two to three, but note

that the improvement decreases with increasing n. Seldom

is it worthwhile to repeat measurements of the type given

in this handbook more than ten times.

3.3.5. POOLING ERRORS

Independent systematic errors are combined algebraically.

That is, if one error is positive (+) and the other negative

(-) , the total of these two errors is their algebraic sum.

If a systematic error can be either positive or negative (±)

then judgement must be exercised when combining it with other

errors. Unless knowledge about an error directs otherwise, the

worst-case combination should be used. This normally means that

the errors are pooled by adding their absolute values, thus

disregarding their algebraic signs. If there is some interdependence (correlation) between individual errors, it may

be taken into account to obtain a pooled error that is smaller

than their worst-case sum.

the standard

is common practice

the random error

24
Random errors are combined on a root-mean-square basis.

That is, the two errors, Aa and Ab, produce a total error,

Ac, given by the equation

2 2 1 Ac = [(Aa) + (Ab) ]^ .

When there is a question as to whether an error is

systematic or random, usual practice is to pool it with

other errors on a worst-case basis.

3.3.6. OBTAINING MEASUREMENT UNCERTAINTIES

In order to estimate a measurement error, it is necessary

to obtain quantitative values for the uncertainties in the data.

The usual source of information for systematic measurement

uncertainties is the manufacturer's accuracy specification

for the particular test equipment involved. An alternative,

and possibly superior, source is a recent calibration certificate

for the instrument, which should include the limits of error

on the calibration results. Lacking either of these sources,

measurement uncertainties can be obtained by measuring a known quantity with the instrument, and comparing the measurement

results with the known value.

Random uncertainties are obtained from a statistical analysis

of the data. Refer to standard textbooks on the subject for

procedures (see Bibliography)

.

25
4.0. DETAILED TEST PROCEDURES

4.1. SENSITIVITY

The sensitivity of a receiver is a measure of its ability to

receive weak signals. To express this ability in quantitative terms,

sensitivity is broadly defined as the smallest R.F. input signal

necessary to produce an acceptable demodulated output signal.

Several types of sensitivity are defined to provide for different

types of receivers and different receiving requirements. Of these,

the following types are described, and measurement methods are

given

1 . Sensitivity (Gain-Limited AM receivers)

2. 6 dB SN/N sensitivity (AM receivers)

3. 12 dB SINAD sensitivity (AM and FM receivers)

4. Quieting sensitivity (FM receivers)

5. Noise factor (AM and FM receivers)

26
4.1.1. SENSITIVITY OF A GAIN-LIMITED AM RECEIVER

4.1.1.1. DEFINITIONS

a. The sensitivity of a gain-limited AI4 receiver is the

open circuit output voltage, in microvolts, from a signal generator

amplitude modulated 30% with a 1000 Hz sinusoid, that will produce

reference audio output power from the receiver output terminals

.

b. A gain-limited receiver is a receiver whose gain and

internal noise are such that, when its input termination has a noise temperature of 290K, reference audio output power cannot be

produced by amplification of system noise alone.

4.1.1.2. PURPOSE

The purpose of this measurement method is to measure the

sensitivity of gain-limited All receivers. For such receivers,

sensitivity is essentially a measure of the total receiver gain.

Tne method ignores the effects of distortion; therefore, for

non-linear receivers it does not yield accurate results.

4.1.1.3. METHOD

The method uses an amplitude modulated signal generator

and a voltmeter or power meter as shown in figure 4.1.1. The

signal generator supplies a known voltage to the receiver at

the measurement frequency. The voltmeter or power meter indicates

the receiver output signal level.

The generator level is adjusted to the open circuit output

voltage that will produce reference audio output power from the

receiver. This voltage is the sensitivity of the receiver.

27
o

I—I ct: I— o

<C I—

I—I I—

(

q: lu

Lu a:.

LxJ 1—

LU

OL Cd ^

LU LU 3 1—

h- o O UJ _1 Q- s: O

>

A

^ 1— LU <: =3 > o 1—

1

UJo 1—

LU 121 DC •=x. o

O CD

<: >-< q; Q ic o

LU O 3

Q- (— I—

21 <: LU

—^—

O

_I 1—<c

LU

LUe3

-H>

-H

-P H

U)C

Q) 03

'd

<U +1 -HeH

o

Io

+J

CO

<U

28
Measurement uncertainties as small as 3% are possible under

best conditions, and range from approximately 5% to 20% under

typical conditions. This method uses rudimentary and commonly

available test equipment.

4.1.1.4. TEST EQUIPMENT REQUIRED

1. Signal generator capable of amplitude modulation

2. Input impedance matching network

3. Termination resistor for receiver audio output port

4a. AF power meter

OR,

4b. A.C. voltmeter

4.1.1.5. PROCEDURE

1. Connect the input port of the receiver to the output port

of the SIGNAL GENERATOR through an IMPEDANCE MATCHING NETWORK

that provides the specified source impedance, , to the receiver

at the measurement frequency, f^. If the signal generator output

impedance equals Z^, no matching network is required.

2a. Connect the TERMINATION RESISTOR having a resistance equal

to the specified load resistance, R^ , and a power rating in excess

of the receiver's rated audio output power level, to the audio

output port of the receiver. Connect the A.C. VOLTMETER across this

resistor

.

OR,

2b. Connect the POWER METER, having an input impedance equal

to the specified load resistance, R^ , to the audio output port of

the receiver.

29
3a. Set the voltmeter on a range to indicate the reference

output power, . The voltage to be measured is given by the equation

o * o £

OR,

3b. Set the power meter on a range to indicate the reference

output power, P^.

4. Set receiver controls as given in Table IV.

5. Tune the signal generator and the receiver to the measurement

frequency, f^

.

6. Adjust the amplitude modulation in the signal generator

to 30% at 10 00 Hz.

7. Adjust the output level of the signal generator to give

reference audio power output, P^ , from the receiver.

8. Determine the open circuit signal voltage, , in microvolts,

at the OUTPUT TERMINALS of the matching network, if used; otnerwise,

at the output terminals of the generator. This is the SENSITIVITY

of the receiver at frequency f^.

4.1.1.6. DATA REQUIRED

1. Record the measurement frequency, f^, in kilohertz or

megahertz.

2. Record the value of source impedance, , in ohms, connected

to receiver input port.

30
TABLE IV

Gain- Limited Sensitivity

Initial Control Settings

contiro L betting

J.

.

canu owxtcn ± . AS aesirea

r x^cv^uciioy 1 uxixxig ^ .

•3 J • } "Do ^Ir XT c ClJS.

4 RP f^s 1 n 4 M ^ V "1 TTmm

•J m TP "i n -J

.

o • AP C.^ ^ n D .

. A 3 V n Tim T TTl 1'iCtXXlUU.lll

7 IjXXIC oaxxi 7 Vw/p t X CJXl dX

Qo . Detector Mode Qo . AMA M

Q Beat Frequency Oscillator Q Ur r

Br u r requency 1 n ±u . JN . A .

11. IF Bandwidth 11. As desired

12. AF Bandwidth 12. As desired

13. Noise Limiter 13. OFF

14. Squelch Level 14. OFF

15 . AGC/MGC Mode Switch 15. MGC

16. Meter Switch 16 . Optional

31
3. Record the value of termination resistance, R^

,

in ohms, connected to receiver audio output terminals.

4a. Record the output voltage, , in volts

OR,

4b. Record the reference output power, , in watts.

5. Record the open circuit signal voltage, E_j^, in microvolts,

at the output terminals of the matching network, if used; otherwise, at the output terminals of the generator. E^ is the sensitivity of the receiver.

4.1.1.7. MEASUREMENT ERRORS

The principal sources of measurement error are the following:

1. Uncertainty, Ae^, in the measured value of E^

2a. Uncertainty, Ae^ , in the measured value of E^

OR,

2b. Uncertainty, '^P^ / in the measured value of

The total relative uncertainty, Ae^(%) , in the receiver

sensitivity, E^, expressed as a percent, is given by the equations

Ae

OR

.(%) = (-^ X loo) +(4^ X loo) ,

AE^(%) = X lOo) +( I

X 100^ .

The uncertainty, AE^, is obtained from the manufacturer's

specifications on the output level indication of the signal

generator. Uncertainties AE^ and/or AP^ are obtained from the

manufacturer's specifications on the voltmeter and/or power

meter, respectively.

32
4.1.2. 6 dB SN/N SENSITIVITY OF A NOISE-LIMITED AM RECEIVER

4.1.2.1. DEFINITIONS

a. The 6 dB SN/N sensitivity of a noise-limited AM receiver

is the open circuit output voltage, in microvolts, from a signal

generator amplitude modulated 30% with a 1000 Hz sinusoid, that

will produce a signal-plus-noise-to-noise ratio (SN/N) of 4

(6 dB) at the reference audio output power level from the receiver

output terminals.

b. A noise- limited receiver is a receiver whose gain and

internal noise are such that, when its input termination has a noise temperature of 290K, reference audio output power can be

produced in its output termination by amplification of system

noise alone.

4.1.2.2. PURPOSE

The purpose of this measurement method is to measure the 6 dB

SN/N sensitivity of noise-limited AM receivers. For such receivers, 6 dB SN/N sensitivity is essentially a measure of the

smallest signal that has a usable strength. The method ignores

the effects of distortion; therefore, for non-linear receivers

it does not yield accurate results.

4.1.2.3. METHOD

The method uses an amplitude modulated signal generator and

a power meter or true rms voltmeter as shown in figure 4.1.2.

The signal generator supplies a known voltage to the receiver

at the measurement frequency. The voltmeter or power meter indicates the receiver output signal level.

The generator level is adjusted to the open circuit output

voltage that will produce a 6 dB signal-plus-noise-to-noise ratio

at reference audio output power from the receiver. This voltage

is the 6 dB SN/N sensitivity of the receiver.

33
o

1—1

d

\— o

<: I—

llj

llj cc: o O LU A

LJ- 1—

LlJ >1—1 o

CE

I—

LU

Q

UJ

C_J CD ^ ^ ^

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UJ (_) 2- 1— ^ CC LU

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34
Measurement uncertainties as small as 3% are possible under

best conditions, and range from approximately 5% to 20% under

typical conditions . This method uses rudimentary and commonly

available test equipment.

4.1.2.4. TEST EQUIPMENT REQUIRED

1 . Signal generator capable of amplitude modulation

2. Input impedance matching network

3. Termination resistor for receiver audio output port

4a. AF power meter

OR,

4b. True rms voltmeter

4.1.2.5. PROCEDURE

1. Connect the input port of the receiver to the output port

of the SIGNAL GENERATOR through an IMPEDANCE MATCHING NETWORK

that provides the specified source impedance, Z^, to the receiver

at the measurement frequency, f^ . If the signal generator output

impedance equals Z^, no matching network is required.

2a. Connect the TERMINATION RESISTOR having a resistance equal

to the specified load resistance, R,^ , and a power rating in excess

of the receiver's rated audio output power level, to the audio output

port of the receiver. Connect the TRUE RMS VOLTMETER across the

resistor

.

OR,

35
2b. Connect the POWER METER, having an input impedance equal

to the specified load resistance, R^ , to the audio output port of

the receiver.

3a. Set the voltmeter on a range to indicate the reference

output power, P^. The voltage to be measured is given by the

equation

E =\/pT7 o ' o £

OR,

3b. Set the power meter on a range to indicate the reference output power, P^.

4. Set the receiver controls as given in Table V.

Note: Check to make sure the maximum gain setting does

not produce signal clipping or compression in the

latter IF amplifier stages. If clipping or compression occurs, reduce RF or IF gain.

5. Tune the signal generator and the receiver to

measurement frequency, f^.

6. Adjust the amplitude modulation in the signal

to 30% at 1000 Hz.

7. With the signal generator connected and its output set

to zero, adjust the receiver AF gain control to produce 25% of

reference audio output power, P^. This will be noise power only.

8. Adjust the output level of the signal generator to give

reference audio output power, P^. This will be approximately 25%

noise power and 75% audio signal power (1000 Hz), and corresponds

to a 6 dB signal-plus-noise-to-noise ratio.

9. Determine the open circuit signal voltage, E^ , in microvolts, at the OUTPUT TERMINALS of the matching network, if used;

otherwise, at the output terminals of the generator. This is

the 6 dB SN/N SENSITIVITY of the receiver at the frequency f^.

36

the

generator
TABLE V

6 dB SN/N Sensitivity

Initial Control Settings

Control Setting

1

.

Band Switch 1

.

As desired

2 . Frequency Tuning 2

.

As desired

3 . Antenna Trimmer 3

.

Peak

4 . RF Gain 4

.

Maximum

5 . IF Gain 5 . Maximum

6 . AF Gain 6 . As required

7 . Line Gain 7. Optional

8 . Detector Mode 8

.

AM

9 . Beat Frequency Oscillator 9 . OFF

10 . BFO Frequency 10 . N.A.

11. IF Bandwidth 11. As desired

12 . AF Bandwidth 12. As desired

13. Noise Limiter 13. OFF

14. Squelch Level 14 . OFF

15 . AGC/MGC Mode Switch 15. MGC

16 . Meter Switch 16 . Optional

37
4.1.2.6. DATA REQUIRED

1. Record the measurement frequency, f ^ , in kilohertz or

megahertz

2. Record the value of source impedance, , in ohms, connected

to receiver input port.

3. Record the value of termination resistance, R^, in ohms,

connected to receiver audio output terminals.

4a. Record the output voltage, E^, in volts.

OR, ' ^

4b. Record the reference output power, , in watts.

5. Record the open circuit signal voltage, E^ , in microvolts.

at the output terminals of the matching network, if used; otherwise,

at the output terminals of ti sensitivity of the receiver.at the output terminals of the generator. E^ is the 6 dB SN/N

4.1.2.7. MEASUREMENT ERRORS

The principal sources of measurement error are the following

1. Uncertainty, AE. , in the measured value of E.

1 1

2a. Uncertainty, AE , in the measured value of E o o

OR,

2b. Uncertainty, AP , in the measured value of P o o

38
The total relative uncertainty, AE^ (%) , in the receiver

sensitivity, E^, expressed as a percent, is given by the

equations

or

/AE. \ / AE • AE^(%) = xlOOj + X looj ,

.(%) = xloo) 4- AE (I

^ X lOo)

The uncertainty, AE^, is obtained from the manufacturer's

specifications on the output level indication of the signal

generator. Uncertainties AE^ and/or AP^ are obtained from

the manufacturer's specifications on the voltmeter and/or

power meter, respectively.

39
4.1.3. 12 dB SINAD SENSITIVITY OF A NOISE-LIMITED AM RECEIVER

4.1.3.1. DEFINITIONS

a. SINAD is an acronym for the phrase "signal plus noise

plus distortion to noise plus distortion ratio."

S + N + D

N + D

P (s+n+d) ^(n+d)

SINAD =

b. The 12 dB SINAD sensitivity of a noise-limited AM receiver

is the open -circuit output voltage, in microvolts, from a signal

generator amplitude modulated 30% with a 1000 Hz sinusoid, that

will produce a SINAD of 16 (12 dB) at no less than 50% of the

reference audio output power from the receiver output terminals

.

c. A noise-limited receiver is a receiver whose gain and

internal noise are such that, when its input termination has a noise temperature of 290K, reference audio output power can be

produced in its output termination by amplification of system

noise alone.

4.1.3.2. PURPOSE

The purpose of this measurement method is to measure the 12 dB

SINAD sensitivity of noise-limited AM receivers. For such receivers,

SINAD sensitivity is a measure of the smallest typical signal that

has usable strength and that produces an audio output signal of

acceptable quality. The method takes into account the effects of

distortion within the receiver; therefore, it can be a more

meaningful measure of sensitivity than 6 dB SN/N sensitivity

for real-world receivers

.

40
4.1.3.3. METHOD

The method uses an amplitude modulated signal generator and

an audio distortion analyzer as shown in figure 4.1.3. The signal

generator supplies a known voltage to the receiver at the

measurement frequency. The distortion analyzer measures the power

in the audio output from the receiver under two conditions; viz.,

(a) with the 1000 Hz modulating signal present, and (b) with the

1000 Hz modulating signal filtered from the audio output power.

The generator level is adjusted to the open circuit output voltage

that causes the ratio of (a) to (b), above, expressed in decibels,

to be 12 dB. This voltage is the 12 dB SINAD sensitivity of the

receiver

.

Measurement uncertainties as small as 5% are possible under

best conditions, and range from approximately 8% to 30% under

typical conditions. This method uses commonly available test

equipment of moderate sophistication.

4.1.3.4. TEST EQUIPMENT REQUIRED

1. Signal generator capable of amplitude modulation

2. Input impedance matching network

3. Termination resistor for receiver audio output port

4. Audio distortion analyzer

4.1.3.5. PROCEDURE

1. Connect the input port of the receiver to the output port

of the SIGNAL GENERATOR through an IMPEDANCE MATCHING NETWORK that

provides the specified source impedance, Z^, to the receiver at

the measurement frequency, f^. If the signal generator output

impedance equals Z ^ no matching network is required.

41
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I— o

<a; I—

t—I (—1

llj UJ ck:

< > U- I—

UJ o

>

»—

1

o t—

UJ

c

UJo o

^ ^

Q z: o

ui o 3

Q. 1— t— S cC UJ

•-H 2: ^

o

_i 1—

<: <

CD UJ

1—! 00 Ul

o q;

I—I Ul I— M

q; >- o _J

h- <:

c/l ^

1-1 <t Q

42
2. Connect the TERMINATION RESISTOR having a resistance equal

to the specified load resistance, R^ , and a power rating in excess

of the receiver's rated audio output power level, to the audio

output port of the receiver. Connect the audio DISTORTION ANALYZER

across this resistor.

3. Set the distortion analyzer on a range to indicate the

reference output power, P^.

4. Set receiver controls as given in Table VI.

Note: Check to make sure the maximum gain setting does not

produce signal clipping or compression in the latter

IF amplifier stages. If clipping or compression

occurs, reduce RF or IF gain.

5. Tune the signal generator and the receiver to the measurement frequency, f^.

6. Adjust the amplitude modulation in the signal generator

to 30% at 1000 Hz.

7. Set the signal generator output level to 10 00 microvolts.

8. Adjust the receiver AF gain control to produce reference

audio output power, P^. This is ^(s+n+d)*

9. Adjust the distortion analyzer so that the 1000 Hz rejection filter tunes out the 1000 Hz modulation from the signal

generator.

10. Measure the noise plus distortion output power, ^(j^+^j)*

11. Calculate SINAD, in decibels, from the equation

P

SINAD (dB) = 10 log 5—2

(n+d)

43
TABLE VI

12 dB SINAD Sensitivity (AM)

Initial Control Settings

Control Setting

1. Band Switch 1. As desired

2. Frequency Tuning 2 . As desired

3. Antenna Trimmer 3. Peak

4 . RF Gain 4 . Maximum

5 . IF Gain 5 . Maximum

6 . AF Gain 6 . As required

7. Line Gain 7. Optional

8. Detector Mode 8. AM

9. Beat Frequency Oscillator '3. OFF

10. BFO Frequency 10. N.A.

11. IF Bandwidtn 11. As desired

12. AF Bandwidth 12. As desired

13. Noise Limiter 13. OFF

14. Squelch Level 14. OFF

15. AGC/xMGC Mode Switcn 15. As desired

16. Meter Switcn 16. Optional

44
12. If SINAD calculated in Step 11 is greater (or less)

than 12 dB , decrease (or increase) the signal generator output

by 3 dB or smaller and repeat Steps 8 through 11. Continue this

procedure until 12 dB SINAD is obtained.

Note: If 12 dB SINAD cannot be reached by INCREASING

the signal generator output, the receiver is

probably distortion-limited. In this case, an

alternate reference SINAD such as 6 dB may be used.

13. Determine the open circuit signal voltage, , in

microvolts, at the OUTPUT TERMINALS of the matching network, if

used; otherwise, at the output terminals of the generator.

This is the 12 dB SINAD SENSITIVITY of the receiver at frequency f

4.1.3.6. DATA REQUIRED

1. Record the measurement frequency, f^ , in kilohertz or

o

megahertz

2. Record the value of source impedance, , in ohms,

connected to receiver input port.

3. Record the value of termination resistance, R^^, in ohms,

connected to receiver audio output terminals.

4. Record the reference output power, , in watts.

5. Record the SINAD ratio in decibels.

6. Record the open circuit signal voltage, E^ , in microvolts.

at the output terminals of the matching network, if used, otherwise,

at the output terminals of 1 sensitivity of the receiverat the output terminals of the generator. E^ is the 12 dB SINAD

45
4.1.3.7. MEASUREMENT ERRORS

The principal sources of measurement error are the

following:

1. Uncertainty, AE^, in the measured value of E^

2. Uncertainty, AP , in the measured value of P ^ o o

3. Uncertainty, AP , in the measured value of P ,

,

n+d n+d

The total relative uncertainty, AE^(%), in the 12 dB SINAD

sensitivity, E^, expressed as a percent, is given by the

equation

AE . \ / n AP \ / -, AP

AE

The uncertainty, AE^ , is obtained from the manufacturer's

specifications on the output level indication of the signal

generator. Uncertainties AP and AP are obtained from the ^ o n+d

manufacturer's specifications on the distortion analyzer.

46
4.1.4. QUIETING SENSITIVITY OF AN FM RECEIVER WITH ONE

OR MORE LIMITERS

4.1.4.1. DEFINITION

The quieting sensitivity of a receiver is the minimum amount

of signal from an unmodulated standard input signal source that

is required to produce 20 decibels of noise quieting measured at

the receiver audio output. (EIA RS-204)

Noise quieting is the reduction of audio noise output power

caused by the presence of an input signal to the receiver.

4.1.4.2. PURPOSE

The purpose of this measurement method is to measure the

quieting sensitivity of FM receivers containing one or more

amplitude limiter stages preceding the FM demodulator circuit.

For such receivers, quieting sensitivity is a measure of the

degree to which its limiters suppress amplitude fluctuations

such as external and internal noise signals. The method ignores

the effects of non-linearity in the audio stages; therefore, it

may yield slightly inaccurate results.

4.1.4.3. METHOD

The method uses an unmodulated signal generator and a true

rms voltmeter or power meter as shown in figure 4.1.4. The signal

generator supplies a known voltage to the receiver at the

measurement frequency. The voltmeter or power meter indicates the

receiver output noise power level.

47
CE C3

=3: ED in o o s

h- I— 1—1 d UJ

-P

r-(>

•^^ -P•Hwc

COcH

-P

(U

•^^dao

4J

cnw

(U Eh

r-i Cm o

—J I—

CJ3 LlJ

48
The generator level is adjusted to the open circuit output

voltage that produces 20 dB of noise quieting as measured with

the voltmeter or power meter. This voltage is the quieting

sensitivity of the receiver.

Measurement uncertainties as small as 3% are possible under

best conditions, and range from approximately 5% to 20% under

typical conditions. This method uses rudimentary and commonly

available test equipment.

4.1.4.4. TEST EQUIPMENT REQUIRED

1. CW signal generator

2. Input impedance matching network

3. Termination resistor for receiver audio output port

4a. AF power meter

OR,

4b. True rms voltmeter

4.1.4.5. PROCEDURE

1. Connect the input port of the receiver to the output

port of the SIGNAL GENERATOR through an IMPEDANCE MATCHING

NETWORK that provides the specified source impedance, , to

the receiver at the measurement frequency, f^. If the signal

generator output impedance equals , no matching network is

required.

49
2a. Connect the TERMINATION RESISTOR having a resistance

equal to the specified load resistance, R^, and a power rating

in excess of the receiver's rated audio output power level,

to the audio output port of the receiver. Connect the TRUE RMS

VOLTMETER across this resistor.

OR,

2b. Connect the POWER METER, having an input impedance equal

to the specified load resistance, R^ , to the audio output port of the

receiver.

3a. Set the voltmeter on a range to indicate 25% of the

d output

the equation

rated power, . The voltage to be measured is given by

E = 0.5 VP R„ o ^ o £

OR,

3b. Set the power meter on a range to indicate 25% of the

rated output power, P^.

4. Set receiver controls as given in Table VII.

5. Tune the signal generator and the receiver to the

measurement frequency, f^.

6. Adjust the signal generator so that the signal is

unmodulated. '

'

7. With the signal generator connected and its output set to

zero, adjust the receiver AF gain control to produce 25% of rated

audio output power, P^ . This will be noise power only.

50
TABLE VII

Quieting Sensitivity

Initial Control Settings

Control Setting

1. Band Switch 1. As desired

2. Frequency Tuning 2. As desired

3 . Antenna Trimmer 3. Peak

4. RF Gain 4. Maximum

5 . IF Gain 5. Maximum

6 . AF Gain 6 . As required

7 . Line Gain 7. Optional

8 . Detector .4ode 8. FM

9 . Beat Frequency Oscillator 9 . OFF

10 . BFO Frequency 10 . N. A.

11. IF Bandwidth 11. As desired

12 . AF Bandwidth 12. As desired

13. Noise Limiter 13. OFF

14 . Squelch Level 14. OFF

15 . AGC/MGC Mode Switch 15 . As desired

16. Meter Switch 16 . Optional

51
8. Increase the output level of the signal generator until the

audio output noise power level is reduced to 0.25% of P (0.0025 P ). o o This is a reduction to 20 dB below the level indicated in Step 7^

above

.

Note: If the output noise power level cannot be

^ reduced to 0.25% of P , select some other

o target value such as 2.5% of P (reduction

o of 10 dB)

.

9. Determine the open circuit signal voltage E. , in microvolts,

at the OUTPUT TERMINALS of the matching network, if used; otherwise,

at the output terminals of the generator. This is the 20 dB

QUIETING SENSITIVITY of the receiver at the frequency f ^

.

4.1.4.6. DATA REQU IRED

1. Record the measurement frequency, f^ , in kilohertz or

megahertz

.

2. Record the value of source impedance, , in ohms,

connected to receiver input port.

3. Record the value of termination resistance, R^ , in ohms,

connected to receiver audio output terminals

.

4a. Record the measured output voltage, E^, in volts,

from Step 3a, above.

OR,

4b. Record the measured output power, 0.25 P^ , in watts,

from Step 3b, above.

5. Record the measured output voltage, 0.1 E^ , in volts,

or the measured output power, 0 .0 0 25 P^ , in watts, from Step 8

above

.

52
(If the 10 dB , or other, level of quieting sensitivity is

measured, record the measured values of output voltage or power

for this criterion.)

6. Record the open circuit signal voltage, in microvolts,

at the output terminals of the matching network, if used; otherwise, at the output terminals of the generator. is the

quieting sensitivity of the receiver

4.1.4.7. MEASUREMENT ERRORS

The principal sources of measurement error are the following

1. Uncertainty, AE_j^, in the measured value of E_j^

'

2. Uncertainty, '^^q ' the measured value of E^

3. Uncertainty, / the measured value of

The total relative uncertainty, Ae^(%) , in the receiver

sensitivity, E^, expressed as a percent, is given by the

equations

AE^(%) = (-^ X loo] +(yJT

^ X looj ,

or

AE .(%) X loo) t(^^^ X lOo)

The uncertainty, AE^, is obtained from the manufacturer's

specifications on the output level indication of the signal

generator. Uncertainties AE^ and/or AP^ are obtained from the

manufacturer's specifications on the voltmeter and/or Dower

meter, respectively.

53
4.1.5. 12 dB SINAD SENSITIVITY OF AN FM RECEIVER WITH

J ONE OR MORE LIMITERS

4.1.5.1. DEFINITIONS

a. SINAD is an acronym for the phrase "signal plus noise

plus distortion to noise plus distortion ratio."

SINAD =

S + ^ + P blNAU = !i£±n±i)

N + D

(n+d)

b. The 12 dB SINAD sensitivity of an FM receiver with one

or more limiters is the open circuit output voltage, in microvolts, from a signal generator frequency modulated ±60% of

maximum rated system deviation with a 1000 Hz sinusoid, that

will produce a SINAD of 16 (12 dB) at no less than 50% of the

reference audio output power from the receiver output terminals

Note: The rated system deviation, in kilohertz, is

found by reference to specifications for the

given system. It is typically ±5 kHz to ±25 kHz.

4.1.5.2. PURPOSE

The purpose of this measurement method is to measure the

12 dB SINAD sensitivity of FM receivers containing one or more

amplitude limiter stages preceding the FM demodulator circuit.

For such receivers, 12 dB SINAD sensitivity is a measure of the

smallest typical signal that has usable strength and that

produces an audio output signal of acceptable quality. The

method takes into account the effects of distortion within the

receiver; therefore, it can be a more meaningful measure of

sensitivity than Quieting Sensitivity for real-world receivers.

54
4.1.5.3. METHOD

The metJiod uses a frequency modulated signal generator and

an audio distortion analyzer as shown in figure 4.1.5. The signal

generator supplies a known input voltage to the receiver at the

measurement frequency. The distortion analyzer measures the power

in the audio output from the receiver under two conditions; viz.,

(a) with the 1000 Hz modulating signal present, and (b) with the

1000 Hz modulating signal filtered from the audio output power.

The generator level is adjusted to the open circuit output voltage

that causes the ratio of (a) to (b), above, expressed in decibels,

to be 12 dB . This voltage is the 12 dB SINAD sensitivity of the

receiver.

Measurement uncertainties as small as 5% are possible under

best conditions, and range from approximately 8% to 30% under

typical conditions. This method uses commonly available test

equipment of moderate sophistication.

4.1.5.4. TEST EQUIPMENT REQUIRED

1. Signal generator capable of frequency modulation

2. Input impedance matching network

3. Termination resistor for receiver audio output port

4. Audio distortion analyzer

4.1.5.5. PROCEDURE

1. Connect the input port of the receiver to the output

port of the SIGNAL GENERATOR through an IMPEDANCE MATCHING

NETWORK that provides the specified source impedance, , to

the receiver at the measurement frequency, f^. If the signal

generator output impedance equals , no matching network is

required.

55
oI—I CC I— o

cC I—

I—I I—

I

s: 00

UJ

UJ ai

o q:

I—I UJ

(- M

q: >• o _J

UJ o

o I—

UJ z

UJ

C_J CJ3 Z Z

cC •--1 q: Q n: o

UJ O 3

Q- (— 1—

s: <: UJ

•-H s: 2:

0

_i 1—

•a: <

UJ

l-H

1/1 GE

>i

-p -H>

-H

+J -HW

CD COQ

g

H

W

o

-P

Q) CO+J

03(D EH

in

•H

Cm

56
2. Connect the TERMINATION RESISTOR having a resistance

equal to the specified load resistance, R,^ , and a power rating

in excess of the receiver's rated audio output power level, to

the audio output port of the receiver. Connect the audio

DISTORTION ANALYZER across this resistor.

3. Set the distortion analyzer on a range to indicate the

reference output power, P^.

4. Set receiver controls as given in Table VIII.

5. Tune the signal generator and the receiver to the

measurement frequency, f^.

6. Adjust the frequency modulation in the signal generator

to ±60% of rated system deviation at 1000 Hz.

7. Set the signal generator output to 1000 microvolts.

8. Adjust the receiver AF gain control to produce rated

audio output power, P . This is P, , , . ^ ^ o (s+n+d)

9. Adjust the distortion analyzer so that the 1000 Hz

rejection filter tunes out the 1000 Hz modulation from the

signal generator.

10. Measure the noise plus distortion output power, P

^^^^.^^^

11. Calculate SINAD, in decibels, from the equation

P

SINAD (dB) = 10 log ° ^(n+d)

12. If SINAD calculated in Step 11 is greater (or less)

than 12 dB , decrease (or increase) the signal generator output

by 3 dB or smaller and repeat Steps 8 through 11. Continue this

procedure until 12 dB SINAD is obtained.

57
TABLE VIII

12 dB SINAD Sensitivity (FM)

Initial Control Settings

Control Setting

1. Band Switch 1. As desired

2. Frequency Tuning 2. As desired

3. Antenna Trimmer 3. Peak

4 . RF Gain 4. Maximum

5 . IF Gain 5 . Maximum

6 . AF Gain 6 . As required

7 . Line Gain 7. Optional

8. Detector Mode 8. FM

9 . Beat Frequency Oscillator 9 . OFF

10 . BFO Frequency 10 . N.A.

11. IF Bandwidth 11. As desired

12. AF Bandwidth 12. As desired

13. Noise Limiter 13. OFF

14 . Squelch Level 14 . OFF

15 . AGC/MGC Mode Switch 15 . As desired

16 . Meter Switch 16 . Optional

58
Note: If 12 dB SINAD cannot be reached by INCREASING

the signal generator output, the receiver is

probably distortion-limited. In this case, an

alternate reference SINAD such as 6 dB may be

used

.

13. Determine the open circuit signal voltage, , in

microvolts, at the OUTPUT TERMINALS of the matching network, if

used? otherwise, at the output terminals of the generator. This

is the 12 dB SINAD SENSITIVITY of the receiver at frequency f^.

4.1.5.6. DATA REQUIRED

1. Record the measurement frequency, f^, in kilohertz or

megahertz

.

2. Record the value of source impedance, , in ohms,

connected to receiver input port.

3. Record the value of termination resistance, R^^ , in

ohms, connected to receiver audio output terminals.

4. Record the reference output power, P^, in watts.

5. Record the SINAD ratio in decibels.

6. Record the open circuit signal voltage, E^ , in

microvolts, at the output terminals of the matching network,

if used; otherwise, at the output terminals of the generator.

is the 12 dB SINAD sensitivity of the receiver.

59
4.1.5.7. MEASUREMENT ERRORS

The principal sources of measurement error are the following:

1. Uncertainty, AE . , in the measured value of E.

1 1

2. Uncertainty, AP , in the measured value of P

o o

3. Uncertainty, AP , , in the measured value of P , n+d

The total relative uncertainty, AE^(%), in the 12 dB SINAD

sensitivity, E^, expressed as a percent, is given by the

equation

AE

The uncertainty, AE^^, is obtained from the manufacturer's

specifications on the output level indication of the signal

generator. Uncertainties AP and AP , , are obtained from the ^ o n+d

manufacturer's specifications on the distortion analyzer.

60
4.1.6. NOISE FACTOR

4.1.6.1. DEFINITION

Receiver noise factor (noise figure) , F, is the ratio of

(a) signal-to-noise power ratio, S^/N^ , at the antenna terminals

to (b) signal-to-noise ratio, S^/N^, at the output terminals of

the receiver, when the input termination is at standard temperature

(290K)

.

S./N.

^ " s"7n~

o o

This definition is an adaptation of the IEEE definition of Average

Noise Factor for the particular case of surveillance receivers.

Noise factor is usually expressed in decibels; that is,

F(dB) = 10 log F.

4.1.6.2. PURPOSE

The purpose of the following measurement methods is to measure

the average noise factor of AM and FM receivers. Noise factor is

a measure of the amount of noise power added to a signal by the

receiver, thereby degrading the signal quality.

Four methods of measurement are given, and the method used will

depend upon the test equipment available, the desired accuracy, and

the time available to devote to the measurement. Noise figure is

usually measured only for the linear parts of the receiver that

precede the demodulatot . For CW and AM receivers, this includes the

RF and IF stages up to the second detector. For FM receivers, this

includes the RF and IF stages up to the first limiter stage. For

receivers with a linear demodulator, such as a product detector,

noise figure may be measured for the entire receiver from the

antenna input terminals to the audio output terminals.

61
4.1.6.3. METHOD - AUTOMATIC NOISE FIGURE METER

This method uses an automatic noise figure meter (ANFM)

,

which includes a switched random noise generator, as shown in

figure 4.1.6.1. The ANFM cyclically switches the noise generator between two output power levels, and automatically computes

noise figure from the output signal of the receiver. The measured noise figure is displayed by the panel meter on the ANFM.

Measurement uncertainties as small as 0.3 dB are possible

under best conditions, and range from approximately 0.5 dB to

1.5 dB under typical conditions. The method uses equipment that

is commonly available for use above 30 MHz, limited availability

between 10 and 30 MHz, but unavailable below 10 MHz. It is

typically quick and convenient to perform, and is especially

convenient when making adjustments to optimize receiver noise

figure

4.1.6.3.1. TEST EQUIPMENT REQUIRED

1. Automatic noise figure meter (ANFM)

2 . Noise generator for use with the ANFM

3. Input impedance matching transformer

4.1.6.3.2. PROCEDURE

1. Connect the input port of the receiver to the output port

of the NOISE GENERATOR through an IMPEDANCE TRANSFORMER that

provides the specified source impedance, Z^, to the receiver at

the measurement frequency, f ^ . If the noise generator output

impedance equals Z , no transformer is needed.

62
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63
2. Connect the input port of the ANFM to the output

last linear IF amplifier stage. Follow the instructions

manufacturer of the ANFM to make this connection.

of th

of th

3. Set receiver controls as given in Table IX.

Note: For some receivers, maximum RF/IF gain may

produce overloading either in the latter IF

stages or in the amplifier of the ANFM. In

this case, set the RF/IF gain to produce an

input level to the ANFM that is from 3 dB to

10 dB greater than the minimum level required

by the ANFM.

Tune the receiver to the measurement frequency, f^

.

Adjust the ANFM according to manufacturer's instrucThis usually includes a calibration adjustment, a mode

selection, and selection of scale range.

6. Measure noise factor, F, in decibels, by following the

procedure given by the manufacturer.

7. Correct the measured value of F as instructed by the

manufacturer. Also correct the results for the effect of the

impedance transformer, if used. This is the noise factor, in

decibels, of the linear portions of the receiver RF/IF stages

when tuned to frequency f ^

.

4.1.6.3.3. DATA REQUIRED

1. Record the measurement frequency, f^ , in kilohertz

or megahertz.

2. Record the value of source impedance, Z^, in ohms,

connected to the receiver input port.

3. Record the measured value of F, in decibels.

4.

5.

tions

.
TABLE IX

Noise Factor, ANFM Method

Initial Control Settings

Control Setting

1. Band Switch 1. As desired

2 . Frequency Tuning 2. As desired

3. Antenna Trimmer 3. Peak

4 . RF Gain 4. Maximum

5 . IF Gain 5. As required

6 . AF Gain 6 . N.A.

7 . Line Gain 7 . N. A.

8 . Detector Mode 8. N.A.

9 . Beat Frequency Oscillator 9 . OFF

10 . BFO Frequency 10 . N.A.

11. IF Bandwidth 11. As desired

12. AF Bandwidth 12 . N.A.

13. Noise Limiter 13 . OFF

14 . Squelch Level 14 . N.A.

15 . AGC/MGC Mode Switch 15. MGC

16 . Meter Switch 16 . N.A.

65
4. Record the Corrections applied to the measured value of

F. These include the following:

a. Noise generator termination temperature

b. VSWR

c. Impedance transformer loss

d. Cable loss

e. Image response

4.1.6.3.4. MEASUREMENT ERRORS

The principal sources of measurement error are the following:

1. Uncertainty,

noise generator

AT , in the noise temperature, T, , of the

2. Uncertainty, AT , of the ambient temperature, T , of

a a the generator termination

3. Uncertainty, AF^, in F due to the VSWR of the generator

impedance

4. Uncertainty, AF^, in F due to image response

5. Uncertainty, ^^q' ^ ^® uncertainty in the

ANFM calibration

The total uncertainty, AF, in the measured value of F will

vary according to the particular ANFM system used. Refer to the

manufacturer's operating manual for the procedure for determining

AF.

66
4.1.6.4. METHOD - Y-FACTOR/POWER METER

This method uses a pair of random noise generators and a power meter as shown in figure 4.1.6.2. The hot and cold noise

generators supply known input noise powers to the receiver in

a band of frequencies which includes that to which the receiver

is tuned. The power meter measures the power levels from the last

linear IF stage. The ratio of the two power levels corresponding

to the two input power levels is the Y-f actor. Noise factor is

computed from the measured Y-factor and the known power levels of

the two generators

.

Measurement uncertainties as small as 0.2 dB are possible

under best conditions, and range from approximately 0.3 dB to

1 dB under typical conditions. The method uses sophisticated

equipment, but it is commonly available.

4.1.6.4.1. TEST EQUIPMENT REQUIRED

1. Hot random noise generator

2. Cold random noise generator

3. Input impedance matching transformer

4 . Power meter

4.1.6.4.2. PROCEDURE

1. Connect the input port of the receiver to the output

port of the HOT NOISE GENERATOR through an IMPEDANCE TRANSFORMER

that provides the specified source impedance, , to the receiver

at the measurement frequency, f^ . If the noise generator output

impedance equals Z , no transformer is needed.

67
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68
2. Connect the input port of the POWER METER to the output

of the last linear IF amplifier stage.

3. Set receiver controls as given in Table X.

Note: For some receivers, maximum RF/IF gain may

produce overloading in the latter IF stages.

In this case, set the controls to produce

maximum RF gain without overload anywhere in

the measurement system.

4. Tune the receiver to the measurement frequency, f^.

5. i«leasure the output power, P^^, from the last linear IF

amplifier stage.

6. Disconnect the hot noise generator and connect the

COLD NOISE GENERATOR in its place.

7. I4easure the output power, P^, from the last linear IF

amplifier stage.

8. Calculate the Y-f actor from the equation

i

p

c

9. Calculate the noise factor from the equation

T^ - YT

F = ^ + 1

290 CY-1)

and

F (dB) = 10 log F

This is the noise factor, in decibels, of the linear portions

of the receiver RF/IF stages when tuned to frequency f^

69
TABLE X

Noise Factor, Y-Factor/Power Meter Method

Initial Control Settings

Control Setting

1. Band Switch 1. As desired

2 . Frequency Tuning 2. As desired

3. Antenna Trimmer 3. Peak

4 . RF Gain , 4. Maximum

5. IF Gain 5 . As required

6 . AF Gain 6 . N. A.

7. Line Gain 7. N.A.

8 . Detector Mode 8 . N. A.

9 . Beat Frequency Oscillator 9

.

OFF

10 . BFO Frequency : 10 . N.A.

11. IF Bandwidth 11. As desired

12 . AF Bandwidth 12 . N.A.

13. Noise Limiter 13. OFF

14 . Squelch Level 14 . N.A.

15 . AGC/MGC Mode Switch 15. MGC

16 . Meter Switch 16 . N.A.

70
4.1.6.4.3. DATA REQUIRED

1. Record the measurement frequency, f^, in kilohertz or

megahertz

2. Record the value of source impedance, , in ohms,

connected to the receiver input port.

3. Record the noise temperature, T^^ , in kelvins, of the

hot noise generator.

4. Record the noise temperature, T^, in kelvins, of

the cold noise generator.

5. Record the output power, P^^ , in milliwatts.

6. Record the output power, , in milliwatts.

7. Record the calculated Y-f actor, Y.

8. Record the calculated value of noise factor, F, in

decibels

4.1.6.4.4. MEASUREMENT ERRORS

The principal sources of measurement error are the following

1. Uncertainty,

^'^i^' noise temperature, T^^ , of the

hot noise generator

2. Uncertainty, AT^, in the noise temperature, T^ , of the

cold noise generator

3. Uncertainty, ^'^^^r the measured value of P^^

4. Uncertainty, AP , in the measured value of P

^ c c

71
The total uncertainty, AF , in the calculated value of F

is given by the equation

AF = Ci AT, + C2 AT + C3 AY. h c

The uncertainty coefficients Ci, C2 , and C3 are given by the

equations

Ci =

C2 =

and

1

290 (Y - 1)

-Y

290 (Y - 1)

T

c

- \

290 (Y - 1)

The uncertainties AT, and AT are obtained from the manufach c turer ' s specifications or from the results of calibrating T^

and T^ . Uncertainty AY is given by the relation

AY = AP, +AP h c

where AP^ and AP^ are obtained from the manufacturer's specifications on the power meter.

The relative measurement uncertainty, AF(dB) , expressed in

decibels, is given approximately, for small uncertainties, by

the equation

AF (dB) = 10 log ( 1 + ^

72
4.1.6.5. METHOD - Y-FACTOR/ATTENUATOR

This method uses a pair of random noise generators and a variable attenuator as shown in figure 4.1.6.3. The hot and cold

noise generators supply known input powers to the receiver in a band of frequencies which includes that to which the receiver

is tuned. The attenuator measures the ratio of the two receiver

output power levels corresponding to the two input power levels

from the generators. Noise factor is computed from the measured

power ratio and the known generator power levels

.

Measurement uncertainties as small as 0.2 dB are possible

under best conditions, and range from approximately 0.3 dB to

1 dB under typical conditions. The method uses sophisticated

equipment, but it is commonly available.

4.1.6.5.1. TEST EQUIPMENT REQUIRED

1. Hot random noise generator

2 . Cold random noise generator

s

3. Input impedance matching transformer

4. Variable attenuator

5. Signal level indicator (voltmeter, power meter,

receiver, etc.)

4.1.6.5.2. PROCEDURE

1. Connect the input port of the receiver to the output

port of the COLD NOISE GENERATOR through an IMPEDANCE TRANSFORMER

that provides the specified source impedance, , to the receiver

at the measurement frequency, f^ . If the noise generator output

impedance equals Z , no transformer is needed.

73
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74
2. Connect the SIGNAL LEVEL INDICATOR to the output of the

last linear IF amplifier stage through the VARIABLE ATTENUATOR.

3. Set receiver controls as given in Table XI.

Note: For some receivers, maximum RF/IF gain may

produce overloading in the latter IF stages.

In this case, set the controls to produce

maximum RF gain without overload anywhere in

the measurement system.

4. Tune the receiver to the measurement frequency, f^.

5. Adjust the attenuator and the sensitivity of the signal

level indicator to produce a convenient indicator reading near

full scale.

6. Record the indicator reading, I .

7. Record the attenuator setting, A^(dB) , in decibels.

8. Disconnect the cold noise generator and connect the

HOT NOISE GENERATOR in its place.

9. Adjust the attenuator to produce the indicator

reading, I . c

10. Record the new attenuator setting, A^(dB) , in decibels.

11. Compute the Y-f actor in decibels from the equation

12. Convert the Y-f actor in decibels to Y-f actor by the

equation

c

Y (dB) = A (dB) - A, (dB) . c

Y = antilog

75
TABLE XI

Noise Factor, Y-Factor/Attenuator Method

Initial Control Settings

Control Setting

1. Band Switch 1. As desired

2. Frequency Tuning 2. As desired

3. Antenna Trimmer 3. Peak

4 . RF Gain 4 . Maximum

5. IF Gain 5 . As required

6 . AF Gain 6 . N. A.

7. Line Gain 7. N.A.

8. Detector Mode 8 . N.A.

9 . Beat Frequency Oscillator 9 . OFF

10 . BFO Frequency 10 . N.A.

11. IF Bandwidth 11. As desired

12 . AF Bandwidth 12 . N.A.

13. Noise Limiter 13 . OFF

14. Squelch Level 14 . N.A.

15 . AGC/MGC Mode Switch 15 . MGC

16 . Meter Switch 16 . N.A.

76
13. Calculate the noise factor from the equation

T, - YT

F = Jl ^ + 1 290 (Y-1) ^ ' and

F (dB) = 10 log F .

This is the noise factor, in decibels, of the linear portions

of the receiver RF/IF stages when tuned to frequency f^.

4.1.6.5.3. DATA REQUIRED

1. Record the measurement frequency, f^ , in kilohertz or

megahertz.

2. Record the value of source impedance, , in ohms,

connected to the receiver input port.

3. Record the noise temperature, T^ , in kelvins , of the

hot noise generator.

4. Record the noise temperature, T^ , in kelvins, of the

cold noise generator.

5. Record the indicator reading, I^, in millivolts or

milliwatts

.

6. Record the attenuator setting, A^ (dB) , in decibels.

7. Record the attenuator setting, A^^ (dB) , in decibels.

8. Record the Y-f actor, Y(dB) , in decibels.

9. Record the numeric Y-f actor, Y.

10. Record the calculated value of noise factor, F,

in decibels.

77
4.1.6.5.4. MEASUREMENT ERRORS

The principal sources of measurement error are the following

1. Uncertainty, AT^ , in the noise temperature, T^^, of the

hot noise generator

2. Uncertainty, AT^ , in the noise temperature, T^ , of the

cold noise generator

3. Uncertainty, AA , in the measured value of A (dB) c c

4. Uncertainty, AA^,^ , in the measured value of Aj^(dB)

The total uncertainty, AF , in the calculated value of F

is given by the equation

AF = Ci AT, + Ca AT + C 3 AY

.

h c

The uncertainty coefficients Ci, C2 , and C3 are given by

the equations

C2 =

and

1

290 (Y-1)

-Y

290 (Y-1)

T

c 290 (Y-1)

The uncertainties AT, and AT are obtained from the manufach c turer's specifications or from the results of calibrating T^

and T^. Uncertainty AY is given by the relation

AA (dB) + AA (dB)

AY = antilog — 10

78
where Aa and AA, are obtained from the manufacturer's

c h

specifications on the variable attenuator.

The relative measurement uncertainty, AF(dB) , expressed in

decibels, is given approximately, for small uncertainties, by

the equation

AF (dB) = 10 log ^1 + .

79
4.1.6.6. METHOD - 3 DB

This method uses a temperature-limited diode (TLD) noise

generator and a 3dB attenuator (hence its name) as shown in

figure 4.1.6.4. The TLD noise generator supplies a known but

adjustable input power to the receiver in a band of frequencies

which includes that to which the receiver is tuned. The signal

level indicator is used to indicate a reference level of output

power

.

With the noise generator output level adjusted to zero, and

with the 3dB attenuator out of the system, the receiver output

power produces an indication on the signal level indicator. Then

the 3 dB attenuator is inserted in the system, and the noise

generator output is increased until the same indicator reading

is obtained. Noise factor is read directly from the calibrated

meter on the TLD noise generator.

Measurement uncertainties as

under best conditions, and range

1.5 dB under typical conditions,

available test equipment, and is

small as 0.3 dB are possible

from approximately 0.5 dB to

The method uses commonly

quick and convenient to perform.

4.1.6.6.1. TEST EQUIPMENT REQUIRED

]_ ^ Temperature-limited diode noise generator

2. Input impedance matching transformer

3 . 3 dB fixed attenuator

4. Signal level indicator (voltmeter, power meter,

receiver, etc.)

80
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81
4.1.6.6.2. PROCEDURE

1. Connect the input port of the receiver to the output por

of the NOISE GENERATOR through an IMPEDANCE TRANSFORMER that

provides the specified source impedance, , to the receiver at

the measurement frequency, f ^ . If the noise generator output

impedance equals , no transformer is needed.

2. Connect the input port of the SIGNAL LEVEL INDICATOR

to the output of the last linear IF amplifier stage.

3. Set receiver controls as given in Table XII.

Note: For some receivers, maximum RF/IF gain may

produce overloading in the latter IF stages

In this case, set the controls to produce

maximum RF gain without overload anywhere in

the measurement system.

4. Tune the receiver to the measurement frequency, f^

.

5. Turn the emission current of the TLD noise generator to

zero (leave the generator connected to tlie measurement system).

6. Adjust the sensitivity of the signal level indicator to

produce a reading near full scale.

7. Record the indicator reading, I.

8. Disconnect the receiver from the signal level indicator.

9. Insert the 3 dB ATTENUATOR between the receiver and the

signal level indicator.

Note: Make certain that the attenuator terminating

impedances are proper so that 3 dB of attenuation

is obtained.

82
TABLE XII

Noise Factor, 3 dB Method

Initial Control Settings

Control Setting

1. Band Switch 1

.

As desired

2. Frequency Tuning 2

.

As desired

3. Antenna Trimmer 3

.

Peak

4. RF Gain 4 . -4 axi mum

5. IF Gain rrD . As required

6 . AF Gain b . N . A

.

7 . Line Gain 7 . N . A

.

8. Detector Mode oo . N . A

.

9 . Beat Frequency Oscillator 9 . OFF

10 . BFO Frequency 10 . N. A.

11. IF Bandwidth 11

.

As desired

12. AF Bandwidth 12. N. A.

13. Noise Limiter 13. OFF

14 . Squelch Level 14. N. A.

15 . AGC/MGC Mode Switch 15 . MGC

16 . Meter Switch 16 . N. A.

83
10. Increase the emission current of the TLD noise generator

to produce the indicator reading, I.

11. Record the indicated value of noise factor in decibels

as read from the emission current meter on the TLD noise generator.

12. Apply a frequency correction to the indicated value of

F(dB), if necessary as described in the manufacturer's operating

manual, to provide a corrected value of F(dB). Also, correct

F(dB) for the effect of ambient temperature within the noise

generator as instructed by the manufacturer. This is the noise

factor, in decibels, of the linear portions of the receiver RF/IF

stages when tuned to frequency f ^

.

4.1.6.6.3. DATA REQUIRED

1. Record the measurement frequency, f ^ , in kilohertz

or megahertz.

2. Record the value of source impedance, Z^, in ohms,

connected to the receiver input port.

3. Record the indicator reading, I, in millivolts or

milliwatts

.

4. Record the indicated value of noise factor, F(dB)

,

in decibels

.

5. Record the frequency-corrected and temperature-corrected

value of noise factor, F(dB), in decibels.

4.1.6.6.4. MEASUREMENT ERRORS

The principal source of measurement error is the calibration

of the TLD noise generator meter. The uncertainty, AF(dB) , in

decibels in the measured value of F will vary according to the

particular noise generator used. Refer to the manufacturer's

operating manual for the procedure for determining AF.

84
4.2. SIGNAL-TO-NOISE RATIO

4.2.1. DEFINITION

Signal-to-noise ratio is the ratio of the signal power

to the noise power in the entire output pass band. This ratio

is usually expressed in decibels.

4.2.2. PURPOSE

The purpose of this measurement method is to measure the

signal-to-noise ratio of the audio output signal from a surveillance receiver. Signal-to-noise ratio is a measure of

the quality of the receiver's output signal. It will vary with

the amount of internal noise in the receiver, with the amount

of input signal to the receiver, and with the signal-to-noise

ratio of the input signal. It may also be a function of

receiver sensitivity, selectivity, and distortion.

4.2.3. METHOD

The method uses a power meter or true rms voltmeter as shown

in figure 4.2. The power meter or voltmeter measures the output

signal level, P^ , when the signal source is turned off (receiver

output is noise only) , and Pg^^^/ when the signal source is turned

on (receiver output is signal plus noise) . The signal-to-noise

ratio is calculated from these two quantities by the equation

S/N = ^ - 1 . n

Measurement uncertainties as under best conditions , and range

0.8 dB under typical conditions,

and commonly available test equi

small as 0.2 dB are possible

from approximately 0.3 dB to

The method uses rudimentary

ment

.

85
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86
4.2.4. TEST EQUIPMENT REQUIRED

1. Termination resistor for receiver output port

2a. AF power meter

OR,

2b. True RMS voltmeter

4.2.5. PROCEDURE

1. Connect the signal source to the receiver input port.

Select whatever matching means that will give the desired

operating conditions.

2. Adjust the receiver according to the desired operating

conditions (see Table XIII).

3. With the signal source output set to zero, measure the

output power, P^ , from the receiver. This will be noise power

only

.

4. Adjust the output signal from the source according to

the desired output level and frequency.

5. Measure the output power, P , , from the receiver. ^ s+n

This will be both signal and noise power.

6. Calculate the ratio, S/N, by the equation

S/N - 1 . n

This is the signal-to-noise ratio of the receiver output

signal under the chosen operating conditions.

87
TABLE XIII

Signal-to-Noise Ratio

Initial Control Settings

Control Setting

1X • DdllU. OW_L Ut^ll X . C? T V

^ • r xt;^utiiiL»y J. LiiiJ-iiy ^ . /S ^ 0 T V* ^

->o • 5 Q C? 1 /Zi

4 "i n 4 Lit: 0Q Xn XT~ 0titj.

5 TF "i n 5 H Q 1 y0 r1 La ti 0 X X c LI

xlX Vjj Ci -I- i. 1 Ac; Lie. 0 X X C LL

7 . TiJ J 1 n1 1 p GiPi \_J C-L -X. 1 J.n1 7 . As rl 0 -1- n XT"f=^ r{LA

8 . 8 . Ac; HLie 0c! X

-j X

v-iCi C r1LI

Q F Vf^ m1 o Ti (^\7 Oq 1

"1 1 "h o T* j_>c;ctL. Xts^Lltiilv^y —1—Ld L.^X Q ("1 c; 1 Y" r\ Lie: 0 X X LI

1 n RFJUJ. 0W In* IT Xr^i^mif^^n CS^J LlC-i i v^_y 1 0 Ac; rlLit-p» Q0 X1 Xy0 Ll

11. IF Bandwidth 11. As desired

12 . AF Bandwidth 12 . As desired

13. Noise Limiter 13. As desired

14. Squelch Level 14 . As desired

15. AGC/MGC Mode Switch 15. As desired

16. Meter Switch 16 . Optional

88
4.2.6. DATA REQUIRED

1. Record all receiver operating parameters selected for

the test. These include the following:

a. Gain control settings

b. Frequency setting

c. Bandwidth

d. Noise limiter setting

e . AGC mode

g. Settings of any other pertinent controls

2 . Record all signal source parameters selected for the

test. These include the following:

a. Frequency

b. Output level

c . Modulation type

d. Modulation frequency

e. Modulation percentage/deviation

f. Source impedance

g. Signal level at receiver input port

3. Record P , in watts

n

4. Record P , , in watts

s+n

5. Record calculated value of S/N

4.2.7. MEASUREMENT ERRORS

The principal source of measurement error is the uncertainty,

AP, in the reading of the AF power meter, or AE in the reading

89
of the true rms voltmeter. The total uncertainty, AS/N (dB)

,

in decibels, in the calculated value of S/N, is given approximately, for small uncertainties, by the equations

AS/N (dB) = 10 log I 1 + 1 ,

AS/N (dB) = 10 log (

1 +

^

•

The uncertainties AP and/or AE are obtained from the

manufacturer's specifications on the power meter or voltmeter,

respectively

.

or

90
4.3. GAIN

Gain is a general term used to denote an increase in signal

level in transmission from one point to another. This section

provides measurement methods for the following receiver gain

parameters

1. Power Gain

2. Dynamic Range

3. Automatic Gain Control Characteristics

4.3.1. POWER GAIN

4.3.1.1. DEFINITION

The power gain of a receiver

(a) the audio power delivered to

termination at a 12 dB SINAD to

from the source connected to the

is the ratio, in decibels, of

the receiver's specified output

(b) the available signal power

receiver's input terminals.

4.3.1.2. PURPOSE

The purpose of this measurement method is to measure the

power gain of a receiver. Power gain is a measure of the

receiver's ability to convert the power of a small modulated

radio frequency signal into a usable audio output signal of

acceptable quality.

4.3.1.3. METHOD

The method is as follows (see figure 4.3.1): The 12 dB

SINAD sensitivity of the receiver is measured; the signal source

impedance is determined; the available input signal power is

calculated; then the power gain is calculated as the ratio, in

decibels, of (1) the rated audio output power and, (2) the

available input signal power.

91
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92
Measurement uncertainties as small as 0.3 dB are possible

under best conditions, and range from approximately 0.4 dB to

1.5 dB under typical conditions. The method uses moderately

sophisticated but commonly available test equipment.

4.3.1.4. TEST EQUIPMENT REQUIRED

1. Signal generator capable of amplitude or frequency

modulation

2. Input impedance matching network

3. Termination resistor for receiver audio output port

4. Audio distortion analyzer

5 . Impedance bridge or vector impedance meter

4.3.1.5. PROCEDURE

1. Connect the input port of the receiver to the output

port of the SIGNAL GENERATOR through an IMPEDANCE MATCHING

NETWORK that provides the specified source impedance, , to the

receiver at the measurement frequency, f ^ . If the signal

generator output impedance equals Z^, no matching network is

required.

2. Connect the TERMINATION RESISTOR having a resistance

equal to the specified load resistance, R,^, and a power rating

in excess of the receiver's rated audio output power level, to

the audio output port of the receiver. Connect the audio

DISTORTION ANALYZER across this resistor.

3. Set receiver controls as given in Table XIV.

9 3
TABLE XIV

Power Gain

Initial Control Settings

^ Control Setting

1. Band Switch 1. As desired

2. Frequency Tuning 2. As desired

3. Antenna Trimmer 3. Peak

4 . RF Gain 4. Maximum

5. IF Gain 5 . Maximum

6 . AF Gain 6 . Maximum

7 . Line Gain 7. Optional

8. Detector _4ode 8 . Aid, FM as

9 . Beat Frequency Oscillator 9 . OFF

10 . BFO Frequency 10 . N .A.

11. IF Bandwidth 11. As desired

12 . AF Bandwidth '. 12 . As desired

13 . Noise Limiter 13 . OFF

14 . Squelch Level 14 . OFF

15 . AGC/MGC Mode Switch 15 . As desired

16. i4eter Switch 16 . Optional

94
4. Measure the 12 dB SINAD SENSITIVITY as outlined in

Section 4.1.3. for AM receivers, or Section 4.1.5. for

FM receivers.

5. Measure the output IMPEDANCE, Z = R + j X , of the ^ s s s source at the terminals that connect to the input terminals

of the receiver. See Section 4.10.

6. Calculate the power, P , available from the source,

a by the equation

E . 2 R

P = ^

= a (R 2 + X ^)

'

where E. is the 12 dB SINAD SENSITIVITY.

1

7. Calculate the power ratio, G, in decibels, by the

equation

15 P

G(dB) = 10 log Y6-p^ . a

The fraction, 15/16, is the fractional part of P^ that is the

audio output signal due to the input signal (the remaining 1/16

is noise power). G(dB) is the power gain of the receiver at

frequency f ^

.

4.3.1.6. DATA REQUIRED

1. Record the measurement frequency, f ^ , in kilohertz or

megahertz

.

2. Record the value of source impedance, , in ohms,

connected to receiver input port.

3. Record the value of termination resistance, R^, in ohms

connected to receiver audio output terminals.

4. Record the reference output power, P^ , in watts.
5. Record the SINAD ratio in decibels.

6. Record the open circuit signal voltage, , in microvolts, at the output terminals of the matching network, if

used; otherwise, at the output terminals of the generator.

is the 12 dB SINAD sensitivity of the receiver.

7. Record the measured value of Z , in ohms.

s

8. Record the calculated value of P , in microwatts.

a

9. Record the calculated value of G, in decibels. G is

the gain of the receiver.

4.3.1.7. MEASUREMENT ERRORS

The principal sources of measurement errors are the

following:

1. Uncertainty, AE^, in the measured value of E^

2. Uncertainty, ^^^r the measured value of P^

3. Uncertainty, AP in the measured value of P ,

,

n+d n+d

4. Uncertainty, AR^ , in the measured value of R^ , and

Ax , in the measured value of X

s s The total relative uncertainty, AG(dB) , in decibels, in

the gain G, is given approximately, for small uncertainties,

by the equation

AG (dB) = 10 log

where AP AP AG _ o a G P P o a and

G = 15 P o 16 P

a

96
The uncertainty, AP , is obtained from the manufacturer' ^ o specifications on the distortion analyzer. The relative

uncertainty, AP /P , in P , is obtained from the equation

AP AE. (R ^-X ^) AR 2X ^ AX

a 2 i +

s s s _|_ s s P E. (R ^+X ^) R (R ^ +X ^) X

a i ss s s s s

The uncertainty AE^ is obtained from the manufacturer's

specifications on the output level indicator of the signal

generator. The uncertainties AR and AX are obtained from ^ s s the manufacturer's specifications on the impedance bridge

or meter.

97
4.3.2. DYNZVMIC RANGE

4.3.2.1. DEFINITIONS

a. Dynamic range is t±ie difference, in decibels, between

the overload level and the minimum acceptable signal level in

a system or transducer. NOTE: The minimum acceptable signal

level of a system or transducer is ordinarily fixed by one or

more of the following: Noise level, low-level distortion,

interference, or resolution level. (IEEE Std 100-1972)

b. Overload level is that level above which operation

ceases to be satisfactory as a result of signal distortion,

overheating, or damage. (IEEE Std 100-1972)

4.3.2.2. PURPOSE

The purpose of this measurement method is to measure the

dynamic range of a receiver. Dynamic range is a measure of the

ability of a receiver to receive a signal of arbitrary strength

with acceptable quality.

4.3.2.3. METHOD FOR AM RECEIVERS WITHOUT AGC

This method uses an amplitude modulated signal generator, a variable attenuator, and a true RMS voltmeter or power meter as shown in figure 4.3.2.1. The signal generator supplies a known input

voltage to the receiver at the measurement frequency. The variable

attenuator temporarily replaces the AF gain control, and adjusts

the audio output level. The voltmeter or power meter measures

the audio output power.

98
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The lower end of the dynamic range is obtained by determining

the input signal voltage that produces a 6 dB output S/N ratio

at the reference output power. The upper end is obtained by determining the signal voltage that produces 1 dB compression at reference output power.

X This method does not take into account the distortion produced

in the receiver under conditions of large input signal power. It

uses conventional and commonly available test equipment. Measurement uncertainties as small as 0.3 dB are possible under best conditions, and range from approximately 0.4 dB to 3 dB under typical

conditions.

4.3.2.3.1. TEST EQUIPMENT REQUIRED

1. Signal generator capable of amplitude modulation

2 . Input impedance matching network

3. Termination resistor for receiver audio output port

4 . Variable AF attenuator

5a. AF power meter

OR,

5b. True RMS voltmeter

4.3.2.3.2. PROCEDURE

1. Connect the input port of the receiver to the output port

of the SIGNAL GENERATOR through an IMPEDANCE MATCHING NETWORK

that provides the specified source impedance, , to the receiver

at the measurement frequency, f^. If the signal generator output

impedance equals Z , no matching network is required.

100
2. Disconnect the output lead from the receiver AF gain control

(slider contact) . Insert the variable AF attenuator between the

open gain control output terminal and the lead that went to that

terminal

.

Note : If the resulting input and output terminations to

the AF attenuator present a severe mismatch to the

attenuator so as to change its calibration, match

the attenuator into the circuit with transformers

or resistive matching networks.

3a. Connect the TERMINATION RESISTOR having a resistance equal

to the specified load resistance, R^, and a power rating in excess

of the receiver's rated audio output power level, to the audio

output port of the receiver. Connect the TRUE RI4S VOLTMETER across

this resistor.

OR,

3b. Connect the POWER METER, having an input impedance equal

to the specified load resistance, R^, to the audio output port of

the receiver.

4a. Set the voltmeter on a range to indicate the rated output

ower, . The voltage to be measured is given by the equation

E = x/P R„ . o > o £

OR,

4b. Set the power meter on a range to indicate the reference

output power, P^.

5. Set receiver controls as given in Table XV.

Tune the signal generator and the receiver to the measurement

frequency, f^

.

101
TABLE XV

Dynamic Range (MGC)

Initial Control Settings

Control Setting

1. Band Switch 1. As desired

2. Frequency Tuning 2. As desired

3. Antenna Trimmer 3. Peak

4. RF Gain 4. Maximum

5. IF Gain 5. Maximum

6. AF Gain 6. Maximum

7. Line Gain 7. Optional

8. Detector Mode 8. AM

9. Beat Frequency Oscillator 9 . OFF

10 . BFO Frequency 10 . N.A.

11. IF Bandwidth 11. As desired

12. AF Bandwidth 12 . As desired

13. Noise Limiter 13. OFF

14 . Squelch Level 14. OFF

15. AGC/MGC Mode Switch 15 . MGC

16 . Meter Switch 16 . Optional

102
7. Adjust the amplitude modulation m the signal generator

to 30% at 1000 Hz.

8. With the signal generator output at zero, adjust the

variable attenuator to produce 20% of reference output power,

P^. This power is entirely noise.

9. Increase the signal generator output to produce reference

output power, P^. This power is approximately 20% noise and 80%

signal, giving a 6 dB S/N ratio.

10. Determine the open circuit signal voltage, E^, in

microvolts, at the OUTPUT TERMINALS of the matching network,

if used; otherwise, at the output terminals of the generator.

This is the lower voltage level of the dynamic range.

11. Increase the variable attenuator setting by exactly

20 dB. This reduces the output power to approximately 0.01 P^.

12. Increase the signal generator output to produce

reference output power, P^.

13. Determine the open circuit signal voltage, E^^ , at the

output terminals of the matching network (or generator)

.

14. Calculate the quantity Ri , in decibels, where

E

.

Ri = 20 log .

15. With the generator set as in Step 12, again increase

the variable attenuator setting by exactly 20 dB. This reduces

the output power to approximately 0.01 P^.

16. Again increase the signal generator output to produce

reference output power, P^.

103
17. Determine the open circuit signal voltage, , at

the output terminals of the matching transformer (or generator)

.

18. Calculate the quantity, / in decibels, where

. E . t R2 = 20 log .

• ' ^ii

19. Proceed as indicated in Steps 11 through 18, each time

changing the variable attenuator setting by 20 dB , and increasing

the signal generator output to successively higher levels to produce reference output power, until the computed value of R

exceeds 21 dB for the first time. (All preceding values of R

are less than 21 dB. 21 dB represents a compression of 1 dB

in the gain of the receiver.)

20. Return the variable attenuator setting to the value

that immediately preceded the final value reached in Step 19.

21. Decrease the signal generator output to again produce

reference output power with the attenuator set as in Step 20.

22. Increase the variable attenuator setting by exactly

10 dB. This reduces the output power to approximately 0.1 P^.

23. Increase the signal generator output to produce

reference output power, P^.

24. Determine the open circuit signal voltage, E

j

^

, at the

output terminals of the matching network (or generator)

.

25. Reduce the signal generator output by approximately

20 dB.

26. Increase the variable attenuator setting by exactly

20 dB . This may increase the output power to approximately P .

104
27. Adjust the signal generator output to produce

reference output power, P^.

28. Determine the open circuit signal voltage, Ej^, at

the output terminals of the matching network (or generator)

.

Ej^ corresponds to an attenuator setting that is an increase

of 20 dB from the setting in Step 24.

29. Calculate the quantity, Rj , in decibels, where

E . R. = 20 log

30a. If Rj is greater than 21 dB , return to Step 20 and

proceed through Step 29 except use a smaller attenuation

change in Step 22; e.g., use 8 dB instead of 10 dB

.

31a. Repeat Step 30a (i.e.. Steps 20 through 29) until

values for E- and E. are found for which R. = 21 dB

.

J 1 D 2 3 OR,

30b. If Rj in Step 29 is less than 21 dB , return to Step

20 and proceed through Step 29 except use a larger attenuation

change in Step 22; e.g. , use 12 dB instead of 10 dB

.

31b. Repeat Step 30b until values for E- and E. are

3 132 found for which Rj = 21 dB.

32. Determine the signal voltage, E^ = Ej ^

, in microvolts.

This is the upper voltage level of the dynamic range.

33. Compute the ratio R^ in decibels, where

= 20 log ^ .

R^ is the dynamic range, in decibels, for the receiver.

105
4.3.2.3.3. DATA REQUIRED

1. Record the measurement frequency, f^, in kilohertz or

megahertz

.

2. Record the value of source impedance, Z , in ohms,

s connected to receiver input port.

3. Record the value of termination resistance, R^, in

ohms, connected to receiver output terminals.

4a. Record the output voltage, E^, in volts

OR,

4b. Record the reference output power, P^, in watts

5. Record the open circuit signal voltage, E^, in

microvolts

.

6. Record each attenuator setting, in decibels, taken

throughout the measurement procedure.

7. Record the open circuit signal voltage, E^, E^, or E^,

in microvolts, for each of the attenuator settings of 6, above.

8. Record the ratio R, in decibels, calculated for each

pair of voltages, E. and E., of Step 7 above.

9. Record the ratio, R,, in decibels.

d

4.3.2.3.4. MEASUREMENT ERRORS

The principal sources of measurement error are the followin

106
1. Uncertainty, AE^, in the measured value of E^^

2. Uncertainty, AE , in the measured value of E u u

3a. Uncertainty, AE , in the measured value of E ^ o o OR,

3b. Uncertainty, AP , in the measured value of P

o o

4. Uncertainty, AA(dB), in the variable attenuator

attenuation

The total relative uncertainty, AE^(dB), in decibels,

in the lower voltage level, E^, of the dynamic range, is given

approximately, for small uncertainties, by the equations

(AE AE

1 + +

g

OR

' " \ E

AE , AP

AE„(dB) = 20 log { 1 + —J^ +

£

o '

2 V } o /

For the upper voltage level, AE^(dB), in decibels, is given

approximately, for small uncertainties, by the equations

/ AE AE 1 AA \

AE^(dB) = 20 log ^

1 + ^ + ^ + i A|_

j

,

).

u o OR

/ AE , AP T AE^(aB, = 20 log (l . + u o I

^

where

AA • AA(dB)

- antilog —0 - 1 .

The uncertainties AE^ and AE^ are obtained from the

manufacturer's specifications on the output level indication

of the signal generator. Uncertainties AE^ , AP^, and AA(dB)

are obtained from the manufacturer's specifications on the rms

voltmeter, AF power meter, and variable attenuator, respectively

107
4.3.2.4. METHOD FOR AM RECEIVERS WITH AGC , OR FM

RECEIVERS WITH ONE OR MORE LIMITERS

The method uses a modulated signal generator and an audio

distortion analyzer as shown in figure 4.3.2.2. The signal

generator supplies a known input voltage to the receiver at

the measurement frequency. The distortion analyzer measures

the power (a) with the 1000 Hz modulating signal present, and

(b) with the 1000 Hz modulating signal filtered from the audio

output power

.

The lower end of the dynamic range is the 12 dB SINAD

sensitivity (cf) of the receiver. The upper end of the range

is established by determining the lowest of the following

three signal levels:

a. The signal voltage that produces a 12 dB SINAD ratio

near the receiver's overload level.

. b. The signal voltage that fires the receiver's overvoltage

protection circuit (if any)

.

c. The signal voltage that reaches the maximum safe level,

above which receiver damage occurs (given as a manufacturer's

specification)

.

The method takes into account the distortion produced in

the receiver, and hence provides meaningful information.

Measurement uncertainties as small as 0.4 dB are possible under

best conditions, and range from approximately 1 dB to 4 dB

,

depending upon circumstances. The method uses moderately

sophisticated but commonly available test equipment.

108
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109
4.3.2.4.1. TEST EQUIPMENT REQUIRED

1. Signal generator capable of amplitude or frequency

modulation

2 . Input impedance matching network

3. Termination resistor for receiver audio output port

' 4. Audio distortion analyzer

4.3.2.4.2. PROCEDURE

1. Connect the input port of the receiver to the output

port of the SIGNAL GENERATOR through an IMPEDANCE MATCHING

NETWORK that provides the specified source impedance, Z^, to

the receiver at the measurement frequency, f^. If the signal

generator output impedance equals Z^, no matching network is

required

.

2. Connect the TERMINATION RESISTOR having a resistance

equal to the specified load resistance, R^^, and a power rating

in excess of the receiver's rated audio output power level, to

the output port of the receiver. Connect the audio DISTORTION

ANALYZER across this resistor.

3. Set receiver controls as given in Table XVI.

4. Measure the 12 dB SINAD SENSITIVITY as outlined in

Section 4.1.3. for AM receivers, or Section 4.1.5. for FM

receivers. The 12 dB SINAD SENSITIVITY, in microvolts, is

the lower voltage level, E^, of the dynamic range.

5. Increase the generator output level to the vicinity

of the receiver's overload level until one of the following

conditions is reached, whichever occurs first:

110
TABLE XVI

Dynamic Range (AGC)

Initial Control Settings

Control Setting

1. Band Switch 1. As desired

2. Frequency Tuning 2. As desired

3. Antenna Trimmer 3. Peak

4 . RF Gain 4. Maximum

5. IF Gain 5. Maximum

6 . AF Gain 6 . As required

7 . Line Gain 7. Optional

8. Detector Mode 8. AM, FM,as required

9 . Beat Frequency Oscillator 9 . OFF

10 . BFO Frequency 10 . N.A.

11. IF Bandwidth 11. As desired

12. AF Bandwidth 12. As desired

13. Noise Limiter 13. OFF

14. Squelch Level 14. OFF

15 . AGC/MGC Mode Switch 15 . AGC as desired

16 . Meter Switch 16 . Optional

111
a. 12 dB SINAD ratio is again obtained. The condition

sought is a DECREASE of SINAD ratio with an INCREASE of

input signal level, and vice versa.

b. The receiver's overvoltage protection circuit is fired.

c. The receiver's specified maximum safe input voltage

is reached.

6. Determine the open circuit signal voltage, E^ in

microvolts, at the output terminals of the matching transformer

(or generator). E^ is the upper voltage level of the dynamic

range

.

7. Compute the ratio R , in decibels, where

= 20 log

R^ is the dynamic range, in decibels, for the receiver.

112
4.3.2.4.3. DATA REQUIRED

1. Record the measurement frequency, f ^ , in kilohertz

or megahertz

2. Record the value of source impedance, , in ohms.

connected to receiver input port.

3. Record the value of termination resistance, R^

,

in ohms, connected to receiver output terminals.

4. Record the reference output power, P^, in watts

5. Record the output voltage, E^, in microvolts

6. Record the signal voltage, E^ , in microvolts

7. Record the ratio R -, , in decibels

d

4.3.2.4.4. MEASUREMENT ERRORS

The principal sources of measurement error are the

following

1. Uncertainty, AE^ , in the measured value of E,^

2. Uncertainty, AE^ , in the measured value of E^

3. Uncertainty, AE^, in the measured value of E^

4, Uncertainty, AP^ , in the measured value of

113
The total relative uncertainty, AE^(dB), in decibels,

in the lower voltage level, E^, of the dynamic range, is

given approximately, for small uncertainties, by the equations

(AE AE

1 + +

£ o OR

AE^(dB) = 20 log f 1 + +

).

- — I . 2 P /

• o /

For the upper voltage level, AE^ (dB) , in decibels, is given

approximately, for small uncertainties, by the equations

(AE AE \

1 + +

j

,

OR (AE , AP \

1 + "E^ + ^ 1 . u o /

The uncertainties AE^ and AE are obtained from the

£ u manufacturer's specifications on the output level indication

of the signal generator. Uncertainties AE or AP are ^ ^ o o obtained from the manufacturer's specifications on the rms

voltmeter or AF power meter, respectively.

114
4.3.3. AUTOMATIC GAIN CONTROL

Automatic gain control (AGC) is a process or means by which

GAIN is automatically adjusted in a specified manner as a function of input or other specified parameters (IEEE Std

100-1972). Of importance to receiver performance are the

static and dynamic AGC characteristics . The former includes

the effect of AGC voltage on system gain and its leveling

effect on output power. The latter includes the attack and

decay time constants of the AGC system.

4.3.3.1. STATIC AGC CHARACTERISTIC; SYSTEM GAIN VS.

AGC VOLTAGE

4.3.3.1.1. DEFINITION

Static AGC characteristic, system gain vs. AGC voltage,

is the functional relationship between the gain of the

AGC-controlled amplifier system and the AGC control voltage.

This characteristic includes all levels of AGC control from

a minimum, which may be zero or an offset from zero, to a maximum, which is normally limited by the dynamic range (cf.)

of the receiver.

4.3.3.1.2. PURPOSE

The purpose of this measurement method is to measure the

static AGC characteristic, in terms of receiver gain as a function of d.c. AGC voltage, for an AM receiver having an

AGC system. This characteristic is one measure of the degree

to which the AGC system is effective in controlling the gain

of the receiver. Effective AGC control usually enhances the

dynamic range of the receiver. The method ignores the means

by which AGC voltage is obtained.

115
4.3.3.1.3. METHOD

The method uses an amplitude modulated signal generator,

an audio distortion analyzer, and a source of variable d.c.

voltage as shown in figure 4.3.3.1. The signal generator

supplies a known input voltage to the receiver at the

measurement frequency. The variable d.c. voltage source

supplies a known AGC voltage that substitutes for the normal

internally generated AGC voltage. The distortion analyzer

measures the receiver output signal level. Gain, as a function

of AGC voltage, is computed from the known input signal level

and the measured output signal level.

Measurement uncertainties as small as 6% are possible under

best conditions, and range from approximately 8% to 40% under

typical conditions. The method uses rudimentary and commonly

available test equipment.

4.3.3.1.4. TEST EQUIPMENT REQUIRED

1. Signal generator capable of amplitude modulation

2. Input impedance matching network

3. Termination resistor for receiver audio output port

4. Audio distortion analyzer

5. Variable, voltage regulated d.c. power supply

6. Impedance bridge or vector impedance meter
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4.3.3.1.5. PROCEDURE

1. Connect the input port of the receiver to the output

port of the SIGNAL GENERATOR through an IMPEDANCE MATCHING

NETWORK that provides the specified source impedance, Z^,

to the receiver at the measurement frequency, f^. If the

signal generator output impedance equals Z^, no matching

network is required.

2. Connect the TERMINATION RESISTOR having a resistance

equal to the specified load resistance, R^ , and a power rating

in excess of the receiver's rated audio output power level, to

the output port of the receiver. Connect the audio DISTORTION

ANALYZER across this resistor.

3. Break the line between the output of the AGC rectifier

and the AGC line (preceding point A as shown in figure 4.3.3.1.).

Note: If the receiver has delayed AGC, break the

line so as not to disrupt this function.

4. Connect the VARIABLE D.C. VOLTAGE SOURCE between point

A, figure 4.3.3.1., and ground. Observe correct polarity.

Note: Normally, correct polarity is with the negative

voltage applied to the AGC line and positive

voltage grounded.

5. Set receiver controls as given in Table XVII.

6. Tune the signal generator and the receiver to the

measurement frequency, f^.

7. Adjust the amplitude modulation in the signal

generator to 30% at 1000 Hz.

118
TABLE XVII

Automatic Gain Control; Gain vs. AGC Voltage

Initial Control Settings

Control Setting

1. Band Switch 1. As desired

2. Frequency Tuning 2 . As desired

3. Antenna Trimmer 3. Peak

4. RF Gain 4. Maximum

5. IF Gain 5 . Maximum

6. AF Gain 6. As required

7. Line Gain 7. Optional XT

8. Detector Mode 8. AM

9 . Beat Frequency Oscillator 9 . OFF

10 . BFO Frequency 10 . N . A

.

11. IF Bandv/idth 11. As desired

12. AF Bandv/idth 12 . As desired

13. Noise Limiter 13. OFF

14. Squelch Level 14. OFF

15 . AGC/MGC iMode Switch 15. AGC

16. Meter Switch 16 . Optional

119
8. With the d.c. voltage set to zero, measure the POWER

GAIN, G(dB) , of the receiver as outlined in Steps 4 through 7,

Section 4.3.1.5.

9 . Increase

steps , e.g., 0.1

each step in the

a. With the d.c. voltage at the selected step, adjust

the output level of the signal generator to produce reference

audio output power. P .

b. Measure the gain as in Step 8, above, for each selected

d.c. voltage step.

10. Continue as indicated in Step 9, above, until the

upper limit, of the dynamic range (cf.) of the receiver

is reached.

11. Plot a graph of gain, G(dB), in decibels, vs. AGC

voltage, E^ ^

, in volts, on semi-logarithm paper. This is

the static AGC characteristic of the receiver.

the d.c. voltage, E^ ^, in suitably small

volt per step, and measure gain, G(dB), at

following way:

4.3.3.1.6. DATA REQUIRED

1. Record the measurement frequency, f ^ , in kilohertz

or megahertz.

2. Record the value of source impedance, Z^, in ohms,

connected to receiver input port.

3. Record the value of termination resistance, R , in

ohms, connected to the receiver audio output terminals.

4. Record the reference output power, P , in watts.

o

120
5. Record the d.c. AGC voltage, E , in volts, at

each step

6. Record the open circuit signal voltage, , in

microvolts, at each step.

7. Record the measured value of Z , in ohms.

s

8. Record the calculated value of P , in microvratts

.

a

9. Record the calculated gain, G, in decibels, at each

step

.

4.3.3.1.7. MEASUREMENT ERRORS

The principal sources of measurement errors are the

follov/ing

1. Uncertainty, LE^, in the measured value of E.

2. Uncertainty, IP , in the measured value of P ^ o o

3. Uncertainty, IR , in the measured value of R , and

s s AX , in the measured value of X . s s

The total relative uncertainty, iG(dB) , in decibels, in

the gain G, is given approximately, for small uncertainties,

by the equation

AG(dB) = 10 log

where

and

G = 15P

o 16P

a

121
The uncertainty, AP , is obtained from the manufacturer's

specifications on the distortion analyzer. The relative

uncertainty, AP /P , in P , is obtained from the equation

a a a

AP AE. (R ^) AR 2X ^ AX

a _ 2 1 + s s s _|_ s s P E. (R ^+X 2) R (R ^) X

* a 1 ss s ss s

- 4.3.3.2. STATIC AGC CHARACTERISTIC; LEVELING EFFECT

4.3.3.2.1. DEFINITION

Static AGC characteristic, leveling effect, is the

functional relationship between audio output signal level

and receiver input signal level.

4.3.3.2.2. PURPOSE

The purpose of this measurement method is to measure the

static AGC characteristic, in terms of its leveling effect on

the audio output signal, for an AM receiver having an AGC system.

This characteristic is another measure of the degree to which

the AGC system is effective in controlling the gain of a receiver.

This method accounts for the over-all effect of the amplifier

and AGC circuits in the receiver.

4.3.3.2.3. METHOD

The method uses an amplitude modulated signal generator and

a true rms voltmeter or power meter as shown in figure 4.3.3.2.

The signal generator supplies a known input voltage to the

receiver at the measurement frequency. The voltmeter or power

meter measures the receiver output signal level. The leveling

effect of the AGC system is displayed graphically by a plot cf

output signal level vs. input signal level.

122
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Measurement uncertainties as small as 8% are possible under

best conditions, and range from approximately 10% to 40% under

typical conditions. The method uses moderately sophisticated

but commonly available test equipment.

4.3.3.2.4. TEST EQUIPMENT REQUIRED

1. Signal generator capable of amplitude modulation

2 . Input impedance matching network

3. Termination resistor for receiver audio output port

4. Audio distortion analyzer

4.3.3.2.5. PROCEDURE

1. Connect the input port of the receiver to the output port

of the SIGNAL GENERATOR through an IMPEDANCE MATCHING NETWORK

that provides the specified source impedance, Z^, to the receiver

at the measurement frequency, f ^ . If the signal generator output

impedance equals Z^, no matching network is required.

2. Connect the TERMINATION RESISTOR having a resistance equal

to the specified load resistance, R^^ , and a power rating in excess

of the receiver's rated audio output power level, to the output

port of the receiver. Connect the audio DISTORTION ANALYZER

across the resistor.

3. Set the receiver controls as given in Table XVIII.

4. Tune the signal generator and the receiver to the

measurement frequency, f^.

5. Adjust the amplitude modulation in the signal generator

to 30% at 1000 Hz.

124
TABLE XVIII

Automatic Gain Control; Leveling Effect

Initial Control Settings

Control Setting

1. Band Switch 1. As desired

2 . Frequency Tuning 2. As desired

3. Antenna Trimmer 3. Peak

4 . RF Gain 4. Maximum

5. IF Gain 5. Maximum

6 . AF Gain 6. As required

7 . Line Gain 7. Optional

8 . Detector Mode 8. AM

9 . Beat Frequency Oscillator 9. OFF

10 . BFO Frequency 10 . N.A.

11. IF Bandwidth 11. As desired

12 . AF Bandwidth 12. As desired

13 . Noise Limiter 13. OFF

14. Squelch Level 14. OFF

15. AGC/MGC Mode Switch 15. AGC

16 . Meter Switch 16 . Optional

125
6. Measure the 12 dB SINAD SENSITIVITY, E., as outlined

1

in Section 4.1.3.

7. Increase the output level of the signal generator by

10 dB, i.e. , to 3. 16 E .

.

1

8. Measure the audio output power, ^ P . This should be

o 1 slightly greater than the reference audio output power, P^.

9. Repeat Steps 7 and 8 until the maximum rated output

power for the receiver is reached.

Note: Changes of input signal level that are smaller

than 10 dB can be made if greater detail of the

AGC characteristic is desired.

10. Plot a graph of output power, in watts, vs. open

circuit input signal level, in microvolts, on semi- logarithm

paper. This is the AGC characteristic, leveling effect, of

the receiver.

4.3.3.2.6. DATA REQUIRED

1. Record the measurement frequency, f^ , in kilohertz or

megahertz

.

2. Record the value of source impedance, Z^, in ohms,

connected to receiver input port.

3. Record the value of termination resistance, R^, in ohms,

connected to receiver audio output terminals.

4. Record the reference output power, P^ , in watts.

5. Record the open circuit input signal voltage, in

microvolts, at each step.

6. Record the output power level, in watts, at each step.

126
4.3.3.2.7. MEASUREMENT ERRORS

The principal sources of measurement error are the

following

1. Uncertainty, AE^ , in the measured value of open

circuit input signal voltage, E^

2. Uncertainty, AP^ or AP^ ^

, in the measured value of

output power, P^ or P^^

The relative uncertainty, AE^(%) , in the signal voltage,

E^ , expressed as a percent, is given by the equation

AE . AE . (%) = —^ X 100

.

1 E . 1

The relative uncertainty, AP^(%) , in the output power, P^

(or Pqj^) / expressed as a percent, is given by the equation

AP

AP (%) = ^ 100.

o P o

The uncertainty, AE^, is obtained from the manufacturer's

specifications on the output level indication of the signal

generator. Uncertainty AP^ is obtained from the manufacturer's

specifications on the distortion analyzer.

The total relative uncertainty, AEP(%) , in a point on the

AGC leveling effect curve is given by the equation

AEP (%) = AE . (%) + AP (%) .

127
4.3.3.3. DYNAMIC AGC CHARACTERISTICS

4.3.3.3.1. DEFINITIONS

a. The dynamic AGC characteristics are the attack and

decay time constants, in microseconds or milliseconds, of the

AGC voltage.

b. For the output of a first-order system forced by a step or an impulse, time constant is the time required to

complete 63.2 percent of the total rise or decay. (IEEE

Std 100-1972)

4.3.3.3.2. PURPOSE

The purpose of this measurement method is to measure the

attack and decay time constants of the AGC system of AM

receivers. These time constants are a measure of quickness

and holding ability of automatic gain control which determine

the uniformity of the receiver's audio output signal.

128
4.3.3.3.3. METHOD

The method uses an unmodulated signal generator, a SPOT

reed relay, and a D.C. oscilloscope as shown in figure

4.3.3.3. The signal generator supplies a known input voltage

to the receiver through the reed relay. The oscilloscope

displays the change in AGC voltage after the relay is

switched. The attack and decay time constants of the AGC

circuit are determined from the display, using the scale

calibrations of the oscilloscope.

Measurement uncertainties as small as 6% are possible under

best conditions, and range from approximately 8% to 40% under

typical conditions. The method uses moderately sophisticated

but commonly available test equipment.

4.3.3.3.4. TEST EQUIPMENT REQUIRED

1. CW signal generator

2. 30 dB attenuator having a characteristic impedance

equal to the specified source impedance, Z^, for the receiver

3. SPOT reed relay

4. D.C. oscilloscope with delayed internal triggering

5. Oscilloscope camera

4.3.3.3.5. PROCEDURE

1. Connect the input port of the receiver to the output

port of the REED RELAY through the 30 dB ATTENUATOR.

2. Connect one of the input ports of the REED RELAY to

the output port of the SIGNAL GENERATOR.

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3. Connect the other input port of the REED RELAY to

ground

.

4. Connect the OSCILLOSCOPE vertical input port to the

AGC bus in the receiver, using a high-impedance (^10

megohm) D.C. probe. Make the connection following the RC

networks that establish the time constants of the AGC

system.

5. Provide a trigger voltage from the coil circuit of

the reed relay to the trigger circuit of the oscilloscope.

6. Set the receiver controls as given in Table XIX.

7. Tune the signal generator and the receiver to the

measurement frequency, f^.

8. Set the output level from the signal generator to

approximately 1,000,000 microvolts.

9. Set the reed relay in the OFF position, i.e., with

its output port grounded.

10. Adjust the horizontal and vertical controls of the

oscilloscope so that when the reed relay is switched to the

ON position, the AGC bus voltage change will be displayed

throughout from its no-signal value to its full-signal

value

.

11. Calibrate the vertical scale in volts per centimeter

and the horizontal scale in seconds per centimeter.

12. Switch the reed relay to the ON position, and

photograph the display of AGC voltage change.

131
TABLE XIX

Automatic Gain Control; Time Constants

Initial Control Settings

Control o Ti- uiiig

1

.

Band Switch nX . r\t> CI ± X fci U.

2 . Frequency Tuning z .

3 . Antenna Trimmer o . "P (Ci ;a V

RF Gain A A/T ^ V T Tn 1 1 TTl inciA J_lllUill

5 . IF Gain 5. ^ 'V T TTl 1 1 Tn FiciXXlllU.Ul

6 . AF Gain 6 . up t lonax

7 . Line Gain 7. Optional

8 . Detector Mode 8 .

9 . Beat Frequency Oscillator 9. Ur r

10 . BFO Frequency 10 . N , A .

11

.

IF Bandwidth 11

.

7\ cr T /iib QfcibJ.rc;Q

12 . AF Bandwidth 12. As desired

13 . Noise Limiter 13 . OFF

14 . Squelch Level 14 . OFF

15 . AGC/MGC Mode Switch 15. AGC

16 . Meter Switch 16 . Optional

132
13. Measure the time constant of the AGC attack time as follows: (a) Determine the starting point of the AGC voltage

change; (b) determine the total AGC voltage change;

(c) determine the point at which the voltage reached 63.2%

of its total change. The attack time constant is the time

interval between (a) and (c)

.

14. Adjust the horizontal controls of the oscilloscope,

if required, so that when the reed relay is switched to the

OFF position, the AGC bus voltage change will be displayed

throughout from its full-signal value to its no-signal value.

Recalibrate the horizontal scale as required.

15. Switch the reed relay to the OFF position, and

photograph the display of the AGC voltage change.

16 . Measure the time constant of the AGC decay time as per Step 13, above. The decay time constant is the time

interval between the starting point of the AGC voltage change

and the point at which the voltage has reached 63.2% of

its final value.

4.3.3.3.6. DATA REQUIRED

1. Record the measurement frequency, f ^ , in kilohertz

or megahertz.

2. Record the open circuit voltage at the output

terminals of the signal generator.

3. Record the scale calibration factors for the oscilloscope

display in volts per centimeter (vertical) and seconds per

centimeter (horizontal).

133
4. Record the measured AVC attack time constant, in

microseconds or milliseconds, and the measured AVC decay

time constant, in milliseconds or seconds.

4.3.3.3.7. MEASUREMENT ERRORS

The principal sources of measurement error are the

following:

1. Uncertainty, At, in the horizontal calibration factor,

t/cm, of the oscilloscope

2. Uncertainty, AV, in the voltage (vertical) reading,

V, of the oscilloscope display

3. Uncertainty, AT, in the time (horizontal) reading, T,

of the oscilloscope display

The total relative uncertainty, At(%) , expressed in percent in either the attack time constant or the decay time

constant, is given by the equation

Uncertainty At is obtained from the manufacturer's specifications on the voltage and time scale calibrators. Uncertainties

AV and AT are obtained from the reading resolution of oscilloscope

display; these are normally estimated from the characteristics of

the actual display.

At (%)

134
4.4. SELECTIVITY

Selectivity is a measure of the extent to which a receiver

is capable of differentiating between a desired signal and

disturbances at other frequencies. (IEEE Std 100-1972)

There are various receiver parameters that describe

selectivity in different ways, for different conditions, and

with differing degrees of adequacy. Selectivity in terms of

the response to a single frequency is described by the following parameters

1. Selectance

2. CW bandwidth

3. Shape factor

4. Modulation acceptance bandwidth

5. Spurious response attenuation

In terms of random signals occupying large regions of spectrum, selectivity is expressed by the parameter,

6. Noise bandwidth.

Parameters explicitly relating to the effects of one or more

disturbing signals on the reception of a desired signal are

the following:

7. Desensitization

8. Crossmodulation

9. Adjacent channel selectivity

10. Intermodulation

135
Finally, receiver response to impulsive-type signals is

expressed by the parameter,

11. Impulse bandwidth.

Measurement methods for these parameters are given in the

following sub-sections

.

4.4.1. SELECTANCE

4.4.1.1. DEFINITION

Selectance is a measure of the falling off in the response

of a resonant device with departure from resonance. It is

expressed as the ratio of the amplitude of response at the

resonance frequency, to the response at some frequency differing

from it by a specified amount. (IEEE Std 100-1972)

The selectance of a receiver is the voltage response

characteristic as a function of frequency around the principal

response frequency of the receiver. It normally pertains to a linear receiver. For non-linear receivers, such as those with

clipping or AGC, selectance may be a function of signal level.

4.4.1.2. PURPOSE

The purpose of this measurement method is to measure the

selectance of a receiver in terms of voltage response

as a function of frequency. This characteristic is a measure

of the spectrum of frequencies, centered around the principal

response frequency, which the receiver will amplify with

significant gain. It is not an adequate measure of the

receiver's ability to deliver an output signal of acceptable

quality in the presence of signals outside of its principal

response

.

136
4.4.1.3. METHOD, POINT-BY-POINT - I

The method uses a variable frequency CW generator, an

accurate frequency meter, and an R.F. voltmeter as shown in

figure 4.4.1.1. The signal generator supplies a known variable

input voltage to the receiver at a variety of frequencies

within the principal response range of the receiver. The

voltmeter measures the I.F. output voltage. The output level

of the signal generator is adjusted to maintain a constant

output voltage at the voltmeter input terminals

.

The voltage gain betv/een the receiver input terminals and

the I.F. output terminals is thus measured at the various

selected frequencies . Selectance is the graphical plot of (a)

the ratio of I.F. output voltage to receiver input voltage

versus (b) measurement frequency.

Note: Because of the good signal-to-noise ratio it

can provide, this method may give better

measurement results at frequencies far removed

from the central frequency than the method given

in Section 4.4.1.4., below. That method may give

better measurement results at frequencies near

the central frequency because of better control

of overloading. Best results may be obtained by

measuring from maximum response to -20 dB or

-30 dB down from maximum response by the method

of Section 4.4.1.4., and then fromi there down

to the noise lim.it by the method of this Section.

Measurement uncertainties as small as 6% are possible under

besu conditions, and range from approximately 8% to 40% under

typical conditions . The method uses simple and commonly

available test equipment.

137
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4.4.1.3.1. TEST EQUIPMENT REQUIRED

1. Variable frequency signal generator

2. Input impedance matching network

3. Frequency meter

4. Isolation network

5. R.F. voltmeter

4.4.1.3.2. PROCEDURE

1. Connect the input port of the receiver to the output port

of the SIGNAL GENERATOR through an IMPEDANCE MATCHING NETWORK

that provides the specified source impedance, , to the receiver

at the measurement frequency, f^. If the signal generator output

impedance equals , no matching network is required.

2. Connect the FREQUENCY METER to the output port of the

signal generator through an ISOLATION NETWORK.

3. Connect the R.F. voltmeter across the output terminals

of the last I.F. stage.

4. Set receiver controls as given in Table XX.

5 . Tune the signal generator and the receiver to the

measurement frequency, f^.

6. Adjust the output level of the signal generator to a value E^^, that is approximately 10 dB below the upper voltage

level of the receiver's dynamic range (cf.).

139
TABLE XX

Selectance, Point-by-Point Method I

Initial Control Settings

Control Setting

1. Band Switch 1. As desired

2. Frequency Tuning 2. As desired

3. Antenna Trimmer 3. Peak

4. RF Gain 4. Relatively low

5. IF Gain 5. Medium

6 . AF Gain 6 . Minimum

7. Line Gain 7. Minimum

8. Detector Mode 8. N.A.

9. Beat Frequency Oscillator 9 . OFF

10. BFO Frequency 10 . N.A.

11. IF Bandwidth 11. As desired

12. AF Bandwidth 12. N.A.

13. Noise Limiter 13. OFF

14 . Squelch Level 14. OFF

15. AGC/MGC Mode Switch 15. MGC

16 . Meter Switch • 16 . N.A.

140
7. Determine the open circuit signal voltage E^^ in

microvolts, at the output terminals of the matching network,

if used; otherwise, at the output terminals of the generator.

8. Adjust the sensitivity of the R.F. voltmeter to produce

a convenient, near full-scale deflection, E . o

9. Measure output voltage, E^, in volts.

10. Compute the voltage ratio, R(f^) , in decibels, as follows

E

R(f ) = 20 log

o E. X 10"^

lO

11. Record R(f ) , in decibels, and the measurement freo quency, f^, in kilohertz or megahertz.

12. Tune the signal generator to a new measurement frequency,

f J , above (or below) f^. The frequency change, Af, where

Af = f, - ,

is somewhat arbitrary and depends upon the degree of detail with

which it is desired to know the selectance.

13. Leave the receiver tuned to frequency f^.

14. Adjust the output level of the signal generator to a value, E^^, that again produced output voltage E^.

15. Determine the open circuit signal voltage, E^^, in

microvolts as in Step 7, above.

16. Compute the voltage ratio, R(fi) , in decibels, as in

Step 10, above.

17. Record R(fi), in decibels, and the measurement frequency,

f J , in kilohertz or megahertz.

141
18. Proceed as indicated in Steps 12 through 17, each time

changing the frequency in convenient small steps. Continue

until the voltage ratio, R, in decibels, is 0 dB or as small

as practicable.

19. Plot the voltage ratio, R, in decibels, as a function

of measurement frequency, f, on rectilinear graph paper. This

plot is the selectance of the receiver.

4.4.1.3.3. DATA REQUIRED

1. Record the measurement frequencies in kilohertz or

megahertz .

2. Record the value of source impedance, , in ohms,

connected to the receiver input port.

3. Record the open circuit signal voltages, in microvolts,

at the output terminals of the matching network, if used;

otherwise, at the ouput terminals of the generator.

4. Record the I.F. output voltage, E^, in volts

5. Record the voltage ratios, R(f), in decibels.

4.4.1.3.4. MEASUREMENT ERRORS

The principal sources of measurement error are the

following :

'

1. Uncertainty, AE. , in the measured values of E.

2. Uncertainty, AE , in the measured value of E

3. Uncertainty, Af, in the measured values of f

142
The total relative uncertainty, AR(dB), in decibels,

in the voltage gain, R, is given approximately, for small

uncertainties , by the equation

AR(dB) = 20 log

where

AE. AE AR ^ 1 o R E. E

X o Uncertainties AE. and AE are obtained from the manufacturer's

1 o specf ications on the output level indicator of the signal

generator and on the R,F. voltmeter, respectively. Uncertainty

Af is obtained from the manufacturer's specifications on the

frequency meter.

4.4.1.4. METHOD, POINT-BY-POINT - II

The method uses a variable frequency CW generator and an

R.F. voltmeter as shown in figure 4.4.1.2. The signal generator

supplies a constant known input voltage to the receiver at a variety of frequencies within the principal response range of

the receiver. The voltmeter measures the I.E. output voltage.

The voltage gain between the receiver input terminals and the

I.E. output terminals is thus measured at the various selected

frequencies. Selectance is the graphical plot of (a) the ratio

of I.E. output voltage to receiver input voltage versus (b)

measurement frequency.

Measurement uncertainties as small as 6% are possible under

best conditions, and range from approximately 8% to 40% under

typical conditions . The method uses simple and commonly

available test equipment. Refer to Note, Section 4.4.1.3.

4.4.1.4.1. TEST EQUIPxMENT REQUIRED

1. Variable frequency signal generator

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2. Input impedance matching network

3. Frequency meter

4. Isolation network

5. R.F. voltmeter

4.4.1.4.2. PROCEDURE

1. Connect the input port of the receiver to the output port

of the SIGNAL GENERATOR through an IMPEDANCE MATCHING NETWORK

that provides the specified source impedance, , to the receiver

at the measurement frequency, f^. If the signal generator output

impedance equals , no matching network is req,uired.

2. Connect the FREQUENCY METER to the output port of the

signal generator through an ISOLATION NETWORK.

3. Connect the R.F. voltmeter across the output terminals

of the last I.F. stage.

4. Set receiver controls as given in Table XX, p. 140.

5. Tune the signal generator and the receiver to the

measurement frequency, f .

6. Adjust the output level of the signal generator to a value E^^ , that is approximately 10 dB below the upper voltage

level of the receiver's dynamic range (cf.).

7. Determine the open circuit signal voltage E^^, in

microvolts, at the output terminals of the matching network,

if used; otherwise, at the output terminals of the generator

8. Adjust the sensitivity of the R.F. voltmeter to

produce a convenient, near full-scale deflection, E .

145
9. Measure output voltage, , in volts.

10. Compute the voltage ratio, I^(fQ) ' decibels as follows

E

R(f ) = 20 log

^ . o' ^ E. X 10"^

lO

11. Record R(f ) , in decibels, and the measurement freo quency, f^ , in kilohertz or megahertz.

12. Tune the signal generator to a new measurement frequency, fj, above (or below) f^. The frequency change, Af,

where

- Af = f, - ,

is somewhat arbitrary and depends upon the degree of detail

with which it is desired to know the selectance. Leave the

generator level the same as in Step 7, above.

13. Leave the receiver tuned to frequency f^.

14. Measure output voltage, , in volts.

15. Compute the voltage ratio, R(fi), in decibels as follows

E

R(fl) = 20 log °^

E. X 10"^

1

16. Record R{fi), in decibels, and the measurement frequency, fi, in kilohertz or megahertz.

17. Proceed as indicated in Steps 11 through 15, each time

changing the frequency in small steps. Continue until the

output voltage, E^, reaches the level produced by the internal

noise of the receiver.

18. Plot the voltage ratio, R, in decibels, as a function

of measurement frequency, f, on rectilinear graph paper. This

plot is the selectance of the receiver.
4.4.1.4.3. DATA REQUIRED

1. Record the measurement frequencies in kilohertz

or megahertz

.

2. Record the value of source impedance, , in ohms,

connected to the receiver input port.

3. Record the open circuit signal voltage, E^^, in microvolts,

at the output terminals of the matching network, if used;

otherwise, at the output terminals of the generator.

4. Record the I.E. output voltages, E^, in volts.

5. Record the voltage ratios, R(f), in decibels.

4.4.1.4.4. MEASUREMENT ERRORS

1. The principal sources of measurement error are the

following

1. Uncertainty, AE., in the measured value of E.

2. Uncertainty, AE , in the measured values of E

3. Uncertainty, Af, in the measured values of f

The total relative uncertainty, AR(dB), in decibels, in

the voltage gain, R, is given approximately, for small

uncertainties , by the equation

AR(dB) = 20 log

where

o

o

147
Uncertainties AE. and AE are obtained from th

1 o specifications on the output level indicator of th

generator and on the R.F. voltmeter, respectively.

Af is obtained from the manufacturer's specificati

frequency meter.

4.4.1.5. METHOD, SWEPT-FREQUENCY

The method uses a swept-frequency CW signal generator and

an oscilloscope as shown in figure 4.4.1.3. The signal generator

supplies a swept frequency signal of constant amplitude to the

receiver. The oscilloscope displays the detected output voltage

from the receiver. Also, the signal generator supplies a linear

sweeping voltage for the horizontal deflection circuits of the

oscilloscope, and marker signals for calibrating the frequency

(horizontal) scale of the display. A camera is used to photograph

the oscilloscope display to obtain a permanent record of the

selectance.

Measurement uncertainties as small as 8% are possible under

best conditions, and range from approximately 12% to 40% under

typical conditions. The method uses simple and commonly

available test equipment.

4.4.1.5.1. TEST EQUIPMENT REQUIRED

1. Swept-frequency signal generator

2. Input impedance matching network

3. Cathode-ray oscilloscope

4. Oscilloscope camera

e manufacturer'

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Uncertainty

ons on the

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4.4.1.5.2. PROCEDURE

1. Connect the input port of the receiver to the output

port of the SIGNAL GENERATOR through an IMPEDANCE MATCHING

NETWORK that provides the specified source impedance, to

the receiver at the measurement frequency, f ^ . If the signal

generator output impedance equals Z^, no matching network is

required.

2. Connect the OSCILLOSCOPE to the detector output as

shown in figure 4.4.1.3.

3. Connect the sweeping voltage output from the generator

to the horizontal input terminals of the oscilloscope.

4. Set receiver controls as given in Table XXI.

5. Tune the receiver to the measurement frequency, f^

.

6. Adjust the output level of the sweep generator, the

sweep width of the sweep generator, and the vertical and

horizontal gains of the oscilloscope to produce a display of

the detector output voltage having sufficient size to fill

the square measurement area of the oscilloscope screen. Use

dc coupling in the oscilloscope. If the receiver bandwidth

is narrow, use as slow a generator sweep rate as practicable.

The output level is adjusted to provide an input signal

voltage that is no greater than 10 dB below the upper voltage

level of the receiver's dynamic range (cf.). The sweep width

is adjusted to display the full range of frequencies of the

principal receiver response, and no more.

7. Turn on sufficient marker generators to calibrate

the horizontal scale of the display in kilohertz or megahertz.

150
TABLE XXI

Selectance, Swept-Frequency Method

Initial Control Settings

Control Setting

1. Band Switch 1. As desired

2 . Frequency Tuning 2. As desired

3. Antenna Trimmer 3. Peak

4. RF Gain 4. Relatively low

5 . IF Gain 5. Medium

6 . AF Gain 6 . Minimum

7 . Line Gain 7. Minimum

8. Detector Mode 8. AM

9 . Beat Frequency Oscillator 9. OFF

10 . BFO Frequency 10 . N.A.

11. IF Bandwidth 11. As desired

12 . AF Bandwidth 12 . N.A.

13 . Noise Limiter 13. OFF

14 . Squelch Level 14 . OFF

15 . AGC/MGC Mode Switch 15 . MGC

16 . Meter Switch 16 . N.A.

151
8. Having obtained a suitable display, and with frequency

marker pips showing, photograph the display. This is the

selectance curve of the receiver.

9. Disconnect the vertical input of the oscilloscope from

the receiver detector circuit, and apply a signal from a square-wave calibration source to calibrate the vertical scale

of the oscilloscope.

10. Determine the vertical scale factor, in volts per

centimeter and record this information on the back of the

photograph.'

11. Detemine the horizontal scale factor from the marker

frequencies, in kilohertz or megahertz per centimeter, and

record this information on the back of the photograph.

4.4.1.5.3. DATA REQUIRED

1. Record the measurement frequency, f^ in kilohertz

or megahertz

.

2. Record the value of source impedance, Z^in ohms,

connected to the receiver input port.

3. Record the open circuit signal voltage, in microvolts,

at the output terminals of the matching network, if used;

otherwise, at the output terminals of the generator.

4. Record the vertical scale factor, in volts per

centimeter

.

5. Record the horizontal scale factor, in kilohertz or

megahertz per centimeter.

152
4.4.1.5.4. MEASUREMENT ERRORS

Because this test is primarily qualitative, no error analysis

is provided here. An estimate of measurement error can be

obtained from the manufacturer's specifications on the various

test equipments used.

153
4.4.2. CW BANDWIDTH

4.4.2.1. DEFINITION

The CW bandwidth of a receiver is the range of frequencies,

in kilohertz or megahertz, that lies between the half-power

points of the selectance curve (cf.).

To the extent that selectance depends upon the operating

conditions of the receiver, CW bandwidth also depends upon these

operating conditions.

4.4.2.2. PURPOSE

The purpose of this measurement method is to measure the CW

bandwidth of an AM receiver. CW bandwidth is a measure of the

spectrum of frequencies , centered around the principal response

frequency, which the receiver will amplify with significant

gain. It is not an adequate measure of the receiver's ability

to deliver an output signal of acceptable quality in the

presence of other signals.

CW bandwidth is measured at an arbitrary gain value, i.e.,

-3 dB from maximum gain. It therefore does not give sufficient

information about the frequency response characteristic so that

different receivers can be intercompared . It has maximum

utility when the frequency response characteristic has a single,

Gaussian-like shape. Only when this is the case does CW bandwidth have the qualitative meaning that is assumed in engineering

j argon

.

4.4.2.3. METHOD, VARIABLE-FREQUENCY GENERATOR

The method uses a variable frequency CW generator, an accurate frequency meter, a 3 dB attenuator, and an R.F. voltmeter

as shown in figure 4.4.2.1. The signal generator supplies a known input voltage to the receiver. The R.F. voltmeter measures

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the I.F. output voltage, and the frequency meter measures the

generator frequency. The 3 dB attenuator is connected between

the signal generator and receiver, both of which are tuned to

the measurement frequency, f^. I.F. output voltage, , is

noted. Then the 3 dB attenuator is removed and the frequency

of the signal generator is adjusted above and below f^ to those

frequencies, f^ and f^, that produce the same output voltage,

E . CW bandwidth is the frequency difference between f and f„

.

o _ . ^ ^ u £

Measurement uncertainties as small as 3% are possible under

best conditions, and range from approximately 6% to 25% under

typical conditions. The method uses simple and commonly available

test equipment.

4.4.2.3.1. TEST EQUIPMENT REQUIRED

1. Variable frequency signal generator

2. Input impedance matching network

3. 3 dB attenuator

4 . Frequency meter

5. Isolation network

6. R.F. voltmeter

4.4.2.3.2. PROCEDURE

1. Connect the input port of the receiver to the output

port of the SIGNAL GENERATOR through an IMPEDANCE MATCHING

NETWORK that provides the specified source impedance , to

the receiver at the measurement frequency, f^. If the signal

generator output impedance equals Z^, no matching network is

required.

156
2 . Connect the FREQUENCY METER to the output port of the

signal generator through an ISOLATION NETWORK.

3. Connect the R.F. voltmeter across the output terminals

of the last I.F. stage.

4. Set receiver controls as given in Table XXII.

5. Tune the signal generator and the receiver to the

measurement frequency, f^.

6 . With the 3 dB attenuator connected between the signal

generator and the matching transformer, adjust the output

level of the generator to a value that is within the linear

operating range of the receiver; i.e., at least 10 dB inside

the lower and upper voltage levels of the receiver's dynamic

range (cf .)

.

7. Determine the open circuit signal voltage E^, in

microvolts, at the output terminals of the matching network,

if used; otherwise, at the output terminals of the generator.

8. Adjust the sensitivity of the R.F. voltmeter to produce

a convenient, near full-scale deflection, E . o

9. Measure output voltage, E^, in volts.

10. Without changing the output level setting of the

generator, remove the 3 dB attenuator and connect the signal

generator directly to the matching network.

11. Increase the frequency of the generator above f^ until

the I.F. output voltage is again E^.

12. Readjust the generator output level control, if

necessary, to produce the value, E^, obtained in Step 7, above.

157
TABLE XXII

CW Bandwidth, Generator Method

Initial Control Settings

Control Setting

1

.

Band Switch 1. As desired

2 . Frequency Tuning 2

.

As desired

3 . Antenna Trimmer 3 . Peak

A4

.

RF Gain 4 . Relativelv low

5 . IF Gain 5 . Medium

6 . AF Gain 6 . Min imum

7 . Line Gain 7 Mini mnTn

8 . Detector Mode 8 . N . A

.

9 . Beat Frequency Oscillator 9 . OFF

10 . BFO Frequency 10 N A

11

.

IF Bandwidth 11 . A <=; rip ^ i c\

12 . AF Bandwidth 12. N. A.

13 . Noise Limiter 13. OFF

14 . Squelch Level 14 . OFF

15 . AGC/MGC Mode Switch 15 . MGC

16. Meter Switch 16. N.A.

158
13. Repeat Steps 11 and 12 until a frequency above is

found that produced when the signal voltage is E^.

14. Measure this frequency, f^.

15. Decrease the frequency of the generator below f^ until

the detector output voltage is again E^.

16 . Proceed as in Steps 12 and 15 until a frequency below

f is found that produces E when the signal voltage is E..

o o 1

17. Measure this frequency, f^.

18. Subtract from f to give the CW bandwidth B(CW).

That is,

B(CW) = - f, .

4.4.2.3.3. DATA REQUIRED

1. Record the measurement frequency, f^, in kilohertz

or megahertz.

2. Record the value of source impedance, Z^, in ohms,

connected to receiver input port.

3. Record the open circuit signal voltage, E^, in

microvolts, at the output terminals of the matching network,

if used; otherwise, at the output terminals of the generator,

4. Record the I.E. output voltage, E^ , in volts.

5. Record the -3dB upper frequency, f^, in kilohertz or

megaherts.

6. Record the -3dB lower frequency, f^, in kilohertz or

megahertz

.

159
7. Record the CW bandwidth, B(CW) , in kilohertz or megahertz.

4.4.2.3.4. MEASUREMENT ERRORS

The principal sources of measurement error are the uncertainties, AdB , in the attenuation of the 3 dB attenuator, and AE , in

o the indicated value of E^. The uncertainty, Af, in the measured

value of frequency is ordinarily insignificant compared with AdB

and AE . o The total relative uncertainty, AB(%) , expressed in percent,

in the measured value of bandwidth, B, is given by the equation

AR ' AB(%) = ~ X 100 ,

where the uncertainty, AB , is given by the equation

AB = (C„ + C ) (2.3 AdB + AE ) I u o

and are the slopes of the selectance curve, in hertz per

volt, at the frequencies f„ and f , respectively. They are

determined by measuring the change, <5E^, in output voltage,

E^ , for a small change, 6f, in frequency around f^ or fu That is

,

6E

o f=f

,

C =

u 6f

6e f=f

For a symmetrical selectance curve, |C = C_u Uncertainties AdB and AE are obtained from the manufacturer's specificao tions on the 3 dB attenuator and R.F. voltmeter, respectively.

160
4.4.2.4. METHOD, SWEPT-FREQUENCY GENERATOR

The method uses a swept- frequency CW signal generator and

an oscilloscope as shown in figure 4.4.2.2. The signal generator

supplies a swept frequency signal of constant amplitude to the

receiver. The oscilloscope displays the detected output voltage

from the receiver. Also, the signal generator supplies a linear

sweeping voltage for the horizontal deflection circuits of the

oscilloscope, and marker signals for calibrating the frequency

(horizontal) scale of the display. A camera is used to obtain a permanent record of the display. The CW bandwidth is found by

determining the width of the display at the half power points.

4.4.2.4.1. TEST EQUIPMENT REQUIRED

1. Swept- frequency signal generator

2. Input impedance matching network

3. Cathode-ray oscilloscope

4. Oscilloscope camera

4.4.2.4.2. PROCEDURE

1. Obtain the selectance curve of the receiver as outlined

in Section 4.5.1.5.

2. Locate the points on the curve that are 71% of the distance

from the base line of the curve to the top of the curve. These are

the 71% voltage gain points or 50% power gain (-3dB) points on

the curve

.

3. Determine the width of the curve, in kilohertz, between

these points, using the scale calibration factor in kilohertz

per centimeter. This is the CW bandwidth of the receiver.

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4.4.2.4.3. DATA REQUIRED

1. Record the measurement frequency, in kilohertz

or megahertz

.

2. Record the value of source impedance, in ohms,

connected to the receiver input port.

3. Record the open circuit signal voltage, in microvolts,

at the output terminals of the matching network, if used;

otherwise, at the output terminals of the generator.

4. Record the vertical scale factor, in volts per

centimeter

.

5. Record the horizontal scale factor, in kilohertz or

megahertz per centimeter.

6. Record the frequencies^ in kilohertz or megahertz,

at the 50% power gain points on the selectance curve.

7. Record the CW bandwidth, B(CW), in kilohertz or

megahertz

.

4.4.2.4.4. MEASUREMENT ERRORS

Because this test is primarily qialitative , no error

analysis is provided here. An estimate of measurement error

can be obtained from the manufacturer's specifications on

the various test equipments used.

163
4.4.3. SHAPE FACTOR

4.4.3.1. DEFINITIONS

Shape Factor is the ratio of (a) the selectance bandwidth

at -6 0 dB below the maximum gain point to (b) the selectance

bandwidth at -6 dB below the maximum gain point.

Selectance bandwidth is the range of frequencies that lies

between two specified points of the selectance curve (c.f.).

Note: When the measurement dynamic range does not permit

measurement over a 60 dB range, shape factor may

be defined in terms of some other gain points,

such as the -40 dB and -6 dB points.

4.4.3.2. PURPOSE

The purpose of this measurement method is to measure the shape

factor of the selectance of a receiver. Shape factor is a measure of the slope of the sides of the selectance curve. It has

importance as a measure of the ability of a receiver to pass the

desired frequency components of an amplitude modulated signal

while at the same time rejecting undesired signals adjacent to

the desired signal.

4.4.3.3. METHOD

The method uses a variable frequency CW generator, an

accurate frequency meter, a 54 d.B attenuator, a 60 dB attenuator,

and an R.F. voltmeter as shown in figure 4.4.3. The signal

generator supplies a known input voltage to the receiver, the

R.F. voltmeter measures the I.F. output voltage, and the frequency

meter measures the generator frequency. The 54 dB and 60 dB

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attenuators are used, in turn, to decrease the input signal

to the receiver when measuring the receiver gain at the -6 dB

and 0 dB points, respectively^ on the selectance curve. The

upper and lower frequencies, f^(-6 dB) , f^(-6n dB ) , f (-6 dB) , f^(-60 dB) , are measured and used to calculate the shape factor,

S , where

" f^(-60dB) - f^(-60dB)

^ " f ( -6dB) - f ( -6dB) •

This method can be used as given only when the receiver

has at least a 60 dB dynamic range. See the Note under

Section 4.4.3.1. above.

Measurement uncertainties as small as 6% are possible under

best conditions, and range from approximately 10% to 40% under

typical conditions. The method uses simple and commonly

available test equipment.

4.4.3.4. TEST EQUIPMENT REQUIRED

1. Variable frequency signal generator

2. Input impedance matching network

3. 54 dB attenuator

4. 60 dB attenuator

5. Frequency meter ^

6. Isolation network

7. R.F. voltmeter
4.4.3.5. PROCEDURE

1. Connect the input port of the receiver to the output

port of the SIGNAL GENERATOR through an IMPEDANCE MATCHING

NETWORK that provides the specified source impedance, , to

the receiver at the measurement frequency, f^ . If the signal

generator output impedance equals Z^, no matching network is

required.

2. Connect the FREQUENCY METER to the output port of the

signal generator through an ISOLATION NETWORK.

3. Connect the R.F. VOLTMETER across the output terminals

of the last I.E. stage.

4. Set the receiver controls as given in Table XXIII.

5. Tune the signal generator and the receiver to the

measurement frequency, f ^

.

6. With the 60 dB ATTENUATOR connected between the signal

generator and the matching transformer, adjust the output level

of the signal generator to a value, E^, that is 10 dB below the

upper voltage level of the receiver's dynamic range (cf .) .

7. Determine the open circuit signal voltage E^ , in

microvolts, at the output terminals of the matching network, if

used; otherwise, at the output terminals of the generator.

8. Measure the output voltage, E^

.

9. Without changing the output level setting of the generator,

remove the 6 0 dB attenuator and connect the 54 dB ATTENUATOR

between the signal generator and the matching network.

167
TABLE XXIII

Shape Factor

Initial Control Settings

Control Setting

1. Band Switch 1. As desired

2 . Frequency Tuning 2. As desired

3 . Antenna Trimmer 3 . Peak

4 . RF Gain 4 . Relatively low

5 . IF Gain 5 . Medium

6 . AF Gain ' 6. Minimum

7. Line Gain 7 . Minimum

8 . Detector Mode 8 . N. A.

9 . Beat Frequency Oscillator 9 . OFF

10. BFO Frequency 10 . N. A.

11

.

IF Bandwidth 11

.

As desired

12 . AF Bandwidth 12 . N.A.

13. Noise Limiter 13 . OFF

14 . Squelch Level 14 . OFF

15 . AGC/MGC Mode Switch 15 . MGC

16 . Meter Switch 16 . N.A.

168
10. Increase the frequency of the generator above f^ until

the I.F. output voltage is again .

11. Readjust the generator output level control, if necessary,

to produce the value, E^, obtained in Step 7 above.

12. Repeat Steps 10 and 11 until a frequency above f^ is

found that produces E^ when the signal voltage is E^.

13. Measure this frequency, f^(-6 dB) . This is the upper

frequency at which the receiver gain is 6 dB below that at f^.

14. Decrease the frequency of the generator below f^ until

the I.F. output voltage is again E^

.

15. Proceed as in Steps 11 and 12 until a frequency below

f^ is found that produces E^ when the input voltage is E^

.

16. Measure this frequency, f^(-6 dB) . This is the lower

frequency at which the receiver gain is 6 dB below that at f^

.

17. Without changing the output level setting of the

generator, remove the 54 dB attenuator and connect the signal

generator directly to the matching network.

18. Increase the frequency of the generator above f^ until

the I.F. output voltage is again E^

.

19. Readjust the generator output level control, if necessary,

to produce the value, E^, obtained in Step 7 above.

20. Repeat Steps 10 and 11 until a frequency above f^ is

found that produces E^ when the signal voltage is E^.

169
21. Measure this frequency, f^(-60 dB) . This is the upper

frequency at which the receiver gain is 60 dB below that at f^.

22. Decrease the frequency of the generator below f^ until

the I.F. output voltage is again E^.

23. Proceed as in Steps 11 and 12 until a frequency below

f is found that produces E when the input voltage is E.

.

o

24. Measure

^

this frequency,

o f^(-60

^1

dB) . This is the lower

frequency at which the receiver gain is 60 dB below that at f^.

25. Subtract ^^(-^ dB) from f^(-6 dB) to give the bandwidth at the -6 dB points.

26. Subtract f . (-60 dB) from f (-60 dB) to give the bandA/ U. width at the -60 dB points.

27. Compute the shape factor, S, by the equation

f (-60dB) - f (-60dB)

S =

^

f ( -6dB) - f „ ( -6dB) • u £

4.4.3.6. DATA REQUIRED

1. Record the measurement frequency, f^ , in kilohertz

or megahertz.

2. Record the value of source impedance, Z^, in ohms,

connected to receiver input port.

3. Record the open circuit signal voltage, E^, in

microvolts, at the output terminals of the matching network

if used; otherwise, at the output terminals of the generator,

170
4. Record the I.F. output voltage, , in volts.

5. Record the -6 dB upper frequency, f^(-6 dB) , in kilohertz

or megahertz.

6. Record the -6 dB lower frequency, f , (-6 dB) , in kilohertz

^ or megahertz.

7. Record the -60 dB upper frequency, f^(-60 dB) , in

kilohertz or megahertz,

8. Record the -60 dB lower frequency, f.(-60 dB) , in

kilohertz or megahertz.

9. Record the shape factor, S , as a numeric ratio, usually

expressed in the form

S = B(-60 dB) / B(-6dB) : 1

4.4.3.7. MEASUREMENT ERRORS

Because this test is primarily qualitative, no error analysis

is provided here. An estimate of measurement error can be obtained

from the manufacturer's specifications on the various test

equipments used.

171
4.4.4. MODULATION ACCEPTANCE BANDWIDTH

4.4.4.1. DEFINITION

The modulation acceptance bandwidth of an FM receiver is

the deviation, in kilohertz, that will produce a 12 dB SINAD

ratio at an RF signal level of 6 dB above the 12 dB SINAD

SENSITIVITY of the receiver.

Although the basic concept of modulation acceptance bandwidth

applies also to an AM receiver, no such receiver parameter has

been so defined.

- 4.4.4.2. PURPOSE

The purpose of this measurement method is to measure the

modulation acceptance bandwidth of an FM receiver. Modulation

acceptance bandwidth is a measure of the maximum deviation of

a frequency modulated carrier that can produce an audio output

signal of acceptable quality. The method takes into account the

effects of distortion of the desired signal within the receiver.

However, it does not take into account the output degradation

effects caused by undesired signals.

4.4.4.3. METHOD

The method uses a frequency modulated signal generator and

an audio distortion analyzer as shown in figure 4.4.4. First,

the 12 dB SINAD sensitivity is measured (cf) . Then, the

generator output level is increased by 6 dB, and the modulation

deviation is increased until a 12 dB SINAD ratio is again obtained.

Twice the deviation, in kilohertz, required for this is the

modulation acceptance bandwidth of the receiver.

172
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Measurement uncertainties as small as 10% are possible under

best conditions, and range from approximately 15% to 50% under

typical conditions . The method uses commonly available test

equipment of moderate sophistication.

4.4.4.4. TEST EQUIPMENT REQUIRED

1. Signal generator capable of frequency modulation

2 . Input impedance matching network

3. Termination resistor for receiver output load

4. Audio distortion analyzer

4.4.4.5. PROCEDURE

1. Measure the 12 dB SINAD SENSITIVITY as outlined in

Section 4.1.5. Refer to Table VIII for initial settings of

receiver controls

.

2. Increase the signal generator output level by exactly

6 dB.

3. Set the distortion analyzer so that the 1000 Hz rejection

filter is NOT in the circuit.

4. Adjust the receiver AF gain control to produce

reference audio output power, P^.

5. Adjust the distortion analyzer so that the lOQO Hz

rejection filter tunes out the 1000 Hz modulation from the

signal generator.

174
6. Measure the noise plus distortion output power, P (n+d)

7. Calculate SINAD in decibels from the equation

P

SINAD CdB) = 10 log o

(n+d)

8. If the SINAD ratio calculated in Step 7 is greater

(or less) than 12 dB , increase (or decrease) the deviation

percentage and repeat Steps 3 through 7 . Continue this

procedure until 12 dB SINAD ratio is obtained.

9. Determine the deviation, f^, in kilohertz, for the

conditions obtained in Step 8. Twice f^ ^^f^) is the MODULATION

ACCEPTANCE BANDWIDTH of the receiver at frequency f .

1. Record the measurement frequency, f^, in kilohertz or

megahertz

.

2. Record the value of source impedance, , in ohms,

connected to receiver input port.

3. Record the value of termination resistance, R^, in

ohms, connected to receiver audio output terminals.

4. Record the reference output power, P^, in watts.

5. Record 12 dB SINAD sensitivity, in microvolts.

6. Record modulation acceptance bandwidth, 2f , in kilohertz.

o

4.4.4.6. DATA REQUIRED

175
4.4.4.7. MEASUREMENT ERRORS

The principal sources of measurement error are the following:

1. Uncertainty, AE^, in the 12 dB SINAD sensitivity, E^

2. Uncertainty, frequency deviation, f^

The total relative uncertainty, Af^(%), expressed in percent,

in the modulation acceptance bandwidth, 2f^, is given approximately

by the equation

The relative uncertainty, AE^(%), in the 12 dB SINAD sensitivity

is obtained as described in Section 4.1.3.7. The uncertainty, Af^,

is obtained from the manufacturer's specifications on the modulation

deviation of the signal generator.

Af^ (%) = AE^ (%) + d

176
4.4.5. SPURIOUS RESPONSE ATTENUATION

Spurious responses occur when a receiver, due to its

circuitry and construction, responds to frequencies other than

those in its principal response band. They are considered to

be those responses of a receiver to a single input frequency

only. Therefore, they are to be distinguished from responses

that occur in the presence of two or more simultaneous signals;

the latter are described by other terms such as cross modulation (cf.) and intermodulation (cf.).

Spurious responses are usually generated when undesired

signals mix with receiver local oscillators or their harmonics

in non-linear stages of the receiver. However,, faulty receivers

having unintended regeneration may produce spurious responses

that are not related to local oscillator frequencies.

Spurious responses that consist of families of related responses can often be identified by the following relationships:

For a single conversion receiver:

pf.LO

± f

IF

f

s q

For a dual-conversion receiver:

± f IF2

f + s q 1

For a triple conversion receiver:

f

+

± f IF3

S qiqaqs

177
where p is an integer or zero denoting the harmonic order of

the local oscillator, q is an integer (not zero) denoting the

harmonic order of the mixer input signal, f and f^.^ denote

J-iU IF

the local oscillator and intermediate frequency, respectively,

and the subscripts are indicative of the number of mixer stages

preceding the signal processing circuitry.

4.4.5.1. DEFINITIONS

a. The spurious response attenuation of a receiver is the

ratio, expressed in decibels, of (a) the input voltage required

to produce reference audio output power due to a signal at a spurious-response generating frequency, to (b) the input voltage

required to produce reference audio output power due to a signal

at the frequency to which the receiver is tuned.

b. A spurious response is any response, other than the

desired response, of an electric transducer or device. (IEEE

Std. 10 0-19 72)

4.4.5.2. PURPOSE

The purpose of this measurement method is to measure the

spurious response attenuation of surveillance receivers. Spurious

response attenuation is a measure of the spectrum of frequencies,

outside of the principal response region, to which the receiver

will respond with measurable output power. It is not an adequate

measure of the receiver's ability to reject undesired signals,

but it does reveal those frequencies where the receiver will be

most susceptible to undesired signals.

The test methods given below have general applicability to

all receiver spurious responses, including image, I.F. feed-through,

local oscillator-related, and extraneously produced responses.

178
4.4.5.3. METHOD - AM RECEIVERS

The method uses a variable-frequency amplitude modulated

signal generator and a power meter or true rms voltmeter as shown in figure 4.4.5.1. The signal generator supplies a known

input voltage to the receiver over a range of frequencies. The

voltmeter or power meter indicates the receiver output signal

level

.

Before searching for spurious responses, the 6 dB SN/N

SENSITIVITY is measured. Then, with the receiver adjusted for

that measurement, the generator output level is increased to

a large value and its frequency is slowly adjusted until a spurious response is produced. The input signal level is

adjusted at the frequency causing the spurious response to

produce reference audio output power. This input level, expressed

as a decibel ratio relative to the 6 dB sensitivity, is the

spurious response attenuation at that frequency. This process

is repeated for the next spurious response.

Measurement uncertainties as small as o . 3 dB are possible under

best conditions, and range from approximately 0.4 dB to 1.5 dB under

typical conditions. This method uses rudimentary and commonly

available test equipment.

4.4.5.3.1. TEST EQUIPMENT REQUIRED

1. Signal generator capable of amplitude modulation

2 . Input impedance matching network

3. Termination resistor for receiver audio output port

179
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180
4a. AF power meter

OR,

4b . True rms voltmeter

4.4.5.3.2. PROCEDURE

1. Connect the input port of the receiver to the output port

of the SIGNAL GENERATOR through an IMPEDANCE MATCHING NETWORK

that provides the specified source impedance, Z^, to the receiver

at the measurement frequency, f^. If the signal generator output

impedance equals Z^, no matching network is required.

2a. Connect the TERMINATION RESISTOR having a resistance

equal to the specified load resistance, R^ , and a power rating

in excess of the receiver's rated audio output power level, to

the audio output port of the receiver. Connect the TRUE RMS

VOLTMETER across the resistor.

OR,

2b. Connect the POWER METER, having an input impedance equal

to the specified load resistance, R^, to the audio output port of

the receiver.

3. Measure the 6 dB SN/N SENSITIVITY as outlined in Section

4.1.2.5.

4. Adjust the output level of the signal generator to

maximum (e.g., 100,000 to 1,000,000 microvolts).

181
5. Slowly tune the frequency of the generator away from

the principal response region, and search for a response from the

receiver's output.

6. When a response is found, reduce the output level of

the generator to give reference audio output power, .

7. Determine the frequency, f^ , in kilohertz or megahertz,

and the open circuit signal voltage, , in microvolts, at the

OUTPUT TERMINALS of the matching network, if used; otherwise, at

the output terminals of the generator.

8. Calculate the ratio, R(S) , in decibels, given by the

following equation:

E

R(S) = 20 log . E

.

1

R(S) is the spurious response attenuation of the receiver,

referenced to the receiver's 6 dB SN/N sensitivity, at the

frequency f^

.

9. Proceed as indicated in Steps 4 through 8, above, until

the entire desired frequency range is covered.

4.4.5.3.3. DATA REQUIRED

1. Record the measurement frequency , f^ , in kilohertz or

megahertz, to which the receiver is tuned.

2. Record the frequencies, f^ , in kilohertz or megahertz,

that cause the spurious response.

182
3. Record the value of source impedance, Z , in ohms,

s connected to receiver input port.

4. Record the value of termination resistance, R^, in ohms,

connected to receiver audio output terminals

.

5a. Record the output voltage, E^, in volts.

OR,

5b. Record the reference output power, P^, in watts.

6. Record the 6 dB SN/N sensitivity, E^, in microvolts.

7. Record the open circuit voltages, E , in microvolts,

at the output terminals of the matching network, if used;

otherwise, at the output terminals of the generator.

8. Record the spurious response attenuation, R(S) , in

decibels, for each spurious response.

4.4.5.3.4. MEASUREMENT ERRORS

The principal sources of measurement error are the following:

1. Uncertainty, AE^, in the measured value of E^

2. Uncertainty, AE , in the measured value of E

3a. Uncertainty, AE^, in the measured value of E^

OR,

3b. Uncertainty, AP , in the measured value of P

183
The total relative uncertainty, AR(dB), in decibels, in

the spurious response attenuation, R, is given approximately,

for small uncertainties, by the equations

AR (dB)

t

OR,

AR (dB)

Uncertainties AE . and AE are obtained from the manufacturer's

1 s specifications on the output level indication of the signal

generator. Uncertainties AE and/or AP are obtained from the ^ o o manufacturer's specifications on the voltmeter and/or power

meter, respectively.

4.4.5.4. METHOD - FM RECEIVERS

The method uses an unmodulated signal generator and a true

rms voltmeter or power meter as shown in figure 4.4.5.2. The

signal generator supplies a known input voltage to the receiver

over a range of frequencies. The voltmeter or power meter

indicates the receiver output noise level.

Before searching for spurious responses, the 20 dB QUIETING

SENSITIVITY is measured. Then, with the receiver adjusted for

that measurement, the generator output level is increased to a large value and its frequency is slowly adjusted until a spurious response is produced. The input signal level is adjusted

at the frequency causing the spurious response to produce 20 dB

noise quieting. This input level, expressed as a decibel ratio

relative to the 20 dB quieting sensitivity, is the spurious

response attenuation at that frequency. This process is

repeated for the next spurious response.

(AE. AE AE \

1 * -E^+ • 1 s o

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I AE. AE , AP \ = 20 log n

^ + IS+ ^ + - ^

j o '

184
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185
Measurement uncertainties as small as 0 . 3 dB are possible under

best conditions, and range from approximately 0.4 dB to 1.5 dB under

typical conditions. This method uses rudimentary and commonly

available test equipment.

4.4.5.4.1. TEST EQUIPMENT REQUIRED

1. CW Signal generator

2. Input impedance matching network

3. Termination resistor for receiver audio output port

4a. AF power meter

OR,

4b, True rms voltmeter

4.4.5.4.2. PROCEDURE

1- Connect the input port of the receiver to the output

port of the SIGNAL GENERATOR through an IMPEDANCE MATCHING

NETWORK that provides the specified source impedance, Z^, to

the receiver at the measurement frequency, f^. If the signal

generator output impedance equals Z^, no matching network is

required.

2a. Connect the TERMINATION RESISTOR having a resistance

equal to the specified load resistance, R^^^ , and a power rating

in excess of the receiver's rated audio output power level,

to the audio output port of the receiver. Connect the TRUE RMS

VOLTMETER across this resistor.

186
OR,

2b. Connect the POWER METER, having an input impedance equal

to the specified load resistance, R^^ , to the audio output port of

the receiver.

3a. Set the voltmeter on a range to indicate 25% of the

rated output power, P^. The voltage to be measured is given

by the equation

3b. Set the power meter on a range to indicate 25% of the

rated output power, P^

.

4. Measure the 20 dB QUIETING SENSITIVITY as outlined in

Section 4.1.4.5.

5. Adjust the output level of generator No. 2 to maximum

(e.g., 100,000 to 1,000,000 microvolts).

6. Slowly tune the frequency of the generator away from

the principal response region, and search for a response from

the receiver's output.

7. When a response is found, reduce the output of the

generator to give 20 dB of noise quieting, measured as outlined

in Section 4.1.4.5.

8. Determine the frequency, f^, in kilohertz or megahertz,

and the open circuit signal voltage, E^ , in microvolts, at the

OUTPUT TERMINAL of the matching network, if used; otherwise,

at the output terminals of the generator.

E

o = 0.5

OR,

187
9. Calculate the ratio, R(S) , in decibels, given by

the following equation:

-. E

R(S) = 20 log . ht

.

1

R(S) is the spurious response attenuation of the receiver,

referenced to the receiver's 20 dB quieting sensitivity, at

the frequency f ^

.

10. Proceed as indicated in Steps 5 through 9, above,

until the entire desired frequency range is covered.

4.4.5.4.3. DATA REQUIRED

!• Record the measurement frequency, f ^ , in kilohertz or

megahertz, to which the receiver is tuned.

2. Record the frequencies, f^, in kilohertz or megahertz,

that cause the spurious response.

3. Record the value of source impedance, Z^, in ohms,

connected to receiver input port.

4. Record the value of termination resistance, R^ , in ohms,

connected to receiver audio output terminals.

5. Record the measured output voltages, E^ , and 0.1 E^,

in volts

.

6. Record the measured output powers, 0.2 5 and

0 .0025 P , in watts.

o

7. Record the 20 dB quieting sensitivity, E^, in

microvolts

.

188
8. Record the open circuit voltages, E^, in microvolts,

at the output terminals of the matching network, if used;

otherwise, at the output terminals of the generator.

9. Record the spurious response attenuation, R(S) , in

decibels, for each spurious response.

4.4.5.4.4. MEASUREMENT ERRORS

The principal sources of measurement error are the following:

1. Uncertainty, AE . , in the measured value of E.

2. Uncertainty, AE^, in the measured value of E^

3a. Uncertainty, AE , in the measured value of E

3b. Uncertainty, AP , in the measured value of P o ' o

The total relative uncertainty, AR(dB) , in decibels, in the

spurious response attenuation, R, is given approximately, for

small uncertainties, by the equations

o o

OR,

AR (dB) = 20 log

OR ,

AR (dB) = 20 log

189
Uncertainties AE. and AE are obtained from the manufacturer's

1 s specifications on the output level indication of the signal

generator. Uncertainties AE and/or AP are obtained from the ^ o o manufacturer's specifications on the voltmeter and/or power

meter, respectively.

190
4.4.6. NOISE BANDWIDTH

4.4.6.1. DEFINITION

The noise bandwidth of a receiver is the width, in kilohertz

or megahertz, of a rectangular selectance curve whose height

and area are equal to the maximum height and enclosed area of

the receiver's actual selectance curve.

4.4.6.2. PURPOSE

The purpose of this measurement method is to measure the

noise bandwidth of surveillance receivers. Noise bandwidth is

a partial measure of the amount of random noise power that will

be delivered from the output terminals of the receiver. It is a useful quantity for calculating output signal-to-noise ratio.

Because it is related only to the average width of the selectance

curve, it is not a good measure of the receiver's ability to

reject non-random signals.

4.4.6.3. METHOD

The method uses a variable frequency CW generator, an

accurate frequency meter, and an R.F. voltmeter as shown in

figure 4.4.6. The signal generator supplies a known input

voltage to the receiver at a variety of frequencies within

the principal response range of the receiver. The voltmeter

measures the I.F. output voltage.

The selectance curve is obtained as described in Section

4.4.1. The height and area under the curve are determined,

and from these quantities noise bandwidth is calculated.

191
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Measurement uncertainties as small as 10% are possible under

best conditions, and range from approximately 15% to 50% under

typical conditions. The method uses simple and commonly available

test equipment.

4.4.6.4. TEST EQUIPMENT REQUIRED

1. Variable frequency signal generator

2. Input impedance matching transformer

3. Frequency meter

4. Isolation network

5. R.F, voltmeter

4.4.6.5. PROCEDURE

1. Measure the selectance as outlined in Section 4.4.1

However, rather than plotting the selectance curve in terms

of voltage gain in decibels versus frequency, plot, on

rectilinear graph paper, the voltage ratio, R(f) , versus

frequency, f.

2. Determine the total area, A, in volts per volt times

hertz, enclosed by the selectance curve.

3. Determine the maximum height, h, in volts per volt, of

the selectance curve.

4. Determine the width, B

of a rectangle whose height is

B(N) is the noise bandwidth of

(N) , in kilohertz or megahertz,

h and whose total area is A.

the receiver.

193
4.4.6.6. DATA REQUIRED

1. Record the measurement frequencies in kilohertz or

megahertz.

2. Record the value of source impedance, , in ohms,

connected to the receiver input port.

3. Record the open circuit signal voltages, in microvol

at the output terminals of the matching network, if used;

otherwise, at the input terminals of the generator.

4. Record the I.F. output voltages, E^ , in volts.

5. Record the voltage ratios, R(f), as a numeric ratio.

6. Record the area, A, in volts per volt times hertz

(v/v) (Hz)

.

7. Record the height, h, in volts per volt.

8. Record the calculated value of noise bandwidth,

B(N), in kilohertz or megahertz.

4.4.6.7. MEASUREMENT ERRORS

The principal sources of measurement error are the

following:

1. Uncertainty, AE^ , in the measured values of E^

2. Uncertainty, AE , in the measured values of E ' o o

3. Uncertainty, Af, in the measured values of f

194
The total relative uncertainty, AB(%), expressed in percent, in the noise bandwidth, B(N)/ is given by the equation

AB (%) = (

^ X 100 ) +

(

^ X 100

^

,

where AA is the uncertainty in the area, A, and Ah, is the

uncertainty in the height, h. Relative uncertainty AA/A is

given by

Relative uncertainty Ah/h is given by

/AE. AE \

h ^ I E. E y

• ^ 1 o /

Uncertainties AE . and AE are obtained from the manufacturer's

1 o specifications on the output level indicator of the signal

generator and on the R.F. voltmeter, respectively. Uncertainty

Af is obtained from the manufacturer's specifications on the

frequency meter.

195
4.4.7. DESENSITIZATION

4.4.7.1. DEFINITION

The desensitization of an AM receiver is the input

voltage level from an undesired signal source which, when

present simultaneously with a desired signal source of a selected level that alone produces reference audio output

power, produces a reduction of 3 dB in the audio output power

as compared with the output in the absence of the undesired

signal

.

Desensitization in an AM receiver may be a function of

desired signal level. It is usually expressed in decibels

above the desired signal level at which the measurement is

made

.

4.4.7.2 PURPOSE

The purpose of this measurement method is to measure the

desensitization of Ai'4 receivers. Desensitization is a measure

of the extent to which receiver gain is reduced by the

presence of an adjacent undesired signal.

4.4.7.3. METHOD

The method uses two signal generators and a voltmeter or

power meter as shown in figure 4.4.7. The signal generators

supply known input voltages at different frequencies to the

receiver through a combining network. The voltmeter or power

meter measured the receiver output signal level that is

produced under the following two conditions:

(1) The first generator is amplitude modulated and adjusted

to produce reference audio output power with the second generator turned off.

196
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(2) The second generator is unmodulated and tuned to a different frequency. Its output level is adjusted until

the audio output power is reduced 3 dB below reference output

power.

The signal level ratio, in decibels, of the two generators

is the desensitization of the receiver.

Measurement uncertainties as small as 0.4 dB are possible

under best conditions, and range from approximately 0.6 dB to

2 dB under typical conditions. This method uses commonly available

test equipment of moderate sophistication.

. 4.4.7.4. TEST EQUIPMENT REQUIRED

1. Signal generator capable of amplitude modulation

2. Variable-frequency CW signal generator

3. Three-port combining network

4 . Input impedance matching network

5. Termination resistor for receiver audio output port

6a. AF power meter

OR,

6b. A.C. voltmeter

198
4.4.7.5. PROCEDURE

1. Connect the two SIGNAL GENERATORS to the input port

of the receiver through the COMBINING NETWORK and IMPEDANCE

MATCHING NETWORK as shown in figure 4.4.7. The matching network

is chosen to present the specified source impedance, , to

the receiver at the measurement frequency, f^. If the output

impedance of the combining network, with signal generators

connected, equals , no matching network is required.

2a. Connect the TERMINATION RESISTOR having a resistance

equal to the specified load resistance, R,^ , and a power rating

in excess of the receiver's rated audio output level, to the

audio output port of the receiver. Connect the A.C. VOLTMETER

across this resistor.

OR,

2b. Connect the POWER METER, having an input impedance equal

to the specified load resistance, R^^ , to the audio output port

of the receiver.

3a. Set the voltmeter on a range to indicate the reference

output power, P^ . The voltage to be measured is given by the

equation

o V o £

OR,

3b. Set the power meter on a range to indicate the reference

output power, P^.

4. Set the controls as given in Table XXIV.

5. Tune signal generator No. 1 and the receiver to the

measurement frequency, f .

199
TABLE XXIV

De sensitization

Initial Control Settings

Control Setting

1. Band Switch 1. As desired

2. Frequency Tuning 2. As desired

3. Antenna Trimmer 3. Peak

4. RF Gain 4. Maximum

5. IF Gain 5 . Maximum

6 . AF Gain 6 . As required

7 . Line Gain 7. Optional

8. Detector Mode 8. AM

9 . Beat Frequency Oscillator 9 . OFF

10 . BFO Frequency 10 . N.A.

11. IF Bandwidth 11. As desired

12. AF Bandwidth 12. As desired

13. Noise Limiter 13. OFF

14. Squelch Level 14. OFF

15. AGC/MGC Mode Switch 15. AGC

16 . Meter Switch 16. Optional

200
6. Adjust the amplitude modulation in signal generator

No. 1 to 30% at 1000 Hz.

7. Adjust the output level of signal generator No. 1 to give

the desired input voltage to the receiver. This will normally lie

within the receiver's dynamic range (cf.). A suitable value is

1000 microvolts.

8. Determine the open circuit signal voltage, , in microvolts, at the output terminals of the matching network, if used;

otherwise, at the output terminals of the combining network.

9. With the output level of signal generator No. 2 set to

zero, adjust the AF gain control to produce reference audio

output power, .

10. Tune signal generator No. 2 to the desired interference

frequency, f^^.

11. With generator No. 2 unmodulated, and with generator

No. 1 set as given above, adjust the output level of generator

No. 2 to produce 3 dB reduction in the audio output power

obtained in Step 9, above.

12. Determine the open circuit signal voltage, E^^, in

microvolts, due to generator No. 2, at the output terminals of

the matching network, if used; otherwise, at the output

terminals of the combing network.

13. Calculate the ratio, D, in decibels, by the following

equation

E

.

D(dB) = 20 log . ^ii

D(dB) is the desensi ti zation of the receiver under conditions

of (1) measurement frequency, f^, (2) interference frequency,

f ^ , and (3) desired signal level, .

201
4.4.7.6. DATA REQUIRED

1. Record the measurement frequency, f^ , in kilohertz or

megahertz

.

2. Record the value of source impedance, Z^, in ohms,

connected to receiver input port.

3. Record the value of

connected to receiver audio

4a. Record the output voltage, , in volts.

OR, "

> ' "

4b. Record the reference output power, , in watts.

5. Record the open Xr- circuit voltages, E. and E. , in ^ ' 1 1 12 ' microvolts, at the output terminals of the matching network,

if used; otherwise, at the output terminals of the combining

network.

6. Record the desensitization, D(dB), in decibels.

4.4.7.7. MEASUREMENT ERRORS

The principal sources of measurement

following

1. Uncertainties, AE . and AE. , in

11 - 12 ' of E. and E.

11 12

2a. Uncertainty, AE , in the measured value of E ' o o

OR,

2b. Uncertainty, AP^, in the measured value of P^

termination resistance, R^, in ohms,

output terminals.

error are the

the measured values

202
The total relative uncertainty, AD(dB) , in decibels, in

the desensitization , D, is given approximately, for small

uncertainties , by the equation

AD (dB) = 20 log

where

or

,^ AE. AE. AE

AD _ 1

1

12 o D

~ E . E . E

11 12 O

AE. AE. T AP

AD _ 1

1

_^ 12 _|_ 1 o D E . E . 2 P

11 12 o

Uncertainties AE . and AE are obtained from the manufac1 1 2 turer ' s specifications on the output level indicator of the

signal generators. Uncertainties AE^ and/or AP^ are obtained

from the manufacturer's specifications on the voltmeter and/or

power meter, respectively.

203
4.4.8. CROSS MODULATION

When cross modulation occurs, the modulation components

of a large undesired signal are transferred to the carrier of

a weak desired signal, and are demodulated along with the

desired signal. Cross modulation may occur at any frequency,

and no particular relationship among the frequencies of the

desired signal, the undesired signal, and the receiver I.F.

amplifier need exist.

4.4.8.1. DEFINITIONS

a. Cross modulation is a type of intermodulati

modulation of the carrier of the desired signal by

signal wave. (IEEE Std 100-1972)

b. Cross modulation is the input voltage level from an

undesired signal source which, when present simultaneously

with a desired signal source that alone produces reference

audio output power, produces 1% of reference audio output

power.

4.4.8.2. PURPOSE

The purpose of this measurement method is to measure the

cross modulation of an AlA receiver. This characteristic is a measure of the ability of a receiver to reject an undesired

signal in the presence of, but on a different frequency from,

the desired signal.

4.4.8.3. METHOD

The method uses two amplitude modulated signal generators

and a voltmeter or power meter as shown in figure 4.4.8. The

signal generators supply known input voltages at different

on due to

an undesired

204
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205
frequencies to the receiver through a combining network. The

voltmeter or power meter measures the receiver output signal

level that is produced under the following two conditions

(1) The first generator is adjusted to produce reference

audio output power with the second generator turned off.

(2) The second generator is tuned to a frequency that

produces a response due to cross modulation. Its level is

adjusted to produce 1% of rated audio output power in the

presence of the first generator's carrier with no modulation

on the first generator.

The open circuit voltage, in microvolts, of the second

generator is the cross modulation of the receiver.

Measurement uncertainties as small as 10% are possible

under best condtions , and range from approximately 12% to 50%

under typical conditions. This method uses rudimentary and

commonly available test equipment.

4.4.8.4. TEST EQUIPMENT REQUIRED

1. Two amplitude modulated, variable-frequency signal

generators

2 . Three-port combining network

3. Input impedance matching network

4. Termination resistor for receiver output output port

5a. AF power meter

OR, -

5b. A.C. voltmeter

206
4.4.8.5. PROCEDURE

1. Connect the two SIGNAL GENERATORS to the input port of

the receiver through the COMBINING NETWORK and IMPEDANCE

MATCHING NETWORK as shown in figure 4.4.8. The matching network

is chosen to present the specified source impedance, , to

the receiver at the measurement frequency, f^. If the output

impedance of the combining network, witn signal generators

connected, equals Z^, no matching network is required.

2a. Connect the TERI4INATI0N RESISTOR having a resistance

equal to the specified load resistance, R^ , and a power rating

in excess of the receiver's rated audio output level, to the

audio output port of the receiver. Connect the A.C. VOLTMETER

across this resistor.

OR,

2b. Connect the POWER METER, having an input impedance equal

to the specified load resistance, R^ , to the audio output port

of the receiver.

3 •» Set the voltmeter on a range to indicate the reference

output power, P^. The voltage to be measured is given by tne

equation

E = Wp R. o V o £

OR,

3b. Set the power meter on a range to indicate the

reference output power, P . o

207
4. Set receiver controls as given in Table XXV.

5. Tune signal generator No. 1 and the receiver to the

measurement frequency, f . o

6. Adjust the amplitude modulation in signal generator

No. 1 to 30% at 1000 Hz.

7. Adjust the output level of signal generator No. 1 to

give the desired input voltage to the receiver. This will

normally lie within the receiver's dynamic range (cf.). A value

of 1000 microvolts is suggested.

8. Determine the open circuit signal voltage, , in

microvolts, at the OUTPUT TERMINALS of the matching network,

if used; otherwise, at the output terminals of the combining

network

.

9. With the output level of signal generator No. 2 set to

zero, adjust the AF gain control to produce reference audio

output power, .

10. Tune signal generator No. 2 to the desired interference

frequency, f^.

11. Adjust the amplitude modulation of generator No. 2 to 30% at 1000 Hz.

12. Adjust generator No. 1 for zero amplitude modulation

(i.e., turn modulation off).

13. With the output level of generator No. 1 still set as in Step 7, above, but unmodulated, adjust the output level of

generator No. 2 to produce 1% of reference audio output power,

P^ . That is, the output level at this Step, due to generator

No. 2, is 20 dB below the output level obtained in Step 9,

above, due to generator No. 1.

208
TABLE XXV

Cross Modulation

Initial Control Sett

Control

1. Band Switch 1.

2. Frequency Tuning 2.

3. Antenna Trimmer 3.

4. RF Gain 4.

5. IF Gain 5.

6. AF Gain 6.

7 . Line Gain 7.

8. Detector Mode 8.

9 . Beat Frequency Oscillator 9 .

10. BFO Frequency 10 .

11. IF Bandwidth 11.

12. AF Bandwidth 12 .

13. Noise Limiter 13.

14 . Squelch Level 14.

15. AGC/MGC Mode Switch 15.

16 . Meter Switch 16 .

ings

Setting

As desired

As desired

Peak

As desired (normally at maximum)

Maximum

As required

Optional

AM

OFF

N.A.

As desired

As desired

OFF

OFF

As desired

Optional

209
14. Determine the open circuit signal voltage, , in

microvolts, due to generator No. 2, at tlie OUTPUT TERMINALS

of the matching network, if used; otherwise at the output

terminals of the combining network. E is the cross modulation ^ c of the receiver under conditions of (1) measurement frequency,

f ^ , (2) interference frequency, f ^ , and (3) desired signal

level , E .

.

1

4.4.8.6. DATA REQUIRED

1. Record the measurement frequency, f^ in kilohertz

or megahertz, to which the receiver is tuned.

2. Record the interference frequency, f^, in kilohertz

or megahertz

3. Record the value of source impedance, , in ohms,

connected to the receiver input port.

4. Record the value of termination resistance, R^ , in

ohms, connected to receiver output terminals.

5a. Record the output voltage, E^ , in volts

OR,

5b. Record the reference output power, , in watts

6. Record the open circuit signal voltage, E^ , in

microvolts

.

7. Record the open circuit signal voltage, E^, in

microvolts

.

210
4.4.8.7. MEASUREMENT ERRORS

The principal sources of measurement error are the

following:

1. Uncertainty, AE , in the measured values of E

c c

2a. Uncertainty, AE , in the measured value of E ^ o o

OR,

2b. Uncertainty, AP , in the measured value of P

o o

The total relative uncertainty, AE^(%) , in the cross

modulation, E^ , expressed as a percent, is given by the

equations

OR

/ AE t / AE \

AE^ (%) = X 100 j + X 100

j

/ AE \ / 1 \

^^c = ("e; ^ i^oj ^ ' j

•

The uncertainty, AE^, is obtained from the manufacturer's

specifications on the output level indication of the signal

generator. Uncertainties AE and/or AP are obtained from the ^ o o manufacturer's specifications on the voltmeter and/or power

meter, respectively.

211
4.4.9. ADJACENT CHANNEL SELECTIVITY

4.4.9.1. DEFINITION

Adjacent channel selectivity is the input voltage level

from a signal source in the adjacent channel of an FM receiver

which, when present simultaneously with a signal in the princip

channel that alone produces a 12 dB SINAD SENSITIVITY (cf.),

degrades the SINAD ratio in the principal channel to 6 dB.

Adjacent channel selectivity is usually expressed in

decibels above the level of the signal in the principal channel

It is also called DESENSITIZATION , referring to FM receivers.

4.4.9.2. PURPOSE

The purpose of this measurement method is to measure the

adjacent channel selectivity of an Fi-l receiver. This

characteristic is a measure of the receiver's ability to

deliver an output signal that is degraded a specified

amount (6 dB) below the normally accepted quality in the

presence of a strong adjacent channel signal.

Although this method is described in terms of degradation

caused by an adjacent channel signal, it applies equally well

to a second signal located at an arbitrary frequency.

212
4.4.9.3. METHOD

This method uses two frequency modulated signal generators

and an audio distortion analyzer as shown in figure 4.4.9.

Generator No. 1 is used to measure the 12 dB SINAD SENSITIVITY

(cf . ) , of the receiver. Then generator No. 2, tuned to an

adjacent channel and modulated with a different audio tone

(400 Hz) , is adjusted to a level sufficient to decrease the

SINAD from 12 dB to 6 dB . The signal level ratio, in decibels,

of the two generators is the desired adjacent channel selectivity

of the receiver.

Measurement uncertainties as small as 0.7 dB are possible under

best conditions, and range from approximately 0.9 dB to 2.5 dB under

typical conditions. This method uses commonly available test

equipment of moderate sophistication.

4.4.9.4. TEST EQUIPMENT REQUIRED

1. Two frequency modulated, variable-frequency signal

generators

2. Three-port combining network

3. Input impedance matching network

4. Termination resistor for receiver audio output port

5. Audio distortion analyzer

4.4.9.5. PROCEDURE

1. Connect the two SIGNAL GENERATORS to the input port of

the receiver through the COMBINING NETWORK and IMPEDANCE

MATCHING NETWORK as shown in figure 4.4.9. The matching network

is chosen to present the specified source impedance, Z , to

213
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214
the receiver at the measurement frequency, f^. If the output

impedance of the combining network, with signal generators

connected, equals , no matching network is required.

2. Connect the TERMINATION RESISTOR having a resistance

equal to the specified load resistance, R, , and a power rating

in excess of the receiver's rated audio output power level, to

the audio output port of the receiver. Connect the audio

DISTORTION ANALYZER across this resistor.

3. Tune the signal generator and the receiver to the

measurement frequency, f^.

4. With generator No. 2 turned off, use generator No. 1

to measure the 12 dB SINAD SENSITIVITY, E^ , as described in

Section 4.1.5.5.

5. Tune signal generator No. 2 to the desired adjacent

channel or other frequency, f ^

.

6. Adjust the frequency modulation of generator No. 2 to

±60% of rated system deviation at (400 Hz). This places the

demodulated audio signal away from the 1000 Hz rejection notch

of the distortion analyzer.

7. Adjust the output level of generator No. 2 to produce

a 6 dB SINAD ratio in the principal channel. Generator No. 1

remains as in Step 2, above, during this time, and the SINAD

ratio is measured using the 1000 Hz rejection filter in the

distortion analyzer.

8. Determine the open circuit signal voltage, E , in

a microvolts, due to generator No. 2, at the OUTPUT TERMINALS

of the matching network, if used; otherwise, at the output

terminals of the combining network.

215
9. Calculate the ratio, R (dB) , in decibels, by the

a following equation:

E

R (dB) = 20 log =r^ a tj

.

1

R (dB) is the adjacent channel selectivity of the receiver

a under conditions of (1) measurement frequency, f^ , (2) adjacent

channel or arbitrary interference frequency, f ^ , and (3)

desired signal level equal to the 12 dB SINAD SENSITIVITY, E^

.

4.4.9.6. DATA REQUIRED

1. Record the measurement frequency, f^ , in kilohertz or

megahertz

2. Record the adjacent channel or arbitrary interference

frequency, f ^ , in kilohertz or megahertz.

3. Record the value of source impedance, Z^, in ohms.

connected to receiver input port

4. Record the value of termination resistance, R^ , in ohms,

connected to receiver output terminals.

5. Record the reference output power, P^, in watts.

6. Record the open circuit signal voltage, E^ , in

microvolts.

7. Record the open circuit signal voltage, E , in

a microvolts

.

8. Record adjacent channel selectivity, R (dB) , in

a decibels.

216
4.4.9.7. MEASUREMENT ERRORS

The principal sources of measurement error are the

following

1. Uncertainty, AE , in the measured value of E

a a

2. Uncertainty, / in the measured value of

3. Uncertainty, AP^_^^ , in the measured value of '^^j^^

The total relative uncertainty, Ar (dB) , in decibels,

3. in the ad j acent channel selectivity , R , is given

a approximately, for small uncertainties, by the equation

/ AE T AP , AP

AR^ ,dB) = 20 log

^ 1 . ^a . i ^o . i ^

n+d

The uncertainty, AE , is obtained from the manufacturer's

a specifications on the output level indication of the signal

generator. Uncertainties AP^ and AP^_^^ are obtained from tl

manufacturer's specifications on the distortion analyzer.

217
4 . 4 . 10 . INTERIVIODULATION DISTORTION

4.4.10.1. DEFINITION

Intermodulation distortion is non-linear distortion of a system or transducer characterized by the appearance in the

output of frequencies equal to the sums and differences of

integral multiples of two or more component frequencies present

in the input wave. NOTE: Harmonic components also present in

the output are usually not included as part of the intermodulation

distortion. When harmonics are included, a statement to that

effect should be made. (IEEE Std 100-1972)

Intermodulation distortion is usually expressed as the

ratio, in decibels, of (a) the signal level of one or more

undesired signals to (b) the signal level of the desired signal

under conditions necessary to produce a prescribed receiver

output signal. These conditions vary with type of equipment

and method of measurement, and are specified below.

4.4.10.2 PURPOSE

The purpose of these measurement methods is to measure

the intermodulation distortion of surveillance receivers.

Intermodulation distortion is a measure of the ability of

the receiver to deliver an output signal of acceptable

quality in the presence of other undesired input signals.

4.4.10.3. METHOD I - SINGLE-SIGNAL METHOD, AM OR

FM RECEIVERS

The single-signal method uses a modulated signal generator,

a variable AF band-pass filter, and an A.C. voltmeter, as shown

218
in figure 4.4.10.1. The signal generator is modulated vrith two

audio signals having different frequencies and known amplitudes.

The generator supplies a known input voltage to the receiver

at the measurement frequency. The variable band-pass filter

selects the modulation and distortion frequencies, which are

measured with the voltmeter.

In this method, intermodulation distortion is expressed as

a voltage ratio, in decibels, of (a) the rms voltage of each of

the distortion products to (b) the rms voltage of the higher

frequency (reference) audio modulation signal.

Measurement uncertainties as small as 0.5 dB are possible

under best conditions, and range from 0.8 dB to 3 dB under

typical conditions. This method uses moderately sophisticated

but commonly available test equipment. The intermodulation

distortion of the signal generator must be small so as not to

obscure the intermodulation products generated v/ithin the

receiver

.

4.4.10.3.1. TEST EQUIPMENT REQUIRED

1. Signal generator capable of amplitude or frequency

modulation

2. Two audio frequency generators

3. AF combining network

4. Input impedance matching network

5. Termination resistor for receiver audio output port

6. Variable audio frequency band pass filter

7. A.C. voltmeter

219
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4.4.10.3.2. PROCEDURE

1. Connect the input port of the receiver to the output

port of the SIGNAL GENERATOR through an IMPEDANCE MATCHING

NETWORK that provides the specified source impedance, Z^, to

the receiver at the measurement frequency f^. If the signal

generator output impedance equals Z^, no matching network is

required

.

2. Connect the TERMINATION RESISTOR having a resistance

equal to the specified load resistance, R^ , and a power

rating in excess of the receiver's rated audio output power

level, to the audio output port of the receiver.

3. Connect the input port of the AF BAND PASS FILTER

across the termination resistor.

4. Connect the A.C. VOLTMETER to the output port of

the band pass filter.

5. Set the voltmeter on a range to indicate reference

output power, P^ . The voltage to be measured is given by the

equation

E = V P^Ro • O VOX/

6. Set receiver controls as given in Table XXVI.

7. Tune the signal generator and the receiver to the

measurement frequency, f^.

8a. If the measurement is to be made on an AM receiver,

adjust AUDIO GENERATOR No. 1 to produce 30% amplitude

modulation at 2500 Hz. Note the setting of the output level

221
TABLE XXVI

Intermodulation Distortion, Method I

Initial Control Settings

Control Setting

1. Band Switch 1. As desired

2. Frequency Tuning 2. As desired

Antenna Trimmer 3. Peak

4. RF Gain 4. As desired

5. IF Gain 5. As desired

6 . AF Gain • 6 . As desired

7. Line Gain 7. Optional

8. Detector Mode 8. AM or FM, as desired

9 . Beat Frequency Oscillator 9 . OFF

10. BFO Frequency 10 . N.A.

T 1

J. J- . J L •

12. AF Bandwidth 12. As desired

13. Noise Limiter 13. OFF

14 . Squelch Level 14 . OFF

15. AGC/MGC Mode Switch 15 . As desired

16 . Meter Switch 16 . Optional

222
control on generator No. 1. Then, with audio generator No. 1

turned off, adjust AUDIO GENERATOR No. 2 to produce 30%

amplitude modulation at 300 Hz. Note the setting of the output

level control on generator No. 2.

OR,

8b. If the measurement is to be made on an FM receiver,

adjust audio generator No. 1 to produce frequency modulation of

±60% of rated system deviation at 2500 Hz. Note the setting of

the output level control on generator No. 1. Then, with generator No. 1 turned off, adjust audio generator No. 2 to produce

frequency modulation at ±60% of rated system deviation at 300 Hz.

Note the setting of the output level control on generator No. 2.

9. Turn audio generator No. 1 back, on so that the signal

generator is modulated with both the 300 and 2500 Hz signals.

10. Adjust the output level of the signal generator to the

value at which the measurement is to be made. Normally, this

will be within the receiver's dynamic range (cf.)

.

11. Determine the open circuit signal voltage, E^, in

microvolts, at the OUTPUT TERMINALS of the matching network,

if used; otherwise, at the output terminals of the generator.

12. With the audio band pass filter tuned to pass the 2500

Hz signal and to attenuate the 300 Hz signal by at least 40 dB

,

adjust the AF gain control to produce reference output power, P^.

This is indicated by the A.C. voltmeter reading, E^, which should

be E times the insertion ratio of the filter at 2500 Hz.

o

13. Record the voltage reading E .

223
14. Adjust the band pass filter to each of the distortion

frequencies, f^, listed in Table XXVII, in turn, and measure

filter output voltage, E^. Adjust the tuning of the filter to

obtain maximum voltage reading at each frequency. It may not

be possible to measure the voltage at every frequency because

some distortion products may be absent or very weak.

TABLE XXVII

Band Pass Filter Frequency, f^

Order of IM Product, n Frequency f (Hz)

1 2500

2 2200

3 1900

4 1600

5 1300

6 1000

7 , 700

8 400

9 100

Note 1: Table XXVII does not include all of the

frequencies for all of the orders listed;

it includes only those for the first nine

orders that fall below the highest modulation

frequency.

Note 2: Use care to distinguish the IM distortion

products from the harmonic distortion

products, which occur at integral multiples

of 300 Hz.

224
15. Calculate the ratio, R(IM) in decibels, between the

output voltage at 2500 Hz and at each of the distortion

products, E^, by the following equation:

E

RCIMI ^ 20 log

^ , En

R(IM) is the intermodulation distortion of the receiver at

frequency f^ when the input signal level is E^ microvolts.

4.4.10.3.3. DATA REQUIRED

1. Record the measurement frequency, f^, in kilohertz

or megahertz

.

2. Record the value of source impedance, Z^, in ohms,

connected to the receiver input port.

3. Record the value of termination resistance, R^ , in

ohms, connected to the receiver output terminals.

4. Record the reference output voltage, E^, in volts.

5. Record the open circuit signal voltage, E_j^, in

microvolts

.

6. Record the intermodulation distortion frequencies,

f^, in hertz, and their corresponding order, n.

7. Record the measured voltages, E and E , of each ^ ' r n of the measured audio frequencies at the output of the

audio filter.

8. Record the intermodulation distortion, R(IM) , in

decibels, for each of the distortion frequencies, f .

225
4.4.10.3.4. MEASUREMENT ERRORS

The principal sources of error are the uncertainties,

AE and AE , in the measured values of E and E . The

r n r n total relative measurement error, AR(dB), in decibels,

in the intermodulation distortion, R(IM) , is given

approximately, for small uncertainties, by the equation

Uncertainties AE and AE are obtained from the manufacturer's

r n specifications on the A.C. voltmeter and band pass filter.

4.4.10.4. METHOD II - TWO-SIGNAL METHOD, AM RECEIVER

This method uses three amplitude modulated signal generators

and a voltmeter or power meter as shown in figure 4.4.10.2.

Signal generators No. 1 and No. 2 supply known input voltages at

a variety of frequencies for the measurement of intermodulation

distortion in the receiver. Generator No. 3 is used to adjust

and calibrate the receiver prior to the measurement. The voltmeter

or power meter indicates the receiver output signal level.

The 6 dB SN/N sensitivity of the receiver is measured at

frequency f^ as described in Section 4.1.2. Then, using

generators No. 1 and No. 2 simultaneously, distortion products

are measured by adjusting the generators, as described below,

to the frequencies and signal levels required to produce

intermodulation distortion output power equal to the reference

output power level. Intermodulation distortion is expressed as the signal levels, in microvolts, required to produce the

specified output power.

Ar (dB) = 20 log

226
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227
Measurement uncertainties as small as 3% are possible under

best conditions / and range from approximately 5% to 20% under

typical conditions. This method uses rudimentary and commonly

available test equipment.

4.4.10.4.1. TEST EQUIPMENT REQUIRED

1. Three signal generators capable of amplitude modulation

2. Signal combining network

3 . Coaxial switch

4. Variable step attenuator

5. Input impedance matching network

6. Termination resistor for receiver audio output port

7a. AF power meter

OR,

7b. True rms voltmeter

4.4.10.4.2. PROCEDURE

1. Connect SIGNAL GENERATORS No. 1 and No. 2 to the

receiver through the COMBINING NETWORK, VARIABLE STEP ATTENUATOR,

COAXIAL SWITCH, and IMPEDANCE MATCHING NETWORK as shown in figure

4.4.10.2. The impedance matching network must provide the specif ie

source impedance, Z^, to the receiver at the measurement frequency

f^. If is equal to the output impedance actually present at

the attenuator output port, no matching network is required.

228
2. Connect SIGNAL GENERATOR No. 3 to the receiver through

the coaxial switch.

3a. Connect the TERMINATION RESISTOR having a resistance

equal to the specified load resistance, R,^ , and a power rating

in excess of the receiver's rated audio output power level, to

the audio output port of the receiver. Connect the TRUE RMS

VOLTI^TER across the resistor.

OR,

3b. Connect the POWER METER, having an input impedance equal

to the specified load resistance, R,^ , to the audio output port

of the receiver.

4a. Set the voltmeter on a range to indicate the reference

output power, P^. The voltage to be measured is given by the

equation

E^ = V P

o ' o £

OR,

4b. Set the power meter on a range to indicate the reference

output power, P^.

5. Set receiver controls as given in Table XXVIII.

6. Turn the coaxial switch to connect generator No. 3

to the impedance matching network.

7. With the output level of generators No. 1 and No. 2 set to zero, tune generator No. 3 and the receiver to the

measurement frequency, f .

229
TABLE XXVIII

Intermodulation Distortion, Methods II and III

Initial Control Settings

Qpi-f- 4- -i O <3 L. I Lliy Ti rr

OdilLl iD W X L-OIi 1

.

O ^ J_ ^ \Ji

2 2

.

Xi O O -1- J_ ^ V-l

3

.

xXJ. An'hpnrir^ L V— i, 1 J. 1 "Pyi X _l_ -L. J.ttittipt L LL L U_ 3 . Peak

4 . X\jL RF VJJ aCI -Li ni. 1 4 . Z\cO H p kl> c _1_

-i J_r-prlVwl

•J • TF Ha "in 5 . aq ciesired

6 . j^F Gain 6 . As required

7 . Line Gain 7

.

Optional

8 . Dpi tp OT" Modp 8

.

AM

9 . Rp'at u \JL. c FTPTTiipnov 1- j_ "".^ 1 1 v^ y Osr*!! V-/ »j v^ -J- ^ -X. lator d v^ j_ 9 , OFF

ijj- Ow T-'^T'prmp'nr'V j_ a_ v-{ c 1 1 y 10 . N . A.

J L • TFXI. XJR^nrlwi di 1 W J_ rlf"h L-l 1 11

.

^ o -1- ^

r^J- X) Cli 1 v-l W X L,l 1 12 . As desired

13. Noise Limiter 13. OFF

14. Squelch Level 14 . OFF

15. AGC/MGC Mode Switch 15 . MGC

16. Meter Switch 16 . Optional

230
8. Adjust the amplitude modulation in generator No. 3

to 30% at 1000 Hz.

9. Set the step attenuator to 10 dB attenuation.

10. With signal generator No. 3 connected and its output

set to zero, adjust the receiver AF gain control to produce

25% of rated audio output power, P^. This will be noise

power only.

11. Adjust the output level of the signal generator to give

reference audio output power, . This will be approximately

25% noise power and 75% audio signal power (1000 Hz) , and

corresponds to a 6 dB signal-plus-noise-to-noise ratio.

12. Determine the open circuit signal voltage, E^, in

microvolts, at the OUTPUT TERMINALS of the matching network,

if used; otherwise, at the output terminals of the variable

attenuator.

13. Set the step attenuator to some large value, e.g.,

80 dB.

14. Adjust generator No. 3 to zero output.

15. Turn the coaxial switch to connect the attenuator to

the combining network.

16. Adjust the modulation on generator No. 1 to 30% at

1000 Hz. Leave generator No. 2 unmodulated.

17. Adjust both generator No. 1 and generator No. 2 to a large output level setting, e.g., 100,000 microvolts. Adjust

output levels to produce equal signal levels at the input to

231
the step attenuator. This can be done as follows: Adjust

generator No. 2 to the same frequency and modulation conditions

as generator No. 1, and use the receiver to indicate when equal

signal levels are obtained. Then turn off the modulation in

generator No. 2.

18. Adjust generator No. 1 to frequency f that is different

3. from f but within the range 0.5 f to 2 f . Leave the receiver o ^ o o tuned to frequency f^.

19. Adjust generator No. 2 to frequency f , where f^^ is

given by one of the entries shown in Table XXIX. The choice of

is determined by which particular intermodulation distortion

product is to be measured. The formula for computing f^^ is the

general equation.

f = m f ± n f, , o a b

where m and n are integers, and the sum, m + n, is the order

of the distortion product (e.g., for m = 1, n = 2, the product

is of third order) .

20. Check to see that the signal levels from the two

generators at the attenuator input are equal.

21. Adjust the step attenuator to produce reference audio

output power. This step is similar to Step 11, above.

22. Determine the open circuit signal voltage, E^, in

microvolts, of either one of the two signals at the OUTPUT

TERMINALS of the matching network, if used; otherwise, at the

output terminals of the variable attenuator. This is the

intermodulation distortion level of the receiver, due to equal

signals at frequencies f^ and f , when tuned to frequency f^

.

232
TABLE XXIX

Frequency f , of Generator No. 2

I M Product Frequency f^^

Second order : f + f a o

If - f

' a o

Third order: 2f + f a o

I'a2f - f I o

^(f + f ) 2 a o

2 ' a o

'

Fourth order: 3f + f a o

I'a3f - f I o

T<|2fa-fol'

i-df^ - fol)

Fifth order: 4f + f a o

|4f - f

' a o

T<2fa + ^o'

i-(|2f^ - f^l) 3 ' a o

r(f + f ) a o T (I f - f I )

' a o

233
4.4.10.4.3. DATA REQUIRED

1. Record the measurement frequency, f^, in kilohertz

or megahertz

.

2. Record the value of source impedance, Z^, in ohms,

connected to the receiver input port.

3. Record the value of termination resistance, R^ , in

ohms, connected to the receiver output terminals.

4. Record the reference output power, , in watts

5. Record the open circuit signal voltage, E^, in

microvolts .

6. Record the intermodulation distortion frequencies,

f and f, , in kilohertz or megahertz,

a b

^

7. Record the intermodulation product order, m + n.

8. Record the intermodulation distortion level, E,,d

in microvolts.

4.4.10.4.4. MEASUREMENT ERRORS

The principal sources of measurement error are the

following

]_ ^ Uncertainty, , , in the measured value of E

d

2a. Uncertainty, AE , in the measured value of E ' o ' o

OR,

234
2b. Uncertainty, AP in the measured value of P o o

The total relative uncertainty, AE^(%), in the intermodulation

distortion, E , expressed as a percent, is given by the equations

OR

AE^ (%)

AE^ (%)

The uncertainty, AE^, is obtained from the manufacturer's

specifications on the output level indication of the signal

generator. Uncertainties AE^ and/or AP^ are obtained from the

manufacturer's specifications on the voltmeter and/or power

meter, respectively.

4.4.10.5. METHOD III - THREE-SIGNAL METHOD, AM RECEIVER

This method uses four amplitude-modulated signal generators

and a voltmeter or power meter as shown in figure 4.4.10.3.

Signal generators No. 1, No. 2 and No. 3, supply known input

voltages at a variety of frequencies for the measurement of

intermodulation distortion in the receiver. Generator No. 4 is

used to adjust and calibrate the receiver prior to the

measurement. The voltmeter or power meter indicates the receiver

output signal level.

The 6 dB SN/N sensitivity of the receiver is measured at

frequency f^ as described in Section 4.1.2. Then, using

generators No. 1/ No. 2, and No. 3 simultaneously, distortion

products are measured by adjusting the generators as described

below, to the frequencies and signal levels required to produce

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intermodulation distortion output power equal to the reference

output power level. Intermodulation distortion is expressed as the signal levels, in microvolts, required to produce the

specified output power.

Measurement uncertainties as small as 3% are possible under

best conditions, and range from approximately 5% to 20% under

typical conditions. This method uses simple and commonly

available test equipment.

4.4.10.5.1. TEST EQUIPMENT REQUIRED

1. Four signal generators capable of amplitude modulation

2. Signal combining network

3. Coaxial switch

4 . Variable step attenuator

5. Input impedance matching network

6. Termination resistor for receiver audio output port

7a. AF power meter

OR,

7b. True rms voltmeter

4.4.10.5.2. PROCEDURE

1. Connect SIGNAL GENERATORS No. 1, No. 2, and No. 3 to the

receiver through the COMBINING NETWORK, VARIABLE STEP ATTENUATOR,

237
COAXIAL SWITCH, and IMPEDANCE MATCHING NETWORK as shown in figure

4.4.10.3. The impedance matching network must provide the specified

source impedance, Z^, to the receiver at the measurement frequency,

f^. If is equal to the output impedance actually present at the

attenuator output port, no matching network is required.

2. Connect SIGNAL GENERATOR No. 4 to the receiver through

the coaxial switch.

3a. Connect the TERMINATION RESISTOR having a resistance equal

to the specified load resistance, R^ , and a power rating in excess

of the receiver's rated audio output power level, to the audio

output port of the receiver. Connect the TRUE RMS VOLTMETER across

the resistor.

3b. Connect the POWER METER, having an input impedance equal

to the specified load resistance, R^ , to the audio output port

of the receiver.

4a. Set the voltmeter on a range to indicate the reference

output power, P^. The voltage to be measured is given by the

equation

4b. Set the power meter on a range to indicate the reference

output power, P .

OR,

OR,

o

5. Set receiver controls as given in Table XXVIII, p. 230.

238
6. Turn the coaxial switch to connect generator No. 4 to

the impedance matching network.

7. With the output levels of generators No. 1, No. 2, and

No. 3 set to zero, tune generator No. 4 and the receiver to the

measurement frequency, f^.

8. Adjust the amplitude modulation in generator No. 4 to

30% at 1000 Hz.

9. Set the step attenuator to 10 dB attenuation.

10. With the signal generator No. 4 connected and its output

set to zero, adjust the receiver AF gain control to produce 25%

of rated audio output power, P^. This will be noise power only.

11. Ajust the output level of generator No. 4 to give

reference audio output power, . This will be approximately

25% noise power and 75% audio signal power (1000 Hz) , and

corresponds to a 6 dB signal-plus-noise-to-noise ratio.

12. Determine the open circuit signal voltage, E^, in

microvolts, at the OUTPUT TERMINALS of the matching network,

if used; otherwise, at the output terminals of the variable

attenuator.

13. Set the step attenuator to some large value, e.g.,

80 dB.

14. Adjust generator No. 4 to zero output.

15. Turn the coaxial to connect the attenuator to the

combining network.

239
16. Adjust the modulation on generator No. 1 to 30% at

100 0 Hz. Leave generators No. 2 and No. 3 unmodulated.

17. Adjust generators No. 1, No. 2, and No. 3 to a large

output level setting, e.g., 100,000 microvolts. Adjust output

levels to produce equal signal levels at the input to the step

attenuator. This can be done as follows: Adjust generators No.

2 and No. 3 to the same frequency and modulation conditions as

generator No. 1, and use the receiver to indicate when equal

signal levels are obtained. Then turn off the modulation in

generators No. 2 and No. 3.

18. Adjust generator No. 1 to frequency f that is different

3. from f but within the range 0.5 f to 2 f . Leave the receiver o o o tuned to frequency f . o

19. Adjust generator No. 2 to frequency and generator

3 to frequency f^, where fj_^ ar solutions to the general equation

No. 3 to frequency f^, where fj_^ and f^ are given by one of the

f =mf ±nf, ±pf. o a b ^ c

The factors m, n, and p are integers, and the sum, m + n + p,

is the order of the distortion product (e.g., for m = 1, n = 1,

and p = 3, the product is of fifth order).

20. Check to see that the signal levels from the three

generators at the attenuator input are equal

.

21. Adjust the step attenuator to produce reference audio

output power. This step is similar to Step 11, above.

240
22. Determine the open circuit signal voltage, E^, in

microvolts, of any one of the three signals at the OUfPUT

TERMINALS of the matching network, if used; otherwise, at the

output terminals of the variable attenuator. This is the

intermodulation distortion level of the receiver, due to

equal signals at frequencies f^, f^, and f^, when tuned to

frequency f^.

4.4.10.5.3. DATA REQUIRED

1. Record the measurement frequency, f^, in kilohertz

or megahertz

.

2. Record the value of source impedance, Z^, in ohms,

connected to the receiver input port.

3. Record the value of termination resistance, R^^ , in

ohms, connected to the receiver output terminals.

4. Record the reference output power, P^, in watts

5. Record the open circuit signal voltage, E^, in

microvolts

.

6. Record the intermodulation distortion frequencies,

f^, fj_^, and f^, in kilohertz or megahertz.

7. Record the intermodulation product order, m + n + p,

8. Record the intermodulation distortion level, E.,, in d

microvolts

.

241
4.4.10.5.4. MEASUREiyiENT ERRORS

The principal sources of measurement error are the

following:

1. Uncertainty, AE,, in the measured value of E ., d d

2a. Uncertainty, AE , in the measured value of E

o' o

OR,

2b. Uncertainty, AP , in the measured value of P o o

The total relative uncertainty, AE^(%), in the intermodulation

distortion, E^, expressed as a percent, is given by the

equations

AE^ (%) = X 100^ + X lOo) ,

OR

The uncertainty, AE^, is obtained from the manufacturer's

specifications on the output level indication of the signal

generator. Uncertainties AE and/or AP are obtained from the

o o manufacturer's specifications on the voltmeter and/or power

meter, respectively.

242
4.4.10.6. METHOD IV - THREE-SIGNAL METHOD, FM RECEIVER

This method uses three signal generators and a distortion

analyzer as shown in figure 4.4.10.4. One signal generator is

frequency modulated; all three supply known input voltages at

a variety of selected frequencies. The distortion analyzer measures

the output SINAD ratio under various input signal conditions.

The 12 dB SINAD SENSITIVITY of the receiver is measured

at frequency f^ as described in Section 4.1.5. Then, using all

three generators simultaneously, distortion products are

measured by adjusting the generators, as described below, to tne

frequencies and signal levels required to produce intermodulation

distortion products having a 12 dB SINAD ratio. Intermodulation

distortion is expressed as the signal levels, in microvolts,

required to produce a 12 dB output SINAD ratio.

Measurement uncertainties as small as 5% are possible under

best conditions, and range from approximately 8% to 30% under

typical conditions. This method uses commonly available test

equipment of moderate sophistication.

4.4.10.6.1. TEST EQUIPMENT REQUIRED

1. Three signal generators capable of frequency modulation

2 . Signal combining network

3. Variable step attenuator

4 . Input impedance matching network

5. Termination resistor for receiver audio output port

6. Audio distortion analyzer

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4.4.10.6.2. PROCEDURE

1. Connect SIGNAL GENERATORS No. 1, NO. 2, and No. 3 to

the receiver through the COMBINING NETWORK, VARIABLE STEP ATTENUATOR,

and IMPEDANCE l^IATCHING NETWORK as shown in figure 4.4.10.4. The

impedance matching network must provide the specified source

impedance, Z^, to the receiver at tne measurement frequency, f^.

If is equal to the output impedance actually present at tne

attenuator output port, no matching network is required.

2. Connect the TERMINATION RESISTOR having a resistance

equal to the specified load resistance, R. , and a power

rating in excess of the receiver's rated audio output power level,

to the audio output port of the receiver. Connect the audio

DISTORTION ANALYZER across this resistor.

3. Set the distortion analyzer on a range to indicate the

rated output power, P^.

4. Set the receiver controls as given in Table XXX.

5. Set the step attenuator to minimum attenuation.

6. With the output levels of generators No. 2 and No. 3

set to zero, tune signal generator No. 1 and the receiver to

the measurement frequency, f . o

7. Adjust the frequency modulation in generator No. 1

to =60% of rated system deviation at 1000 Hz.

8. Measure the 12 dB SINAD SENSITIVITY, E^, as outlined

in Section 4.1.5.5.

9. Set the step attenuator to some large value, e.g.,

80 dB.

245
TABLE XXX

Intermodulation Distortion, Method IV

Initial Control Settings

Control Q o -h +- n T-i rr

± . Band Switch 1

z . Frequency Tuning 2 iAO O _L J_ ti

o Antenna Trimmer ir dJs.

4 RF Gain 4 PlciXX lllLllll

c3 . IF Gain 5. ilCl^XlllLilll M^vi mmn

0 . AF Gain 6. 7\ C? "K* ITT V*

7 Line Gain 7. \jy> J-\J llci 1.

DO • Detector Mode 8. FM

Qy . Beat Frequency Oscillator 9.

BFO Frequency 10 . LN • /A. •

XX . IF Bandwidth 11.

Xz . AF Bandwidth 12. As desired

X J . Noise Limiter 13. OFF

14. Squelch Level 14 . OFF

15. AGC/MGC Mode Switch 15 . As desired

16 . Meter Switch 16 . Optional

246
10. Adjust the generators No. 1, No. 2, and No. 3 to a large output level setting, e.g., 100,000 microvolts. Adjust

output levels to produce equal signal levels at the input to

tne step attenuator. This can be done as follows: Adjust

generators No. 2 and No. 3 to the same frequency and

modulation conditions as generator No. 1, and use the

receiver to indicate when equal signal levels are obtained.

Then turn off the modulation in generators No. 2 and No. 3.

11. Adjust generator No. 1 to frequency f that is different

from f but within the range 0.5 f to 2 f . Leave the receiver

o ^ o o tuned to frequency f^.

12. Adjust generator No. 2 to frequency f^^ and generator

No. 3 to frequency f^, where f^ and f^ are given by one of

the solutions to the general equation

f =mf ±nf, ±pf. o a b ^ c

The factors m, n, and p are integers, and the sum^ m + n = p,

is the order of the distortion product (e.g., for m = 1/ n = 1/

and p = 3, the product is of fifth order) .

13. Check to see that the signal levels from the three

generators at the attenuator input are equal.

14. Adjust the step attenuator to produce 12 dB SINAD ratio.

15. Detemnine the open circuit signal voltage, E^, in

microvolts, of any one of the three signals at the OUTPUT

TERMINALS of the matching network, if used; otherwise, at the

output terminals of the variable attenuator. This is the

intermodulation distortion level of tne receiver, due to equal

signals at frequencies f , f, , f , when tuned to frequency f .

247
4.4.10.6.3. DATA REQUIRED

1. Record the measurement frequency, f^, in kilohertz

or megahertz

.

2. Record the value of source impedance, Z^, in ohms,

connected to the receiver input port.

3. Record the value of termination resistance, R^

,

in ohms, connected to the receiver output terminals.

4. Record the reference output power, P^, in watts

5. Record the open circuit signal voltage, E_j^, in

microvolts.

6. Record the intermodulation distortion frequencies,

f , f, , and f , in kilohertz or megahertz,

a b c

^

7. Record the intermodulation product order, m + n + p,

8. Record the intermodulation distortion level, E,, in d

microvolts.

4.4.10.6.4. MEASUREMENT ERRORS

The principal sources of measurement error are the

following

1. Uncertainty, ^E^, in the measured value of E^

2. Uncertainty, AP^, in thy measured value of P^

3. Uncertainty, '^Pj^+j^^ measured value of P^^^^

248
The total relative uncertainty, lE^{%) , in the intermodulation

distortion, E^, expressed as a percent, is given by the

equation

The uncertainty, ^E^, is obtained from the manufacturer's

specifications on the output level indication of the signal

generator. Uncertainties ilP and iP , are obtained from the ^ o n+d

manufacturer's specifications on the distortion analyzer.

249
4.4.11. IMPULSE BANDWIDTH

4.4.11.1. DEFINITION

The impulse bandwidth of a receiver is the ratio of (a)

the peak voltage response, E , of the receiver to (b ) twice

P

the gain-spectral intensity product, 2GS , where G is the

receiver voltage gain from input terminals to demodulator

input and S is the spectral intensity of the impulse input

signal . . -

-

This is an operational definition of impulse bandwidth

rather than a descriptive definition. A descriptive

definition, based upon fundamental considerations, has not

yet been derived. As a consequence, the method of measuring

impulse bandwidth does not follow steps that have an obvious

relationship to bandwidth.

4.4.11.2. PURPOSE

The purpose of this measurement method is to measure the

impulse bandwidth of a receiver. Impulse bandwidth is a measure of the degree of distortion (time dispersion) suffere

by an impulsive signal as it passes through the receiver. It

is useful in predicting the interference susceptibility of

the receiver to impulsive signals.

The method given below is useful only for receivers that

have nearly synchronously-tuned tuned circuits with

near-Gaussian selectance. Field intensity meters are usually

designed this way^ whereas other types of receivers often

are not. Receivers with sharp filters (e.g., resonant crystal

filters), and with rectangular passbands (e.g., mechanical

and/or crystal lattice filters) will produce a response to

impulses that is unsuitable for calculating impulse bandwidth

by this method.

250
4.4.11.3. METHOD

The method uses an impulse generator and an oscilloscope

as shown in figure 4.4.11.1. The impulse generator supplies a periodic train of very narrow pulses to the receiver. The

oscilloscope displays the I.F. output voltage response.

Impulse bandwidth is determined by (1) dividing the total

area enclosed by the envelope of the oscilloscope display

by the maximum total height of the display to obtain an

effective length of the pattern, (2) converting this effective

length to time duration of the response, and (3) taking the

reciprocal of this time duration, which is impulse bandwidth.

This method requires that the repetition rate of the

impulse generator be no greater than one-fifth of the CW

bandwidth of the receiver.

Measurement uncertainties as small as 8% are possible under

best conditions, and range from approximately 10% to 30% under

typical conditions. The method uses moderately sophisticated

but commonly available test equipment.

4.4.11.4. TEST EQUIPMENT REQUIRED

1. Wide-band impulse generator

2. 20 dB attenuator or lossy impedance matching network

3. Cathode-ray oscilloscope (delayed or expandable sweep

is helpful)

4. Oscilloscope camera

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4.4.11.5. PROCEDURE

1. Connect the input port of the receiver to the output

port of the IMPULSE GENERATOR through a 20 dB resistive attenuator whose characteristic impedance equals that of the specified

source impedance, Z^. If the load impedance required by the

impulse generator does not equal the characteristic impedance of

the attenuator, provide a proper RESISTIVE MATCHING NETWORK

between generator and attenuator.

2. Connect the vertical input port of the OSCILLOSCOPE

to the output of the last linear I.F. amplifier of the receiver.

3. Set receiver controls as given in Table XXXI.

4. Tune the receiver to the measurement frequency, f^

.

5. Adjust the output level of the generator to 80 dB

above 1 microvolt per megahertz.

6. Adjust the repetition rate of the generator, if adjustable, to between 100 and 1000 pulses per second. The repetition

rate must be no less than one-fifth the receiver CW bandwidth (cf.!

7. Adjust the oscilloscope to obtain a pattern that fills the

calibrated area on the screen. Adjust the horizontal sweep to a convenient, known value. Adjust the trigger circuit to obtain a stable display.

8. Photograph the display, or trace its outline on a sheet

of transparent material.

9. Determine the total area, A, in square centimeters,

enclosed by the pattern. Use a planimeter, or count squares, or

use whatever other means are available.

253
TABLE XXXI

Impulse Bandwidth

Initial Control Settings

Control Setting

1. Band Switch 1. As desired

2. Frequency Tuning 2. As desired

3. Antenna Trimmer 3. Peak

4. RF Gain 4. Medium

5. IF Gain 5 . Medium

6. AF Gain 6 . Optional

7. Line Gain 7. Optional

8. Detector Mode ' 8. Optional

9 . Beat Frequency Oscillator 9 . OFF

10 . BFO Frequency 10 . N.A.

11. IF Bandwidth 11. As desired

12 . AF Bandwidth 12. Optional

13. Noise Limiter 13. OFF

14. Squelch Level 14. OFF

15. AGC/MGC Mode Switch 15. MGC

16. Meter Switch 16 . Optional

254
255
10. Determine the height, h, in centimeters, of the pattern

between the points at which the height is maximum (see figure

4.4.11.2. )

.

11. Determine the horizontal scale factor, T, in seconds

per centimeter, from the sweep speed calibration of the

oscilloscope.

12. Compute the impulse bandwidth, B(Imp) , in kilohertz,

by the following equation

,-r ^ h (cm) X 10"^

B (Imp) = Aicm^) X T (sec/cm)

4.4.11.6. DATA REQUIRED

1. Record the measurement frequency, f^ , in kilohertz

or megahertz.

2. Record the output level setting, in decibels above 1

microvolt per megahertz, of the impulse generator.

3. Record the horizontal sweep rate, T, in seconds per

centimeter of the oscilloscope.

4. Record the area. A, in square centimeters, and height,

h, in centimeters, of the oscilloscope pattern.

5. Record the impulse bandwidth, B(Imp) in hertz or

kilohertz

.

4.4.11.7. MEASUREMENT ERRORS

The principal sources of measurement error are the

following

1. Uncertainty, AA, in the measured value of area, A

256
2. Uncertainty, Ah, in the measured value of height, h

3. Uncertainty, AT, in the horizontal scale factor, T

The total relative uncertainty, AB(%), expressed in

percent, in the impulse bandwidth, B{Imp), is given by

the equation

Uncertainties AA and Ah are obtained by estimating the

reading resolution of the scope display. Uncertainty AT is

obtained from the manufacturer's specifications on the sweep

circuit of the oscilloscope.

AB

257
4.5. INTERFERENCE SUSCEPTIBILITY

The interference susceptibility of a receiver is a measure

of its ability to withstand the effects of undesired signals

and noise that tend to interfere with reception of desired

signals. To express this ability in quantitative terms,

interference susceptibility is broadly defined as the smallest

undesired signal level necessary to produce a specified

degradation in the desired demodulated signal from the receiver.

Normally, a receiver is susceptible to interfering signals

by two mechanisms: conduction and radiation. Measurement

methods for conducted interference are generally similar to

other methods given in this handbook. However, presently

available methods for measuring radiated interference are

generally inadequate or worthless because of the large

inaccuracies and variations of results that they provide. The

meaningful measurement of radiated interference susceptibility

requires a knowledge of the electric and magnetic fields at,

and in the presence of, the receiver. Present methods for

determining such fields throughout the frequency range covered

by this handbook have errors that typically range from 100% to

500%, and may reach 1000% or higher, depending upon the

circumstances. Measurements in shielded enclosures, as presently

practiced, are essentially meaningless because of the large

standing waves usually present. Adequate anechoic chambers are

not yet developed for frequencies below 10 0 MHz. Parallel-plate

configurations give satisfactory results only at very low

frequencies, and coaxial line enclosures are similarly limited.

Open-field arrangements are usually not practical because of

the space, power, and interference problems. But underlying

all of these configuration problems is the lack of basic

techniques for determining the strength of perturbed near fields

with adequate accuracy.

258
4.5.1. CONDUCTED INTERFERENCE SUSCEPTIBILITY OF A

NOISE-LIMITED AM RECEIVER

4.5.1.1. DEFINITION

Conducted interference susceptibility of an AM receiver is

the voltage, in microvolts, of a signal that is amplitude

modulated 30% with a 10 00 Hz sinusoid, which when applied to

a specified pair of receiver terminals, will produce a SINAD

ratio of 16 (12 dB) at the reference audio output power from

the receiver output terminals.

4.5.1.2. PURPOSE

The purpose of this measurement method is to measure the

conducted interference susceptibility of noise-limited AM

receivers. For such receivers, conducted interference

susceptibility is a measure of the receiver response to signals

that are conducted into the receiver by paths other than via

the antenna terminals. Such paths include power, audio, and

control line connections

.

259
4.5.1.3. METHOD

The method uses an amplitude modulated signal generator, an

insertion network and an audio distortion analyzer as shown in figure 4.5.1. A separate measurement is made at each

accessible line terminal. The generator supplies a known input

voltage to the selected terminal at the measurement frequency

through the insertion network. The distortion analyzer

measures the audio output power from the receiver under two

conditions; viz., (a) with the 1000 Hz modulating signal present,

and (b) with the 1000 Hz modulating signal filtered from the

audio output power. The generator level is adjusted to the

voltage that causes the ratio of (a) to (b) , above, expressed

in decibels, to be 12 dB. This voltage is the conducted

interference susceptibility of the selected terminal of the

receiver.

Measurement uncertainties as small as 5% are possible under

best conditions, and range from approximately 8% to 30% under

typical conditions. This method uses commonly available test

equipment of moderate sophistication.

4.5.1.4. TEST EQUIPMENT REQUIRED

1. Signal generator capable of amplitude modulation

2 . Input impedance matching network

3. Termination resistor for receiver audio output port

4. Audio distortion analyzer

5 . Input termination

6 . Insertion network

7. R.F. voltmeter

260
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4.5.1.5. PROCEDURE

1. Connect the output port of an INSERTION NETWORK,

whose characteristics are suitable for the measurement (see

Section 5.2.7.) , to the selected receiver terminal at which the

measurement is to be made (power line, audio line, control

line, AGC line, etc.). Refer to figure 4.5.1. for connection

arrangements

.

2. Connect the input port of the receiver to the output port

of the SIGNAL GENERATOR through an IMPEDANCE MATCHING NETWORK

that provides the specified source impedance, Z^, to the receiver

at the measurement frequency, f^. If the signal generator output

impedance equals , no matching network is required.

3. Connect the TERMINATION RESISTOR having a resistance equal

to the specified load resistance, R^^ , and a power rating in excess

of the receiver's rated audio output power level, to the audio

output port of the receiver. Connect the audio DISTORTION ANALYZER

across this resistor.

4. Set the distortion analyzer on a range to indicate the

rated output power, P^.

5. Set receiver controls as given in Table XXXII.

6. Tune the signal generator and the receiver to the

measurement frequency, f^.

7. Adjust the amplitude modulation in the signal generator

to 30% at 1000 Hz.

8. Measure the 12 dB SINAD SENSITIVITY, E,, as outlined

1

in Section 4.1.3.5.

262
TABLE XXXII

Conducted and Radiated Interference Susceptibility (AM)

Initial Control Settings

Control Setting

1. Band Switch 1. As desired

2. Frequency Tuning 2. As desired

3. Antenna Trimmer 3 . Peak

4 . RF Gain 4 . Maximum

5. IF Gain 5 . Maximum

6 . AF Gain 6 . As required

7 . Line Gain 7. Optional

8. Detector Mode 8. AM

9 . Beat Frequency Oscillator 9 . OFF

10 . BFO Frequency 10 . N.A.

11. IF Bandwidth 11. As desired

12. AF Bandwidth 12 . As desired

13 . Noise Limiter 13. OFF

14. Squelch Level 14 . OFF

15. AGC/MGC Mode Switch 15 . As desired

16 . Meter Switch 16 . Optional

263
9 . Disconnect the signal generator

transformer at the receiver input port,

TERMINATION, Z^, in its place.

10. Connect the signal generator to the input port of the

insertion network at the selected receiver terminal.

11. Set the generator output level to maximum (e.g.,

100,000 to 1,000,000 microvolts),

12. Vary

of interest,

(cf . )

.

13. When a response is produced, adjust the generator output

level to produce a 12 dB SINAD ratio at reference audio output

power , P . ^ o

Note: If the generator output level is not large enough

to produce a 12 dB SINAD ratio, do one of the

following things:

from the impedance

and connect the

the generator frequency to cover all frequencies

including f^ and spurious response frequencies

(1) Insert a power amplifier between the generator

output port and the insertion network input

port. Choose an amplifier with sufficient gain and

power capability to produce a 12 dB SINAD ratio.

(2) Adjust the voltage gain of the insertion

network as necessary to allow a 12 dB SINAD

ratio to be reached.

(3) If (1) or (2) do not work, or if they would

produce voltages that would cause equipment failure,

stop the procedure at this point.

264
14. Measure the signal frequency, f ^ , in kilohertz or

megahertz, and voltage , in microvolts, at the selected

receiver terminal with an R.F. VOLTMETER. This voltage is

the conducted interference susceptibility of the selected

terminal at receiver frequency, f ^ , and interference

frequency , f _. .

Note: If the test was stopped as per (3) under

Step 13, determine the signal voltage, E , m

at the selected terminal and report the

results as follows: "The conducted interference susceptibility is in excess of

(E ) microvolts."

m

4.5.1.6. DATA REQUIRED

1. Record the measurement frequency, f^ , in kilohertz

or megahertz.

2. Record the value of source impedance, Z^, in ohms,

connected to receiver input port.

3. Record the value of termination resistance, R^ , in

ohms, connected to receiver audio output terminals.

4. Record the reference output power, , in watts.

5. Record the 12 dB SINAD sensitivity, E^ , in microvolts

6. Record the interference frequency, f ^ , in kilohertz

or megahertz.

7. Record the interference susceptibilitv voltage, E^

or E , in microvolts

.

m

8. Record the selected receiver terminal at which f . : and E. are determined.

J

265
4.5.1.7. MEASUREMENT ERRORS

The principal sources of measurement error are the

following

1. Uncertainty, AE . , in the measured value of E.

: :

2. Uncertainty, AP , in the measured value of P o o

3. Uncertainty, AP , in the measured value of P ,

,

n+d n+d

The total relative uncertainty, AE^ (%) , expressed in

percent, in the conducted interference susceptibility, E^

is given by the equation

The uncertainty, AE^ , is obtained from the manufacturer's

specifications on the R.F. voltmeter. Uncertainties AP and

AP , , are obtained from th n+d

the distortion analyzer.

e manufacturer's

o specifications on

266
4.5.2. CONDUCTED INTERFERENCE SUSCEPTIBILITY OF

AN FM RECEIVER WITH ONE OR MORE LIMITERS

4.5.2.1. DEFINITION

Conducted interference susceptibility of an FM receiver is

the voltage, in microvolts, of a signal that is frequency

modulated ±60% of maximum rated system deviation with a 1000 Hz

sinusoid, which, when applied to a specified pair of receiver

terminals, will produce a SINAD ratio of 16 (12 dB) at the

reference audio output power from the receiver output terminals.

The purpose of this measurement method is to measure the

conducted interference susceptibility of FM receivers containing

one or more amplitude limiter stages preceding the FM demodulator

circuit. For such receivers, conducted interference susceptibility

is a measure of the receiver response to signals that are conducted

into the receiver by paths other than via the antenna terminals.

Such paths include power, audio, and control line connections.

The method uses a frequency modulated signal generator, an

insertion transformer, and an audio distortion analyzer as shown in figure 4.5.2. A separate measurement is made at each

accessible line terminal. The generator supplies a known input

voltage to the selected terminal at the measurement frequency

through the insertion transformer. The distortion analyzer

measures the audio output power from the receiver under two

conditions; viz., (a) with the 1000 Hz modulating signal present,

and (b) with the 1000 Hz modulating signal filtered from the

audio output power. The generator level is adjusted to the

4.5.2.2. PURPOSE

4.5.2.3. METHOD

267
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voltage that causes the ratio of (a) to (b) , above, expressed

in decibels, to be 12 dB. This voltage is the conducted

interference susceptibility of the selected terminal of the

receiver

.

Measurement uncertainties as small as 5% are possible under

best conditions, and range from approximately 8% to 30% under

typical conditions. This method uses commonly available test

equipment of moderate sophistication.

4.5.2.4. TEST EQUIPMENT REQUIRED

1. Signal generator capable of frequency modulation

2. Input impedance matching network

3. Termination resistor for receiver audio output port

4. Audio distortion analyzer

5. Input termination

6 . Insertion network

7 . R . F . vo 1 tme te r

4.5.2.5. PROCEDURE

1. Connect the output port of an

whose characteristics are suitable for

Section 5.2)^ to the selected receiver

measurement is to be made (power line,

line, AGC line, etc.). Refer to figure

arrangements

.

INSERTION NETWORK

the measurement (see

terminal at which the

audio line, control

4.5.2. for connection

269
2. Connect t±ie input port of the receiver to the output

port of the SIGNAL GENERATOR through an IMPEDANCE MATCHING

NETWORK that provides the specified source impedance, Z^, to

the receiver at the measurement frequency, f^. If the signal

generator output impedance equals , no matching network is

required.

3. Connect the TERMINATION RESISTOR having a resistance

equal to the specified load resistance, R^ , and a power rating

in excess of the receiver's rated audio output power level, to

the audio output port of the receiver. Connect the audio

DISTORTION ANALYZER across this resistor.

4. Set the distortion analyzer on a range to indicate the

rated output power, P^. ,

5. Set receiver controls as given in Table XXXIII.

6. Tune the signal generator and the receiver to the

measurement frequency, f^

.

7. Adjust the frequency modulation in the signal generator

to ±60% of rated system deviation at 1000 Hz.

8. Measure the 12 dB SINAD SENSITIVITY, E^ , as outlined

in Section 4.1.5.5.

9 . Disconnect the signal generator from the impedance

transformer at the receiver input port, and connect the

TERMINATION, Z^ , in its place.

10 . Connect the signal generator level to the input port

of the insertion network.

11. Set the generator output level to maximum (e.g.,

100,000 to 1,000,000 microvolts).

270
TABLE XXXIII

Conducted and Radiated Interference Susceptibility (FM)

Initial Control Settings

Control Setting

1. Band Switch 1. As desired

2. Frequency Tuning 2. As desired

3. Antenna Trimmer 3. Peak

4 . RF Gain 4. Maximum

5 . IF Gain 5. Maximum

6 . AF Gain 6. As required

7. Line Gain 7. Optional

8. Detector Mode 8. FM

9. Beat Frequency Oscillator 9 . OFF

10 . BFO Frequency 10 . N.A.

11. IF Bandwidth 11. As desired

12. AF Bandwidth 12. As desired

13. Noise Limiter 13 . OFF

14 . Squelch Level 14 . OFF

15 . AGC/MGC Mode Switch 15. As desired

16 . Meter Switch 16 . Optional

271
12. Vary the generator frequency to cover all frequencies of

interest, including f^ and spurious response frequencies (cf.).

13. When a response is produced, adjust the generator output

level to produce a 12 dB SINAD ratio at reference audio output

power , P . o

Note: If the generator output level is not large

enough to produce a 12 dB SINAD ratio, do

one of the following things:

(1) Insert a power amplifier between the generator

output port and the insertion network input port.

Choose an amplifier with sufficient gain and power

capability to produce a 12 dB SINAD ratio.

(2) Adjust the voltage gain of the insertion network

as necessary to allow a 12 dB SINAD ratio to be reached,

(3) If (1) or (2) do not work, or if they would

produce voltages that would cause equipment

failure, stop the procedure at this point.

14. Measure the signal frequency, f ^ , in kilohertz or

megahertz, and voltage E ^ , in microvolts, at the selected

receiver terminal with an R.F. VOLTMETER. This voltage is

the conducted interference susceptibility of the selected

terminal at receiver frequency, f^ , and interference

frequency , f _. .

Note: If the test was stopped as per (3) under

Step 13, determine the signal voltage, E^,

at the selected terminal and report the

results as follows: "The conducted

interference susceptibility is in excess

of (E ) microvolts."

m

272
4.5.2.6. DATA REQUIRED

1. Record the measurement frequency, f ^ , in kilohertz or

megahertz

2. Record the value of source impedance, , in ohms,

connected to receiver input port.

3. Record the value of termination resistance, R|^ , in

ohms , connected to receiver audio output terminals

.

Record the reference output power, , in watts

5. Record the 12 dB SINAD sensitivity, , in

microvolts

.

6. Record the interference frequency, f ^ , in kilohertz

or megahertz

7. Record the interference susceptibility voltage, E_. or E , in microvolts.

m

8. Record the selected receiver terminal at which f

.

D and E. are determined.

D

4.5.2.7. MEASUREMENT ERRORS

The principal sources of measurement errors are the

following

1. Uncertainty, AE . , in the measured value of E.

: :

2. Uncertainty, AP , in the measured value of P ' o o

3. Uncertainty, AP , -, , in the measured value of P , ^ n+d n+d

273
The total relative uncertainty, AE^ (%) , expressed in

percent, in the conducted interference susceptibility/ E_. is given by the equation

The uncertainty, AE . , is obtained from the manufacturer's

: specifications on the R.F. voltmeter. Uncertainties AP and ^ o APn+d are obtained from the manufacturer's specifications on

the distortion analyzer.

AE . (%) 100

274
4.5.3. RADIATED INTERFERENCE SUSCEPTIBILITY OF A

NOISE-LIMITED AM RECEIVER

4.5.3.1. DEFINITION

Radiated interference susceptibility of an AM receiver is

the field strength, in volts per meter, of an electromagnetic

field that is amplitude modulated 30% v/ith a 1000 Hz sinusoid,

which, when incident upon the most receptive region of the

receiver, v.'ill produce a SINAD ratio of 16 (12 dB) at the rated

audio output pov/er from the receiver output terminals .

The purpose of this measurement method is to measure the

radiated interference susceptibility of noise-limited AM

receivers. For such receivers, radiated interference susceptibility

is a measure of the receiver response to radiated electromagnetic

fields that produce signals in the receiver by paths other than

via the receiver antenna. Such paths include pov7er cords, audio

and control lines, and leakage paths through openings in the

receiver enclosure.

Note: The method given belov: is only indicative of

4.5.3.2. PURPOSE

the basic principle of measurement. It is not

given as a recommended method that v/ill give

accurate results . See the discussion given

under Section 4.5.

275
4.5.3.3. METHOD

The method uses an amplitude modulated signal generator, an

antenna, and an audio distortion analyzer as shown in figure

4.5.3. The generator and antenna produce a known radiation field

strength at the measurement frequency. The distortion analyzer

measures the audio output power from the receiver under two

conditions; viz., (a) with the 1000 Hz modulating signal present,

and (b) with the 1000 Hz modulating signal filtered from the

audio output power. The radiated field strength is adjusted to

a level that causes the ratio of (a) to (b) , above, expressed

in decibels, to be 12 dB. This field strength is the radiated

interference susceptibility of the receiver.

Measurement uncertainties are seldom less than 200%, and

may be as great as 1000% under typical conditions. The method

uses commonly available test equipment of moderate

sophistication

.

4.5.3.4. TEST EQUIPMENT REQUIRED

1. Signal generator capable of amplitude modulation

2. Input impedance matching network

3. Termination resistor for receiver audio output port

4. Audio distortion analyzer

5. Input termination (shielded)

6 . Antenna

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4.5.3.5. PROCEDURE

1. Connect the input port of the receiver to the output port

of the SIGNAL GENERATOR through an IMPEDANCE MATCHING NETWORK

that provides the specified source impedance, , to the receiver

at the measurement frequency, f ^ . If the signal generator

output impedance equals , no matching network is required.

2. Connect the TERMINATION RESISTOR having a resistance equal

to the specified load resistance, R^, and a power rating in excess

of the receiver's rated audio output level, to the audio output

port of the receiver. Connect the audio DISTORTION ANALYZER

across this resistor.

3. Set the distortion analyzer on a range to indicate the

rated output power, P^.

4. Set receiver controls as given in Table XXXII, p. 263.

5. Tune the signal generator and the receiver to the

measurement frequency, f^.

6. Adjust the amplitude modulation in the signal generator

to 30% at 1000 Hz.

7. Measure the 12 dB SINAD SENSITIVITY, E^ , as outlined

in Section 4.1.3.5.

8. Disconnect the signal generator from the impedance

transformer at the receiver input port, and connect the SHIELDED

TERMINATION, Zg / in its place.

9 . Connect the signal generator to the terminals of the

ANTENNA.

278
10. Set the generator output level to maximum (e.g., 100,000

to 1,000,000 microvolts).

11. With the antenna approximately 30 meters from the

receiver, vary the generator frequency to cover all frequencies

of interest, including f^ and spurious response frequencies (cf.).

12. When a a response is produced, adjust the orientation of

the receiver for maximum response, keeping the antenna 30 meters

from the receiver at the closest point.

13. Adjust the generator output level to produce a 12 dB

SINAD ratio.

Note: If the radiated field strength is not large

enough to produce a 12 dB SINAD ratio, do one

of the following things

(1) Move the antenna closer to receiver.

(2) Insert a power amplifier between the generator

output port and the antenna terminals . Choose an

amplifier with sufficient gain and power capability

to produce a 12 dB SINAD ratio.

14. Determine the signal frequency, f ^ , and field strength,

Ej , in volts per meter, at the location of the receiver by standard

techniques. This field strength is the radiated interference

susceptibility of the receiver for receiver frequency, f^, and

interference frequency, f..

279
4.5.3.6. DATA REQUIRED

1. Record the measurement frequency, f^ , in kilohertz or

megahertz

.

2. Record the value of source impedance, , in ohms,

connected to receiver input port.

3. Record the value of termination resistance, R^ , in

ohms, connected to receiver audio output terminals.

4. Record the reference output power, P^, in watts

5. Record the 12 dB SINAD sensitivity, E^ , in

microvolts

.

6. Record the antenna-to-receiver distance.

7. Record the interference frequency, f ^ , in kilohertz

or megahertz.

8. Record the radiated interference susceptibility field

strength, E_, , in volts per meter.

4.5.3.7. MEASUREMENT ERRORS

Measurement uncertainties depend upon local circumstances

and are difficult to predict for the general case. See discussion

given under Section 4.5.

280
4.5.4. RADIATED INTERFERENCE SUSCEPTIBILITY OF

AN FM RECEIVER WITH ONE OR MORE LIMITERS

4.5.4.1. DEFINITION

Radiated interference susceptibility of an FM receiver is

! the field strength, in volts per meter, of an electromagnetic

:, field that is frequency modulated ± 60% of maximum rated system

deviation with a 1000 Hz sinusoid, which, when incident upon the

most receptive region of the receiver, will produce a SINAD

ratio of 16 (12 dB) at the rated output power from the receiver

output terminals

.

4.5.4.2. PURPOSE

The purpose of this measurement method is to measure the

radiated interference susceptibility of FM receivers containing

one or more amplitude limiter stages preceding the FM demodulator

circuit. For such receivers, radiated interference susceptibility

is a measure of the receiver response to radiated electromagnetic

fields that produce signals in the receiver by paths other than

via the receiver antenna. Such paths include power cords, audio

and control lines , and leakage paths through openings in the

receiver enclosure.

Note: The method given below is only indicative of the

basic principle of measurement. It is not given as

a recommended method that will give accurate results

.

See the discussion given under Section 4.5.

281
4.5.4.3. METHOD

The method uses a frequency modulated signal generator, an

antenna, and an audio distortion analyzer as shown in figure

4.5.4. The generator and antenna produce a known radiation field

strength at the measurement frequency. The distortion analyzer

measures the audio output power from the receiver under two

conditions; viz., (a) with the 1000 Hz modulating signal present,

and (b) with the 1000 Hz modulating signal filtered from the

audio output power. The radiated field strength is adjusted to

a level that causes the ratio of (a) to (b) , above, expressed

in decibels, to be 12 dB. This field strength is the radiated

interference susceptibility of the receiver.

Measurement uncertainties are seldom less than 200%, and

may be as great as 1000% under typical conditions. The method

uses commonly available test equipment of moderate sophistication.

4.5.4.4. TEST EQUIPMENT REQUIRED

1. ^ Signal generator capable of frequency modulation

2. Input impedance matching network

3. Termination resistor for receiver audio output port

4. Audio distortion analyzer

5. Input termination

6 . Antenna

282
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283
4.5.4.5. PROCEDURE

1. Connect the input port of the receiver to the output

port of the SIGNAL GENERATOR through an IMPEDANCE MATCHING

NETWORK that provides the specified source impedance, Z^, to

the receiver at the measurement frequency, f^. If the signal

generator output impedance equals Z^, no matching network is

required.

,2. Connect the TERMINATION RESISTOR having a resistance

equal to the specified load resistance, R^ , and a power rating

in excess of the receiver's rated audio output power level, to

the audio output port of the receiver. Connect the audio

DISTORTION ANALYZER across the resistor.

3. Set the distortion analyzer on a range to indicate the

rated output power, P^.

4. Set receiver controls as given in Table XXXIII, p. 271.

5. Tune the signal generator and the receiver to the

measurement frequency, f^.

6. Adjust the receiver modulation in the signal generator

to ±60% of rated system deviation at 1000 Hz.

7. Measure the 12 dB SINAD SENSITIVITY, E^ , as outlined

in Section 4.1.5.5.

8. Disconnect the signal generator from the impedance

transformer at the receiver input port, and connect the SHIELDED

TERMINATION, Z^, in its place.

9. Connect the signal generator to the ANTENNA terminals.

10-. Set the generator output level to maximum (e.g.,

100,000 to 1,000,000 microvolts).

284
11. with the antenna approximately 30 meters from the

receiver, vary the generator frequency to cover all frequencies

of interest, including f^ and spurious response frequencies

(cf .) .

12. When a response is produced, adjust the orientation of

the receiver for maximum, response, keeping the antenna 30 meters

from the receiver at the closest point.

13. Adjust the generator output level to produce a 12 dB

SINAD ratio.

Note: If the radiated field strength is not large

enough to produce a 12 dB SINAD ratio, do one

of the follo\ving things:

(1) Move the antenna closer to receiver.

(2) Insert a povrer amplifier betvreen the generator output port

and the antenna terminals. Choose an amplifier v.'ith sufficient

gain and povrer capability to produce a 12 dB SINAD ratio.

14. Determine the signal frequency, f., and field strength,

E_. , in volts per meter, at the location of the receiver. This

field strength is the radiated interference susceptibility of

the receiver for receiver freauency, f , and interference

frequency , f ^

.

4.5.4.6. DATA REQUIRED

1. Record the measurem.ent frequency, f^, in kilohertz or

megahertz

.

2. Record the value of source impedance, Z^, in ohms,

connected to receiver input port.

285
3. Record the value of termination resistance, , in

ohms, connected to receiver audio output terminals.

4. Record the reference output power, , in watts.

5. Record

microvolts

.

the 12 dB SINAD sensitivity, E. , in

6. Record the antenna-to-receiver distance

7. Record the interference frequency, f ^ , in kilohertz

or megahertz.

' 8. Record the radiated interference susceptibility field

strength, E_. , in volts per meter.

4.5.4.7. MEASUREMENT ERRORS

Measurement uncertainties depend upon local circumstances

and are difficult to predict for the general case. See

discussion given under Section 4.5.

286
4.6. EMISSION

Energy from internal signal sources within a receiver may

produce undesired emissions, either conducted or radiated, via

the receiver's antenna, power cord, audio cables, and control

cables. Potential sources of this energy are (1) oscillators

used for frequency conversion, (2) beat frequency oscillators,

(3) oscillators used for synchronous detection, (4) convertertype power supplies, and (5) spurious oscillations from unstable

circuits

.

Measurement methods for conducted emission are generally

sim.ilar to other methods given in this handbook. However,

presently available methods for measuring radiated emission

are generally inadequate or worthless because of the large

inaccuracies and variations of results that they provide.

Errors typically range from 100% to 500%, and may reach 1000%

or higher, depending upon the circumstances. Measurem.ents in

shielded enclosures, as presently practiced, are essentially

meaningless because of the large standing waves usually

present. Adequate anechoic chambers are not yet developed

for frequencies below 100 MKz. Open-field arrangements are

usually not practical because of the space, power, and interference problemiS . But underlying all of these configuration

problems is the lack of basic techniques for determining the

strength of perturbed near fields v;ith adequate accuracy.

4.6.1. CONDUCTED EMISSION

4.6.1.1. DEFINITION

Conducted emission is electromagnetic energy that is

propagated along a conductor.

287
Conducted emission is usually expressed as the power,

in dBm, available from specified receiver terminals.

4.6.1.2. PURPOSE

The purpose of this measurement method is to measure the

radio frequency power that is available at each of the

receiver's accessible terminals, and which is generated by

sources within the receiver. This power may be radiated or

otherwise conveyed from the receiver to other electronic

devices, causing undesired interference.

288
4.6.1.3. METHOD

The method uses a sensitive, tunable, frequency-selective

voltmeter and a variable-frequency CW signal generator as shown in figure 4.6.1. The voltmeter measures the signal

level of internal sources at the selected receiver

terminals . The signal generator is used to calibrate the

voltmeter. Conducted emission, in dBm ^ is computed from

the voltmeter reading and the impedance level at the

terminals

.

Measurem.ent uncertainties as small as 0.3 dB are

possible under best conditions, and range from 0.5 dB to

1.5 dB under typical conditions. This method uses commonly

available test equipment, but requires some specialized

accessories

.

4.6.1.4. TEST EQUIPMENT REQUIRED

1. Tunable, frequency-selective voltmeter

2. Variable frequency CW generator

3. Insertion network

4. Line impedance network

4.6.1.5. PROCEDURE

1. Connect the input port of the SELECTIVE VOLTMETER to

the selected terminals of the receiver through an INSERTION

NETWORK or LINE IMPEDANCE NETWORK as shown in figure 4.6.1.

The networks should provide proper terminations for both the

selective voltmeter and the receiver.

289
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2. Set receiver controls as given in Table XXXIV.

3. Set the voltmeter for maximum sensitivity.

4. Tune the voltmeter until it indicates a response to a signal coming from the measurement terminals.

5. Adjust voltmeter sensitivity to indicate the level

of the response.

6. Disconnect the voltmeter from the insertion or line

impedance netvrork and connect it to the SIGNAL GENERATOR.

7. Tune the generator to the frequency that produced the

voltmeter response. Record this frequency, f ^ , in kilohertz

or megahertz.

8. Adjust the output level of the generator to produce

the same response as that produced by the signal from the

receiver

.

9. Determine the available povrer, P (f ) , in dBm, from

g r the generator in Step 7, above, by determining the generator

open circuit voltage, E^, and generator source impedance,

Z (see Section 4.10.).

s

10. Calculate the available oovrer, P (f ) , in dBm, from the

r r

' receiver by ADDING the loss, L, in dB , of the insertion or line

impedance network at frequency f^. P_^(f^)is the conducted

emission, in dBm, of the receiver at frequency f^.

291
TABLE XXXIV

Conducted Emission

' Initial Control Settings

Control Setting

1. Band Switch 1 . As desired

2. Frequency Tuning 2. . As desired

3. Antenna Trimmer Peak

4. RF Gain A4 . Maximum

5. IF Gain c3 . Maximum

6 . AF Gain (-D .

7\ c /~i T t^e^ t\S QcbXrcU

7. Line Gain 7 . As desired

8. Detector Mode o

o . As desired

9 . Beat Frequency Oscillator 9 . As desired i normally uln;

10 . BFO Frequency 10 . As desired

11. IF Bandwidth 11 . Optional

12. AF Bandwidth 12 . Optional

13 . Noise Limiter 13. OFF

14. Squelch Level 14 . OFF

15 . AGC/MGC Mode Switch 15 . As desired

16 . Meter Switch 16 . Optional

292
11. Repeat Steps 3 through 10

produce a voltmeter response. Be

and harmonic frequencies of known

at other frequencies that

sure to include fundamental

sources with the receiver.

4.6.1.6. DATA REQUIRED

1. Record receiver control settings and operational

information

.

2. Record frequencies, f ^ , of conducted emissions.

3. Record voltmeter readings of conducted emissions.

4. Record the generator power, P (f ) , in dBm, available ^ g r at frequency f^

5. Record the loss, in dB , at frequency f_^, of the

insertion or line impedance network.

6. Record the conducted emission power, Pj-(f^) t in

dBm, for each frequency, f^.

4.6.1.7. MEASUREMENT ERRORS

The principal sources of measurement error are the following:

1. Uncertainty, AP , in the measured value of P

g g

2. Uncertainty, AL , in the measured loss, L, of the

insertion or line impedance network

The total relative uncertainty, AP^ (dB) , in decibels,

in the conducted emission, P^, expressed in dBm, is given

approximately, for small uncertainties, by the equation

AP

r

(dB) = 10

293
Relative uncertainty AP^/P^ is given by the equation

AP AE AZ

_g _ o g +

s P E z g g s

where AE is the uncertainty in the measured value of

g

generator voltage, E^, and AZ^ is the uncertainty in the

measured value of source impedance, Z^.

Uncertainty AE is obtained from the manufacturer's

g

specifications on the selective voltmeter; AZ is obtained

s from the specifications on the impedance meter used to

measure Z ; AL is obtained from the specifications on the

s equipment (power meter, voltmeter, etc.) used to measure

insertion loss, L.

294
4.6.2. RADIATED EMISSION

4.6.2.1. DEFINITION

Radiated emission is the field strength, in volts per

meter, produced by radiation from the receiver, due to signal

sources within the receiver, at a specified point external to

the receiver.

Note: Because the antenna used with the receiver

may not be uniquely specified, radiated

emission as considered in this Section will

not include radiation via the receiver's

antenna terminals.

4.6.2.2. PURPOSE

The purpose of this measurement method is to measure the

field strength of electromagnetic energy radiated from all

parts of the receiver except the antenna terminals. Radiation

may come from internal sources via the power, audio, or

interconnecting cables, and/or from leakage paths in the

receiver's enclosure. Receiver radiation is a measure of the

receiver's interference potential to other electronic or

communications equipment.

Note: The method given below is only indicative

of the basic principle of measurement. It

is not given as a recommended method that

will give accurate results. See the discussion

given under Section 4.6.

295
4.6.2.3. METHOD

The method uses a field intensity meter (FIM) as shown

in figure 4.6.2. The FIM measures the field intensity at a point in space that has a specified relationship to the

receiver; this relationship depends upon the measurement

frequency, and is given in the procedure below.

Measurement uncertainties are seldom less than 10 0% and

may be as great as 1000% under typical conditions. The method

uses commonly available test equipment of moderate

sophistication

.

4.6.2.4. TEST EQUIPMENT REQUIRED

1. Field intensity meter

2. Shielded termination for receiver's antenna port

3. Power line filter

4.6.2.5. PROCEDURE, ELECTRIC FIELD, 14 KHZ TO

100 MHZ

1. Place the receiver on a ground plane that meets the

specifications of MIL-STD-462, paragraph 4.2.1.2.

2 . Connect the receiver through the POWER LINE FILTER to

the source of primary power. Bond the filter to the ground

plane at a point at least 2 meters from the receiver.

3. Attach the SHIELDED TERMINATION to the receiver's

antenna port.

4. Adjust the electrical settings of the receiver for the

desired operating conditions.

296
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5. Tune the FIM to the measurement frequency, or place

the FIM in the swept- frequency mode.

6. Scan the receiver with the FIM

locate the sites of maximum radiation,

as required for maximum pick-up.

7. When radiation is detected, position the FIM probe

1 meter from the nearest point to the receiver, and adjust

the orientation of the probe and the frequency of the FIM

for maximum FIM response.

8. Measure the field intensity with the FIM. This is

the receiver radiation, in volts per meter, at the measurement

frequency for the selected receiver operating conditions.

9. Repeat Steps 4 through 8, above, until the desired

range of frequencies and receiver operating conditions are

covered.

4.6.2.6. DATA REQUIRED

1. Record receiver control settings and operating

conditions

.

2. Record frequency of radiated emissions.

3. Record field intensity of radiated emissions.

4.6.2.7. MEASUREMENT ERRORS

Measurement uncertainties depend upon local circumstances

and are difficult to predict for the general case. See

discussion given under Section 4.6.

probe (antenna) to

Orient the FIM probe

298
4.7. ii::z Dzu^Y

4.7.1. DEFINITION

Time delay is the tine interval between the manifestation

of a signal at one point and the manifestation or detection of

-he saiTie signal at another point. (IEEE Std 100-1972)

4.7.2. PUEPOSE

The purpose of this measurement method is to m^easure the

time delay of signals passing through s\irveillance receivers.

Time delay is important when combining two or more receivers

in multiple-diversity receiving systems , or in position-plotting

systems

.

4.7.3. METHOD

This method uses a modulated signal generator, a matched

pair of detectors, and a cathode-ray oscilloscope as shovm in

figure 4.7. The generator supplies a modulated signal of known

modulation frequency "^c che receiver. The matched detectors

supply demodulated signals zo -he two vertical input channels

of rhe oscilloscope, which operates in a dual-channel mode.

The oscilloscope displays zhe time displacement betvreen the two

demodulated signals, and -ime delay is measured graphically from

this display.

This method is mcsz useful vrhen the zime delay is longer

than twice zhe reciprocal bandwidth cr, if -chey are approximately

equal, time delay musz be approximately proportional to reciprocal

bandwidth. Otheir^vise , accuracy may suffer.

299
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Measurement uncertainties as small as 2% are possible under

best conditions, and range from 3% to 10% under typical conditions.

This method uses commonly available test equipment of moderate

sophistication.

4.7.4. TEST EQUIPMENT REQUIRED

1. Signal generator capable of external amplitude or

frequency modulation

2. Audio signal generator

3. Frequency meter

4. Isolation network

5. Variable attenuator

6 . Two matched envelope detectors

7. Two matched frequency - modulation detectors

8. Cathode-ray oscilloscope with dual-channel mode

of operation

9 . Oscilloscope camera

4.7.5. PROCEDURE

1. Connect the input port of the receiver to the output

port of the SIGNAL GENERATOR through the VARIABLE ATTENUATOR.

2. Connect DETECTOR No. 1 to the junction of the signal

generator and the variable attenuator.

301
3. Connect DETECTOR No. 2 to the output of the last I.E.

amplifier stage of the receiver. If detector No. 1 matches the

detector built into the receiver, the receiver's detector may

be used in place of detector No. 2.

4. Connect each detector output to a vertical input port

of the dual channel OSCILLOSCOPE.

5. Connect the output port of the AUDIO GENERATOR to the

EXTERNAL MODULATION input port of the signal generator.

6. Connect the FREQUENCY METER through an ISOLATION NETWORK

to the junction of the audio generator and the signal generator.

7. Set the receiver controls as given in Table XXXV.

8. Set oscilloscope controls as given in Table XXXVI.

9 . Tune the signal generator and the receiver to the

measurement frequency, f^

.

10. Adjust the oscilloscope vertical gains to maximum,

and approximately equal

.

11a. If the measurement is on an AM receiver, adjust the

amplitude modulation of the signal generator to 30% at a very

low frequency, e.g., 25 hertz.

OR

lib. If the measurement is on an FM receiver, adjust the

frequency modulation of the signal generator to ±60% of rated

system deviation at a very low frequency, e.g., 25 hertz.

302
TABLE XXXV

Time Delay

Initial Control Settings

Control Setting

1 . Band Switch

2. Frequency Tuning

3 . Antenna Trimmer

4 . RF Gain

5. IF Gain

6 . AF Gain

7. Line Gain

8. Detector Mode

9. Beat Frequency Oscillator

10 . BFO Frequency

11. IF Bandwidth

12. AF Bandwidth

13 . Noise Limiter

14 . Squelch Level

15. AGC/MGC Mode Switch

16. Meter Switch

1 . As desired

2. As desired

3. Peak

4 . Moderate

5 . Moderate

6 . Optional

7. Optional

8. AM or FM

9 . Off

10. N.A.

11. As desired

12 . Optional

13. Off

14. Off

15 . Optional

16 . Optional

303
TABLE XXXVI

Oscilloscope Control Settings

Control

1 . Mode

2. Channel 1 Gain

3 . Channel 2 Gain

4 . Sweep speed

5. Trigger Mode

6 . Trigger Phase

Setting

1. Chopped

2. As required

3. As required

4. As required

5. Internal, Ch

6. Zero

304
12. Adjust the signal generator output to maximum, e.g.,

approximately 100,000 to 1,000,000 microvolts.

13. Adjust oscilloscope controls to obtain a stable trace

from detector No. 1. Display from 5 to 15 cycles of the

sinusoid pattern.

14. Adjust the variable attenuator to produce approximately

the same output from detector No. 2 as from detector No. 1.

15. Note the time relationship between the traces of the

output signals from detectors No. 1 and No. 2. There is usually

a small time displacement between the two traces.

16 . Increase the frequency of the audio generator. The

trace from detector No. 2 should move relative to that of

detector No. 1.

17. Determine if the frequency can be increased sufficiently

to cause the two traces to be in exact phase alignment, so they

can be superimposed, without having the signal from detector

No. 2 decrease in amplitude by more than 3 dB. This is a function

of r-eceiver CW bandwidth. If this is possible, adjust the audio

generator to a frequency, f^, where the two traces are exactly

in phase on the screen.

18. Measure frequency f with the frequency meter.

a

19. Calculate t by the equation

1

T =

f

a

T is the time delay of the receiver at frequency f .

305
20. Confirm the value of t in the following way:

Increase the generator to the frequency fj^ that causes the

two traces to again be exactly in phase, if possible. Under

this condition,

1

T =

For T = 1/f as in Step 18, above, then f, will equal 2f . In

general.

m m + 1

T =

fx fa f2 - fl

'

where m is an integer.

If the receiver bandwidth prevents obtaining a trace from

detector No. 2 with modulation frequency f^, then x cannot be

checked in this way.

21. If the receiver bandwidth prevents obtaining a trace

)m detector No. 2 with m^ above, proceed as follows:from detector No. 2 with modulation frequency f as in Step 17,

a

a. Adjust the audio generator to the frequency, f^, at which

the output from detector No. 2. is approximately 3 dB below that

of detector No. 1. -

'

b. Measure the time interval. At, between a zero crossing

point on the output of detector No. 1 and a same zero crossing

point of the same slope on the output of detector No. 2. Expand

the horizontal scale to facilitate this measurement. Photograph

the display, if desired.

306
c

.

Determine time delay, t, by the equation

T = At

4.7.6. DATA REQUIRED

1. Record the measurement frequency, f^, in kilohertz or

megahertz

.

2. Record the variable attenuator setting. A, in decibels.

3. Record the modulation/demodulation mode, AM or FM.

4. Record the oscilloscope adjustments; particularly note

the horizontal sweep speed.

5. Record the audio generator frequencies, f , f , or f , a b c in hertz.

6. Record the measured value of At, in milliseconds.

7. Record the calculated value of time delay, t, in

microseconds or milliseconds.

4.7.7. MEASUREMENT ERRORS

The principal sources of measurement error are the following:

1. Uncertainties

,

Af

a'

Af. and Af

c'

in the measured values

of f and f c

2. Uncertainty, A (At), in the measured value of At.

307
3 . Uncertainty, A (At ) , in the superposition of the two

traces in Step 17, above.

When using Steps 17, 18, and 19 to measure x, the total

relative uncertainty, At(%), expressed in percent, in t , is

given by the equation

At (%) =1 + X 100 ,

where T is the time, in seconds, for the trace to sweep across

the screen

.

When using Step 20 to measure x, Ax(%) is given by the

equation

/ Af Af A (At ) \

AX (%) =(-f^- ^^jx • ^ a b '

When using Step 21 to measure x, Ax(%) is given by the

equation

- 4t (%) . X 100 .

Uncertainties Af , Af , and Af are obtained from the

a a c manufacturer's specifications on the frequency meter.

Uncertainties A (At) and A (At ) are obtained from the

a manufacturer's specifications on the horizontal sweep

circuits of the oscilloscope.

308
4.8. FREQUENCY STABILITY

The frequency stability of a receiver may be considered in

two different ways. First, the various oscillators within the

receiver may change frequency because of electrical or physical

changes to which they respond. Second, the various circuits

that provide frequency selectivity within the receiver may

change their response characteristics for the same reasons.

Both of these changes can cause degradation in receiver

performance

.

Only oscillator stability is discussed in this section.

Methods for measuring the stability of frequency sensitive

transducers generally are the same as for measuring

selectivity (cf.).

The method given in this section applies to frequency

fluctuations that occur at a rate that is slower than approximately one hertz per second; there is no limit in principle to

the slowness of fluctuation for which this method applies. The

method may lose utility for fluctuations faster than one hertz

per second because of instrument limitations. However, the

method is applicable to most stability problems encountered

with surveillance receivers, and no attempt is made here to

divide these problems into the two poorly defined categories

of short-term stability and long-term stability.

4.8.1. DEFINITION

The frequency stability of a receiver is the change in

oscillator frequency per unit change in a frequency-perturbing

parameter. Examples of such parameters include (1) time,

(2) temperature, (3) voltage, (4) atmospheric pressure, and

(5) humidity.

309
4.8.2. PURPOSE

The purpose of this measurement method is to measure the

frequency stability of the oscillators contained within

surveillance receivers. Examples of such oscillators are

(1) tunable oscillators used for frequency conversion,

commonly called local oscillators, (2) beat frequency

oscillators used to render keyed CW signals audible, and

(3) oscillators used for synchronous detection of suppressed

carrier signals. The frequency stability of such oscillators

is a measure of the receiver's ability to receive stable

signals without drift in spite of changes in power supply

and ambient conditions.

4.8.3. METHOD

The method uses a stable CW generator, a precision

electronic counter, and a digital printer as shown in

figure 4.8. The generator delivers a signal at a known

frequency to the receiver. The counter measures the

frequency from the IF section for receivers operating in

the AM and FM modes, and from the AF section for CW and

SSB modes . The printer provides a hard copy record of the

counter output. <

.

I.F. output signal frequency is measured under controlled

conditions where the frequency-perturbing parameter is

changed in a known way. Frequency stability is obtained from

a graphical plot of I.F. output frequency versus this

parameter.

Measurement uncertainties as small as 0.2 Hz are possible

under best conditions, and range from 0.2 Hz to 1 Hz under

typical conditions. The method requires sophisticated but

commonly available test equipment.

310
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4.8.4. TEST EQUIPMENT REQUIRED

1. Stable CW signal generator

2. Electronic counter

3. Digital printer

4. Equipment as required to produce controlled changes

in operating conditions, such as (1) variable autotransformer

,

(2) environmental chamber.

4.8.5. PROCEDURE

1. Connect the CW SIGNAL GENERATOR to the input port

of the receiver.

2. Connect the DIGITAL COUNTER to the output of the IF

amplifier, if the measurement is not to include the BFO

stability. Otherwise, connect the counter to the output

terminals of the audio amplifier.

3. Connect the DIGITAL PRINTER to the counter per

manufacturer's instructions.

4. Arrange the receiver as required for the desired test.

For example

a. If the test is to measure frequency as a function of

line voltage, connect the receiver line cable to a regulated,

adjustable, and metered supply of the proper voltage and

frequency

.

b. If the test is to measure frequency as a function of

environmental conditions, install the receiver in a suitable

environmental chamber that provides the required control and

metering of the environmental parameter.

312
c. If the test is to measure frequency as a function of

time for special operating conditions, such as those indicated

in a and b, above, provide a clock to monitor this parameter.

For "average" operating conditions, special auxiliary

equipment may not be required.

5. Set receiver controls as given in Table XXXVII.

6. Tune the signal generator and the receiver to the

measurement frequency, f^

.

7. Adjust the output level of the generator to produce

a clean output signal from the IF or audio sections.

8. Measure the generator frequency, f ^ , with the counter.

9. Measure the IF output signal frequency, fj^^/ with the

counter

.

10. Measure the audio output signal frequency, f ^, with

the counter (CW and^SB modes only) .

11. Repeat Steps 8 through 10, above, according to the

desired information. That is, repeat the measurements as often

as desired to obtain the stability as a function of time with

the desired density of measurement points; repeat as required

by changes in test conditions per Step 4, above.

12. Plot, on rectilinear graph paper, the measured frequency

as a function of the frequency-perturbing parameter (voltage,

temperature, time, etc.).

13. Determine the slope of the curve plotted in Step 12,

above, at any point of interest. The slope is the FREQUENCY

STABILITY of the oscillator at that particular operating

point.

313
TABLE XXXVII

Frequency Stability

Settings

Control Setting

1. Band Switch 1. As desired

2. Frequency Tuning 2. As desired

3. Antenna Trimmer 3. Peak

4 . RF Gain ^

'.' 4. As required

5. IF Gain 5. As required

6 . AF Gain 6. As required

7. Line Gain 7. Optional

8. Detector Mode 8. As desired

9 . Beat Frequency Oscillator 9 . As desired

10 . BFO Frequency 10 . As desired

11. IF Bandwidth 11. Optional

12. AF Bandwidth 12. Optional

13. Noise Limiter 13. OFF

14 . Squelch Level , .. 14. OFF

15. AGC/MGC Mode Switch 15. As desired

16 . Meter Switch 16 . Optional

314
4.8.6. DATA REQUIRED

1. Record the measurement frequency, f^ , in kilohertz

or megahertz.

2. Record the IF output signal frequency, ^ j_f'

kilohertz or megahertz.

3. Record the audio output signal frequency, f r: , in

a £

hertz or kilohertz.

4. Record the value of the frequency-perturbing parameter,

and correlate it with the measured IF or audio signal frequency.

4.8.7. MEASUREMENT ERRORS

The principal sources of measurement errors are the

following

1. Uncertainty, Af , in the measured value of each

frequency, f

2. Uncertainty, '^^g' frequency of the stable CW

generator, due to drift

3. Uncertainty in the value of the frequency-perturbing

parameter selected for the test

The total relative uncertainty, Af^(%) , in percent, in

the measured value of frequency, f, is given by the equation

Uncertainties Af and Af are obtained from the manufacturer's

g

specifications on the signal generator and on the electronic

counter

.

315
4.9. FREQUENCY READOUT ERROR

4.9.1. DEFINITION

Frequency readout error is the frequency difference, in hertz

or kilohertz, between the receiver's indicated reception frequency

and the frequency to which the receiver is tuned.

4.9.2. PURPOSE

The purpose of this measurement method is to measure

the frequency readout error of surveillance receivers. Readout

error affects the ease with which the receiver can be tuned to

receive a signal of a given carrier frequency.

4.9.3. METHOD

The method uses a stable CW generator and a precision

electronic counter as shown in figure 4.9. The generator

delivers a signal at a known frequency to the receiver.

The counter measures the frequency of the I.F. signal. The

receiver is tuned until the I.F. signal is at the specified

frequency. The difference between the receiver's indicated

frequency and the generator frequency is the readout error.

The measurement uncertainty is determined primarily by the

readout resolution of the receiver's frequency display. The

method uses sophisticated but commonly available test

equipment.

4.9.4. TEST EQUIPMENT REQUIRED

1. Stable CW signal generator

2. Electronic counter

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4.9.5. PROCEDURE

1. Connect the CW SIGNAL GENERATOR to the input port

of the receiver.

2. Set receiver controls as given in Table XXXVIII.

3. Tune the signal generator to the measurement, f^

.

4. Adjust the output level of the generator to produce

a clean output signal from the I.F. section of the receiver.

5. Measure the generator frequency, f^, with the COUNTER.

6. Connect the counter to the output of the I.F. amplifier

section.

7. Tune the receiver near f^, and adjust the tuning to

produce an I.F. signal with a frequency equal to the

manufacturer's specified intermediate frequency, fj_f

8. Read the indicated reception frequency, f^, on the

receiver's frequency readout display.

9. Calculate the frequency difference, Af^, in hertz or

kilohertz, between f^ and f^ by the equation

Af = f - f r r o

318
TABLE XXXVIII

Frequency Readout Error

Initial Control Settings

Con tro

1

S ett ing

1

.

Band Switch 1

.

As desired

2 . Frequency Tuning 2

.

As desired

3 . Antenna Triitimer 3 . Peak

4 . RF Ga in 4 . As required

5 . IF Gain 5 . As required

6 . AF Gain 6 . As desired

7 7 I LV^^llCtJ- 8. Detector Mode 8 . AM, FM, as desired

9 . Beat Frequency Oscillator 9. Off

10, BFO Frequency 10. N.A.

11. IF Bandwidth 11

.

Optional

12. AF Bandwidth 12 . Optional

13. Noise Limiter 13. Off

14 . Squelch Level 14. Off

15. AGC/MGC Mode Switch 15. As desired

16 . Meter Switch 16. Optional

319
Af^ is the frequency readout error of the receiver at the

indicated reception frequency, f^. If Af^ is positive, f^ is

qreater than f ; if Af is neqative, f is less than f . ^ o r r o

4.9.6. DATA REQUIRED

1. Record the measurement frequency, f^, in kilohertz

or megahertz

.

2. Record the intermediate frequency, fj_£/ in kilohertz

or megahertz

.

3. Record the indicated reception frequency, f^, in

kilohertz or megahertz.

4. Record the frequency readout error, Af^, in hertz

or kilohertz

.

4.9.7. MEASUREMENT ERRORS

The principal source of measurement error is normally the

uncertainty in the receiver's frequency display, which is

determined by its readout resolution. In this case, the total

measurement uncertainty, A(Af^), in hertz, in the measured

readout error, Af , is the receiver readout resolution. This

r is obtained from the manufacturer's specifications, or by

inspection of the readout indicator.

320
4.10. IMPEDANCE

The requirements for impedance measurement in surveillance

receivers usually pertain to antenna input impedance and IF

and/or AF output impedance. Because these impedances involve

active components , measurement methods are required that do

not significantly alter the impedance whose value is to be

measured.

4.10.1. DEFINITIONS

a. Input impedance is the impedance presented by the

receiver to the signal source.

b. Output impedance is the impedance presented by the

receiver to a termination.

c. Impedance is the ratio, at a given frequency, of

(a) the sinusoidal voltage across a pair of terminals to

(b) the corresponding sinusoidal current, at the same

frequency, passing into and out of the pair of terminals.

4.10.2. PURPOSE

The purpose of these measurement methods is to measure the

input and output impedances at the accessible ports of

receivers. These impedances determine in large part the

ability of a receiver to deliver output signals of acceptable

quality at adequate power levels

.

Impedance is a function of frequency. Input impedances

are normally measured at frequencies in the range to which

the receiver is tuned. Output impedances are measured at audio

frequencies, and at intermediate frequencies (IF's) when the

receiver is provided with a suitable I.F. output network and

321
connector. Further, the input and output impedances of special

circuits, such as local oscillator inputs or outputs can be

measured by these methods.

Measurement uncertainties as small as 4% are possible under

best conditions, and range from 5% to 20% under typical

conditions. The method requires sophisticated but commonly

available test equipment.

4 . 10 . 3 . METHOD I - VECTOR IMPEDANCE METER

The method uses a variable frequency vector impedance meter

as shown in figure 4.10.1. The impedance meter contains its own

signal source, detector networks, and output display. Impedance

is read directly from the meter display.

This method is suitable for measuring both input and output

impedances. It is particularly suited for impedance measurement

when the network under test can tolerate only a very small test

signal because of low-level active devices.

4.10.3.1. TEST EQUIPMENT REQUIRED

1. Vector impedance meter

4.10.3.2. PROCEDURE

1. Connect the VECTOR IMPEDANCE METER probe to the

terminals of the receiver at which the measurement is to be

made

.

2. Set receiver controls as given in Table XXXIX.

3. Tune the vector impedance meter to the measurement

frequency, f .

322
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323
TABLE XXXIX

Impedance, Methods I and II

Initial Control Settings

Control Setting

1. Band Switch 1. As desired

2. Frequency Tuning 2. As desired

3

.

Antenna Trimmer . 3. As desired

4. RF Gain 4 . As desired

5. IF Gain 5. As desired

6. AF Gain 6 . As desired

7. Line Gain 7. As desired

8. Detector Mode 8 . Optional

9 . Beat Frequency Oscillator 9 . OFF

±u1 n . rsr u r requency xu1 n . N.A

11. IF Bandwidth 11. As desired

12. AF Bandwidth 12 . As desired

13. Noise Limiter 13. OFF

14. Squelch Level 14. OFF

15. AGC/MGC Mode Switch 15. As desired

16 . Meter Switch 16 . Optional

324
4. Read the impedance indicated by the

meter indication is in terms of magnitude,

angle, 0, convert to real, R, and reactive,

the following equations

meter. If the

Z I , and phase

X, parts by

Z = R + jX

where

R = I Z I cos 0

X = I Z

I sin 0

5. Record the values of R and X as the terminal impedance

at frequency f^

.

4.10.3.3. DATA REQUIRED

1. Record the measurement frequency, f^ , in kilohertz

or megahertz

.

2. Identify the terminals at which the measurement is made.

3. Record the measured values of |z| and 0.

4. Record the calculated values of R and X.

4 . 10 . 3 . 4 . MEASUREMENT ERRORS

The measurement uncertainty is given by the manufacturer's

specifications on the impedance meter.

325
4.10.4. METHOD II - IMPEDANCE BRIDGE

The method uses a variable frequency signal generator, an

impedance bridge, and a signal detector as shown in figure

4.10.2. The generator provides current for the bridge circuit,

and the detector indicates the null condition. The bridge is

adjusted for a null at the measurement frequency, and impedance

is read from the dial settings on the bridge.

This method is suitable for measuring both input and output

impedances, but for some receivers it must be used with care

when measuring input impedance. The required signal level

across the measuring terminals of the bridge is usually greater

than for Method I, above, which can produce erroneous results

because of nonlinear network components.

Measurement uncertainties as small as 4% are possible under

best conditions, and range from 5% to 20% under typical

conditions. The method uses moderately sophisticated but

commonly available test equipment.

4.10.4.1. TEST EQUIPMENT REQUIRED

1. CW signal generator

2. Impedance bridge

3. Null detector

4.10.4.2. PROCEDURE

1. Connect the SIGNAL GENERATOR, IMPEDANCE BRIDGE, and

NULL DETECTOR as shown in figure 4.10.2. Connect the bridge

measuring terminals to the terminals of the receiver at which

the measurement is to be made. For most situations, use a coaxial cable for this connection.

326
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Ll_

o

LU

i

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327
2. Set receiver controls as given in Table XXXVIX, p. 324.

3. Tune the generator to the measurement frequency, f^.

4. Adjust the generator output level to near maximum

(e.g., between 0.1 and 1.0 volt).

5. Adjust the null detector sensitivity to indicate

bridge output. If the null detector is tunable, tune it to

6. Adjust the bridge for an initial balance, following

the manufacturer's instructions.

7. Measure the receiver impedance desired, following the

manufacturer's instructions.

8. Record the indicated readings of R and X from the

bridge dials

.

9. Apply frequency corrections to the dial readings,

if necessary.

10 . Correct the measurement results for the effects of the

cable connecting the bridge to the receiver terminals , following

the manufacturer's instructions. This usually entails measuring

the parameters of the cable, and applying these results by

means of formulae or charts supplied by the manufacturer.

11. Record the corrected values of R and X as the terminal

impedance at frequency f ^

.

12. Reduce the generator output level by 10 dB, and repeat

Steps 6 through 11. If the measurement results differ from the

original, reduce the generator output further until the results

do not change or until they are degraded by noise. The variation

328
of R and/or X with bridge drive level is an indication of

excessive signal at the measurement terminals. The values

obtained at the lowest drive level are normally the most

nearly correct. If a stable measurement result cannot be

obtained because of this cause, use Method I, above.

4.10.4.3. DATA REQUIRED

1. Record the measurement frequency, f^, in kilohertz

or megahertz.

2. Identify the terminals at which the measurement is

made

.

3. Record the calculated values of R and X.

4 . 10 . 4 . 4 . MEASUREMENT ERRORS

The measurement uncertainty is given by the manufacturer's

specifications on the impedance meter.

329
4. 11. STANDING WAVE RATIO

The requirements for VSWR measurements on surveillance

receivers usually pertain to the antenna input and IF output

ports. Because the ports connect to active circuits within

the receiver, measurement methods are required that do not

significantly alter the VSWR whose value is to be measured.

4.11.1. DEFINITION

a. Standing wave ratio is the ratio of the amplitude of

a standing wave at an antinode to the amplitude at a node.

(IEEE STD 100-1972)

. b. The voltage standing wave ratio, VSWR, at a specified

port of a receiver is the ratio of (a) the absolute value of

the port's reflection coefficient, |r|, plus unity (1), to

(b) unity minus the absolute value of the port's reflection

coefficient.

1 + I r I VSWR =

1 - r

c. The reflection coefficient, F, at a port is given by

the equation

Z - Z

P = _E I

z + z

' p

^

where Z^ = complex impedance looking into the port,

Z^ = reference impedance.

Note: From the above definitions, VSWR can be expressed

by the normalized relationship.

Z VSWR = ^ . r When Zp < Z^, the VSWR at the port is usually expressed by

the relationship

Z VSWR = ^ . p

330
4.11.2. PURPOSE

The purpose of this measurement method is to measure the

VSWR at the accessible ports of surveillance receivers. VSWR

is a measure of the receiver's ability to transfer power to and

from the circuits connected to these ports.

4.11.3. METHOD

The method uses a variable frequency vector impedance meter

as shown in figure 4.11. The impedance meter contains its own

signal source, detector networks, and output display. VSWR is

obtained by first measuring the impedance at the port, and

then computing VSWR by means of a Z-9 chart.

I-leasurement uncertainties as small as 6% are possible under

best conditions, and range from approximately 8% to 20% under

typical conditions . The method uses sophisticated but commonly

available test equipment.

4.11.4. TEST EQUIPMENT REQUIRED

1. Vector impedance meter

2. Z-3 chart paper (or Sm.ith chart paper)

4.11.5. PROCEDURE

1. Connect the VECTOR IMPEDANCE METER probe to the termdnals

of the receiver at which the measurement is to be made.

2. Set receiver controls as given in Table XXXX.

3. Tune the vector impedance meter to the measurement

frequency, f^.

331
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332
TABLE XXXX

Standing Wave Ratio

Initial Control Settings

Setting

-L. 1 • 1

,

As desired

2 2 As desired

3

.

7\ -p +- p

J. L« 1111-p ;3C-t "PtI X X. -L TTimPT 1 L LI L J_ 3

.

As desired

4 XVL RF C-iPi VJd-l-ll \ n 4 . As desired

•J • J-J- wCl-l-ll As desired

o • AT? 1 n a\j • As desired

7 ±j-Lilc: odXll 7 As des ired

o • Oo "H o "f* 1^ QO • Optional

q Ro;^"!" T? "V'^iirT 1 1 o r^\7 Oq/^i "I 1 -j- o y~ o tr: d L. r i.ti'^Llt-iloy woOJ—I—Ld L-wi. q OFF

TI) orXT' w XT' v~ lO r~T i T >^ /^\7 r X fcit^ Lit- 1 1 oy X1 0w • N .A

11. IF Bandwidth 11. As des ired

12. AF Bandwidth 12. As desired

13. Noise Limiter 13. OFF

14 . Squelch Level 14 . OFF

15. AGC/:4GC :4ode Switch 15. As desired

16. Meter Switch 16 . Optional

333
4. Read the impedance indicated by the meter.

5. Plot \z\ and G on Z-0 CHART PAPER. If the impedance

meter gives the real part, R, and imaginary part, X, of Z,

normalize these values and plot on a Smith chart.

6. Determine the VSWR circle on the Z-0 chart (or Smith

chart) by constructing a circle whose center is at the origin

of the chart and which passes through the point |z| , 0 (or R

and X, normalized) .

7. With Z-0 paper, determine the value of VSWR by locating

the point of intersection between the Z/Z - axis and the circle.

Read the value for which Z/Z^ > 1. (On the Smith chart, the VSWR

is the intersection of the circle and the real axis.) This is

the VSWR at the port. Express VSVJR as a ratio of this number

to unity (e.g., 1.5:1 or 3:1, etc.).

4.11.6. DATA REQUIRED

1. Record the measurement frequency, f^ , in kilohertz

or megahertz.

2. Identify the terminals at which the measurement is made.

3. Record the measured values of |z| and 0.

4. Record the calculated values of R and X.

5. Record the value of VSWR, determined from Z-0 chart.

334
4.11.7. MEASUREMENT ERRORS

The principal sources of measurement error are the

following

1. Uncertainty, A|z|, in the measured value of |z|

2. Uncertainty, AG, in the measured value of 0

3. Uncertainty, A (VSWR) , in the reading resolution of

the points on the Z-0 chart

The total relative uncertainty, A VSWR (%), in percent,

in the VSWR of the specified receiver port, is given by the

equation

AVSWR (%) = X lOo) . . loo) . . lOo) .

Uncertainties A|z| and AG are obtained from the manufacturer's

specifications on the impedance meter. Uncertainty A (VSWR) is

estimated from the readability of the plot on the Z-G chart.

335
4.12. DETECTORS

Procedures for testing the characteristics of various types

of detectors separately from the receiver as a system are not

given in this handbook because they have limited value in the

evaluation of receiver performance. Detector performance is an

integral part of overall receiver performance. Thus, the

procedures given in Sections 4.1 through 4.11 either do, or can,

include the effects of the selected detector mode on the

measured receiver parameter.

The procedures cited above are given explicitly only for

AM and/or FM detector modes. A portion of those procedures also

applies to testing done in the CW and SSB detector modes.

Specifically, these include the following:

Section 4 .1. 1. Gain-limited Sensitivity

Section 4 . 1. 2. 6 dB SN/N Sensitivity

Section 4 . 1. 3. 12 dB SINAD Sensitivity

Section 4 .3. 1. Power Gain

Section 4 .3. 2. Dynamic Range

Section 4 .3. 3. Automatic Gain Control

Section 4 .4. 8. Cross Modulation

Section 4 .4. 7. Desensi tization

To test in the CW or SSB modes, the procedure for the AM mode

is followed with the exception of the choice of detector and

BFO settings, which are selected as required by the test.

336
4.13. AUDIO SECTION

Although the audio amplifier portion of a receiver is only

one of several sections through which a signal must pass, its

characteristics are normally measured separately from other

sections. The characteristics of primary interest are gain,

frequency response, power output, linearity, distortion, hum,

and noise. Methods for measuring these parameters are discussed

separately in this section. Also included in this section are

measurement methods for noise limiter and squelch circuits.

4.13.1. AUDIO GAIN

4.13.1.1. DEFINITION

Audio gain is the ratio

an audio amplifier delivers

operating conditions to (b)

source

.

4.13.1.2. PURPOSE

The purpose of this measurement method is

gain of the audio section of surveillance rece

parameter is a measure of the receiver's abili

demodulated signal into a usable output signal

quality

.

4.13.1.3. METHOD

The method uses an audio signal generator and a distortion

analyzer as shown in figure 4.13.1. The signal generator supplies

a known input voltage at the measurement frequency, f ^ , to the

audio section of the receiver. The distortion analyzer measures

the level and distortion percentage of the audio output power.

, m decibels, of (a) the power that

to a specified load under specified

the available power of a specified

to measure the

ivers . This

ty to amplify a of acceptable

337
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338
The generator's available output power is adjusted to a level that produces either rated audio output power or an audio

output power that contains 10% distortion. The ratio of receiver

output power to generator available power in decibels, is the

audio gain of the receiver at this distortion level.

Measurement uncertainties as small as 0.5 dB are possible

under best conditions, and range from approximately 0.7 dB to

2 dB under typical conditions. The method uses commonly

available test equipment.

4.13.1.4. TEST EQUIPMENT REQUIRED

1. Audio signal generator

2. Termination resistor for receiver audio output port

3. Distortion analyzer

4.13.1.5. PROCEDURE

1. Connect the output port of the SIGNAL GENERATOR through

a cable to the receiver's AF gain control. Break the connection

between this gain control and the circuit preceding the control.

2. Connect the TERMINATION RESISTOR having a resistance equal

to the specified load resistance, R^, and a power rating in excess

of the receiver's rated audio output power level, to the audio

output port of the receiver. Connect the audio DISTORTION

ANALYZER across this resistor.

3. Set the distortion analyzer on a range to indicate the

rated output power, P^

.

4. Tune the signal generator to the measurement frequency,

f . This is normally 1000 Hz.

o

^ 339
5. Adjust the AF gain control to maximum gain setting.

6. Adjust the output level of the signal generator to

produce either rated audio output power or 10% distortion in the

termination resistor as measured with the distortion analyzer.

7. Measure the total audio output power, P , (i.e. signal

plus noise plus distortion) in the termination resistor, , with the distortion analyzer. Use the equation

E

2 P =

°

where is the voltage reading of the analyzer.

8. Determine the available power, "aP , from the generator.

Use the equation

E

1

E

2 P =

a 4 R

' g

where is the open circuit voltage and R^ is the output

impedance of the generator.

9. Calculate the gain, G, in decibels, by the equation

P

G(dB) = 10 log . a

G(dB) is the audio gain of the receiver, at the measurement

frequency, f^ , for rated audio output power or 10% distortion in

the termination resistor as measured with the distortion analyzer.

4.13.1.6. DATA REQUIRED

1. Record the measurement frequency, f ^ , in hertz or kilohertz .

2. Record the total audio output power, P^, in milliwatts

or watts

.

340
3. Record the generator available power, P , in

a mi lliwatts

.

4. Record the audio gain, G, in decibels.

4.13.1.7. MEASUREMENT ERRORS

The principal sources of measurement error are the

following

1. Uncertainty, AP , in the measured value of P o o

2. Uncertainty, AP , in the measured value of P -' a a

The total relative uncertainty, AG(dB), in decibels, in

the gain, G, is given approximately, for small uncertainties,

by the equation

Uncertainties AP and AP are obtained from the manufacturer's

o a specifications on the distortion analyzer and signal generator,

respectively

.

AG (dB) = 10

341
4.13.2. AUDIO FREQUENCY RESPONSE

4.13.2.1. DEFINITION

Audio frequency response is the gain characteristic as a function of frequency of the audio section of the receiver.

4.13.2.2. PURPOSE

The purpose of these measurement methods is to measure

the audio frequency response of surveillance receivers. This

characteristic is a measure of the spectrum of audio frequencies which the receiver will amplify with significant gain.

Four methods are discussed. The first three use audio

frequency signals, and deal with the audio section alone.

The fourth method uses a modulated RF signal, and therefore

includes the selectivity effect of the receiver pre-detection

stages. The third method uses a swept-frequency technique,

whereas the remaining methods use the point-by-point technique.

4.13.2.3. METHOD - AF POINT-BY-POINT - I

This method uses a variable frequency audio signal generator, an accurate frequency meter, and a power meter or true

rms voltmeter as shown in figure 4.13.2.1. The signal generator supplies a known input voltage at a variety of frequencies

to the audio section of the receiver. The power meter or voltmeter measures the audio output level. The generator output

level is adjusted to maintain constant output power from the

receiver. The gain of the audio section is measured at various

selected frequencies. Audio frequency response is the graphical

plot of audio gain versus measurement frequency.

342
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343
Measurement uncertainties as small as 0.5 dB are possible

under best conditions, and range from approximately 0.7 dB

to 2 dB under typical conditions. The method uses commonly

available test equipment.

4.13.2.3.1. TEST EQUIPMENT REQUIRED

1. Audio signal generator

2. Frequency meter

3. Termination resistor for receiver audio output port

4a. AF power meter

OR,

4b. A.C. voltmeter

4.13.2.3.2. PROCEDURE

1. Connect the output port of the SIGNAL GENERATOR through

a cable to the receiver's AF gain control. Break the connection

between this gain control and the circuit preceding the control.

2a. Connect the TERMINATION RESISTOR having a resistance equal

to the specified load resistance, R^, and a power rating in excess

of the receiver's rated audio output power level, to the audio

output port of the receiver. Connect the A.C. VOLTMETER across

this resistor.

OR,

2b. Connect the POWER METER, having an input impedance equal

to the specified load resistance, R^, to the audio output port

of the receiver.

344
3a. Set the voltmeter on a range to indicate the reference

ut pc

equation

output power, . The voltage to be measured is given by the

E =\/P Ro . o ^ o £

OR,

3b. Set the power meter on a range to indicate the reference

output power, P^.

4. Tune the signal generator to a frequency, f^, near

that at which the audio gain is maximum.

5. Adjust the AF gain control to maximum gain setting.

6. Adjust the output level of the signal generator to

produce reference audio output power, P^.

7. Determine the available power, P , from the generator.

a Use the equation

P = — a 4 R

g

where is the open circuit voltage and R^ is the output

impedance of the generator.

8. Calculate the gain, G(f^), in decibels, at frequency

f , by the equation m

G(fJ = 10 log ^ . a

9 . Tune the generator to a new measurement frequency above

(or below) f^. The frequency change is somewhat arbitrary and

depends upon the degree of detail with which it is desired to

know the frequency response.

345
10. Adjust the generator output level to produce reference

audio output power, P^.

11. Determine the generator available power, P , at the new

a measurement frequency.

12. Calculate the audio gain as in Step 8, above.

13. Proceed as indicated in Steps 9 and 12, above,

the desired audio frequency range is covered, or until

measured audio gain is unity (0 dB)

.

14. Plot the audio gain, G, in decibels, as a measurement frequency on rectilinear graph paper,

the audio frequency response of the receiver.

4.13.2.3.3. DATA REQUIRED

1. Record the measurement frequencies, f, in hertz or

kilohertz.

2. Record the reference audio output power, P^ , in

milliwatts or watts.

3. Record the generator available powers, P , in

a milliwatts or watts

.

4. Record the audio gain, G, in decibels.

4.13.2.3.4. MEASUREMENT ERRORS

The principal sources of measurement error are the

following:

the measured value of P^

until

the

function of

This plot is

1. Uncertainty, AP , in

346
2. Uncertainty, IP , in the measured value of P

a a

The total relative uncertainty, iG(dB), in decibels,

in the gain, G, is given approximately, for small uncertainties,

by the equation

/ IP -P \

AG (dB) = 10 log (l + +

j o a

Uncertainties IP and IP are obtained from the manufacturer's

o a specifications on the distortion analyzer and signal generator,

respectively

.

347
4.13.2.4. METHOD - AF POINT-BY-POINT - II

This method uses a variable frequency audio signal generator,

an accurate frequency meter, and a power meter or true rms voltmeter as shown in figure 4.13.2.2. The signal generator supplies

a constant known input voltage at a variety of frequencies to the

audio section of the receiver. The power meter or voltmeter measures the audio output level. The gain of the audio section is

measured at various selected frequencies. Audio frequency

response is the graphical plot of audio gain versus measurement

frequency

.

/Measurement uncertainties as small as 0.5 dB are possible

under best conditions, and range from approximately 0.7 dB to

2 dB under typical conditions. The method uses commonly available test equipment.

4.13.2.4.1. TEST EQUIPMENT REQUIRED

1. Audio signal generator

2. Frequency meter

3. Termination resistor for receiver audio output port

4a. AF power meter '

OR,

4b. A.C. voltmeter

348
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4.13.2.4.2. PROCEDURE

1. Connect the output port of the SIGNAL GENERATOR through

a cable to the receiver's AF gain control. Break the connection

between this gain control and the circuit preceding the control.

2a. Connect the TERMINATION RESISTOR having a resistance equal

to the specified load resistance, R^, and a power rating in excess

of the receiver's rated audio output power level, to the audio

output port of the receiver. Connect the A.C. VOLTMETER across

this resistor.

2b. Connect the POWER METER, having an input impedance equal

to the specified load resistance, R^ , to the audio output port

of the receiver.

3a. Set the voltmeter on a range to indicate the reference

output power, P^ . The voltage to be measured is given by the

equation

3b. Set the power meter on a range to indicate the reference

4. Tune the signal generator to a frequency, f^, near that

at which the audio gain is maximum.

5. Adjust the AF gain control to maximum gain setting.

OR,

OR,

output power, P

o

350
6. Adjust the output level of the signal generator to produce

reference audio output power, P . o

7. Determine the available power, P , from the generator.

a Use the equation

E. 2 P =

^ a 4 R

g

where E. is the open circuit voltage and R is the output

1 g

impedance of the generator.

8. Calculate the gain, G(f ), in decibels at frequency f , ^ m ^ m

by the equation

G (y = 11 log . a

9 . Tune the generator to a new measurement frequency above

(or below) f^. The frequency change is somewhat arbitrary and

depends upon the degree of detail with which it is desired to

know the frequency response

.

10. With the generator available power the same as in Step

7/ above, measure the power, P^ , delivered to the termination

resistor at the new measurement frequency

11. Calculate the audio gain by the equation

P.

G (fj = 10 log . a

12. Proceed as indicated in Steps 9 through 11, above, until

the desired audio frequency range is covered, or until the measured

audio gain is unity (0 dB)

.

351
13. Plot the audio gain, G, in decibels, as a measurement frequency on rectilinear graph paper,

the audio frequency response of the receiver.

function of

This plot is

4.13.2.4.3. DATA REQUIRED

1. Record the measurement frequencies, f, in hertz or

kilohertz.

2. Record the delivered audio output power, P^ , in

milliwatts or watts,

3. Record the generator available power, P , in milliwatts.

a

4. Record the audio gain, G, in decibels.

4.13.2.4.4. MEASUREMENT ERRORS

The principal sources of measurement area are the

following

1. Uncertainty, AP^, in the measured value of P^

2. Uncertainty, AP , in the measured value of P ^ a a

The total relative uncertainty, AG(dB), in decibels, in

the gain, G, is given approximately, for small uncertainties,

by the equation

Uncertainties AP^ and AP are obtained from the manufacturer's

d a specifications on the distortion analyzer and signal generator,

respectively

.

AG (dB) = 10 lo

352
4.13.2.5. METHOD - AF SWEPT-FREQUENCY

This method uses a swept- frequency audio signal generator

and an oscilloscope as shov/n in figure 4.13.2.3. The generator

supplies a swept frequency signal of constant amplitude to the

receiver. The oscilloscope displays the receiver's output

signal which represents the frequency response of the receiver's

audio section. Also, the generator supplies a linear sweeping

voltage for the horizontal deflection circuits of the oscilloscope. A camera is used to photograph the oscilloscope display

to obtain a permanent record of the audio frequency response

characteristic

.

This is a qualitative measurement method, and measurement

uncertainties may range from 10% to 100%, depending upon circumstances. The method uses equipment that is commercially available, but which may not be included in the average laboratory

inventory

.

4.13.2.5.1. TEST EQUIPMENT REQUIRED

1. Swept-f requency audio signal generator

2. Termination resistor for receiver audio output port

3. Linear AF detector

4. Cathode-ray oscilloscope

5. Oscilloscope camera

4.13.2.5.2. PROCEDURE

1. Connect the output port of the SV7EPT -FREQUENCY GENERATOR

through a cable to the receiver's AF gain control. Break the

connection between this gain control and the circuit preceding

the control.

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2. Connect tJie TERMINATION RESISTOR having a resistance equal

to the specified load resistance, R^, and a power rating in excess

of the receiver's rated audio output power level, to the audio

output port of the receiver.

3. Interconnect the receiver output, DETECTOR, and

OSCILLOSCOPE as shown in figure 4.13.2.3.

4. Connect the sweeping voltage output from the generator

to the horizontal input terminals of the oscilloscope.

5. Adjust the output level of the sweep generator, the

sweep width of the sweep generator, and the vertical and horizontal

gains of the oscilloscope to produce a display of the detected

receiver output signal having sufficient size to fill the square

measurement area of the oscilloscope screen. The generator output

level is adjusted to provide a convenient or selected input signal

voltage, E^ , to the audio section that is within the linear range

of the audio amplifier.

6. Having obtained a suitable display, photograph or trace

the display. This is the audio frequency response of the receiver.

7. Calibrate the vertical axis, in volts per centimeter,

with a signal from a square-wave calibration source. Record this

information on the back of the photograph.

8. Calibrate the horizontal axis, in hertz per centimeter,

with the marker generators provided in the sweep generator.

Record this information on the back of the photograph.

4.13.2.5.3. DATA REQUIRED

1. Record the generator input signal voltage, E^, in volts.

2. Record the vertical scale factor in volts per

centimeter

.

355
3. Record the horizontal scale factor in hertz per

centimeter

.

4.13.2.5.4. MEASUREMENT ERRORS

Because this is a qualitative measurement method, no error

analysis is given. However, the measurement uncertainty may be

estimated from the manufacturer's specifications on the test

equipment used.

4.13.2.6. METHOD - RF POINT-BY-POINT

This method uses an amplitude or frequency modulated signal

generator and a power meter or true rms voltmeter as shown in

figure 4.13.2.4. The signal generator supplies a known input

voltage to the receiver at the measurement frequency, modulated

with a known audio frequency signal. The voltmeter or power

meter indicates the receiver output signal level.

The audio modulation frequency is varied while maintaining

a constant modulation percentage or deviation, and the receiver

output level is measured as a function of this frequency. The

relative response of the output signal is the audio frequency

response of the overall receiver.

Measurement uncertainties as small as 0.5 dB are possible

under best conditions, and range from approximately 0.7 dB

to 2 dB under typical conditions. The method uses commonly

available test equipment.

4.13.2.6.1. TEST EQUIPMENT REQUIRED

1. Signal generator capable of amplitude or frequency

modulation

2. Audio frequency signal generator

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3. Frequency meter

4. Input impedance matching network

5. Termination resistor for receiver audio output port

6a. AF power meter

OR, *

6b. True rms voltmeter

4.13.2.6.2. PROCEDURE

1. Connect the input port of the receiver to the output port

of the SIGNAL GENERATOR through an IMPEDANCE MATCHING NETWORK

that provides the specified source impedance, Z^, to the receiver

at the measurement frequency, f ^ . If the signal generator

output impedance equals Z^, no matching network is required.

2a. Connect the TERMINATION RESISTOR having a resistance equal

to the specified load resistance, R,^ , and a power rating in excess

of the receiver's rated audio output power level, to the audio

output port of the receiver. Connect the TRUE RMS VOLTMETER

across the resistor.

OR,

2b. Connect the POWER METER, having an inout imoedance equal

to the specified load resistance, R,^ , to the audio outout port

of the receiver.

3a. Set the voltmeter on a range to indicate the reference

output power, P^. The voltage to be measured is given by the

equation

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358
OR,

3b. Set the power meter on a range to indicate the reference

output power, P^.

4. Set receiver controls as given in Table XXXXI

.

5. Tune the signal generator and the receiver to the

measurement frequency, f^.

6a. If the measurement is to be made on an AM receiver,

adjust the amplitude modulation in the signal generator to

30% at 100 0 Hz, using the external AUDIO SIGNAL GENERATOR.

OR,

6b. If the measurement is to be made on an FM receiver,

adjust the frequency modulation in the signal generator to

± 60% of rated system deviation at 1000 Hz, using the external

AUDIO SIGNAL GENERATOR.

7. Adjust the output level of the signal generator to a value within the dynamic range (cf.) of the receiver, and the

AF gain control to a value within the linear range of its audio

amplifier, to produce reference audio output power, .

8. Tune the audio signal generator to a new measurement

frequency, f, above (or below) 10 00 Hz. The frequency change is

somewhat arbitrary and depends upon the degree of detail with

which it is desired to know the frequency response.

9. Measure the power, P^ , delivered to the termination

resistor, R , at this new modulation frequency.

359
TABLE XXXXI

Audio Frequency Response

,

RF Method

Initial Control Settings

Control Setting

1. Band Switch 1. As desired

2 . Frequency Tuning 2 . As desired

3

.

Antenna Trimmer , 3. Peak

4 . RF Gain ^ 4. Maximum

5 IF Gain 5. Maximum

AF Gain 6 . As required

7

.

Line Gain 7 . Optional

8 . Detector Mode 8. AM or FM , as required

9 . Beat Frequency Oscillator 9 . OFF

10 . BFO Frequency 10 . N. A.

11

.

IF Bandwidth X -L • rT.o LI t- o X i. t; LI

12 . AF Bandwidth 12 . As desired

13 . Noise Limiter 13. OFF

14 . Squelch Level 14. OFF

15 . AGC/MGC Mode Switch 15 . AGC

16 . Meter Switch 16 . Optional

360
10. Proceed as indicated in Steps 8 and 9, above, until the

desired audio frequency range is covered, or until the measurement

results become meaningless because of insufficient signal-to-noise

ratio

.

11. Calculate the relative output level by selecting the

maximum measured delivered power, (max) , and calculating

the ratios, R(f)/ in decibels, of P^(max) to each of the other

measured levels at audio frequencies, f. Use the equation,

P^ (max)

R(f) = P^(f)

where P^(f) is the measured delivered power at frequency f.

12. Plot the power ratio, R, in decibels, as a function of

audio frequency, f, on rectilinear graph paper. This plot is the

audio frequency response of the receiver.

4.13.2.6.3. DATA REQUIRED

1. Record the measurement frequency, f^, in kilohertz or

megahertz

2. Record the value of source impedance, , in ohms,

connected to receiver input port.

3. Record the value of termination resistance, R^ , in

ohms, connected to receiver audio output terminals.

4a. Record the output voltage, E^ in volts

OR,

4b. Record the reference output power, P^, in watts

361
5. Record the open circuit signal voltage, , in

microvolts, at the output terminals of the matching network,

if used; otherwise, at the output terminals of the generator.

6. Record the audio modulation frequencies, f, in hertz

or kilohertz.

7. Record the delivered audio output power, P^, in

milliwatts or watts.

8. Record the ratio, R(f), in decibels, for each

modulation frequency, f.

The principal measurement error is the uncertainty, AP^

in the measured value of P^. The total uncertainty, AR(dB),

in decibels, in the ratio, R(f), is given approximately,

for small measurement uncertainties, by the equation

4.13.2.6 .4. MEASUREMENT ERRORS

AR (dB) = 10

d

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d

specifications on the AF power meter or rms voltmeter.

362
4 . 13. 3. AUDIO LINEARITY

4.13.3.1. DEFINITIONS

a. Linearity of a transducer is the deviation of its transfer

function from a constant value as function of one or more signal

parameters

.

b. Transfer function is a relationship between one system

variable and another that enables the second variable to be

determined from the first. (57 IRE 26. S2)

This section on audio linearity is concerned with the change

of audio gain as a function of audio signal level.

4.13.3.2. PURPOSE

The purpose of this measurement method is to measure the

linearity of the audio section of surveillance receivers.

This parameter is a measure of the receiver's ability to

amplify a demodulated signal into an output signal of

acceptable quality.

4.13.3.3. METHOD

The method uses an audio signal generator and a power meter

or true rms voltmeter as shown in figure 4.13.3. The signal

generator supplies a known input voltage at the measurement

frequency, f ^ , to the audio section of the receiver. The power

meter or voltmeter measures the audio output level.

The audio output power is measured for various levels of

input signal. A plot of output versus input power displays the

deviation of the transfer function from a constant value.

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This method does not take into account the distortion produced

by the audio amplifier as it is operated in the non-linear region

of its transfer function.

Measurement uncertainties as small as 0.5 dB are possible

under best conditions, and range from approximately 0.7 dB to

2 dB under typical conditions. The method uses commonly

available test equipment.

4.13.3.4. TEST EQUIPMENT REQUIRED

1. Audio signal generator

2. Termination resistor for receiver audio output port

3a. AF power meter

OR,

3b. True rms voltmeter

4.13.3.5. PROCEDURE

1. Connect the output port of the SIGNAL GENERATOR through

a cable to the receiver's AF gain control. Break the connection

between this gain control and the circuit preceding the control.

2a. Connect the TERMINATION RESISTOR having a resistance equal

to the specified load resistance, R^, and a power rating in excess

of the receiver's rated audio output power level, to the audio

output port of the receiver. Connect the TRUE RMS VOLTMETER

across the resistor.

365
OR,

2b. Connect the POWER METER, having an input impedance equal

to the specified load resistance, R^ , to the audio output port

of the receiver.

3. Tune the signal generator to the measurement

frequency, f^. This is normally 1000 Hz.

4. Adjust the AF gain control to maximum gain setting.

5. With the signal generator output set at zero, measure the

output power, P^ , from the receiver. This will be entirely noise.

6. Adjust the output level of the generator to produce an

audio output power, P^ , that is 100 times (20dB above) P^.

7. Measure the total audio output power, P^ , (i.e., signal

plus noise plus distortion) delivered to the termination

resistor, R„. If P., is measured with the voltmeter, use the

£ d

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where E is the voltage across R„

.

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8. Determine the available power, P , from the generator.

a Use the equation

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where E^ is the open circuit voltage and R^ is the output

impedance of the generator.

366
9. Increase the output level of the generator to produce

an audio output level that is a selected amount greater than

, Step 6. The amount selected is somewhat arbitrary, and

depends upon the degree of detail with which it is desired to

know the transfer function.

10. Measure the delivered power, P^, of Step 9, above, and

calculate the corresponding available power, P , from the

a generator.

11. Proceed as indicated in Steps 9 and 10, above, until the

desired power range is covered. Suitable stopping points are

(1) when the delivered power equals the receiver's rated audio

output power, P^, or (2) when the distortion level of the

delivered power reaches a selected value, e.g., 15%.

12. Plot the delivered power, in watts or milliwatts, against

the generator available power, in milliwatts or microwatts, on

rectilinear or log-log graph paper (not semi-log paper) . This

plot displays the linearity of the receiver's audio section. A

point of reference is the generator available power level at

which the plot falls 1 dB below a straight-line extrapolation of

the low-level portion of the curve. This input level is usually

expressed as voltage across the input terminals of the amplifier.

4.13.3.6. DATA REQUIRED

1. Record the measurement frequency, f ^ , in hertz or

kilohertz

.

2. Record the audio output powers, P^ and P^, in milliwatts

or watts

.

3. Record the generator available powers, P , in milliwatts

a or watts

.

367
4.13.3.7. MEASUREMENT ERRORS

The principal sources of measurement error are the

following:

1.^' Uncertainties, AP and AP ^ , in the measured value of

n d

P and P,

a d

2. Uncertainty, AP , in the measured value of P

a a

The relative uncertainties, AP (%), AP, (%), and AP (%) n d a in percent, in the measured values of P , P ,

, and P , respectively,

are given by the equations

AP

AP (%) = X 100 , n P n AP

AP^ (%) = -p^ X 100 , d

AP

AP (%) = X 100 . a 1: a Uncertainties AP , AP,, and AP are obtained from the manufacturer's

n d a specifications on the instruments used to measure P , AP, , and ^ n d

AP . a

368
4 . 13 . 4 . AUDIO DISTORTION

4.13.4.1. DEFINITION

Distortion is an undesired change in waveform. (IEEE

STD 100-1972)

The types of distortion that can occur in an audio amplifier

are the follov/ing:

a. Amplitude

b. Amplitude-frequency

c. Delay

d. Harmonic

e. Intermodulation

f. Phase

Types a, d, and e are normally caused by a nonlinearity in the

real part of the transfer function. Types b, c, and f are normally

caused by nonlinearity in the imaginary part of the transfer

function

.

Distortion is expressed as a percent, referenced to the level

of the audio output povrer.

4.13.4.2. PURPOSE

The purpose of this measurement method is to measure the audio

distortion of surveillance receivers caused by NONLINEARITY IN THE

369
REAL PART of the transfer function of the receiver's audio section.

The types of distortion generated are amplitude, harmonic, and

intermodulation . Distortion is a measure of the receiver's ability

to amplify a demodulated signal into an output signal of acceptable

quality

.

4.13.4.3. METHOD

The method uses an audio signal generator and a distortion

analyzer as shown in figure 4.13.4. The signal generator

supplies a known input voltage at the measurement frequency, f^,

to the audio section of the receiver. The distortion analyzer

measures the percentage distortion at rated audio output power.

Measurement uncertainties as small as 8% are possible under

best conditions, and range from approximately 10% to 50% under

typical conditions. The method uses commonly available test

equipment.

4.13.4.4. TEST EQUPMENT REQUIRED

1. Audio signal generator

2. Termination resistor for receiver audio output port

3. Distortion analyzer

4.13.4.5. PROCEDURE

1. Connect the output port of the SIGNAL GENERATOR through

a cable to the receiver's AF gain control. Break the connection

between this gain control and the circuit preceding the control.

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2. Connect the TERMINATION RESISTOR having a resistance

equal to the specified load resistance, R^ , and a power rating

in excess of the receiver's rated audio output power level, to

the audio output port of the receiver. Connect the audio

DISTORTION ANALYZER across this resistor.

3. Set the distortion analyzer on a range to indicate the

rated output power, P^.

4. Tune the signal generator to the measurement frequency,

f . This is normally 1000 Hz.

o

5. Adjust the AF gain control to maximum gain setting.

6. Adjust the output level of the signal generator to

produce reference audio output power, P^.

7. Adjust the distortion analyzer so that the 1000 Hz

rejection filter tunes out the 1000 Hz modulation from the

signal generator.

8. Measure the noise plus distortion output power, P^j^^.^^)*

9. Measure the signal voltage, E^, in millivolts, across

the AF gain control.

10. Calculate the percent distortion, D(%) , by the equation

D(%) = ^-^^ X 100 . o This is the distortion of the amplifier for a signal of amplitude

E . at frequency f .

4.13.4.6. DATA REQUI RED

1. Record the measurement

kilohertz. .

frequency, f , in hertz or

372
2. Record tJie input signal voltage, E. , in millivolts.

3. Record the total audio output power, , in milliwatts

or watts

.

in milliwatts or watts.

5. Record the percent distortion, D(%).

4.13.4.7. MEASUREMENT ERRORS

The principal sources of measurement error are the

following:

1. Uncertainty, AP , in the measured value of P o o

2. Uncertainty, AP , , in the measured value of P , , ^ n+d n+d

The total relative uncertainty, AD(%), expressed as a percent, in the percent distortion, D(%) , is given by the

equation

4 . Record the noise plus distortion output power, P n+d'

AD (%)

Uncertainties AP and

specifications on the

o AP , -, are obtained from the manufacturer's n+d

distortion analyzer.

373
4.13.5. HUM AND NOISE

4.13.5.1. DEFINITION

Hum and noise are the low-pitched composite tone at the

receiver output caused by fluctuations in the power supply.

Note: Noise is any audible undesired signal present at the

output. (IEEE Std 100-1972)

4.13.5.2. PURPOSE

The purpose of this measurement method is to measure the

maximum hum and noise power output of surveillance receivers

due to sources in the detector, audio, and power supply

circuits. Hum and noise power level is expressed as the ratio,

in decibels, below the receiver's reference audio output

power level, P^ . This method does not include hum and noise

from sources in the RF or IF circuits . The amount of hum and

noise power is a measure of the receiver's ability to produce

an output signal of acceptable quality.

4.13.5.3. METHOD

The method uses a power meter or true rms voltmeter as shown in figure 4.13.5. The receiver gain controls are

adjusted for minimum RF/IF gain and maximum AF gain, and the

total output power is measured. This is the maximum hum and

noise level of the receiver's audio amplifier.

Measurement uncertainties as small as 0.5 dB are possible

under best conditions, and range from approximately 0.7 dB

to 2 dB under typical conditions. The method uses commonly

available test equipment.

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1. Termination resistor for receiver audio output port

2a. AF power meter

OR,

2b. True RMS voltmeter

4.13.5.5. PROCEDURE

la. Connect the TERMINATION RESISTOR having a resistance

equal to the specified load resistance, R^ , and a power rating

in excess of the receiver's rated audio output power level, to

the audio output port of the receiver. Connect the TRUE RMS

VOLTMETER across this resistor.

OR, -

lb. Connect the POWER METER, having an input impedance

equal to the specified load resistance, R^ , to the audio

output port of the receiver.

2. Adjust the RF/IF gain controls for minimum gain setting.

3. Adjust the AF gain control for maximum gain setting.

4. Set detector switch in desired position. If CW or SSB

mode is selected, set BFO for desired operating conditions.

5. Measure the output power, P^, from the receiver. If

the output level is measured with the voltmeter, compute the

output power by the relation

E

2 p = n

where E is the true rms output voltage across R

o ^ ^

376
6. Calculate the ratio, R (dB) , in decibels, of the hum

n and noise power, P , to the reference audio output power, P

bv the equation

P

(dB) = 10 log ^ . o

R^ (dB) is the hum and noise power, relative to the receiver's

reference output power level, for the chosen operating conditions.

4.13.5.6. DATA REQUIRED

1. Record the reference audio output power, P^ , in milliwatts

or watts

.

2. Record the measured hum and noise power, P^, in

milliwatts or watts.

3. Record the power ratio, R^(dB) , in decibels.

4.13.5.7. MEASUREMENT ERRORS

The source of measurement error is the uncertainty,J r AP , in

n the measured value of P . The total uncertainty, AR (dB) , in

n n decibels, in the value of R^(dB), is given approximately, for

small uncertainties, by the equation

^ n ' Uncertainty AP is obtained from the manufacturer's specifications

n on the power meter or rms voltmeter.

AR (dB) = 10 n

377
4.13.6. NOISE LIMITER THRESHOLD

4.13.6.1. DEFINITION

The noise limiter threshold of a receiver is the voltage

level, in volts, at which limiting action begins.

4.13.6.2. PURPOSE

The purpose of this measurement method is to measure the

clipping threshold of a noise limiter located in the audio

section of surveillance receivers. The clipping or noise

limiter threshold is a measure of the effectiveness of the

receiver's noise limiter to suppress the interference effects

of static- and pulse- type noise.

is not suitable for testing the performance of

limiter circuits nor circuits having a floating

4.13.6.3. METHOD

The method uses a modulated signal generator and an

oscilloscope as shown in figure 4.13.6. The signal generator

supplies a test signal which is clipped by the receiver's

noise limiter and displayed on the oscilloscope. The noise

limiter threshold is determined from the calibrated

oscilloscope display.

Measurement uncertainties as small as 2% are possible under

best conditions, and range from approximately 4% to 15% under

typical conditions. The method uses commonly available test

equipment

.

This method

pre-demodulator

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4.13.6.4. TEST EQUIPMENT REQUIRED

1. Signal generator capable of amplitude or frequency

modulation

2. Input impedance matching network

3. Cathode- ray oscilloscope

4. Terminating resistor for receiver audio output port

5a. AF power meter

' OR, '

5b. True rms voltmeter

4.13.6.5. PROCEDURE

1. Connect the input port of the receiver to the output port

of the SIGNAL GENERATOR through an IMPEDANCE MATCHING NETWORK

that provides the specified source impedance, , to the receiver

at the measurement frequency, f ^ . If the signal generator output

impedance equals , no matching network is required.

2. Connect the OSCILLOSCOPE across the output of the noise

limiter circuit in the receiver.

3a. Connect the TERMINATION RESISTOR having a resistance equal

to the specified load resistance, R^ , and a power rating in excess

of the receiver's rated audio output power level, to the audio

output port of the receiver. Connect the TRUE RMS VOLTMETER across

the resistor.

380
OR,

3b. Connect the POWER METER, having an input impedance equal

to the specified load resistance, R^ , to the audio output port

of the receiver.

4a. Set the voltmeter on a range to indicate the reference

output power, . The voltage to be measured is given by the

equation

o ^ o Z OR,

4b. Set the power meter on a range to indicate the reference

output power, P^

.

5. Set receiver controls as given in Table XXXXII

.

6. Tune the signal generator and the receiver to a suitable

measurement frequency, f^.

7a. If the measurement is to be made with the receiver in an

AM detector mode (or CW, SSB) , adjust the generator for amplitude

modulation of 30% at 1000 Hz.

OR,

7b. If the measurement is to be made with the receiver in an

FM detector mode, adjust the generator for frequency modulation

of ±60% of rated system deviation at 1000 Hz.

8. With the generator output level set to zero, adjust the

RF , IF, and AF gain controls to their maximum gain settings.

9. Set the noise limiter control to the desired position.

381
TABLE XXXXII

Noise Limiter Threshold

Initial Control Settings

Control Setting

1. Band Switch 1. As desired

2. Frequency Tuning 2. As desired

3- Antenna Trimmer 3. Peak

4. RF Gain 4. Maximum

5. IF Gain 5 . Maximum

6 . AF Gain 6 . As desired

7. Line Gain 7. Optional

8. Detector Mode 8. AM, CW, or SSB

9 . Beat Frequency Oscillator 9 . OFF

10. BFO Frequency 10 . N. A.

11. IF Bandwidth 11. As desired

12. AF Bandwidth 12 . As desired

13. Noise Limiter 13 . ON

14. Squelch Level 14 . OFF

15. AGC/MGC Mode Switch 15. As desired

16 . Meter Switch 16 . Optional
10. Increase the generator output level until clipping of

the 1000 Hz demodulated signal just begins as seen on the

oscilloscope display.

11. Note the audio output power from the receiver. If it

exceeds twice the reference output power, reduce the AF gain

control to produce approximately twice reference output power.

12. Increase the generator output level by 6 dB above that

of Step 10 above. This should produce a well-defined clipped

1000 Hz waveform.

13. Determine the positive and negative amplitudes, and

, of the clipped 1000 Hz signal, using the calibrated vertical

scale of the oscilloscope. and are the positive and

negative noise limiter thresholds, respectively, of the receiver

for the limiter setting of Step 9, above.

4.13.6.6. DATA REQUIRED

1. Record the operating conditions of the receiver.

2, Record the positive clipping voltage, , in volts.

3. Record the negative clipping voltage, V , in volts.

4.13.6.7. MEASUREMENT ERRORS

The principal source of measurement error is the uncertainty,

AV, in the measured values of and V^. The uncertainty, AV (%),

in percent, in V^ and/or V^, is given by the equation

AV (%) = X 100 . p ,n

Uncertainty AV is obtained from the manufacturer's specifications

on the calibrator used to calibrate the oscilloscope vertical

scale

.

383
4.13.7. SQUELCH SENSITIVITY

4.13.7.1. DEFINITION

The audio squelch sensitivity of a receiver is the minimum

value of the standard test input signal source, which, when

modulated at standard test modulation, will open the receiver

squelch. (EIA RS-204)

4.13.7.2. PURPOSE

The purpose of this measurement method is to m.easure the

squelch sensitivity of surveillance receivers. This parameter

is a measure of receiver's ability to break squelch on a weak signal.

4.13.7.3. METHOD

The method uses an amplitude or frequency modulated signal

generator and an audio distortion analyzer as shown in figure

4.13.7. The signal generator supplies a known input voltage

to the receiver at the measurement frequency. The distortion

analyzer measures the power in the audio output from the receiver.

With the generator output level set to zero, the squelch control

is adjusted to reduce the audio noise output power to at least

40 dB below the unsquelched value. Then the generator level is

adjusted to the voltage that causes a continuous audio output

level that is no less than 10 dB below reference output power.

This voltage is the squelch sensitivity of the receiver.

Measurement uncertainties as sm.all as 5% are possible under

best conditions, and range from approximately 8% to 30% under

typical conditions. This method uses commonly available test

equipment of moderate sophistication.

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4.13.7.4. TEST EQUIPMENT REQUIRED

1. Signal generator capable of amplitude or frequency

modulation

2. Input impedance matching network

3. Termination resistor for receiver audio output port

4. Audio distortion analyzer

4.13.7.5. PROCEDURE :

1. Connect the input port of the receiver to the output port

of the SIGNAL GENERATOR through an IMPEDANCE MATCHING NETWORK

that provides the specified source impedance, , to the receiver

at the measurement frequency, f ^ . If the signal generator output

impedance equals , no matching network is required.

2. Connect the TERMINATION RESISTOR having a resistance equal

to the specified load resistance, R^ , and a power rating in excess

of the receiver's rated audio output power level, to the audio

output port of the receiver. Connect the audio DISTORTION ANALYZER

across this resistor.

3. Set the distortion analyzer on a range to indicate the

rated output power, P^.

4. Set receiver controls as given in Table XXXXIII.

5. Tune the signal generator and the receiver to the

measurement frequency, f^.

6a. If the measurement is to be made on an AM receiver,

adjust the generator for amplitude modulation of 30% at 1000

Hz,

386
TABLE XXXXIII

Squelch Sensitivity

Initial Control Settings

Control Setting

1. Band Switch 1. As desired

2. Frequency Tuning 2. As desired

3. Antenna Trimmer 3. Peak

4. RF Gain 4. Maximum

5. IF Gain 5. Maximum

6. AF Gain 6 . As required

7 . Line Gain 7. Optional

8. Detector Mode 8 . AM, FM, as desired

9 . Beat Frequency Oscillator 9 . OFF

10 . BFO Frequency 10 . N.A.

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12. AF Bandwidth 12. As desired

13 . Noise Limiter 13 . OFF

14 . Squelch Level 14 . As required

15. AGC/MGC Mode Switch 15 . As desired

16 . Meter Switch 16 . Optional

387
OR, .

6b. If the measurement is to be made on an FM RECEIVER,

adjust the generator for frequency modulation of ±60% of

rated system deviation at 1000 Hz.

7. Set the squelch control for minimum squelch.

8. Measure the 12 dB SINAD SENSITIVITY, E., as outlined

1

in Section 4.1.3. for AM receivers, or Section 4.1.5. for FM

receivers

.

9. Set the generator output level to zero.

10. Measure the audio output power,

noise only.

11. Adjust the squelch control to reduce the audio output

power to at least 0.0001 P (40 dB below P )

, or lower if the ^ o n squelch is a triggered system.

12. Increase the generator output to the first (lowest)

level that just produces a continuous audio output power level

that is no less than 10 dB below reference output power, P^.

13. Determine the open circuit signal voltage, E^ , in

microvolts, at the OUTPUT TERMINALS of the matching network,

if used; otherwise at the output terminals of the generator.

This is the SQUELCH SENSITIVITY of the receiver at frequency f^.

4.13.7.6. DATA REQUIRED

1. Record the measurement frequency, f ^ , in kilohertz or

megahertz

.

2. Record the value of source impedance, , in ohms,

connected to receiver input port.

P . This will be

n

388
3. Record tJie

ohms , connected to

value of

receiver

termination resistance,

audio output terminals

.

in

4. Record the reference output power, , in watts.

5. Record the 12 dB SINAD sensitivity, , in microvolts.

6. Record the output noise power, P^, in milliwatts.

7. Record the squelch sensitivity, , in microvolts.

4.13.7.7. MEASUREMENT ERRORS

The principal sources of measurement error are the

following

1. Uncertainty, AE , in the measured value of E

s s

2. Uncertainty, AP , in the measured value of P o o

3. Uncertainty, AP , , in the measured value of P ^ n+d n+d

The total relative uncertainty, AEg(%), in the squelch

sensitivity, E^ , expressed as a percent, is given by

the equation

The uncertainty, AE^ , is obtained from the manufacturer's

specifications on the output level indication of the signal

manufacturer's specifications on the distortion analyzer.

enerator. Uncertainties AP and AP

o n+d are obtained from the

389
4 . 14 . POWER SUPPLY SECTION

Receiver power supply parameters that are of primary interest

are the following:

a. Input power

b. Output voltage

c. Voltage regulation; line and load

d. Ripple and noise

Methods for measuring these parameters are discussed in this

section.

The measurement of power supply parameters alone may not be

meaningful in predicting overall receiver performance. Receiver

parameters that are affected by power supply parameters are best

tested by directly measuring those parameters under various

power supply conditions. The tests given above may be repeated

under conditions of low and high supply voltages to fully assess

the receiver's performance characteristics.

4.14.1. INPUT POWER

4.14.1.1. DEFINITION

Input power is the power, in watts, drawn by the receiver

through its power cable from the primary source of operating

energy. It may be a.c. or d.c, depending upon the design of

the receiver power supply circuit.

390
4.14.1.2. PURPOSE

The purpose of this measurement method is to measure the

input power drawn by surveillance receivers during normal

operation. Input power is a measure of the energy required

to operate the receiver.

4.14.1.3. METHOD

The method uses a signal generator, a true rms voltmeter,

and either (a) an a.c. wattmeter for a.c. primary source, or

(b) a voltmeter and ammeter for d.c. primary source as shown

in figure 4.14.1. The signal generator supplies an input signal

to the receiver so as to operate the receiver at maximum rated

audio output power, as indicated by the true rms voltmeter. The

wattmeter or voltmeter-ammeter pair measure the power drawn

from the primary source of energy, such as an a.c. generator

or a storage battery.

Measurement uncertainties as sm.all as 2% are possible under

best conditions, and range from 4% to 15% under typical

conditions. The method uses rudimentary and commonly available

test equipment.

4.14.1.4. TEST EQUIPMENT REQUIRED

1. Signal generator capable of amplitude modulation

2. Input impedance matching network

3. Termination resistor for receiver audio output port

4 . True rms voltmeter

5 . A.C. wattmeter

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6. D. C. voltmeter

7. D.C. ammeter

4.14.1.5. PROCEDURE

la. For a.c. power source, connect the receiver's power

cord through the A.C. WATTMETER to the primary power source.

lb. For d.c. power source, connect the receiver's hot

power cable through the D.C. AMI4ETER to the primary power

source and connect the return power cable to the remaining

power source terminal. Connect the D.C. VOLTMETER across the

output terminals of the source. Observe correct polarity.

2. Connect the input port of the receiver to the output

port of the SIGNAL GENERATOR through an IMPEDANCE MATCHING

NETWORK that provides the specified source impedance, , to

the receiver at the measurement frequency, f^. If the signal

generator output impedance equals , no transformer is

required.

3. Connect the TERMINATION RESISTOR having a resistance

equal to the specified load resistance, R,^ , and a power rating

in excess of the receiver's rated audio output power level,

to the audio output port of the receiver. Connect the TRUE RMS

VOLTMETER across the resistor.

4. Set the voltmeter on a range to indicate the rated

output power, P^. The voltage to be measured is given by the

equation

OR,

393
5. Set receiver controls as given in Table XXXXIV.

6. Tune the signal generator and the receiver to the

measurement frequency, f^

.

7. Adjust the amplitude modulation in the signal generator

to 30% at 1000 Hz.

8. With the RF , IF, and AF gain controls set to their

minimum gain settings, and the function switch set in STANDBY

position, record the wattmeter reading, Pj_g / in watts, or the

D.C. voltmeter and D.C. ammeter readings, V. and I. , in volts ^ is is

and amperes, respectively.

9. For the d.c. power source, compute the input power,

P^^ , in watts , by the equation

P. = V. I. IS IS IS

P^^ is the input power drawn by the receiver under standby

conditions

.

10. Adjust the receiver RF/IF gain controls to their maximum

gain settings.

11. With the signal generator connected and its output set

to zero, adjust the receiver AF gain control to produce 1%

rated audio output power, P^. This will be noise power only.

12. Adjust the output level of the signal generator to give

rated audio output power, P .

13. Record the wattmeter reading, P. , in watts, or the ^ im

D.C. voltmeter and D.C. ammeter readings, V. and I. , in ^ im im

volts and amperes, respectively.

394
TABLE XXXXIV

Input Power

Initial Control Settings

Control

- Setting

1. Band Switch 1. As desired

2 . Frequency Tuning 2. As desired

3. Antenna Trimmer 3. Peak

4 . RF Gain 4. As required

5. IF Gain 5. As required

6 . AF Gain 6. As required

7. Line Gain 7. Optional

8. Detector Mode 8. AM

9 . Beat Frequency Oscillator 9 . As desired

10 . BFO Frequency 10 . Optional

11. IF Bandwidth 11. Optional

12. AF Bandwidth 12. Optional

13 . Noise Limiter 13. OFF

14 . Squelch Level 14 . OFF

15 . AGC/MGC Mode Switch 15. As desired

16 . Meter Switch 16 . Optional

395
14. For the d.c. power supply, compute the input power,

P. , in watts, by the equation im' II ^

P . = V. I

.

im im im

P^^ is the input power drawn by the receiver under conditions

of rated audio output power.

4.14.1.6. DATA REQUIRED

1. Record rated audio output power, P^ , in milliwatts

or watts . J- - .

• ^

2. Record standby input power, / in watts.

3. Record standby input voltage, , in volts.

4. Record standby input current, / in amperes.

5. Record maximum input power, ^ ^.x^' watts.

6. Record maximum input voltage, V^^, in volts.

7. Record maximum input current, ^^^i in amperes.

4.14.1.7. MEASUREMENT ERRORS

The principal sources of measurement error are the

following

1. Uncertainty, AP. , in the measured input power, P. or

p.im

2. Uncertainty, AV . , in the measured input voltage, V.

or V.im

396
3. Uncertainty, AI^, m the measured input current,

or I.im

The relative uncertainty, AP^(%), in percent, in the input

power, p. , is given by the equations

AP.

AP. C%) = X 100 , i

OR

/AV \ /AI.

^^i " I "V^ j+ V

-^^^

Uncertainties AP. , AV. , and AI. are obtained from the

manufacturer's specifications on the wattmeter, D.C. voltmeter,

and D.C. ammeter, respectively.

397
4.14.2. OUTPUT VOLTAGE

4.14.2.1. DEFINITION

Output voltage is the voltage, in volts, at the output

terminals of the power supply section of the receiver.

4.14.2.2. PURPOSE

The purpose of this measurement method is to measure the

output voltages of the power supply section of surveillance

receivers. Output voltage is a measure of the ability of the

power supply to deliver the energy required by the receiver.

The receiver power supply may provide output voltages

of several different levels and current capacities. This

method is applicable to each individual voltage level.

4.14.2.3. METHOD

The method uses a D.C. voltmeter as shown in figure 4.14.2.

The voltmeter is placed across the selected output terminals

in the power supply, and the voltage indication is read.

Measurement uncertainties as small as 1% are possible under

best conditions, and range from 2% to 10% under typical

conditions. The method uses rudimentary and commonly available

test equipment.

4.14.2.4. TEST EQUIPMENT REQUIRED

1. D.C. voltmeter

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4.14.2.5. PROCEDURE

1. Adjust the receiver to the desired operating conditions.

2. Set the D.C. VOLTMETER to the highest range setting

provided. Make sure this is greater than the maximum D.C.

voltage delivered by the power supply, as stated in the

receiver's operating manual.

3. Connect the voltmeter to the selected terminals in the

power supply circuit. Observe correct polarity.

4. Measure the D.C. voltage, V, at the selected terminals.

Adjust the range setting as required to give a meter deflection

in the upper two-thirds portion of the scale.

5. Record the measured voltage. This is the output voltage

at the selected terminals of the power supply under the operating

conditions established in Step 1, above.

4.14.2.6. DATA REQUIRED

1. Record selected operating conditions of the receiver.

2. Record each measured D.C. voltage, V, in millivolts or

volts . V

4.14.2.7. MEASUREMENT ERRORS

The principal source of measurement error is the uncertainty,

AV, in the measured D.C. voltage, V. The total measurement

uncertainty, AV(%), in percent, in the measured value of voltage,

V, is given by the equation

AV (%) = ^ X 100.

Uncertainty AV is obtained from the manufacturer's specifications

on the D.C. voltmeter.

400
4.14.3. VOLTAGE REGULATION

4.14.3.1. DEFINITION

Voltage regulation is the maximum change in output voltage

as a result of a specified change in line voltage, output load,

temperature, or time.

Voltage regulation is usually expressed in percent of

output voltage level.

4.14.3.2. PURPOSE

The purpose of these measurement methods is to measure the

voltage regulation of receiver power supplies under variations

of line voltage and audio output power. Voltage regulation is

a partial measure of the potential stability and output signal

quality of the receiver.

4.14.3.3. METHOD - LINE REGULATION

The method uses a signal generator, a true rms voltmeter,

a D.C. differential voltmeter, a variable auto- trans former

with voltmeter, and a variable D.C. primary power supply with

voltmeter as shown in figure 4.14.3.1. The signal generator

supplies an input signal to the receiver so as to operate the

receiver at a selected audio output power level, as indicated

by the true rms voltmeter. The D.C. differential voltmeter

measures the receiver's power supply output voltage and the

change therein produced by changes in the primary power supply

voltage. These latter changes are produced by the variable

auto-transformer or the variable D.C. primary power source.

The primary supply line voltage is set to a standard value

and the receiver's power supply output voltage, V , is measured.

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Then the primary supply voltage is changed a prescribed amount

and the change in the receiver's power supply output voltage,

AV , is measured. The line regulation is the ratio AV /V , o ^ o o expressed as a percent.

Measurement uncertainties as small as 2% are possible under

best conditions, and range from 4% to 15% under typical

conditions. The method uses rudimentary and commonly available

test equipment.

4.14.3.3.1. TEST EQUIPMENT REQUIRED

1. Signal generator capable of amplitude or frequency

modulation

2. Input impedance matching network

3. Termination resistor for receiver audio output port

4. True rms voltmeter

5. D.C. differential voltmeter

6. Variable auto-transme ter , equipped with an

output A.C. voltmeter

7. Variable D.C. power supply, equipped with an

output D.C. voltmeter.

4.14.3.3.2. PROCEDURE

la. For A.C. power source, connect the receiver's A.C.

power cord to the output socket of the VARIABLE AUTO-TRANSFORMER

.

Connect the auto- trans former to the primary power source.

OR,

403
lb. For D.C. power source, connect the receiver's D.C.

power cord to the output terminals of the VARIABLE D.C. POWER

SUPPLY.

2. Connect the D.C. DIFFERENTIAL VOLTMETER to the selected

terminals in the receiver's power supply. Observe correct

polarity.

3. Set the differential voltmeter to a range that is higher

than the voltage to be measured, as given by the receiver's

operating manual.

4 . Connect the input port of the receiver to the output

port of the SIGNAL GENERATOR through an IMPEDANCE MATCHING

NETWORK that provides the specified source impedance, , to the

receiver at the measurement frequency, f^. If the signal generator

output impedance equals , no matching network is required.

5. Connect the TERMINATION RESISTOR having a resistance equal

to the specified load resistance, R^, and a power rating in excess

of the receiver's rated audio output power level, to the audio

output port of the receiver. Connect the TRUE RMS VOLTMETER

across the resistor.

6. Set the voltmeter on a range to indicate the rated audio

output power, P^ . The voltage to be measured is given by the

equation

E =yj P R„ . o ' o £

7. Set receiver controls as given in Table XXXXV.

404
TABLE XXXXV

Voltage Regulation

Initial Control Settings

Control Setting

1. Band Switch 1. As desired

2. Frequency Tuning 2. As desired

3. Antenna Trimmer 3. Peak

4. RF Gain 4. Maximum

5. IF Gain 5 . Maximum

6. AF Gain 6 . As required

7. Line Gain 7. Optional

8. Detector Mode 8. AM, FM, as desired

9 . Beat Frequency Oscillator 9 . OFF

10 . BFO Frequency 10 . N.A.

±± . ir Bandwiatn ±1 . Optional

12. AF Bandwidth 12 . Optional

13. Noise Limiter 13. OFF

14. Squelch Level 14. OFF

15. AGC/MGC Mode Switch 15 . AGC

16 . Meter Switch 16 . Optional

405
8. Tune the signal generator and the receiver to the

measurement frequency, f ^

.

9a. If the measurement is to be made on an AM receiver,

adjust the amplitude modulation in the signal generator to

30% at 10 0 0 Hz.

OR,

9b. If the measurement is to be made on an FM receiver,

adjust the frequency modulation in the signal generator for

±60% of rated system deviation at 1000 Hz.

10. Adjust the receiver to the desired operating conditions.

This may be (a) on standby, (b) operating with zero audio output

power, (c) operating with rated audio output power, (d) operating

at some intermediate audio output power, or (e) operating under

some special mode of operation.

11a. Adjust the auto-transformer for normal operating supply

voltage, , as specfied in the receiver's operating manual.

For example, this may be 115 volts A.C.

OR,

lib. Adjust the variable D.C. power supply for normal

operating supply voltage, , as specified in the receiver's

operating manual. For example, this may be 2 8 volts D.C.

12. Measure the output voltage, , of the receiver's

power supply as selected in Step 2, above, using the

differential voltmeter.

13. Reduce the supply voltage applied to the receiver to

the lower operating limit specified in the receiver's operating

manual. For example, on A.C. this voltage may be 105 volts; on

D.C. this voltage may be 24 volts.

406
14. Measure the change in cutout vcltage, , of the

oi

receiver's pov/er supply/ using the differential voltmeter.

15. Calculate the relative voltage change, , in percent,

by the equation

AV

o

R is the receiver's voltage regulation due to a decrease in

1 line voltage for the operating conditions selected in Step 10

,

above

.

16. Increase the supply voltage applied to the receiver

to the upper operating limit specified in the receiver's

operating manual. For example, on A.C. this voltage may be

125 volts; on D.C. this voltage may be 32 volts.

17. Measure the change in output voltage, AV , of the

o 2 receiver's power suooly, from, the value V obtained in Steo - ^ ^ o 12, above, using the differential voltmeter.

18. Calculate the relative voltage change, R , in percent,

2 by the equation

IV

R„ (%) = X 100

^ V

o

R^ is the receiver's voltage regulation due to an increase in

line voltage for the operating conditions selected in Step

10 , above

.

4.14.3.3.3. DATA REQUIRED

1. Record the selected operating conditions of the

receiver

.

407
2. Record the supply voltages, , in volts.

3. Record the receiver's power supply voltage, V^, in

volts

4. Record the changes in power supply voltage, AV^ , in

millivolts or volts.

5. Record the calculated line voltage regulation, R,

in percent.

4.14.3,3.4. MEASUREMENT ERRORS

The principal sources of measurement error are the

following : ' , ^

1. Uncertainty, AV^ , in the supply voltage,

2. Uncertainty, AV , in the measured value of V

o o

3. Uncertainty , A (AV^) , in the measured values of AV^

The total uncertainty, AR(%) , in percent, in the value

of R, is given by the equation

Uncertainties AV , AV , and A(AV ) are obtained from the

s o o manufacturer's specifications on the several voltmeters used

in this method.

AR

408
4.14.3.4. METHOD - LOAD REGULATION

The method uses a signal generator, a true rms voltmeter,

a D.C. differential voltmeter, a variable auto-transformer

with voltmeter, and a variable D.C. primary power supply with

voltmeter as shown in figure 4.14.3.2. The signal generator

supplies an input signal to tne receiver so as to operate the

receiver at a selected audio output power level, as indicated

by the true rms voltmeter. The D.C. differential voltmeter

measures the receiver's power supply output voltage, , and

the change therein, iV^ , produced by the change in the pov/er

required by the receiver. This change in power is the difference

between the power drav/n under no-signal conditions and the

power under full signal conditions. The load regulation is the

ratio LV /V , expressed as a percent,

o o ^

^

The primary supply line voltage is set to a standard value

and the receiver's pov7er supply output voltage, , is measured.

Then the load on the receiver's povrer supply is changed a prescribed amount and the change in the output voltage,

AV , is measured. The load reaulation is the ratio iV /V . o - o o

Measurement uncertainties as small as 2% are possible under

best conditions, and range from 4% to 15% under typical

conditions. The method uses rudimentary and commonly available

test equipment.

4.14.3.4.1. TEST EQUIPMENT REQUIRED

1. Signal generator capable of amplitude or frequency

modulation

2. Input impedance matching network

3. Termination resistor for receiver audio output port

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4 . True rms voltmeter

5. D.C. differential voltmeter

6. Variable auto-transmeter , equipped with an

output A.C. voltmeter

7. Variable D.C. power supply, equipped with an

output D.C. voltmeter.

4.14.3.4.2. PROCEDURE

1. Connect the receiver's power cord to either the VARIABLE

AUTO-TRANSFORMER (A.C. power cord) or the VARIABLE D.C. POWER

SUPPLY (D.C. power cord).

2. Connect the D.C. DIFFERENTIAL VOLTMETER to the selected

terminals in the receiver's power supply. Observe correct

polarity

.

3. Set the differential voltmeter to a range that is higher

than the voltage to be measured, as given by the receiver's

operating manual

.

4. Connect the input port of the receiver to the output

port of the SIGNAL GENERATOR through an IMPEDANCE MATCHING

NETWORK that provides the specified source impedance, , to the

receiver at the measurement frequency, f^. If the signal generator

output impedance equals Z^j no matching network is required.

5. Connect the TERMINATION RESISTOR having a resistance equal

to the specified load resistance, R^^ , and a power rating in excess

of the receiver's rated audio output power level, to the audio

output port of the receiver. Connect the TRUE RMS VOLTMETER across

the resistor.

411
6 . power

,

Set the voltmeter on a range to indicate the rated output

P . The voltage to be measured is given by the equation

E =v/p~r7 . o ^ o £

7. Set receiver controls as given in Table XXXXVf P* 405.

8. Tune the signal generator and the receiver to the

measurement frequency, f ^

.

9a. If the measurement is to be made on an AM receiver,

adjust the frequency modulation in the signal generator

to 30% at 1000 Hz.

OR,

9b. If the measurement is to be made on an FM receiver,

adjust the frequency modulation in the signal generator

for ±60% of rated system deviation at 1000 Hz.

10. Adjust the A.C. or D.C. supply voltage to the receiver

for normal operating supply voltage, , as specified in the

receiver's operating manual. For example, on A.C. this may be

115 volts; on D.C. this may be 28 volts.

11. Put the receiver in operating condition, but set the

RF , IF, and AF gain controls to their minimum gain settings.

12. Measure the output voltage, , of the receiver's

power supply, using the differential voltmeter.

13. Adjust the receiver RF/IF gain controls to their maximum

gain settings

.

412
14. With the signal generator connected and its output set

to zero, adjust the receiver AF gain control to produce 1%

rated audio output power, . This will be noise power only.

15. Adjust the output level of the signal generator to give

rated audio output power, .

16. Measure the change in output voltage, AV^ , of the

receiver's power supply, using the differential voltmeter.

17. Calculate the relative voltage change, r(%) , in percent, by the equation

AV

R(%) = X 100 . o

is the receiver's voltage regulation due to a change in

power supply load from minimum to maximum load, for the

operating condition selected in Step 11, above.

4.14.3.4.3. DATA REQUIRED

1. Record the selected operating conditions of the

receiver

.

2. Record the supply voltages, , in volts.

3. Record the receiver's power supply voltage, , in

volts

.

4. Record the changes in power supply voltage, AV^, in

millivolts or volts.

5. Record the calculated load voltage regulation, R,

in percent.

413
4.14.3.4.4. MEASUREMENT ERRORS

The principal sources of measurement errors are the

following

1. Uncertainty/ -^^g / supply voltage,

2. Uncertainty, AV , in the measured value of V

o o

3. Uncertainty, A (AV ), in the measured values of AV

o o

The total uncertainty, AR(%), in percent, in the value

of R, is given by the equation

Uncertainties AV , AV , and A (AV ) are obtained from the

s o o manufacturer's specifications on the several voltmeters used

in this method.

AR (%)

414
4 . 14 . 4 . RIPPLE AND NOISE

4.14.4.1. DEFINITION

Power supply ripple and noise is the total rms A.C. voltage

that appears superimposed upon the D.C. output voltage.

4.14.4.2. PURPOSE

The purpose of this measurement method is to measure the

ripple and noise voltage of receiver povrer supplies. Ripple

and noise voltages are a potential source of hum and noise

interference in the receiver, and can reduce the quality of

the audio output povrer.

4.14.4.3. METHOD

The m.ethod uses a true rm.s voltm.eter and a cathode-ray

oscilloscope as shovrn in figure 4.14.4. The voltm.eter is placed

across the selected output terminals in the receiver povrer

supply, and the ripple and noise voltage is read. The

oscilloscope displays the A.C. voltage waveform to reveal the

presence of deleterious voltage spikes or oscillations.

Measurement uncertainties as sm.all as 1% are possible under

best conditions, and range from 2% to 10% under typical

conditions . The method uses rudim.entary and commonly available

test equipment.

4.14.4.4. TEST EQUIPMENT REQUIRED

1. True rms voltmeter

2. Cathode-ray oscilloscope

415
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416
4.14.4.5. PROCEDURE

1. Adjust the receiver to the desired operating conditions.

2. Set the TRUE RMS VOLTMETER to the highest range setting

provided. Make sure this is greater than the maximum D.C. voltage

delivered by the power supply, as stated in the receiver's

operating manual

.

3. Connect the voltmeter and the OSCILLOSCOPE, in parallel,

to the selected terminals in the power supply circuit.

4. Measure the A.C. voltage, , at the selected terminals.

Adjust the range setting as required to give a meter deflection

in the upper two-thirds portion of the scale.

5. Record the measured voltage, . This is the rms value

of the ripple and noise voltage at the selected terminals of

the power supply under the operating conditions established in

Step 1, above.

6. The oscilloscope display provides information about

the ripple and noise waveform. It can yield the peak value

of voltage excursions and the nature of the ripple and noise.

4.14.4.6. DATA REQUIRED

1. Record the operating conditions of the receiver.

2. Record the ripple and noise voltage, V^, in millivolts

or volts

.

417
4.14.4.7. MEASUREMENT ERRORS

The principal source of measurement error is the uncertainty,

AV^ , in the measured value of V^. The total uncertainty, AV^(%),

in percent, in the value of , is given by the equation

^

'• AV

AV^ (%) = X 100 . r

Uncertainty AV^ is obtained from the manufacturer's specifications

on the rras voltmeter.

NOTE: If the frequency range of the rms voltmeter

extends to zero frequency (D.C.) , connect a D.C. blocking capacitor in series with the

voltmeter's ungrounded terminal when meas-

; uring V .

418
5.0. TEST EQUIPMENT

5.1. GENERAL REQUIREMENTS

Test equipment of the types required to perform the

measurements described in this handbook must measure a variety

of quantities over the frequency range of D.C. to ] 00 MHz or

higher. Such equipment has become fairly well standardized,

and a wide range of types and quality is available.

Because the quality of a measurement depends ultimately

upon the quality of the test apparatus, the highest quality

instruments, commensurate with the desired results, should

be chosen. Give close attention to such matters as shielding,

filtering, mechanical stability, electrical stability, control

smoothness, display readability, and operating convenience.

Most test methods require interconnecting several pieces of

apparatus, and their compatibility and operating ease in a complex measurement system can be an important factor.

5.2. SPECIAL REQUIREMENTS

A listing of all the technical specifications of the

relevant test equipment, including the routine as well as

the unique requirements, is beyond the scope of this

handbook. Most requirements are well known by knowledgeable

technicians. This section will cover only those special

requirements that are critical to the procedures included in

Section 4.0.

419
5.2.1. RF SIGNAL GENERATORS

5.2.1.1. HARMONIC AND SPURIOUS OUTPUT

Harmonic and spurious output should be at least 30 dB

below the desired signal. Certain tests, such as spurious

response and intermodulation , require better than this.

External filters may be used to obtain the necessary signal

purity

.

5.2.1.2. LEAKAGE

Low leakage is essential. The generator must have adequate

shielding and filtering. Safe leakage levels vary from one test

to another, and cannot be specified. However, each test set-up

can and should be checked for leakage by observing the receiver

response (a) to the generated signal with the output control

set to zero, and (b) to changes in the test configuration. If

evidence of leakage is found, provide additional shielding

(e.g., a shielded box) and filtering (e.g., in the power line an

interconnecting cables).

5.2.2. VOLTMETERS

5.2.2.1. TRUE RMS VOLTMETERS

True rms voltmeters are required to measure the rms value

of random noise signals and signals comprised of a mixture of

random and non-random signals. Conventional voltmeters, which

contain an envelope detector, averaging circuits, and whose

output is displayed as an equivalent rms value, give inaccurate

measurements of random and semi-random signals. Conventional

voltmeters may be used to indicate a reference level of

random signals, or of semi-random signals when the mix does

not vary, but a true rms meter should be used to MEASURE such

levels

.

420
5.2.2.2. D.C. DIFFERENTIAL VOLTMETERS

Power supply regulation can best be measured with a differential voltmeter because of its superior resolution.

If a differential voltmeter is unavailable, one can be

simulated with a stable, variable D.C. voltage source in

series with a sensitive, low-range voltmeter.

5.2.3. IMPEDANCE METERS

Conventional RF impedance bridges often give erroneous

results when measuring the impedance of an active network.

The cause of this is the large signal voltage across the network

that is required to obtain adequate bridge detector sensitivity

at null. The large voltage may alter the operating point of the

active device in the network, and the impedance may then become

a function of the bridge voltage. The solution is to decrease

the voltage needed across the active network terminals.

The vector impedance meter technique maintains good

sensitivity even with small signal levels. It has been found

suitable for many applications where an impedance bridge gives

variable results.

5.2.4. IMPEDANCE MATCHING NETWORKS

An impedance matching network may consist of (a) an impedance

transformer, or (b) a resistive matching network. A transformer

has a low insertion loss, but tends to be narrow band. A resistive

matching network is generally broad band, and for many measurements

its higher insertion loss is of no consequence.

The electrical characteristics of any matching network must

be known so that the measurement results can be corrected for its

effects in the test set-up.

421
5.2.5. ISOLATION NETWORKS

An isolation network may be required between a frequency meter

and the point of measurement to prevent the input impedance of

the frequency meter from affecting the other parts of the measurement

system. Suitable networks include the following:

. a. Attenuator network

b. Directional coupler

c. High-impedance probe

d. Signal splitter

The network is chosen on the basis of frequency, circuit impedance,

and signal level.

5.2.6. COMBINING NETWORKS

Combining networks are required when two or more signal

generators are connected into a common circuit. A variety

of means can be used to combine sources. These include the

following:

Resistive summing networks

Hybrid multi-port networks

Directional couplers

Signal splitters (in reverse)

Attenuator networks

Multi-tap transformers

b.

c

.

d.

e

.

The particular choice of combining network is selected on the

basis of frequency, circuit impedance, signal level, and

number of signal sources to be combined.

422
5.2.7. INSERTION NETWORKS

An insertion network is used to inject a test signal into,

or extract a signal from, a receiver via a power, audio, or

interconnecting cable. It must provide a known coupling ratio

between input and output terminals, and must not adversely

disturb the circuit into which it connects. Suitable networks

include the following:

a. Transformer

b. R-C coupling network

c. L-C coupling network

The particular choice and design of insertion network is

selected on the basis of frequency, circuit impedance, signal

level, load current, and cable configuration. The electrical

characteristics of the network can be determined by

measurement using standard procedures.

5.2.8. LINE IMPEDANCE NETWORKS

A line impedance network is used to extract a signal from

a receiver via the power cable for conducted interference measurements. A suitable network for use from 300 kHz to 25 MHz has

been described by the IEEE (56 IRE 27. SI) , and its schematic is

shown in figure 5.2.8. The installation and use of this network

is described in the standard cited above.

For frequencies below 300 kHz and above 25 MHz, a similar

network with suitable component values may be designed.

423
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424
5.3. INVENTORY REQUIREMENTS

A complete list of the major equipment required to

perform these test procedures is given in Table XXXXVI

.

Minor items, such as cables, connectors, test leads, probes,

etc., are not listed because a qualified technician will

know what is required.

5.3.1. EQUIPMENT IN USASATEC INVENTORY

Of the required equipment, those items that are listed in

the USASATEC Electronic Equipment Catalog (dated March 1970;

updated through August 1, 1972) are identified in Table XXXXVI

by "Yes." These items are believed to be suitable for these

test procedures, based upon the descriptions given in the

catalog

.

5.3.2. EQUIPMENT NOT IN USASATEC INVENTORY

Major equipment not listed in the USASATEC catalog are

identified in Table XXXXVI by "No." Items marked with an

asterisk (*) are not listed in the catalog, but can be

readily obtained either by purchase or by building them in

the electronics shop. Items marked with a double asterisk

(**) are not available in the USASATEC inventory in models

sufficient to cover the complete frequency range or level

range required by these procedures. All of this equipment

is discussed below.

5.3.2.1. DETECTOR, AF

The af detector is used to rectify the audiofrequency

signal from the receiver before presentation to the oscilloscope in the swept-f requency method of testing for audiofrequency response. A standard detector circuit is suitable

here, e.g., a half-wave rectifier using a semiconductor

diode and having an input frequency range of approximately

10 to 10,000 Hz.

425
TABLE XXXXVI

Test Equipment Requirements

Type of Equipment Listed in ASA Catalog

1. Analyzer

,

distortion, AF Yes

2. Antennas Yes

3. Attenuator , fixed, 3, 30, 54, and 60 dB Yes

4. Attenuator , variable, AF Yes

5. Attenuator , variable, IF Yes

6. Attenuator , variable, RF Yes

7. Autotransformer , variable, 60 Hz power Yes

8. Bridge, RF impedance Yes

9 . Camera, oscilloscope Yes

10 . Detector

,

AF * 11. Detector

,

IF, envelope, 2 ea. matched *

12 . Detector

,

IF, FM, 2 ea. matched *

13. Detector

,

null, RF Yes

14. Filter, variable band pass, AF Yes

15. Filter, power line * 16 . Generator

,

audiofrequency Yes

17. Generator

,

noise, hot/cold * * 18. Generator

,

noise, temperature-limited diode No

19. Generator

,

signal, RF, AM Yes

20 . Generator

,

signal, RF, CW Yes

21. Generator

,

signal, RF , FM ** 22. Generator

,

swept-frequency , AF No

23 . Generator

,

swept-frequency , RF * * 24. Indicator

,

signal level Yes

25. Meter, AC voltmeter Yes

26 . Meter , AC wattmeter Yes

27. Meter, AF power Yes

28 . Meter, automatic noise figure **

426
Table XXXXVI (contd.)

Type of Equipment Listed in ASA Catalog

29. Meter, DC ammeter Yes

30. Meter, DC differential voltmeter Yes

31. Meter, DC voltmeter Yes

32. Meter, field intensity Yes

33. Meter, frequency counter Yes

34. Meter, IF power **

35. Meter, RF voltmeter Yes

36. Meter, selective RF voltmeter No

37. Meter, true RMS Yes

38. Meter, vector impedance No

39. Network, combining, AF , 3-port * 40. Network, combining, RF , 3-port **

41. Network, combining, RF , 4-port * 42. Network, impedance matching, RF **

43. Network, line impedance * 44. Network, insertion * 45. Network, isolation * 46. Oscilloscope, DC Yes

47. Oscilloscope, dual channel Yes

48. Oscilloscope, wide band Yes

49. Power supply, variable DC Yes

50. Printer, digital No

51. Switch, coaxial * 52. Termination, resistive, AF load *

53. Termination, resistive, RF input, shielded *

427
5.3.2.2. DETECTOR, IF, ENVELOPE

The test procedure for time delay for an AM receiver

requires two matched envelope detectors which operate at

the receiver's intermediate frequency. These detectors may

be constructed using standard AM detector circuits with

components matched to within approximately 5% or less.

5.3.2.3. DETECTOR, IF, FM

The test procedure for time delay for an FM receiver

requires two matched FM detectors which operate at the

receiver's intermediate frequency. These detectors may

be constructed using standard FM detector circuits with

components matched to within approximately 5% or less.

5.3.2.4. FILTER, POWER LINE

This filter may be one of many standard radio frequency

interference filters designed for this purpose. It should

provide at least 40 dB attenuation to rf signals from 10 kHz

to 100 MHz, and have a voltage and current rating suitable

for the receiver under test.

5.3.2.5. GENERATOR, NOISE, HOT/COLD

Fixed- temperature random noise generators, suitable for

these test procedures, are not available at USASATEC for use

below 10 MHz. A suitable generator for this range would

have the following specifications

a. Frequency range: 0 Hz to above 10 0 MHz

b. Hot noise temperature: 373 K ± 1 K

c. Cold noise temperature: 77 K ± 1 K

428
5.3.2.6. GENERATOR, NOISE, TEMPERATURE-LIMITED DIODE

Commercial temperature-limited diode noise generators,

suitable for these test procedures, are available with the

following brief specifications:

a. Frequency range: 100 kHz to 500 MHz

b. Noise temperature range: 300 K to 12,000 K

c. Source Impedance: 5 0 ohms

d. . VSWR: <1.05

e. Accuracy: Approximately 3% or better

5.3.2.7. GENERATOR, SIGNAL, RF , FM

The USASATEC catalog does not list any FM signal

generators with frequency coverage below approximately

20 MHz. The specifications required to perform these test

procedures are generally the same as for FM signal generators

on hand, but with coverage extending to the lowest radio

frequency of interest.

5.3.2.8. GENERATOR , SWEPT-FREQUENCY AF

A swept-frequency signal generator for testing audiofrequency response by the swept-frequency method will have

the following brief specifications

a. Frequency range: 20 Hz to 20 kHz

b. Sweep width: 0 to 20 kHz

c. Output voltage: 1 volt rms into 50 ohms

d. Horizontal output: 5 volts, peak-to-peak, sawtooth

Such a generator is available from commercial suppliers.

429
5.3.2.9. GENERATOR, SWEPT-FREQUENCY , RF

The USASATEC catalog does not list any rf sweptfrequency generators with frequency coverage below approximately 700 kHz. The specifications required to perforin

these test procedures are generally the same as for rf

swept-frequency generators on hand, but with coverage

extending to the lowest radio frequency of interest.

5.3.2.10. METER, AUTOMATIC NOISE FIGURE

The USASATEC catalog does not list any automatic

noise figure meters with frequency coverage below 10 MHz.

This is the lowest frequency available with commercial

meters; therefore, no procurement recommendations are

made at this time

.

5.3.2.11. METER, IF POWER

The USASATEC catalog does not list any IF power meters

for measuring power levels below 10 mw full scale. Commercial power meters are available with adequate sensitivities

for use over most of the frequency range required by these

test procedures

.

5.3.2.12. METER, SELECTIVE RF VOLTMETER

A selective rf voltmeter for measuring conducted

emission may consist of a stable radio receiver having

an accurate signal level meter calibrated in microvolts.

Suitable available instruments include field intensity

meters, and selective voltmeters designed for this purpose. Communications receivers are often not suitable

for this purpose because of an inaccurate metering system.

430
5.3.2.13. METER, VECTOR IMPEDANCE

Commercial vector impedance meters, suitable for these

test procedures, are available with the following brief

specifications :

a. Frequency range: 5 Hz to 100 MHz

b. Impedance range: 1 ohm to 10 0 K ohms

c. Phase angle range: 0 to ±90 degrees

d. Accuracy: Impedance: ±5% or better

Phase angle: ±6 degrees or better

5.3.2.14. NETWORK, COMBINING

Commercial 3-port and 4-port combining networks are

available that cover much of the frequency range used in

these test procedures. When commercial networks are

unavailable, suitable networks can normally be assembled

in the electronics shop using standard circuits. See

Section 5.2.6. for a list of suitable networks.

5.3.2.15. NETWORK, IMPEDANCE MATCHING, RF

Commercial impedance matching networks are available

for standard line impedances. Non-standard impedances

can be matched by building-out the required impedance with

resistive networks.

5.3.2.16. NETWORK, LINE IMPEDANCE

A suitable line impedance network is described in

Section 5.2.8.

431
5.3.2.17. NETWORK, INSERTION AND ISOLATION

Insertion and isolation networks are discussed in

Sections 5.2.7. and 5.2.5., respectively.

5.3.2.18. PRINTER, DIGITAL

< Commercial digital printers are available for printing

the readout from the digital frequency counter used in

these procedures.

5.3.2.19. SWITCH, COAXIAL

Commercial coaxial switches are available that are

suitable for use in these test procedures.

5.3.2.20. TERMINATION, RESISTIVE, AF LOAD

The af output port termination resistor may be any noninductive resistor having the specified resistance and the

power rating, or greater, required by the receiver.

5.3.2.21. TERMINATION, RESISTIVE, RF INPUT

The rf input port termination resistor may be any

low-noise, non-inductive, shielded resistor having the

specified resistance and a VSWR of 1.0 5 or less at the

measurement frequency. It shall be fitted with a connector

that mates with the receiver's input connector.

432
5.4. CALIBRATION REQUIREMENTS

5.4.1. CALIBRATION SCHEDULE

Test equipment must be calibrated periodically to insure

that the expected performance is actually obtained. A regular

calibration schedule should be established for each instrument,

and followed faithfully. The schedule is based on the type of

equipment and the amount of use it gets. Typically, intervals

between calibrations range from 30 days to two years. No specific

schedules can be given that apply to all laboratories, but

schedules for equipment in a given laboratory can be based

upon the following considerations:

a. Recalibrate as recommended by the manufacturer of the

instrument

.

b. Analyze the calibration history of an instrument to

determine if and how much it was out of calibration when

recalibrated. Base the new schedule on the results of this

historical study.

An instrument may be recalibrated at times other than the

scheduled periodic calibration for the following reasons:

a. Obviously faulty performance.

b. Recal ibration following repairs, readjustments, or

replacement of parts

.

c. Recalibration prior to a critical measurement.

d. Recalibration following return from being loaned to

another group.

433
5.4.2. CALIBRATION INFORMATION

To be useful, the calibration report must contain the

following minimum information:

{. a. The VALUE of the quantity being measured (voltage,

frequency, attenuation, dial correction, scale factor, etc.)

expressed in units consistent with the readings on the

instrument.

b. The calibration UNCERTAINTY in the value of the quan

tity being measured. This includes both the systematic

uncertainty and the random uncertainty, stated separately,

and expressed either in the units of the quantity being

measured, in percent, or in decibels.

c. The test conditions prevailing during the measurement .

With this information, the absolute accuracy of the

instrument is known, and its behavior can be intelligently

evaluated over a period of time.

434
6.0. RECOMMENDATIONS

6.1. VERIFICATION OF PROCEDURES

Procedures listed in Table II with status symbols "U" or "P"

have not been fully tried and tested in all particulars sufficient

to verify that they are suitable and without fault for the

intended purpose. Steps should be taken to evaluate them; to

demonstrate their worth and/or shortcomings.

6.2. PARAMETERS NOT COVERED

The procedures contained in Section 4.0. cover a majority of

the receiver parameters that are most commonly measured. However,

procedures have not been worked out for other parameters that

may be significant in certain applications. Such procedures should

be developed as necessary. These parameters include the following:

a. Incidental FM

b. Phase distortion, both RF and AF

c. Reciprocal mixing

d. Response to internally generated spurious signals

("birdies")

e. Sweep- tuning linearity

f. AFC capture bandwidth

g. Noise limiter efficiency

h. Detector linearity

i. Detector efficiency

j. Diversity transfer sensitivity

k. Overload protection threshold

1. Power supply transient recovery

m. Tuning backlash, mechanical and/or electrical

435
6.3. IMPROVED PROCEDURES

Certain of the procedures listed in Table II are either

completely inadequate for the intended purpose (e.g., 4.5.3.,

4.5.4., and 4.6.2.) or can be improved upon by applying newly

developed principles or techniques. These improvements will

require R&D effort on the part of qualified metrologists , and

should be carried out according to the need. Parameters for

which present procedures are inadequate or which warrant

improvement include the following:

a

.

Radiated interference susceptibility

b. Radiated emission

c

.

Dynamic range

d. Spurious response attenuation

e

.

Cross modulation

f Intermodulation distortion

g- Impulse bandwidth

h. Conducted interference susceptibility

i

.

Time delay

j • Selectance

Radiated susceptibility and emission measurements are hamstrung

by the lack of effective techniques for measuring in the near field

and in shielded enclosures. New probes and radically new enclosure

designs are needed by many agencies for a wide variety of purposes.

Measurement techniques for parameters involving receiver

nonlinearities (cross modulation, intermodulation, etc.) give

marginal results because of nonlinearities and distortion products

in the test equipment itself. Alternate techniques might be

possible; for example, the noise power ratio (NPR) technique shows

promise for measuring intermodulation distortion

.

436
Measurements requiring large amounts of time, such as

searching for intermodulation products or spurious responses,

or which require large amounts of data, such as selectance or

AGC leveling effect, can benefit from elementary automation

techniques

.

The measurement of receiver impulse response, and related

parameters such as impulse bandwidth and phase distortion, are

hampered by inadequate definitions and standards for pulse

quantities . A time-domain description of receiver behavior may

have some advantages over the traditional frequency-domain

description

.

Finally, conducted susceptibility and emission measurements

are often meaningless because of line impedance variations and

uncertainties . Improved insertion and line impedance network

designs are needed, or alternate techniques must be developed.

437
BIBLIOGRAPHY

Barghausen, A. F. , et al., "Equipment Characteristics

and Their Relation to System Performance for Tropospheric

Communication Circuits," NBS Tech. Note 103, January 1963.

Crow, E. L. , Davis, F. A., and Maxfield, M. W. , Statistics

Manual, Dover Publications, New York, 1960.

Florman, E. F., and Tary, J. J., "Required Signal-To-Noise

Ratios, RF Signal Power, and Bandwidth For Multichannel

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1962 .

Henney, K. , Radio Engineering Handbook, Fifth Edition,

McGraw-Hill, New York 19 59.

Landee, R. W. , Davis, D. C, and Albrecht, A. P., Electronic

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439
NBS-114A (REV. 7-73)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBSIR 73-3332. Gov't Accession

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

xcoL r c u u. 1 c o ri.ciiiu. uu UK lo r ou.r v ciiiaric. c x\t:Ccivcxb

Below 100 MHz

5. Publication Date Octobe r 1973

6. Performing Organization Code

7. AUTHOR(S)

M. G. Arthur

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS , Boulder Labs.

DEPARTMENT OF COMMERCE

Boulder, CO 80302

10. Project/Task/Work Unit No. 2729103

11. Contract/Grant No. MIPR Number

ASA 101-72

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

U. S. Array Security Agency

-u- " Fort Huachuca, Arizona

13. Type of Report & Period Covered

Final

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most signiticant information. If document includes a significant

bibliography or literature survey, mention it here.)

This handbook contains test raethods and procedures for radio receivers of

advanced design that operate in the frequency range belovi^ 100 MHz. Sixty- one methods are given for testing forty receiver characteristics such as

sensitivity, selectivity, gain, interference susceptibility, audio charac ter is tic s

,

power supply characteristics, and others. Each receiver characteristic is

defined. For each method, the following information is given: (a) test

equipment required, (b) step by step procedure, (c) data required, and

(d) measurement error computation. The handbook also includes a general

discussion of standard test conditions, suitable test equipment, and measurement errors.

17. KEY WORDS fsix to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons)

Electronic measurements; electronic test equipment; measurement errors;

radio receivers; receiver characteristics; receiver testing.

18. AVAILABILITY Unlimited

1 X ' For Official Distribution. Do Not Release to NTIS

1

' Order From Sup. of Doc, U.S. Government Printing Office Washington. D.C. 20402. SD Cat. No. CU

1 ! Order From National Technical Information Service (NTIS)

Springfield, Virginia 22151

19. SECURITY CLASS

(THIS REPORT)

UNCLASSIFIED

21. NO. OF PAGES

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

22. Price

USCOMM-DC 29042-P74

U.S. GOVERNMENT PRINTING OFFICE: 1 974 _ 784-576 / 1262 REGION NO.