U.S. DEPARTMENT OF COMMERCE • National Telecommunications and Information Administration

report series

NTIA Report TR-12-486 

Case Study: Investigation of Interference 

into 5 GHz Weather Radars from 

Unlicensed National Information 

Infrastructure Devices, Part III

John E. Carroll

Geoffrey A. Sanders

Frank H. Sanders

Robert L. Sole

U.S. DEPARTMENT OF COMMERCE

June 2012 

NTIA Report TR-12-486 

Case Study: Investigation of Interference 

into 5 GHz Weather Radars from 

Unlicensed National Information 

Infrastructure Devices, Part III

John E. Carroll

Geoffrey A. Sanders

Frank H. Sanders

Robert L. Sole

iii

DISCLAIMER 

This report identifies certain commercial equipment and materials to specify adequately the 

technical aspects of the reported results. In no case does such identification imply 

recommendation or endorsement by the National Telecommunications and Information 

Administration (NTIA), nor does it imply that the material or equipment identified is the best 

available for this purpose. 

NTIA acquired the interference data presented in this report from a legacy FAA Terminal 

Doppler Weather Radar (TDWR) receiver called the Sigmet RVP8. This is the receiver used at 

TDWR field stations as of the release of this report. A newer receiver, the Sigmet RVP9, is being 

developed by the FAA. NTIA plans an additional joint interference study with the FAA on this 

new receiver. 

This report does not propose any interference thresholds for TDWR receiver protection; the FAA 

is responsible for determining interference criteria for its systems. Interference levels that are 

analyzed in this report are presented solely for the purpose of demonstrating the interference 

analysis process. 
iv
v

CONTENTS 

Figures............................................................................................................................................ vi

Tables ............................................................................................................................................ vii

Abbreviations ............................................................................................................................... viii

Executive Summary ....................................................................................................................... ix

1 Introduction ...................................................................................................................................1

2 Dynamic Frequency Selection Overview .....................................................................................4

3 Development of New FCC DFS Certification Waveforms ..........................................................5

4 Measurement and Analysis of U-NII Device Emission Spectra ...................................................6

4.1 Measurement Technique .......................................................................................................6

4.2 Measurement Results ............................................................................................................7

5 EMC Analysis for Interference Coupling from U-NII Devices to TDWRS ..............................10

5.1 Calculation of Mainbeam Coupling Distances and Coupling Factors between 

U-NII Devices and TDWRS ................................................................................................10

5.2 Calculation of Coupling Factors into TDWR Antenna Sidelobes When U-NII 

Devices Are Deployed at Lower Heights ............................................................................12

5.3 Description and Analysis of the TDWR Emission Spectrum .............................................13

5.4 EMC Coupling Analyses .....................................................................................................15

5.4.1 Mainbeam-to-Mainbeam Coupling ...........................................................................15

5.4.2 U-NII Mainbeam-to-TDWR Sidelobe Coupling ......................................................17

6 Results and Conclusions from the EMC Analysis ......................................................................19

7 References ...................................................................................................................................21

Appendix A . Calculated Frequency-Dependent Rejection (FDR) Curves and 

Coordination Distances between TDWR Receivers and U-NII Transmitters ...............................22

A.1 Calculation of Frequency-Distance Separation Curves to Protect TDWR Receiver .........22

A.2 Calculation of Frequency Dependent Rejection (FDR) .....................................................23

A.2.1 Frequency-Distance Curves for Frame-Based U-NII Systems ................................26

A.2.2 Frequency-Distance Curves for 802.11-Based U-NII Systems ...............................28
vi 

FIGURES 

Figure 1. RSMS preselector block diagram. ....................................................................................6

Figure 2. Comparative radiated emission spectra for ten different 5 GHz U-NII 

transmitters, in a 1 MHz measurement bandwidth, referenced to peak 

fundamental power (dBc). ................................................................................................8

Figure 3. The central 200 MHz (100 MHz on each side of the fundamental 

frequency) of the U-NII emission spectra of Figure 1. ....................................................9

Figure 4. Mainbeam coupling geometry scenario for a TDWR and a U-NII. ...............................11

Figure 5. Power received from the TDWR at a U-NII location in Oklahoma City, 

OK throughout one complete monitor (or normal volume) scan. ..................................12

Figure 6. TDWR radiated emission spectrum in a 1 MHz bandwidth...........................................13

Figure 7. TDWR emission spectrum within 40 MHz of the fundamental 

frequency. .......................................................................................................................14

Figure A-1. TDWR measured IF frequency selectivity. ................................................................24

Figure A-2. TDWR IF response (normalized). ..............................................................................24

Figure A-3. FDR for TDWR IF selectivity for frame-based U-NII transmitters. ..........................25

Figure A-4. FDR for TDWR IF selectivity for 802.11-based U-NII transmitters. ........................25

Figure A-5. Distances needed to protect TDWR from frame-based U-NII 

transmitters (H = 304 meters, TDWR mainbeam coupling). .........................................26

Figure A-6. Distances needed to protect TDWR from frame-based U-NII 

transmitters (H = 152 meters, TDWR mainbeam coupling). .........................................27

Figure A-7. Distances needed to protect TDWR from frame-based U-NII 

transmitters (H = 30 meters, TDWR sidelobe coupling). ..............................................27

Figure A-8. Distances needed to protect TDWR receivers from 802.11-based 

U-NII transmitters (H = 304 meters, main-beam coupling). ..........................................28

Figure A-9. Distances needed to protect TDWR from 802.11-based U-NII 

transmitters (H = 152 meters, main-beam coupling). .....................................................29

Figure A-10. Distances needed to protect TDWR from 802.11-based U-NII 

transmitters (H = 30 meters, sidelobe coupling). ...........................................................29
vii 

TABLES 

Table 1. Newly developed Bin 1 Waveform certification test protocol for DFS 

certification. ......................................................................................................................5

Table 2. Parameters for mainbeam-to-mainbeam U-NII-to-TDWR EMC analysis. .....................15

Table 3. System parameters for U-NII mainbeam-to-TDWR sidelobe example 

EMC analysis. ................................................................................................................17

Table 4. Limits on U-NII EIRP on a TDWR frequency required to preclude 

interference to TDWR receivers at given separation distance. ......................................19

Table 5. Requirements for U-NII unwanted spectrum emission suppression at 

given separation distances from TDWRs for some example U-NII 

device EIRP levels. ........................................................................................................20

Table A-1. ITM Settings. ...............................................................................................................23

Table A-2. TDWR Parameters. ......................................................................................................23

Table A-3. U-NII emission spectra for FDR calculations for frame-based devices. .....................31

Table A-4. U-NII emission spectra for FDR calculations for frame-based devices. .....................32
viii 

ABBREVIATIONS 

AGL Above Ground Level 

AP Access Point 

CBS cavity-backed spiral 

dB decibel 

dBc decibels relative to carrier

dBi decibels relative to isotropic 

dBm decibels relative to 1 milliwatt 

DFS Dynamic Frequency Selection 

DOC Department of Commerce 

EIRP Equivalent Isotropically Radiated Power 

EMC Electromagnetic Compatibility 

FAA Federal Aviation Administration 

FCC Federal Communications Commission 

FDR Frequency Dependent Rejection 

GHz gigahertz 

GMF Government Master File 

IF Intermediate Frequency 

I/N Interference-to-Noise Ratio 

ITS Institute for Telecommunication Sciences 

LNA low-noise amplifier 

MHz megahertz 

mW milliwatt 

NTIA National Telecommunications and Information Administration 

OFR off-frequency rejection 

OOB out-of-band 

OSM Office of Spectrum Management 

PRI Pulse repetition interval 

RF Radio frequency 

RSMS Radio Spectrum Measurement System 

TDWR Terminal Doppler Weather Radar 

U-NII Unlicensed National Information Infrastructure 

μs microsecond 

VSG vector signal generator 

YIG yttrium-iron-garnet (filter) 
ix

EXECUTIVE SUMMARY 

In early 2009, the Federal Aviation Administration (FAA) became aware of interference to their 

Terminal Doppler Weather Radars (TDWR) that operate in the 5600–5650 MHz band, and 

provide quantitative measurements of gust fronts, windshear, microbursts, and other weather 

hazards for improving the safety of operations in and around major airports (45 airports at the 

time of this writing). Engineers from the Institute for Telecommunication Sciences (ITS) and the 

Office of Spectrum Management (OSM), both part of the National Telecommunications and 

Information Administration (NTIA), and the FAA traveled to a site of reported TDWR 

interference in San Juan, Puerto Rico. They performed an extensive series of field measurements 

in the San Juan area and determined the interference is caused by unlicensed national 

information infrastructure (U-NII) dynamic frequency selection (DFS) devices, from different 

manufacturers, operating in the same frequency band as these Federal radar systems. These 

U-NII devices employ technology that is supposed to detect the presence of nearby radar systems 

and change operating frequencies to prevent interference to these incumbent radar systems. Part I 

of this report series details the results of this measurement effort. 

After determining the interference source, ITS engineers undertook a study of these U-NII 

devices in controlled environments at the ITS laboratory in Boulder, CO, and with a controlled 

TWDR system at the FAA’s TDWR program support facility (PSF) in Oklahoma City, OK. 

These tests were performed to examine DFS detection performance of U-NII devices in the 

presence of TDWR signals, explore the interference levels at which TDWR performance visibly 

degrades, and examine the U-NII device frequency off-tuning required to eliminate interference 

artifacts on the TDWR display from incorrectly configured U-NII devices. ITS obtained several 

U-NII devices from various manufacturers to test against simulated TDWR waveforms at ITS, 

and against an engineering TDWR system at the PSF in Oklahoma City. ITS performed the tests 

with representatives from the respective manufacturers present to witness testing and provide 

engineering support. Part II of this report series describes these tests and field measurements. 

This report, Part III of the series, describes U-NII device emission spectra and introduces 

proposed changes to test waveforms used by the Federal Communications Commission (FCC) 

during DFS device certification testing. These waveforms more accurately represent TDWR 

waveforms. These new waveforms not only duplicate currently used TDWR waveform 

parameters but also include a random element to help protect the TDWR should the FAA change 

the TDWR pulse repetition intervals in the future. 

This report also details the measurements and analysis that determine the power levels at which 

TDWR receivers experience interference from U-NII emissions at an interference-to-noise (I/N) 

ratio of -8 dB (a point at which TDWR display performance visibly degrades with the legacy 

Sigmet RVP8 receiver).1

The maximum allowable interference power that can be coupled cochannel in TDWR receivers without exceeding the I/N level of -8 dB is shown to be -119 

dBm/MHz at the antenna terminals. This equates, for example, to an interference power density 

of -43 dBm/MHz for mainbeam-to-mainbeam coupling between TDWRs and U-NII transmitters 

 

1

 The value of -8 dB I/N is used solely for the purpose of demonstrating interference analysis techniques. The FAA 

has not determined interference protection criteria for this receiver. 
x

at a distance of 8 km, or -22 dBm/MHz for TDWR sidelobe to U-NII mainbeam coupling at a 

distance of 2 km. These power density thresholds are a function of separation distance between 

TDWR receivers and U-NII transmitters. 

This report analyzes the distances at which U-NII transmissions can be expected to routinely 

couple into TDWR receivers. U-NII devices on rooftops, towers, and other high points that are 

153 m to 305 m (500 to 1000 ft) above ground level, as NTIA observed in San Juan, PR, will 

couple into TDWR mainbeams at distances within 25 km to 41 km (16 mi to 25 mi), 

respectively, of TDWR stations. 

The Appendix presents frequency-dependent rejection (FDR) curves with generalized parameters 

to illustrate potential required coordination distances. With TDWR antenna main-beam coupling, 

the radars need about ±30 MHz of frequency separation from frame-based U-NII devices with a 

spatial distance of 5 to 10 km, depending on the U-NII device. For the on-frequency condition, 

the separation distance is about 95 km with a U-NII height of 305 meters and about 75 km for a 

U-NII height of 153 meters, both of which are typically beyond the line-of-sight distance 

between TDWR stations and U-NII devices. For TDWR antenna sidelobe coupling, the 

requirement is about ±30 MHz of frequency separation with a nominal distance less than 1 km. 

For the on-frequency condition, the separation distance is about 24 km. 

With main-beam coupling and ±30 MHz of frequency separation from 20 MHz wide 802.11-

based U-NII devices operating at an EIRP of +17 dBm,2TDWRs need a protection distance of 

11 km. For 40 MHz wide 802.11 devices with a frequency separation of ±30 MHz, the distance 

is 35 km; that distance is reduced to 15 km at a frequency separation of 50 MHz above the center 

frequency and 10 km below the center frequency with a 50 MHz frequency separation. 

For the on-frequency condition for 802.11 devices with a U-NII EIRP of +17 dBm, the 

separation distance is about 94 km for U-NII antenna heights of 304 meters and about 75 km for 

U-NII antenna heights of 152 meters, both of which are beyond the typical line-of-sight 

separation distance between TDWR stations and U-NII devices. 

With TDWR antenna sidelobe coupling to 802.11 device emissions, the frequency separation 

requirement from 20 MHz wide U-NII devices is about ±30 MHz with a spatial distance less 

than 1 km. For the case of 40 MHz wide 802.11-based U-NII devices, the required frequency 

separation is about ±40 MHz with a spatial separation distance of less than 1 km. For the onfrequency condition, the separation distance is about 22.5 km for the 20 MHz wide 802.11 

transmitters and about 18 km for the 40 MHz wide 802.11 transmitter.

 

2

 As defined in 47 CFR § 15.407(a). 
CASE STUDY: INVESTIGATION OF INTERFERENCE INTO 5 GHZ WEATHER 

RADARS FROM UNLICENSED NATIONAL INFORMATION INFRASTRUCTURE 

DEVICES, PART III

John E. Carroll,3 Geoffrey Sanders,3Frank H. Sanders,3and Robert L. Sole4

In early 2009, the Federal Aviation Administration (FAA) became aware of 

interference to Terminal Doppler Weather Radars (TDWRs) that operate in the 

5600–5650 MHz band and provide measurements of gust fronts, windshear, 

microbursts, and other weather hazards for improved safety of operations in and 

around airports. National Telecommunications and Information Administration 

(NTIA) engineers, with assistance from FAA engineers, determined the 

interference to be caused by some unlicensed national information infrastructure 

(U-NII) dynamic frequency selection (DFS) devices operating in the same 

frequency band as TDWR systems. These devices use DFS technology that is 

supposed to detect the presence of nearby co-channel radars and change operating 

frequencies to prevent interference to those radars. This report, the third of a 

three-part series, describes some U-NII emission spectra and introduces an 

additional set of TDWR test waveforms that the Federal Communications 

Commission (FCC) may use during DFS U-NII device testing. This report also 

explores the distances and geometries at which interference to TDWRs from 

U-NII devices is likely to occur. 

Key words: dynamic frequency selection; electromagnetic compatibility; radar interference; 

radar performance degradation; RF interference; spectrum sharing technology; 

terminal Doppler weather radar; unlicensed national information infrastructure 

1 INTRODUCTION 

The Terminal Doppler Weather Radar (TDWR) system, introduced in 1993, operates in the 

5600–5650 MHz band, and provides quantitative measurements of gust fronts, windshear, 

microbursts, and other weather hazards which the Federal Aviation Administration (FAA) uses 

to improve the safety of operations at major airports (45 airports at the time of this writing). 

“During the period from 1964 to 1986, at least 32 accidents and incidents have occurred in which 

windshear was identified as a contributing factor. These accidents resulted in over 600 fatalities 

and nearly 250 injuries. There is evidence to suggest that if undocumented “close calls” and 

general aviation statistics were included, these figures would be much higher.” [1] TDWRs 

improve the management of air traffic through forecasting of gust fronts and induced wind shifts, 

 

3

 Institute for Telecommunication Sciences (ITS), National Telecommunications and Information Administration 

(NTIA), U.S. Department of Commerce (DOC), Boulder, CO. 

4

 Office of Spectrum Management (OSM), NTIA, Washington, DC. 
2

detection of precipitation, and detection of other hazardous weather phenomena, including 

turbulence and tornados. 

Beginning in early 2009, the FAA became aware of interference to TDWRs, including one in 

San Juan, PR. An informal investigation by the FAA concluded that Unlicensed National 

Information Infrastructure (U-NII) devices were responsible. U-NII systems now operate in the 

5250–5350 and 5470–5725 MHz bands, alongside many Federal radar systems, including the 

TDWR, but are required to employ dynamic frequency selection (DFS) technology to detect the 

presence of a nearby radar system and change operating frequencies to prevent interference to 

the radar. The Federal Communications Commission (FCC), the National Telecommunications 

and Information Administration (NTIA), other Federal agencies, and industry representatives 

collaborated to develop rules and compliance measurement procedures for U-NII devices 

equipped with DFS technology. After three years of bench and field testing prototypes from 

many manufacturers, the FCC finalized DFS rules in March 2006 and granted the first DFS 

device certification in August 2006. The U-NII devices are authorized to operate under Part 15 

rules for unlicensed devices and as such they are not permitted to cause interference to allocated 

and protected systems. Descriptions and an overview of DFS technology are provided in [2] and 

[3]. 

At the request of the FAA, NTIA engineers from the Institute for Telecommunication Sciences 

(ITS) and the Office of Spectrum Management (OSM) performed a TDWR interference study in 

San Juan, Puerto Rico from March 9 to 20, 2009. They performed a series of field measurements 

that confirmed 5 GHz U-NII devices, from various manufacturers, as the interference source at 

San Juan. The results of these measurements appear in [2]. Building on the San Juan results, 

FAA engineers subsequently determined that similar interference at other TDWRs in the United 

States was caused by U-NII devices. Work at San Juan showed that only a minority of all DFS 

devices caused interference to TDWRs. The next step was to determine why only some DFS 

devices failed to detect local TDWR signals. 

DFS testing moved later in 2009 to the ITS laboratory in Boulder, Colorado, and the FAA Mike 

Monroney Aeronautical Center TDWR program support facility (PSF) in Oklahoma City, 

Oklahoma. ITS engineers tested various 5 GHz U-NII devices in controlled laboratory and field 

environments against laboratory-generated TDWR signals and the signals of the PSF TDWR. 

Laboratory testing consisted of synthesizing 24 unique TDWR waveforms whose parameters 

were provided by the FAA. Those 24 waveforms were generated using an Agilent E4438C 

vector signal generator (VSG). ITS also performed supplemental laboratory testing of the U-NII 

devices against the “Bin 1 Waveform” [2] used in the FCC certification process. Overall, 

laboratory tests examined DFS detection performance of U-NII devices, from various 

manufacturers, in the presence of emulated TDWR signals. 

Field testing took place at the PSF TDWR. This TDWR is not a part of the national operational 

network; the FAA made it available to NTIA for field testing. The field tests examined DFS 

detection performance of the same U-NII devices as had been examined in the laboratory in the 

presence of an actual, radiated TDWR signal. The field tests also determined the interference 

levels at which TDWR performance visibly degrades, examined the amount of U-NII device 

frequency off-tuning required to eliminate interference strobes from incorrectly configured 
3

U-NII devices, and explored how U-NII device energy impacts TDWR performance when the 

interference couples into TDWR antenna sidelobes. Those results appear in [4]. 

This report describes the development of a set of new, more representative TDWR radar 

waveforms for the FCC to use during DFS device certification testing. These newly-developed 

waveforms contain randomizations that can provide limited protection for future TDWR pulse 

repetition intervals (PRIs), provided they are not radically different from existing waveforms. 

This report also details the measurements and analysis required to determine the frequency 

separation needed to protect the TDWR legacy Sigmet RVP8 receiver from U-NII emissions to 

an interference-to-noise (I/N) ratio of -8 dB. At I/N ratios of greater than -8 dB, the data 

presented in [4] indicate TDWR display performance begins to visibly degrade. NTIA engineers 

performed RF emission spectra measurements of sampled 5 GHz U-NII transmitters at the ITS. 

Section 4 describes the methodology and results for these measurements. Using these 

measurement data, and a given scenario describing the geometry between a TDWR station and a 

U-NII transmitter, NTIA engineers have developed effective isotropic radiated power (EIRP) 

limits for U-NII devices that will protect TDWR receivers to an I/N level of -8 dB. 

Section 5 of this report describes this electromagnetic compatibility (EMC) analysis. Finally,

Section 6 provides a summary of results and conclusions from this EMC analysis. Appendix A

contains detailed frequency versus distance separation curves that can be used to protect the 

TDWR given the frequency separation between the TDWR and the U-NII devices or the spatial 

distance between them. 
4

2 DYNAMIC FREQUENCY SELECTION OVERVIEW 

In June 2006, the FCC released a Memorandum Opinion and Order [3] containing an Appendix 

specifying measurement procedures for certifying U-NII devices for compliance with the DFS 

requirements in the 5250–5350 MHz and 5470–5725 MHz frequency bands. U-NII devices 

operating in these bands do not have to follow any FCC guidelines for modulation or coding 

schemes, but must detect and avoid incumbent Federal radar systems. 

The operational behavior required of a U-NII device operating in the 5250–5350 MHz and 5470–

5725 MHz frequency bands is: 

1. U-NII devices must use DFS in order to detect nearby radar systems with received signal 

strength above the DFS detection threshold [3] of -62 or -64 dBm peak power.5The required 

detection bandwidth [3] is specified as a minimum of 80% of the device’s 99% transmission 

power bandwidth. 

2. Before a U-NII device can transmit on a channel, it must perform a Channel Availability 

Check [3] for 60 seconds to ensure no radar system is operating on the selected channel. 

3. The U-NII device then transmits Network Initiation [3] signals that allow other U-NII 

devices to associate. 

4. During normal operation, the U-NII device monitors the channel (called In-Service 

Monitoring [3]) to ensure that there are no radar systems on the Operating Channel [3]. 

5. If the U-NII device detects radar systems during In-Service Monitoring, the Operating 

Channel must be vacated to prevent interference to nearby radar systems. 

6. Once the U-NII device has detected radar systems on a given channel, it must not utilize that 

channel for a minimum of 30 minutes. 

Sections 6 and 7 in the Appendix of [3] specify five sets of radar test waveform types and FCC 

certification procedures for U-NII devices requiring DFS. The waveforms were developed by 

NTIA, the FCC, and ITS in coordination with the wireless industry. The waveforms simulate 

signals from various radars operating in the bands 5250–5350 and 5470–5725 MHz. The 

waveforms are generated by a test set-up designed and built by ITS and used by the FCC 

laboratory for device certification. Alternative test systems have been approved by the FCC. 

The “Short Pulse Radar Type 1 Waveform,” hereafter referred to in this document as the “Bin 1 

Waveform,” was developed specifically to protect the TDWR. It has a PRI of 1428 microseconds 

(μs), a pulse width of 1 μs, and 18 pulses per burst [3]. 

 

5

 A detection threshold of -62 dBm applies to devices with less than 200 mW equivalently isotropically radiated 

power (EIRP) within the detection bandwidth. For devices with 200 mW or greater EIRP, the -64 dBm threshold 

applies. These values assume a receiver antenna gain of 0 dBi. 
5

3 DEVELOPMENT OF NEW FCC DFS CERTIFICATION WAVEFORMS 

During the testing described in [4], it became apparent that the Bin 1 Waveform currently used 

by the FCC for DFS certification testing does not accurately represent the actual TDWR 

waveforms. To alleviate this problem, new Bin 1 Waveforms have been proposed (jointly 

created by the FCC, NTIA, and industry representatives over the course of many months) that 

not only duplicate currently used TDWR waveforms but also include a random element to help 

protect the TDWR should any improvements be made to the system in the future if and when its 

waveform parameters are changed. 

The existing DFS certification protocol for the Bin 1 Waveform requires that a minimum of 30 

trials be performed with each trial consisting of a single burst of 18 1-μs long pulses with a fixed 

PRI of 1428 μs from each pulse to the next. 

The new Bin 1 Waveforms replace the fixed 1428 μs PRI and 18 pulses in a burst with 

waveforms that vary PRI and the number of pulses transmitted. The pulse width remains at 1 μs. 

The waveforms follow the guidelines provided in Table 1. 

Table 1. Newly developed Bin 1 Waveform certification test protocol for DFS certification. 

Test Pulse Width

(μs)

PRI

(μs)

Number

of Pulses

A 1

15 unique PRI values randomly selected 

from the list of 23 PRI values currently used 

by the TDWR

 6 {

 

 

 

 }

B 1

15 unique PRI values randomly selected 

within the range of 518 to 3066 μs, with a 

minimum increment of 1 μs, excluding PRI 

values selected in Test A

 {

 

 

 

 }

The new Bin 1 Waveform certification test protocol is broken into two parts, or tests. Test A 

consists of waveforms that use existing TDWR parameters. Test B consists of waveforms whose 

PRI values will be chosen randomly in 1 μs increments from the range of 518 μs to 3066 μs. 

This PRI range spans the existing range of current TDWR PRI values and provides the flexibility 

to add future radar waveforms. In Table 1, PRIμs refers to the PRI value in microseconds. 

Additionally, if more than 30 waveforms are required for the Bin 1 Waveform testing, then each 

additional waveform will be generated using the methods described for Test B and must also be 

unique and not repeated from the original 30 waveforms from either Tests A or B. 

 

6

 The “ceil” function is defined as rounding up to the nearest integer. 
6

4 MEASUREMENT AND ANALYSIS OF U-NII DEVICE EMISSION SPECTRA 

4.1 Measurement Technique 

The radiated emissions of selected 5 GHz U-NII Access Point (AP) transmitters were obtained 

by positioning measurement antennas within a few meters of each of the transmitters.7 ITS 

engineers performed radiated measurements in an indoor lab environment with calibrated, 

broadband double-ridged-waveguide horn antennas. The antenna separations were typically at 

the limit of 

 

 , where was the longest linear dimension of either the U-NII antenna or the 

measurement horn (whichever was larger), and was the wavelength of the radiation at 5625 

MHz. 

The measurement antenna output was connected to the current version of the NTIA Radio 

Spectrum Measurement System (RSMS) RF front-end preselector, diagrammed in Figure 1. 

Figure 1. RSMS preselector block diagram. 

The preselector output was connected to the input of a spectrum analyzer. The preselector and 

spectrum analyzer were controlled using custom measurement software to acquire each emission 

spectrum using a stepped-frequency, rather than a more conventional swept-frequency, 

measurement algorithm. The stepped-frequency algorithm and the preselector design are 

described more fully in [5]. 

 

7 For some 802.11 indoor devices measured, the spectra were measured with hardline connections to the 

transmitters due to extremely low device EIRP resulting in reduced emission spectra dynamic range.
7

The advantage of this combination of custom-built hardware and stepped-frequency algorithm 

for the acquisition of U-NII emission spectra is that the widest possible dynamic range is 

obtained in the resulting spectra, along with the best possible measurement system sensitivity. 

The variable front-end attenuator is used to adjust the effective sensitivity of the measurement 

system at each measured frequency, the stepped-frequency algorithm is used to allow the 

attenuator to be adjusted at each individual measurement frequency, and the YIG filter rejects 

strong off-frequency signal power when the measurement system is tuned to frequencies in the 

out-of-band (OOB) and spurious portions of the emission spectra. 

While the NTIA/ITS measurement system is capable of achieving up to 140 dB of dynamic 

range under optimum conditions [5], the U-NII spectrum measurement results only spanned a 

dynamic range of between 75 and 90 dB, depending on which device was being measured. This 

result was due to the low EIRP power that the U-NII transmitters produced. 

The bandwidth of the measurement system was 1 MHz. This was less than the emission 

bandwidth of any of the sampled U-NII transmitters. Using this bandwidth ensured that the ratio 

of power measured at the U-NII fundamental frequency to the power measured in the OOB and 

spurious regions of the emission spectra remained constant. If the measurement bandwidth 

exceeded the U-NII emission bandwidth, the ratio of power in the OOB and spurious regions to 

the power measured at the U-NII fundamental frequency would decrease, and the OOB and 

spurious emissions would appear higher than they really are relative to the power at fundamental 

frequency. 

4.2 Measurement Results 

Figures 2 and 3 show the measured emission spectra for the devices. The data presented in these 

figures show only the actual emissions of the U-NII devices; the measurement system noise floor 

is not shown for the sake of graphical clarity, but was measured to be -94 dBm in a 1 MHz 

bandwidth. Because each device transmitted at a unique EIRP and the measurement distance 

varied from one device to the next, the absolute power measured in a 1 MHz bandwidth varied 

from one to the next. Furthermore, the difference between the power measured at the 

fundamental frequency of each device and the total power that each device radiated varied as a 

function of of that bandwidth ratio.8Therefore, plotting the raw measured spectra would 

be unhelpful in the context of this study. 

Because each U-NII device transmitted a unique EIRP, and because the devices’ relatively low 

EIRPs turned out to be the limiting factor in the dynamic range of the measurements, the 

individual emission spectra for each device vary in dynamic range. The higher each device’s 

EIRP was, the wider the dynamic range over which its spectra were measured and are graphed in 

the figures. However for all U-NII devices tested, the emission measurements had enough 

dynamic range to analyze the potential for interference to TDWR receivers. 

 

8 The total radiated power is fixed, but the power measured at the U-NII fundamental frequency varies as 

a function of 10log(Bmeas), where Bmeas is the measurement bandwidth, only when Bmeas < Bemission, where 

Bemission is the total U-NII emission bandwidth. In contrast, the power measured in the OOB and spurious 

regions is a power density that generally varies as 10log(Bmeas) for any value of Bmeas, even if Bmeas

exceeds Bemission. 
8

To analyze the interference potential into TDWR receivers, the U-NII emission spectra need to 

be assessed with regard to the rate at which the emissions roll off with separation from the U-NII 

fundamental frequency, and also how low the ultimate suppression level of these spectra happens 

to be. Therefore, in Figures 2 and 3, the U-NII emission spectra have been normalized to 0 dB at 

the U-NII fundamental frequency, and the emission spectra are plotted in terms of decibels 

relative to the power at the fundamental level (decibels relative to carrier or dBc). Figure 2

shows relative roll-off rates and ultimate suppression levels for the variety of U-NII transmitters 

and Figure 3 shows the roll-off rates for the U-NII devices in the region within 200 MHz of the 

fundamental frequencies 

Figure 2. Comparative radiated emission spectra for ten different 5 GHz U-NII transmitters, in a 

1 MHz measurement bandwidth, referenced to peak fundamental power (dBc). 
9

Figure 3. The central 200 MHz (100 MHz on each side of the fundamental frequency) of the 

U-NII emission spectra of Figure 1. 

The U-NII devices vary substantially in their ultimate suppression levels, as can be seen in 

Figure 2. At worst (putting aside the -35 dBc emission spike produced by the Manufacturer E 

U-NII device) they achieve at least -50 dBc; at best, they achieve suppression levels of 

between -70 and -80 dBc. 
10

5 EMC ANALYSIS FOR INTERFERENCE COUPLING FROM U-NII DEVICES TO 

TDWRS 

Following the measurement of the emission spectra of the U-NII devices, ITS engineers 

performed an EMC analysis to determine what U-NII ultimate suppression limits are required to 

protect TDWRs from interference. These limits can then be used to determine the required 

frequency separation between U-NII devices and TDWRs to mitigate interference. 

This analysis is divided into the following subsections: 

1. Calculation of U-NII device distances from TDWRs that result in mainbeam coupling, and 

associated coupling factors. 

2. Calculation of the sidelobe antenna coupling factors that can occur when U-NIIs are 

deployed at lower heights and at locations that are relatively close to TDWRs, but not in the 

TDWR antenna mainbeam, using the data presented in [4] as an example. 

3. Description and analysis of the TDWR emission spectrum (which is required to understand 

the circumstances under which U-NII receivers’ DFS algorithms will see TDWR energy at 

amplitudes above the critical threshold of -64 dBm). 

4. Calculations of U-NII device power levels that may couple energy into the TDWR antenna 

mainbeam and sidelobes without causing interference artifacts on the radar display. 

5.1 Calculation of Mainbeam Coupling Distances and Coupling Factors between U-NII

Devices and TDWRS 

TDWR antennas have a mainbeam that is 0.55 degrees wide at the 3 dB points (in both vertical 

and horizontal polarizations) with 50 dBi of gain. Although the TDWR beam can be depressed to 

0.5 degrees below horizontal, the beam is not ordinarily scanned below +0.2 degrees elevation 

angle. The question that presents itself for a mainbeam coupling analysis is: how far away 

(geographically) does a U-NII need to be, if it is deployed on a high tower or rooftop, to preclude 

coupling of its energy into the mainbeam of a nearby TDWR? 

With an assumption that the U-NII height above ground level (AGL) might be 153 or 305 m 

(500 and 1000 ft, respectively),9geometrical analysis needs to take into account the curvature of 

the Earth. Figure 4 provides a description of the geometry for these scenarios. Although the 

diagram in Figure 4 assumes flat terrain, rising terrain can create the same elevation effect for 

U-NII devices.

 

9

 NTIA engineers observed these heights for U-NII devices in San Juan, PR. The FCC has documented such heights 

for U-NII devices as well; see http://transition.fcc.gov/Daily_Releases/Daily_Business/2012/db0319/DOC313074A1.txt. 
11

Figure 4. Mainbeam coupling geometry scenario for a TDWR and a U-NII.

If the Earth is considered to be smooth and round, then the distance, d, in kilometers where it has 

dropped a height, h, in meters, is: √ . Therefore, the correct equation for TDWR beam 

height above ground is: 

 (

 

 )

 

(1)

where,

 = height of TDWR beam (meters AGL) at distance, d, from the TDWR; 

 = height of TDWR tower (meters AGL) = 27 m AGL; 

 = distance between a TDWR and a U-NII (kilometers); 

 = TDWR minimum beam elevation angle (degrees) = 0.2 deg; 

1000 = conversion of distance from kilometers to meters. 

Reducing all of the constants, (1) becomes: 

 

 

 

 

(2)

The values of d where (2) yields TDWR mainbeam heights of 153 and 305 m (500 and 1000 ft) 

AGL are approximately 25 and 41 km (16 and 25 mi), respectively. 

The salient characteristic of this geometry is that any U-NII devices at heights of 153 to 305 

meters AGL on a smooth, round Earth will couple into TDWR mainbeams if they are located 
12

within 25 to 41 km (16 to 25 mi) of a TDWR, respectively. With this geometry, any U-NII 

devices at these assumed heights couple energy into the 50 dBi-gain main-beam of the TDWR 

antenna and therefore have an antenna coupling factor of at least 50 dB (assuming the U-NII 

device antenna is 0 dBi; U-NII device antenna gain in the direction of a nearby TDWR will 

result in an even higher antenna coupling factor). 

5.2 Calculation of Coupling Factors into TDWR Antenna Sidelobes When U-NII Devices 

Are Deployed at Lower Heights 

Figure 5 shows the power received from the TDWR at a rooftop location in Oklahoma City 

throughout one complete monitor (or normal volume) scan. These data were taken during the 

measurement effort described in [4]. The power from the TDWR, measured with a 6.5-dBi gain 

cavity back spiral (CBS) antenna with circular polarization, has been corrected to the level that 

would be exposed to a U-NII device with a 0-dBi gain antenna and whose polarization is 

matched to the TDWR antenna polarization.

Figure 5. Power received from the TDWR at a U-NII location in Oklahoma City, OK throughout 

one complete monitor (or normal volume) scan. 

The sidelobe coupling factor between a U-NII and a TDWR will vary with deployment height 

and distance from the radar. Using the data in [4] as a real-world example, we can calculate the 

maximum sidelobe coupling factor between the TDWR and U-NIIs that were approximately 11 

meters AGL at a distance of 4.8 km (2.97 miles). Using (38) in [6]: 
13

 

 (3)

where,

 = receive power (dBm); 

 = transmit power (dBm); 

 = transmit gain (dBi); 

 = receive gain (dBi); 

 = frequency (MHz); 

 = distance (km). 

Re-arranging to solve for the gain of the TDWR antenna sidelobe: 

 . (4)

Using (4) and Figure 5 with = -20 dBm, = 84 dBm, = 0 dBi, = 5625 MHz, and = 4.8 

km, the TDWR antenna sidelobe coupling factor is +17 dBi. This value is used in the subsequent 

EMC analysis. 

5.3 Description and Analysis of the TDWR Emission Spectrum 

The measured emission spectrum of a TDWR is shown in Figure 6. A detail of that spectrum, 

showing its characteristics within 40 MHz of its fundamental frequency, is shown in Figure 7. 

Figure 6. TDWR radiated emission spectrum in a 1 MHz bandwidth. 
14

Figure 7. TDWR emission spectrum within 40 MHz of the fundamental frequency. 

Using the emission spectra shown in Figures 6 and 7, it is possible to calculate, for a given 

amount of off-tuning from its fundamental frequency, the distance from the TDWR at which it 

will generate -62 dBm/MHz of power10 in a DFS receiver with a 0-dBi gain antenna. For 

example, if the amount of frequency off-tuning is taken to be 30 MHz, then the distance where 

the TDWR produces -62 dBm/MHz in a 0-dBi antenna-gain DFS receiver can be calculated from 

the TDWR’s emission spectrum, which is 78 dB lower at  30 MHz than at its fundamental 

frequency (Figure 7). Solving (3) for the distance parameter (and including a new term for the 

TDWR’s off-frequency rejection) yields: 

 . (5)

Using = 84 dBm; = -78 dB; = 50 dBi; = 0 dBi; = -62 dBm/MHz; and f = 5625 

MHz; this gives a distance of d = 3348 meters = 3.3 km. 

TDWR mainbeam antenna coupling will occur with U-NII devices operating at heights between 

153 and 305 m AGL at distances within 25 to 41 km. However, the TDWR emission spectrum 

at its 30 MHz off-tuned points only produces enough power to exceed the DFS trigger 

threshold at distances within 3.3 km, assuming a 1 MHz U-NII device detection bandwidth. 

 

10 For DFS detection bandwidths that exceed 1 MHz, the received power level will be larger. 
15

5.4 EMC Coupling Analyses 

A complete EMC analysis for TDWRs and U-NII devices requires that the minimum distance 

between TDWR stations and U-NII transmitters be specified along with a determination of the 

maximum I/N level that would be allowed in the TDWR receiver (e.g., -8 dB).11 Using those 

limits, compatible operations between TDWRs and U-NII devices can be realized. By examining 

the emission spectrum measurements of the U-NII devices, the minimum amount of frequency 

separation between U-NII transmitters and TDWRs can also be determined. 

In the next two sub-sections, ITS presents analyses to determine the required suppression level of 

unwanted U-NII device emissions that would be needed based on two scenarios: mainbeam-tomainbeam coupling, and U-NII antenna mainbeam to TDWR antenna sidelobe coupling. The 

methodology presented here can be extended to other scenarios as well; the Appendix presents 

general-purpose sets of distance-versus-frequency separation curves. 

5.4.1 Mainbeam-to-Mainbeam Coupling 

The goal is to determine the maximum EIRP that a U-NII device could transmit on a TDWR 

frequency without exceeding an I/N level of -8 dB in the TDWR receiver. This I/N limit is based 

on the U-NII device co-channel power on the TDWR frequency. The following calculations 

determine the maximum EIRP allowed from a U-NII device situated at a hypothetical distance of 

8 km from a TDWR system. TDWR system parameters are given in Table 2.

Table 2. Parameters for mainbeam-to-mainbeam U-NII-to-TDWR EMC analysis. 

Parameter Value

TDWR Receiver Bandwidth 1 MHz

TDWR Receiver Noise Figure 1.4 dB

Loss Between TDWR Antenna Feed and Receiver 

Low Noise Amplifier Input

2 dB

TDWR Antenna Gain 50 dBi

Separation Distance Between TDWR Station and 

U-NII Transmitter 8 km (hypothetical)

Frequency of the TDWR 5625 MHz

The energy coupling equation for these two systems is (using (3)): 

 (6)

where, 

 

11 An of -8 dB is used only as an example to demonstrate the analytical approach. It approximates the level 

where strobes became barely visible in TDWR data with the radar’s newest receiver, the Sigmet RVP8, as 

documented in [4]. 
16

 = maximum transmitted U-NII device EIRP power level that does not exceed 

 in the TDWR receiver in a 1 MHz bandwidth on the TDWR frequency; 

 = maximum power allowed in the TDWR receiver before interference exceeds 

 ;

 = gain of the TDWR antenna (50 dBi); 

 = TDWR frequency (5625 MHz); 

 = Separation distance (8 km).

The value of is given by: 

 (

 

 

)

 

(7)

where, 

 = Boltzmann’s constant ( 

 

); 

 = TDWR receiver temperature ( );

 = TDWR receiver bandwidth ( Hz); 

 = TDWR receiver noise figure (1.4 dB); 

 = loss between the TDWR antenna feed and receiver LNA input (2 dB); 

(

 

 

)

 

= I/N threshold for TDWR interference (-8 dB).

Using (7), 

 

 

 

.

The result of -119 dBm in a 1 MHz bandwidth for is important because this is the level of 

interference that must not be exceeded in the TDWR receiver before TDWR data is visibly 

contaminated on the radar display. This interference power threshold is independent of U-NII 

device power and distance from a TDWR.

Using -119 dBm as in (6), we calculate the maximum U-NII device EIRP, in a 1 MHz 

bandwidth, at a hypothetical distance of 8 km without causing interference, assuming antenna 

mainbeam-to-mainbeam coupling: 

 

 

 

 

.

In other words: with a U-NII device situated 8 km away from a TDWR, any U-NII device 

emissions coupling into a TDWR antenna mainbeam on a TDWR frequency and exceeding an 

EIRP of 

 

 will result in an 

 

 in a TDWR receiver. 

The interference power threshold on a TDWR frequency can be translated into ultimate 

suppression level of U-NII device unwanted emissions. For example, if a U-NII transmitter 
17

hypothetically situated 8 km from a TDWR generated an EIRP of +17 dBm/MHz,12 then the 

ultimate suppression level of its unwanted emissions on the TDWR frequency would need to be 

at least 

 (  ) relative to the power per megahertz at the U-NII 

fundamental frequency. 

If, conversely, the EIRP of a hypothetical U-NII transmitter were less than the maximum 

specified power of +17 dBm/MHz, then the required suppression would decrease by a 

corresponding amount. For example, if the U-NII device EIRP were 0 dBm/MHz, then the 

required minimum suppression value for the U-NII unwanted emissions on the TDWR frequency 

would only need to be relative to the power per megahertz at the fundamental 

frequency. 

5.4.2 U-NII Mainbeam-to-TDWR Sidelobe Coupling 

The goal is to determine the maximum EIRP that a U-NII could transmit on a TDWR frequency 

without in the TDWR receiver if the U-NII only couples into a TDWR antenna 

sidelobe. Sidelobe coupling occurs if the U-NII device is located below the lower edge of 

the -3 dB beamwidth of the TDWR antenna. The following calculations determine the maximum 

EIRP allowed from a U-NII device situated at a hypothetical distance of 2 km from a TDWR 

system. TDWR system parameters are given in Table 3. TDWR antenna sidelobe coupling is 

more likely to occur when U-NII devices are located in close proximity to a TDWR. This is 

because TDWR antennas are located 27 m (88 ft) AGL and TDWR antenna beams generally 

have a minimum elevation angle of +0.2 degrees (Figure 4).

For example, during the tests performed in Oklahoma City [4], several U-NII devices were 

operated on a rooftop at a height of 11 m (35 ft) AGL at a distance of approximately 5 km (3 mi) 

from a TDWR. The TDWR antenna feed was located 27 m (88 ft) AGL. Neglecting Earth 

curvature, the U-NII devices were 0.3 degrees below the TDWR horizon. Since the Oklahoma 

City TDWR antenna never scanned below an elevation angle of 0.3 degrees above its horizon, 

the U-NII device was always at least 0.6 degrees below the TDWR antenna mainbeam and, thus, 

always coupled into the TDWR sidelobes. Sidelobe coupling geometry is expected to occur more 

frequently than mainbeam-to-mainbeam coupling. However, interference cases have been 

reported for U-NII devices on skyscrapers in New York City and in rural areas where the U-NII 

device was placed on a high ridge or mountain. 

Table 3. System parameters for U-NII mainbeam-to-TDWR sidelobe example EMC analysis. 

Parameter Value

TDWR Receiver Bandwidth 1 MHz

TDWR Receiver Noise Figure 1.4 dB

 

12 Transmission power limits for U-NII devices in the 5.47–5.725 GHz band are provided by a set of 

detailed rules in 47 CFR Part §15.407 (2). The maximum EIRP allowed is +17 dBm/MHz. 
18

Parameter Value

Loss Between TDWR Antenna Feed and Receiver 

Low Noise Amplifier Input 2 dB

TDWR Antenna Sidelobe Gain (Figure 5) +17 dBi

Separation Distance Between TDWR Station and 

U-NII Transmitter 2 km (hypothetical)

Frequency of the TDWR 5625 MHz

The maximum EIRP that can be radiated in a 1 MHz bandwidth at a distance of 2 km from the 

U-NII without causing interference, if mainbeam-to-sidelobe coupling occurs and 

 , will be (using (6)):

 

 

 

 

.

In other words: with a U-NII device situated 2 km away from a TDWR, any U-NII device 

emissions coupling into a TDWR antenna sidelobe on a TDWR frequency and exceeding an 

EIRP of will result in an in a TDWR receiver. 

The interference power threshold on a TDWR frequency can be translated into an ultimate 

suppression level of U-NII device unwanted emissions. For example, if a U-NII transmitter,

hypothetically situated 2 km from a TDWR, generated an EIRP of +17 dBm/MHz, then the 

ultimate suppression level of its unwanted emissions coupling into a TDWR antenna sidelobe on 

the TDWR frequency would need to be at least: 

 ( 

 ) relative to 

the power per megahertz at the U-NII fundamental frequency. 

If, conversely, the EIRP of a hypothetical U-NII transmitter were less than the maximum 

specified power of +17 dBm/MHz, then the required suppression would decrease by a 

corresponding amount. For example, if the U-NII device EIRP were 0 dBm/MHz, then the 

required minimum suppression value for the U-NII unwanted emissions coupling into a TDWR 

antenna sidelobe on the TDWR frequency would only need to be: relative to 

the power per megahertz at the fundamental frequency. 
19

6 RESULTS AND CONCLUSIONS FROM THE EMC ANALYSIS 

ITS engineers measured the emission spectra and roll-off rates of several representative U-NII 

devices (Figures 2 and 3). These data indicate the level of unwanted emissions generated by 

these devices. Ultimate suppression levels currently range from as little as -35 dBc (an isolated 

case) to a typical range of -55 dBc to -80 dBc. 

1. U-NII devices on rooftops, towers, and other high points (Figure 4) that are 153 to 305 m 

(500 to 1000 ft) AGL will couple into TDWR mainbeams at distances within 25 and 41 km 

(16 and 25 mi), respectively, of TDWRs. 

2. U-NII devices located on high terrain or at significant heights above AGL can couple into 

TDWR mainbeams at distances greater than 41 km (25 mi). 

3. Maximum TDWR sidelobe gain can be taken to be +17 dB for EMC analyses, based on 

empirical data (Figure 5).

4. U-NII devices will not detect off-tuned TDWR emissions at 30 MHz from TDWR 

frequencies if they are more than 3.3 km from TDWRs, even if mainbeam coupling occurs. 

5. EMC analyses show that, in order to preclude interference at from any 

external source to a TDWR receiver, the co-channel interference power level coupled into a 

TDWR at the antenna terminals must not exceed -119 dBm/MHz. The FAA has not 

determined what ratio is required for the TDWR Sigmet RVP8 receiver. 

6. Based on this interference power threshold value of -119 dBm/MHz, Tables 4 and 5 show the 

results of the example EMC analyses for mainbeam-to-mainbeam and mainbeam-to-sidelobe 

coupling for U-NII devices to TDWRs. Table 4 shows the U-NII device absolute EIRP limits 

on TDWR frequencies and Table 5 shows the requirements for suppression of unwanted 

U-NII emissions for these two coupling conditions. 

Table 4. Limits on U-NII EIRP on a TDWR frequency required to preclude interference to 

TDWR receivers at given separation distance. 

Coupling Condition

Absolute U-NII EIRP Limit 

(on the TDWR Frequency)

Mainbeam-to-Mainbeam at 8 km 

 

 

U-NII Mainbeam to TDWR Sidelobe at 2 km 

 

 
20

Table 5. Requirements for U-NII unwanted spectrum emission suppression at given separation 

distances from TDWRs for some example U-NII device EIRP levels. 

Coupling Condition

Unwanted Spectrum 

Suppression Requirement for 

Hypothetical U-NII EIRP of 

+17 dBm/MHz

Unwanted Spectrum 

Suppression Requirement for 

Hypothetical U-NII EIRP of 

0 dBm/MHz

Mainbeam-to-Mainbeam at 

8 km

-60 dBc;

Note in Figure 3, the frame- based 

systems met this requirement at 

±30 MHz off-frequency from 

their fundamentals.

Note in Figure 3, the 802.11-

based systems did not meet this 

level at ±30 MHz off-frequency 

from their fundamentals.

-43 dBc

U-NII Mainbeam to TDWR 

Sidelobe at 2 km -39 dBc -22 dBc

7. Emission spectra of the measured 802.11-based devices have slower emission spectrum rolloffs than those of frame-based U-NII devices. On this basis alone, the 802.11-based devices 

might be expected to produce more interference than frame-based devices. But the 802.11 

devices operate indoors and use lower EIRPs and lower deployment heights than framebased devices. These characteristics should reduce the likelihood of interference from 802.11 

U-NII devices to TDWR receivers. 

8. For U-NII devices with emission bandwidths wider than 20 MHz (e.g., Manufacturer G), 

EMC analyses need to be performed on a case-by-case basis. 
21

7 REFERENCES 

[1] U.S. Department of Transportation, Federal Aviation Administration, Advisory Circular 

00-54, Pilot Windshear Guide, Nov. 1988. 

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/list/AC%200

0-54/$FILE/AC00-54.pdf, accessed on Sept. 25, 2010.

[2] Carroll, J. E., F. H. Sanders, R. L. Sole, and G. A. Sanders, “Case Study: Investigation of 

Interference into 5 GHz Weather Radars from Unlicensed National Information 

Infrastructure Devices, Part I,” NTIA Report TR-11-473, November 2010. Downloadable 

at: http://www.its.bldrdoc.gov/publications/2548.aspx. 

[3] Federal Communications Commission, Revision of Parts 2 and 15 of the Commission’s 

Rules to Permit Unlicensed National Information Infrastructure (U-NII) devices in the 5 

GHz band, ET Docket No.03-122, Memorandum Opinion and Order, 21 FCC Record 7672 

(2006). http://hraunfoss.fcc.gov/edocs_public/attachmatch/FCC-06-96A1.pdf, accessed on 

Jul. 8, 2010. 

[4] Carroll, J. E., F. H. Sanders, R. L. Sole, and G. A. Sanders, “Case Study: Investigation of 

Interference into 5 GHz Weather Radars from Unlicensed National Information 

Infrastructure Devices, Part II,” NTIA Report TR-11-479, July 2011. Downloadable at: 

http://www.its.bldrdoc.gov/publications/2554.aspx. 

[5] Sanders, F.H., R.L. Hinkle, and B.J. Ramsey, “Measurement Procedures for the Radar 

Spectrum Engineering Criteria (RSEC),” NTIA Report TR-05-420, March 2005. 

Downloadable at: http://www.its.bldrdoc.gov/publications/2450.aspx. 

[6] Sanders, F., “Derivations of Relationships Among Field Strength, Power in TransmitterReceiver Circuits and Radiation Hazard Limits,” NTIA Memorandum TM-10-469, June 

2010. Downloadable at: http://www.its.bldrdoc.gov/publications/2507.aspx.
22

APPENDIX A. CALCULATED FREQUENCY-DEPENDENT REJECTION (FDR) 

CURVES AND COORDINATION DISTANCES BETWEEN TDWR RECEIVERS AND 

U-NII TRANSMITTERS 

A.1 Calculation of Frequency-Distance Separation Curves to Protect TDWR Receiver 

OSM has calculated the frequency-distance separation curves for protection of TDWR receivers 

from U-NII transmitters using the Irregular Terrain Model (ITM) propagation model13 after link 

budget analyses determined the maximum U-NII interference power in the TDWR receiver and 

the corresponding required path loss. For site-specific calculations, additional parameters would 

have to be known such as the terrain profile and exact antenna heights. Equation (1) is used to 

determine the U-NII interference power in the TDWR receiver. 

 

(A-1)

Solving for LP when the IMax is already known, results in (2).

 

(A-2)

where: 

LP = Path loss (dB), 

PT = EIRPU-NII (+17 dBm; max allowed power under FCC rules),

IMax = Maximum permissible U-NII interference power (dBm/MHz) in TDWR receiver, 

FDR = Frequency dependent rejection (FDR) (dB), 

GR = TDWR antenna gain (dBi), 

LS = System loss (2 dB). 

The ITM propagation model was run in Broadcast mode with a delta H of 90 meters in smoothEarth reverse mode (simulating rolling terrain) to calculate the distance that meets the 

requirement for path loss (LP). The input values for the ITM model are shown in Table A-1. ITM 

takes into account the transmitter and receiver antenna heights and the curvature of the Earth 

with diffraction included. The TDWR antenna height was set at 27 meters while the U-NII 

antenna heights were set to 30, 152, and 304 meters in separate ITM runs. The TDWR mainbeam 

antenna gain was used for U-NII heights of 152 and 304 meters in the analyses. For a U-NII 

antenna height of 30 meters, the sidelobe TDWR antenna gain was used. 

 

13 The NTIA Microcomputer Spectrum Analysis Models (MSAM) software was used for this analysis. It can be 

found here: http://ntiacsd.ntia.doc.gov/msam/. 
23

Table A-1. ITM Settings. 

Mode of Variability Broadcast Dielectric 15

Delta H 90 Conductivity 0.005

U-NII Transmitter Height m

304

152

30

Surface Refractivity 301

Radio Climate Continental temperate

Percent Time 50

TDWR Receiver Height m 27 Percent Location 50

Transmitter Site Criteria Very careful Percent Confidence 50

Receiver Site Criteria Very careful Polarity Horizontal

The parameters of the TDWR used in the calculations are shown below in Table A-2. 

Table A-2. TDWR Parameters. 

Parameter Value

3 dB IF BW (MHz) 1

Noise Figure (dB) 1.4

Interference Threshold (I/N dB) -8

Receiver Noise Power (dBm/MHz) -112.6

Maximum Interference Level (dBm/MHz) -120.6

TDWR Antenna mainbeam Gain (dBi)

For U-NII height of 52 and 304 meters 50

TDWR Antenna sidelobe Gain (dBi) at -4 degrees

For U-NII height of 30 meters 17

System Loss (dB) 2

TDWR Antenna Height (m) 27

A.2 Calculation of Frequency Dependent Rejection (FDR) 

FDR is a key element in EMC link budget calculations. NTIA calculated the FDR for the TDWR 

receiver versus each of the U-NII transmitters with their measured emission spectra, for a range 

of ±100 MHz on the TDWR center frequency. Figure A-1 shows the TDWR’s measured IF 

frequency selectivity. 
24

Figure A-1. TDWR measured IF frequency selectivity. 

An important factor when calculating the FDR is the roll-off of the receiver’s IF response past 

the last measured value. In Figure A-1 the data were measured to a level of about 50 dB below 

the peak value. Adding additional power to gather more data made the receiver operate in a nonlinear fashion. Therefore to determine the TDWR’s IF roll-off, the slope of the IF curve can be 

extended to a point at ±10 MHz from the center and its response compared to the response at 

1 MHz. 

Figure A-2. TDWR IF response (normalized). 

-60

-50

-40

-30

-20

-10

0

10

-5 -4 -3 -2 -1 0 1 2 3 4 5

Data points

used in FDRCAl program

TDWR IF Response

Measured at San Juan

Puerto Rico Jan. 2009

by ITS

Fq dB

-5.0 -50.00

-4.0 -48.11

-3.6 -48.40

-3.0 -42.83

-2.4 -34.08

-2.0 -27.31

-1.6 -20.04

-1.0 -8.49

-0.56 -3.00

0.0 0.00

0.46 -3.00

1.0 -12.61

1.6 -23.18

2.0 -28.13

2.4 -32.42

3.0 -38.04

3.6 -42.99

4.0 -45.30

5.0 -50.00

Frequency in MHz

response in dB

TDWR IF Response (normalized)

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

10

0 1 2 3 4 5 6 7 8 9 10 11

76 dB

12 dB

Frequency in MHz

response in dB

TDWR IF Response (normalized)
25

Figure A-2 shows that at 1 MHz the value is -12 dB and at 10 MHz the value is -76 dB, therefore 

the slope of the TDWR’s IF curve is about 64 dB per decade. Using these parameters, the 

TDWR receiver’s FDR versus the U-NII transmitters was calculated. The result is shown below 

in Figure A-3 for the frame-based U-NII transmitters, and Figure A-4 for 802.11-based U-NII 

transmitters. That FDR data was then used in the models to calculate the frequency-distance 

curves with the ITM propagation model. Since the U-NII emission bandwidth is greater than the 

TDWR 3-dB IF bandwidth, the on-tune FDR is non-zero; it varies as 10*log(bandwidth ratio). 

Figure A-3. FDR for TDWR IF selectivity for frame-based U-NII transmitters. 

Figure A-4. FDR for TDWR IF selectivity for 802.11-based U-NII transmitters.

0

10

20

30

40

50

60

70

80

90

100

-100 -90 -80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 100

Manufacturer A Model 2

Manufacturer E Model 1

Manufacturer D Model 1

Manufacturer A Model 3

Manufacturer A Model 5

Manufacturer C Model 1

F (MHz)

FDR (dB) FDR for TDWR IF Selectivity versus Frame-based U-NII Transmitters

10

20

30

40

50

60

70

-100 -90 -80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 100

Manufacturer G Model 1 40MHz Mode

Manufacturer G Model 1 20MHz Mode

Manufacturer F Model 3

Manufacturer F Model 2

F (MHz)

FDR (dB) FDR for TDWR IF Selectivity versus 802.11-based U-NII Transmitters
26

A.2.1 Frequency-Distance Curves for Frame-Based U-NII Systems 

OSM calculated the frequency-distance separations for the TDWR receiver and the frame-based 

U-NII transmitters with the U-NII EIRP set to the maximum allowed level of +17 dBm.14 The 

results are shown in Figures A-5 and A-6 for TDWR mainbeam coupling with U-NII antenna 

heights of 304 and 152 meters. It is noted that not all U-NII devices transmit the maximum 

allowable EIRP. Figure A-7 shows the distances needed to protect a TDWR from a frame-based 

U-NII transmitter at an antenna height of 30 meters, via TDWR sidelobe coupling. 

Figure A-5. Distances needed to protect TDWR from frame-based U-NII transmitters 

(H = 304 meters, TDWR mainbeam coupling). 

 

14 Note that not all U-NII devices transmit the maximum allowable EIRP. 

0

10

20

30

40

50

60

70

80

90

100

-100 -90 -80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 100

Manufacturer A Model 2

Manufacturer E Model 1

Manufacturer D Model 1

Manufacturer A MOdel 3

Manufacturer A Model 5

Manufacturer C Model 1

U-NII Height: 304 Meters

F (MHz)

Distance (km)

Distances to Protect TDWR from Frame-based U-NII Transmitters (304 Meters H)
27

Figure A-6. Distances needed to protect TDWR from frame-based U-NII transmitters 

(H = 152 meters, TDWR mainbeam coupling). 

Figure A-7. Distances needed to protect TDWR from frame-based U-NII transmitters 

(H = 30 meters, TDWR sidelobe coupling). 

0

10

20

30

40

50

60

70

80

-100 -90 -80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 100

Manufacturer A Model 2

Manufacturer E Model 1

Manufacturer D Model 1

Manufacturer A MOdel 3

Manufacturer A Model 5

Manufacturer C Model 1 U-NII Height: 152 Meters

F (MHz)

Distance (km)

Distances to Protect TDWR from Frame-based U-NII Transmitters (152 Meters H)

0

5

10

15

20

25

-100 -90 -80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 100

Manufacturer A Model 2

Manufacturer E Model 1

Manufacturer D Model 1

Manufacturer A MOdel 3

Manufacturer A Model 5

Manufacturer C Model 1

U-NII Height: 30 meters

F (MHz)

Distance (km)

Distances to Protect TDWR from Frame-based U-NII Transmitters (30 meters H) 
28

Figures A-5 and A-6 show that, with TDWR antenna main-beam coupling, the radar needs about 

±30 MHz of frequency separation from the frame-based U-NII devices with a spatial distance of 

5 to 10 km, depending on the U-NII device. For the on-frequency condition, the separation 

distance is about 95 km with a U-NII height of 305 meters and about 75 km for a U-NII height of 

153 meters, both of which are typically beyond the line-of-sight distance between TDWR 

stations and U-NII devices. 

Figure A-7 shows that with TDWR antenna sidelobe coupling the requirement is about ±30 MHz 

of frequency separation with a nominal spatial distance less than 1 km. For the on-frequency 

condition, the separation distance is about 24 km. 

A.2.2 Frequency-Distance Curves for 802.11-Based U-NII Systems 

OSM calculated the separation distances for TDWR receivers and 802.11-based U-NII 

transmitters with the U-NII EIRP set at the maximum allowed level of +17 dBm.15 The results 

are shown in Figures A-8 and A-9 for TDWR main-beam coupling with U-NII antenna heights at 

304 and 152 meters. 

Figure A-8. Distances needed to protect TDWR receivers from 802.11-based U-NII transmitters 

(H = 304 meters, main-beam coupling).

 

15 Note that not all U-NII devices transmit the maximum allowable EIRP.

0

10

20

30

40

50

60

70

80

90

100

-100 -90 -80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 100

Manufacturer G model 1 40MHz Mode

Manufacturer G Model 1 20MHz Mode

Manufacturer F Model 3

Manufacturer F Model 2

U-NII Height: 304 Meters

F (MHz)

Distance (km)

Distances to Protect TDWR from 802.11-based U-NII Transmitters (304 Meters H)
29

Figure A-9. Distances needed to protect TDWR from 802.11-based U-NII transmitters 

(H = 152 meters, main-beam coupling). 

Figure A-10. Distances needed to protect TDWR from 802.11-based U-NII transmitters 

(H = 30 meters, sidelobe coupling). 

0

10

20

30

40

50

60

70

80

-100 -90 -80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 100

Manufacturer G model 1 40MHz Mode

Manufacturer G Model 1 20MHz Mode

Manufacturer F Model 3

Manufacturer F Model 2

U-NII Height: 152 Meters

F (MHz)

Distance (km)

Distances to Protect TDWR from 802.11-based U-NII Transmitters (152 meters H)

0

5

10

15

20

25

-100 -90 -80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 100

Manufacturer G model 1 40MHz Mode

Manufacturer G Model 1 20MHz Mode

Manufacturer F Model 3

Manufacturer F Model 2

U-NII Height: 30 meters

F (MHz)

Distance (km)

Distances to Protect TDWR from 802.11-based U-NII Transmitters (30 meters H)
30

Figures A-8 and A-9 show that, with main-beam coupling and ±30 MHz of frequency separation 

from the 20 MHz wide 802.11-based U-NII devices operating at an EIRP of +17 dBm, TDWRs 

need a protection distance of 11 km. For the 40 MHz wide 802.11 signal with a frequency 

separation of ±30 MHz the distance is 35 km. Note that since this 802.11 signal is not 

symmetrical, the lower side of its emission requires a protection distance of 26 km. That distance 

is reduced to 15 km at a frequency separation of 50 MHz above the center frequency and 10 km 

below the center frequency with a 50 MHz frequency separation. 

As expected, the wider bandwidth of 40 MHz wide 802.11 signals results in greater separation 

distances when the devices are off-frequency. If the U-NII bandwidths were even wider (e.g., 80 

and 160 MHz wide 802.11 channels), the separation distances will increase. Since the 802.11 

devices have slower spectral roll-off than the frame-based devices (Figure 2) these results are 

expected. 

For the on-frequency condition with a U-NII EIRP of +17 dBm, the separation distance is about 

94 km for U-NII antenna heights of 304 meters and about 75 km for U-NII antenna heights of 

152 meters, both of which are beyond the typical line-of-sight separation distance between 

TDWR stations and U-NII devices. 

Figure A-10 shows that with TDWR antenna sidelobe coupling, the frequency separation 

requirement from the 20 MHz wide 802.11-based U-NII devices is about ±30 MHz with a spatial 

distance less than 1 km. For the case of the 40 MHz wide 802.11-based U-NII device, the 

required frequency separation is about ±40 MHz with a spatial separation distance of less than 1 

km. For on-frequency condition, the separation distance is about 22.5 km for the 20 MHz wide 

802.11 transmitters and about 18 km for the 40 MHz wide 802.11 transmitter. 

Tables A-3 and A-4 list the data points of U-NII emission spectra used for FDR calculations. The 

U-NII device emission spectra roll-off at 15 dB per decade when the value goes below the noise 

floor of the measurement system. A 15 dB per decade roll-off is typically used in calculations of 

solid-state transmitters. Where the fields contain data, the actual emission spectra level relative 

to the peak power is indicated. 
31

Table A-3. U-NII emission spectra for FDR calculations for frame-based devices. 

ΔF

Frequency

(MHz)

Normalized Spectra Emission (dB)

Manufacturer

C Model 1

Manufacturer

A Model 5

Manufacturer

A Model 3

Manufacturer

D Model 1

Manufacturer

E Model 1

Manufacturer

A Model 2

-200 Roll-off Roll-off Roll-off -63 -61 Roll-off

-180 Roll-off Roll-off Roll-off -63 -60 Roll-off

-160 Roll-off Roll-off Roll-off -62 -60 Roll-off

-140 Roll-off Roll-off Roll-off -63 -59 Roll-off

-120 Roll-off Roll-off Roll-off -62 -57 Roll-off

-100 -82 Roll-off Roll-off -60 -58 -83

-90 -81 -82 Roll-off -61 -59 -83

-80 -80 -82 Roll-off -61 -59 -83

-70 -80 -81 Roll-off -60 -60 -81

-60 -78 -80 Roll-off -60 -59 -81

-50 -75 -79 -76 -60 -60 -79

-40 -71 -76 -75 -59 -59 -79

-30 -60 -72 -71 -59 -58 -73

-20 -46 -46 -48 -57 -45 -46

-10 -29 -15 -16 -40 -31 -15

-3 dB

-4.2 MHz

-3 dB

-5.9 MHz

-3 dB

-5.9 MHz

-3 dB

-5.8 MHz

-3 dB

-3.9 MHz

-3 dB

-6 MHz

0 0 0 0 0 0 0

-3 dB

4.2 MHz

-3 dB

5.8 MHz

-3 dB

6.2 MHz

-3 dB

4.0 MHz

-3 dB

4 MHz

-3 dB

5.7 MHz

10 -30 -16 -16 -44 -27 -16

20 -49 -48 -47 -54 -46 -47

30 -60 -73 -67 -60 -56 -68

40 -62 -74 -67 -61 -57 -69

50 -62 -75 -68 -61 -61 -69

60 -62 -76 -68 -61 -61 -69

70 -62 -77 -70 -61 -62 -69

80 -62 -77 -71 -61 -61 -69

90 -62 -78 -73 -61 -62 -69

100 -62 -80 -74 -61 -62 -69

120 -62 -83 -76 -61 -63 -71

140 -66 -84 Roll-off -61 -66 -73

160 -67 Roll-off Roll-off -61 -69 -76

180 -68 Roll-off Roll-off -61 -69 -78

200 -70 Roll-off Roll-off -63 -71 -81

3 dB

Bandwidth 

(MHz)

9.4

3 dB

Bandwidth 

(MHz)

11.7

3 dB

Bandwidth 

(MHz)

12.1

3 dB

Bandwidth 

(MHz)

9.8 MHz

3 dB

Bandwidth 

(MHz)

7.9

3 dB

Bandwidth 

(MHz)

11.7
32

Table A-4. U-NII emission spectra for FDR calculations for frame-based devices. 

ΔF

Frequency

(MHz)

Normalized Spectra Emission (dB)

Manufacturer 

F Model 2

Manufacturer 

F Model 3

Manufacturer G Model 1 

(20MHz) mode

Manufacturer G Model 

1 (40MHz) mode

-200 -54 -57 -59 -56

-180 -54 -57 -58 -56

-160 -54 -57 -58 -56

-140 -53 -57 -58 -56

-120 -54 -57 -57 -56

-100 -53 -57 -57 -54

-90 -54 -56 -56 -53

-80 -55 -57 -55 -52

-70 -53 -57 -55 -49

-60 -53 -57 -53 -45

-50 -53 -55 -53 -41

-40 -49 -53 -52 -35

-30 -45 -45 -44 -33

-20 -30 -36 -35 -18

-10 -15 -19 -15 -0.1

-3 dB

-8.8 MHz

-3 dB

-8.1 MHz

-3 dB

-8.2 MHz

-3 dB

-17.5 MHz

0 0 0 0 0

-3 dB

8.2 MHz

-3 dB

7.6 MHz

-3 dB

8.3 MHz

-3 dB

17.6 MHz

10 -15 -25 -17 -0.5

20 -32 -41 -37 -22

30 -47 -47 -46 -36

40 -52 -53 -51 -41

50 -53 -54 -54 -44

60 -54 -56 -55 -47

70 -54 -54 -57 -50

80 -53 -55 -57 -52

90 -54 -56 -57 -54

100 -55 -56 -58 -55

120 -55 -57 -59 -56

140 -56 -58 -61 -57

160 -55 -56 -61 -58

180 -57 -57 -62 -58

200 -57 -58 -64 -58

3 dB

Bandwidth 

(MHz)

17

3 dB

Bandwidth 

(MHz)

15.7

3 dB

Bandwidth 

(MHz)

16.5

3 dB

Bandwidth 

(MHz)

35.1
FORM NTIA-29 U.S. DEPARTMENT OF COMMERCE 

(4-80) NAT’L. TELECOMMUNICATIONS AND INFORMATION ADMINISTRATION

BIBLIOGRAPHIC DATA SHEET

1. PUBLICATION NO.

TR-12-486

2. Government Accession No. 3. Recipient’s Accession No.

4. TITLE AND SUBTITLE

Case Study: Investigation of Interference into 5 GHz Weather Radars from Unlicensed 

National Information Infrastructure Devices, Part III

5. Publication Date

June 2012

6. Performing Organization Code

ITS.M

7. AUTHOR(S)

John E. Carroll, Geoffrey A. Sanders, Frank H. Sanders, and Robert L. Sole

9. Project/Task/Work Unit No.

8. PERFORMING ORGANIZATION NAME AND ADDRESS 3152012-300

Institute for Telecommunication Sciences

National Telecommunications & Information Administration

U.S. Department of Commerce

325 Broadway

Boulder, CO 80305

10. Contract/Grant Number.

11. Sponsoring Organization Name and Address

National Telecommunications & Information Administration

Herbert C. Hoover Building

14th & Constitution Ave., NW

Washington, DC 20230

12. Type of Report and Period Covered

14. SUPPLEMENTARY NOTES

15. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant bibliography or 

literature survey, mention it here.)

In early 2009, the Federal Aviation Administration (FAA) became aware of interference to Terminal Doppler Weather 

Radars (TDWRs) that operate in the 5600–5650 MHz band and provide measurements of gust fronts, windshear, microbursts, 

and other weather hazards for improved safety of operations in and around airports. National Telecommunications and 

Information Administration (NTIA) engineers, with assistance from FAA engineers, determined the interference to be caused 

by some unlicensed national information infrastructure (U-NII) dynamic frequency selection (DFS) devices operating in the 

same frequency band as TDWR systems. These devices use DFS technology that is supposed to detect the presence of nearby 

co-channel radars and change operating frequencies to prevent interference to those radars. This report, the third of a threepart series, describes some U-NII emission spectra and introduces an additional set of TDWR test waveforms that the Federal 

Communications Commission (FCC) may use during DFS U-NII device testing. This report also explores the distances and 

geometries at which interference to TDWRs from U-NII devices is likely to occur.

16. Key Words (Alphabetical order, separated by semicolons)

dynamic frequency selection; electromagnetic compatibility; radar interference; radar performance degradation; RF 

interference; spectrum sharing technology; terminal Doppler weather radar; unlicensed national information infrastructure

17. AVAILABILITY STATEMENT

UNLIMITED.

FOR OFFICIAL DISTRIBUTION.

18. Security Class. (This report)

Unclassified

20. Number of pages

46

19. Security Class. (This page)

Unclassified

21. Price:
NTIA FORMAL PUBLICATION SERIES 

NTIA MONOGRAPH (MG) 

A scholarly, professionally oriented publication dealing with state-of-the-art research or an 

authoritative treatment of a broad area. Expected to have long-lasting value. 

NTIA SPECIAL PUBLICATION (SP) 

Conference proceedings, bibliographies, selected speeches, course and instructional materials, 

directories, and major studies mandated by Congress. 

NTIA REPORT (TR) 

Important contributions to existing knowledge of less breadth than a monograph, such as results 

of completed projects and major activities. Subsets of this series include: 

 NTIA RESTRICTED REPORT (RR) 

Contributions that are limited in distribution because of national security classification or 

Departmental constraints. 

 NTIA CONTRACTOR REPORT (CR) 

Information generated under an NTIA contract or grant, written by the contractor, and 

considered an important contribution to existing knowledge. 

 JOINT NTIA/OTHER-AGENCY REPORT (JR) 

This report receives both local NTIA and other agency review. Both agencies’ logos and 

report series numbering appear on the cover. 

NTIA SOFTWARE & DATA PRODUCTS (SD) 

Software such as programs, test data, and sound/video files. This series can be used to transfer 

technology to U.S. industry. 

NTIA HANDBOOK (HB) 

Information pertaining to technical procedures, reference and data guides, and formal user's 

manuals that are expected to be pertinent for a long time. 

NTIA TECHNICAL MEMORANDUM (TM) 

Technical information typically of less breadth than an NTIA Report. The series includes data, 

preliminary project results, and information for a specific, limited audience. 

For information about NTIA publications, contact the NTIA/ITS Technical Publications Office at 325 

Broadway, Boulder, CO, 80305 Tel. (303) 497-3572 or e-mail info@its.bldrdoc.gov. 

This report is for sale by the National Technical Information Service, 5285 Port Royal Road, Springfield, 

VA 22161,Tel. (800) 553-6847.