NIST Technical Note 1937

Development of Laboratory Test 

Methods for RF-Based Electronic 

Safety Equipment: Guide to the 

National Fire Protection Association

1982 Standard

Audrey K. Puls

William F. Young 

Kate A. Remley

Jacob Healy

Luis A. Gonzalez

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NIST Technical Note 1937

Development of Laboratory Test 

Methods for RF-Based Electronic 

Safety Equipment: Guide to the 

National Fire Protection Association 

1982 Standard 

Audrey K. Puls

William F. Young 

Kate A. Remley

Jacob Healy

Luis A. Gonzalez

RF Technology Division

Communications Technology Laboratory

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October 2016

U.S. Department of Commerce 

Penny Pritzker, Secretary

National Institute of Standards and Technology 

Willie May, Under Secretary of Commerce for Standards and Technology and Director
Certain commercial entities, equipment, or materials may be identified in this

document in order to describe an experimental procedure or concept adequately.

Such identification is not intended to imply recommendation or endorsement by the

National Institute of Standards and Technology, nor is it intended to imply that the

entities, materials, or equipment are necessarily the best available for the purpose. 

National Institute of Standards and Technology Technical Note 1937

Natl. Inst. Stand. Technol. Tech. Note 1937, 74 pages (October 2016) 

CODEN: NTNOEF

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i

Executive Summary

The National Institute of Standards and Technology (NIST) with support from the Department of 

Homeland Security has been working with the National Fire Protection Association (NFPA) to 

develop standards and test methods for radio-frequency personal alert safety systems (RF PASS). 

The RF PASS systems are incorporated into a firefighter’s gear and are used to alert a base station 

when the firefighter is in distress, has been motionless for more than 30 seconds, or to alert the 

firefighter in case an evacuation is necessary. 

The material here covers the development of several test methods either already adopted by the 

NFPA or targeted for future revisions of NFPA 1982 Personal Alert Safety Systems. These test 

methods represent five RF PASS deployment conditions: a highly reflective (high multipath) RF 

environment, a prescribed amount of attenuation in a point-to-point communication link, a multihop connection path, in-band wireless activity, and temporary exposure to high-power, in-band RF 

interference. The data and developed testing are based on currently used RF PASS frequencies:

450 MHz, 900 MHz, and 2.4 GHz.

This technical note uses various experimental setups that utilize a combination of equipment 

including, but not limited to, spectrum analyzers, signal generators, power combiners, anechoic 

chambers, and reverberation chambers. Specific experimental setups are discussed in the sections 

in which they apply. 

In developing the test methods, several key aspects of the test setup are investigated in detail. For 

example, electric field uniformity within the test chambers, created by different antennas, was 

examined to determine which antenna would provide the lowest variability in signal level over the 

testing plane. In support of the multipath test, the RF reflective behavior of a reverberation 

chamber was evaluated. Finally, interference testing required establishing the duty cycles and 

power levels appropriate for anticipated deployment environments. 

Supporting material from previous RF PASS in-field testing, along with correlated RF propagation 

measurements are used to set test parameter values. For example, the attenuation values used for 

the various links represent typical conditions measured in the field and reported in prior NIST 

work. Some in-field data are also used in establishing the interference duty cycles and power 

levels. The ultimate goal was to establish methods and parameter values that mimic real 

deployment conditions in a laboratory setting to the extent possible. 

Finally, the intent of this document is to provide users of the test methods with insight into how 

the tests were developed and why certain procedures and values were adopted. This document is 

not intended to give step-by-step directions on how each test should be conducted. Rather, the 

material contained in this document should answer questions that may arise during the application 

of the tests. Thus, the aim is to capture the insight gained by the test developers in a manner that 

will allow others to obtain the same understanding in a shorter time period. 

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Development of Laboratory Test Methods for RFBased Electronic Safety Equipment: Guide to 

the National Fire Protection Association 1982

Standard

Audrey K. Puls, William F. Young, Kate A. Remley, Jacob Healy, and Luis A. Gonzalez

RF Technology Division

National Institute of Standards and Technology

325 Broadway, Boulder, CO 80305

Abstract: We discuss a variety of standardized test methods that have been developed to assess 

radio-frequency personal alert safety systems (RF PASS) that are used as “firefighter down” 

beacons. The test methods found in this document represent five RF PASS deployment conditions: 

a highly reflective (high multipath) RF environment; a prescribed amount of attenuation in a pointto-point communication link; a multi-hop reception path; in-band wireless activity; and temporary 

exposure to high-power, in-band RF interference. The tests and corresponding data are based on 

current RF PASS frequencies: 450 MHz, 900 MHz, and 2.4 GHz. The test environments, tests, and 

measured data are discussed in detail to accompany the National Fire Protection Association’s 

standard “NFPA 1982: Personal Alert Safety Systems.”

Key words: anechoic chamber; firefighter; interference; multipath; personal alert safety system; 

point-to-point radio communications; path loss; radio-wave propagation; reverberation chamber; 

wireless system.

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Contents

Executive Summary......................................................................................................................... i

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

2. Field Uniformity Tests................................................................................................................ 2

2.1 Calculating Field Uniformity................................................................................................ 3

2.2 Effect of Antenna Type......................................................................................................... 6

2.3 NIST Field-Uniformity Measurement Results...................................................................... 8

2.3.1 462 MHz ........................................................................................................................ 8

2.3.2 915 MHz ........................................................................................................................ 9

2.3.3 2.4 GHz .......................................................................................................................... 9

2.3.3.1 Uniformity Testing with 13 Collection Points...................................................... 10

2.3.3.2 Uniformity Testing with 25 Collection Points...................................................... 11

2.3.4 Conclusion ................................................................................................................... 13

2.4 Field Uniformity Measurement Uncertainty Analysis........................................................ 14

2.4.1 Type A Uncertainties................................................................................................... 14

2.4.2 Type B Uncertainties ................................................................................................... 14

2.4.3 Combined Uncertainty................................................................................................. 14

3. Multipath Test and Reverberation Chambers........................................................................... 16

3.1 Introduction......................................................................................................................... 16

3.2 Background......................................................................................................................... 18

3.3 Quality of the Reverberation Chamber............................................................................... 19

3.4 Calibration Process ............................................................................................................. 19

3.5 Multipath Testing of an RF PASS System ......................................................................... 20

3.6 Results................................................................................................................................. 24

4. Configuration Considerations for Point-Point, Multi-Hop, and Interference Testing.............. 25

4.1 Path Loss Measurements for Anechoic Chamber............................................................... 26

4.1.1 Measurement of Cable Loss for an Individual Anechoic Chamber Setup................... 27

4.1.2 Determining Antenna Type for RF PASS Testing Configuration ............................... 27

4.1.3 Path Loss between Two Anechoic Chambers.............................................................. 29

4.1.3.1 Chambers 1 and 2.................................................................................................. 30

4.1.3.2 Chambers 1 and 2 with Added Attenuation.......................................................... 31

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4.1.4 RF PASS Performance between Two Anechoic Chambers ........................................ 32

4.2. Reverberation Chamber Calibration and RF PASS Stirrer Speed Dependency ................ 32

4.2.1 Reverberation Chamber Calibration ............................................................................ 32

4.2.2 Stirrer Speed Dependency 2.4 GHz Manufacturer 3 RF PASS................................... 33

4.2.3 Stirrer Speed Dependency 900 MHz Manufacturer 1 RF PASS ................................. 34

4.2.4 Stirrer Speed Dependency 900 MHz Manufacturer 2 RF PASS ................................. 35

4.3. Path Loss across Four Chambers....................................................................................... 36

4.3.1 Path Loss Calculations................................................................................................. 36

5. Point-to-Point, Multi-Hop and Interference Testing................................................................. 37

5.1 Point-to-Point Motion and Evacuation Alarm Test ............................................................ 37

5.1.1 Description................................................................................................................... 37

5.1.2 NIST Tests: Point-to-Point Motion Alarm Results...................................................... 39

5.1.3 Evacuation Alarm Test Results.................................................................................... 42

5.1.4 Point-to-Point Test Uncertainty Analysis.................................................................... 43

5.1.4.1 Combined Uncertainty.......................................................................................... 44

5.2 Multi-Hop Test.................................................................................................................... 45

5.2.1 Description................................................................................................................... 45

5.2.2 NIST Results................................................................................................................ 46

5.3 Low-Power Interference Testing ........................................................................................ 47

5.3.1 Introduction.................................................................................................................. 47

5.3.2 The Target Value of Interference................................................................................. 49

5.3.3 Measurement System................................................................................................... 50

5.3.4 Specific Interference Test Configurations for 900 MHz and 2.4 GHz Systems.......... 51

5.3.5 Measurement Procedure for Interference Testing........................................................ 52

5.3.6 NIST Results................................................................................................................ 54

5.4. High-Power Interference Testing....................................................................................... 55

5.4.1 Creating the Interfering Signal..................................................................................... 55

5.4.2 Setup, Procedure, and Test........................................................................................... 55

5.4.3 Signal Generation......................................................................................................... 58

5.4.3.1 Background........................................................................................................... 58

5.4.3.2 Theory................................................................................................................... 58

5.4.3.3 Method .................................................................................................................. 59

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5.4.3.4 Plots....................................................................................................................... 60

5.4.4 NIST Results................................................................................................................ 61

5.4.4.1 Manufacturer 3 High-Power Interference Test Results........................................ 61

5.4.4.2 Manufacturer 1 High-Power Interference Test Results........................................ 62

6. Conclusion ................................................................................................................................ 63

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1. Introduction

Personal Alert Safety Systems (PASS) are used by firefighters to indicate an emergency

“firefighter-down” condition. In traditional PASS, when a firefighter is motionless for 30 seconds, 

a loud, audible alarm is emitted from the body-worn PASS beacon, alerting firefighters nearby that 

another firefighter is in distress [1]. RF-based PASS is a relatively new product technology that 

can potentially extend the reach of the PASS beacon from the firefighter to the incident command 

station outside a structure. They also allow the incident commander to send an “evacuate” 

command to the firefighter inside a structure, a new and potentially life-saving technology. 

For firefighting companies that choose to use RF-based PASS, test methods to assess performance 

under representative environmental conditions can increase confidence in the use of this 

technology. To this end, two NIST-developed test methods were incorporated into the 2013 

revision of “NFPA 1982 Personal Alert Safety Systems” [1] to test the operation of RF PASS 

under typical point-to-point attenuation (path loss) conditions and in the presence of in-band RF 

interference (coexistence). These two test methods were also detailed in [2] and [3]. Additional 

test methods have recently been developed at NIST. One method tests the operation of RF-based 

PASS systems in highly reflective, “multipath” environments such as factories, refineries, and 

warehouses. A second test is designed to evaluate RF-based PASS performance in high-attenuation 

environments such as subways and large high-rise buildings. Work is underway to test RF-based

PASS in the presence of strong interfering signals. Note that over-the-air performance tests (as 

opposed to cabled tests) are necessary because system-level verification is required and antennas 

may be integrated into the PASS or self-contained breathing apparatus. This complicates test 

procedures. The details on how these over-the-air test methods are implemented in a laboratory 

environment is the subject of this Technical Note.

From 2008 through 2016, the Department of Homeland Security funded researchers from the 

National Institute of Standards and Technology (NIST) to support the development of rigorous test 

methods for RF-based PASS systems. NIST researchers performed several field tests to 

characterize RF propagation channels in representative firefighting conditions where RF-based 

PASS communication was expected to be poor, focusing on point-to-point signal penetration into 

and out of medium-and large-sized structures. The researchers conducted side-by-side tests of the 

RF channel characteristics (path loss and reflectivity) and RF-based PASS in order to determine 

parameters and metrics for laboratory-based tests.

NIST Technical Note 1559 [3] summarizes NIST measurements made in seven environments: an 

urban canyon (downtown Denver, CO), a 12-story apartment building, three one-story office 

buildings, a high-rise office building, and a convention center. These studies summarized the level 

of path loss and multipath (given by the metric “root-mean-square (RMS) delay spread”) between 

the incident command and portable RF PASS. This study showed a total path loss of approximately 

100 dB for a point-to-point link. This study also reported measured values of RMS delay spread 

ranging from tens of ns to over 400 ns. 

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NIST Technical Note 1546 “Measurements to Support Modulated-Signal Radio Transmissions for 

the Public-Safety Sector” [5] describes measurements in which the level of multipath measured in 

three environments: an office corridor, an oil refinery, and a subterranean tunnel. Values of RMS 

delay spread ranged from tens to over 200 ns. 

NIST Technical Note 1792 details additional studies where RF PASS were deployed in a subway 

and in the Empire State Building in New York City. Here, path-loss values up to 260 dB were 

observed. The RF PASS systems that utilized repeaters were found to be able to penetrate deeper.

Based on the NIST measurement studies, parameter values used in the NFPA test methods were 

recommended as 100 dB for a point-to-point link, ~260 dB for a multiple-hop system, and at least 

400 ns for RMS delay spread. The anechoic/reverberation chamber set-ups in the test methods 

described below meet these requirements. Details on how the test chambers are configured to 

provide these parameter values are given below. 

The development of these laboratory-based test methods for RF PASS required investigation into 

components of the test setup, parameter settings, and electromagnetic environments in order to 

ensure a robust, repeatable test with sufficiently low measurement uncertainty. Once those

parameters were well-established, the actual test configurations were constructed. 

In the next several sections, the concepts of field uniformity, path loss (or channel attenuation), 

multipath and interference are discussed. The information should help in understanding how these 

elements support the basic concepts of the test methods discussed in the later sections of this 

document. 

Throughout this document various acronyms are used which are outlined in Table 1.

Table 1. Acronyms

Acronym Definition

NIST National Institute of Standards and Technology

RF PASS Radio-Frequency Personal Alert Safety System

NFPA National Fire Protection Association

PXI PCI eXtension (Used for Signal Generation)

SA Spectrum Analyzer

SG Signal Generator

RC Reverberation Chamber

AC Anechoic Chamber

2. Field Uniformity Tests

All of the RF PASS test methods in NFPA 1982 require the use of anechoic chambers. Ideally, the 

anechoic chamber configuration should provide the same electromagnetic (EM) or RF signal 

conditions to the portable unit and base station at a specified region within the chamber to support 

repeatability of the test results. A uniform field1at a specific region within the anechoic chamber 

theoretically allows the RF PASS to be placed in any orientation at that location and experience 

 

1 Uniform field in this document is used to describe an isotropic field. An isotropic field is uniform in all orientations.

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the same or similar field conditions. In order to quantify the electric field uniformity, field strengths 

were determined at the specific frequencies of interest, namely 462 MHz, 915 MHz, and 2.4 GHz.

The frequencies listed here are in the nominal carrier frequencies or within communication bands 

of the RF PASS systems used in developing the test methods.

2.1 Calculating Field Uniformity

To verify the field uniformity across the test platform in each anechoic chamber, a three-axis field 

probe was used. The electric field probe collected measurements in volts/meter (V/m) which in 

post processing were normalized by the minimum value measured with (1). Figure 1 details the 

basic probe collection setup at the table surface in the anechoic chamber. A dielectric square table 

sits at the bottom of the anechoic chamber, as shown in Figure 1, and the two data measurement 

patterns on the surface of the table are shown in Figure 2 and Figure 3. Figure 4 illustrates the 

probe x-, y-, and z-orientation.

The normalized uniformity, reported in decibels (dB) was based on the total field, i.e., the 

contribution from all three of the orthogonal components. If the variation in the total field across 

the middle 30 cm by 30 cm of the platform was less than 3 dB, the field was considered uniform.

Other standards use 6 dB as the threshold for uniformity measurements. However, due to the small 

platform size in this case a tighter standard of 3 dB is required. The normalized field at each point 

is given by equation (1).

Normalized Field (dB)

= 20 × log10 (

Specific Probe Value Averaged Over Three Components (

V

m

)

Minimum Probe Value Across Entire Table (

V

m

)

)

(1)

Two different measurement patterns were used. The first pattern, shown in Figure 2, consisted of 

13 measurement points [6]. The uniformity of the field was determined by interpolating between 

measured values and plotting the contour mapping of the resultant field. This measurement 

approach is used in the NFPA 1982, 2013 edition standard [1]. 

To adapt the field uniformity measurement process more closely to traditional EMC standards 

such as [6], a larger number of points were collected, with the option to ignore up to 25 % of the 

points. Twenty-five measurement points are utilized in the pattern shown in Figure 3. In 

determining the field uniformity, 25 % of the 25 points could be discarded. 

The anechoic chamber used by NIST for this and other tests throughout this technical note is 

187.96 cm (74 inches) high, 91.44 cm (36 inches) wide and long, and has 100 dB shielding. 

Chambers with different dimensions can be used so long as they are rated for the frequency of the 

device under test. 

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Figure 1. Setup for Field Uniformity Test.

A key feature of the setup in Figure 1 is the inclusion of the RF amplifier. This ensures that the 

signal read by the probe is sufficiently above the minimum sensitivity of the field probe. Also, 

Figure 1 depicts an anechoic chamber with a table area that is less than 0.5 m by 0.5 m. The relative 

proximity of the sides of the chamber to some DUT’s can make it difficult to achieve a uniform 

field at the measurement plane. The measurements and discussions below provide examples of 

how a lack of uniformity can be overcome.

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Figure 2.Table top placed within the anechoic chamber showing markings where a 3-axis field probe was 

placed. These 13 points were used for the 450 MHz, 900 MHz, and 2.4 GHz uniformity tests.

Figure 3. Table top placed within the anechoic chamber showing markings where a 3-axis field probe was 

placed. These 25 points were used for the 2.4 GHz uniformity test.

Figure 4. Field probe and orientation in chamber.

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2.2 Effect of Antenna Type

The type of antenna at the top of the anechoic chamber can affect the measured field uniformity.

The measured field uniformity at the test platform for several antenna types is studied in this 

section. These antenna types are used throughout the document. The antenna types are listed in 

Table 2.

Table 2. Antennas and specifications.

The VSWR was measured for each antenna to verify its performance with the specifications listed 

above. A vector network analyzer was connected through an anechoic chamber to each antenna 

and the S11 parameter was measured. This was converted to VSWR and plotted for the frequency 

band of interest, as shown in Figure 5.

Frequency Range of Operation Gain VSWR Polarization

Patch A 2.4 GHz-2.5 GHz 8 dBi < 1.5:1 avg. Left hand circular

Patch B 2.4 GHz-2.5 GHz 8 dBi < 1.5:1 avg. Right hand circular

Patch C 2.4 GHz-2.5 GHz 7 dBi < 1.5:1 Right hand circular

Horn 1 GHz-18 GHz 6 dBi 3.5:1 max

<2:1 above 1.5 GHz Linear

Helix 2.4 GHz-2.5 GHz 10 dBi < 1.3:1 Right hand circular

Discone 25 MHz-1300 MHz 2 dBi Omnidirectional

Patch D 430 MHz-450 MHz 7 dBi 3dBd < 1.5 freq resonance Right hand circular

Patch E 902 MHz- 928 MHz 9 dBi 1.3 Left hand Circular

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Figure 5. Measured VSWR of various antennas. (a) Patch B; (b) Patch C; (c) Horn; (d) Helix; (e) Patch D; 

and (f) Patch E.

2.4 2.425 2.45 2.475 2.5 1

1.5

2

2.5

3

3.5

4

Frequency (GHz)

 (a)

2.4 2.425 2.45 2.475 2.5 1

1.5

2

2.5

3

3.5

4

Frequency (GHz)

 (b)

0.9 1.3 1.7 2.1 2.5

1

1.5

2

2.5

3

3.5

4

Frequency (GHz)

 (c)

2.4 2.425 2.45 2.475 2.5

1

1.5

2

2.5

3

3.5

4

Frequency (GHz)

 (d)

430 435 440 445 450

1

1.5

2

2.5

3

3.5

4

Frequency (MHz)

 (e) VSWR

902 908.5 915 921.5 928

1

1.5

2

2.5

3

3.5

4

Frequency (MHz)

(f)

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2.3 NIST Field-Uniformity Measurement Results

In the following sections we show contour plots using the data from the uniformity tests. The 

contour plots have an x and y axis labeled with measurements that replicate the dimensions of the 

platform within the chamber where the probe was placed. The contour plots take the coordinates 

of each point where the probe was placed and plots the respective ‘heights’ of the field strength. 

When only thirteen data points are used, a manual interpolation between points calculates the 

average value between points to help fill in the contour plot. With 25 points interpolation was not 

necessary. Different colors are filled in and the lines representing different strengths are labeled to 

help illustrate the differences in field strength.

2.3.1 462 MHz

The lowest frequency tested in the anechoic chambers was 462 MHz. The setup as shown in Figure 

1, with the 3-axisfield probe positioning shown in Figure 2 yielded the following successful results

with less than 3 dB variation across the 30 cm by 30 cm square. Antenna D, as described in Table 

3 was used for this test. Figure 6 below shows the contour plot of the uniformity results where the 

white circles mark the field probe measurement locations and linear interpolation was used 

between points. For this frequency, data for the measurement pattern in Figure 3 were not 

collected.

Figure 6. Uniformity results for 462 MHz antenna showing less than 3 dB variation across 30 cm by 30 cm 

square.

Side Opposite Bulkhead (cm)

Front Face (With Door) (cm)

Selected data points Minimum power point

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2.3.2 915 MHz 

The setup shown in Figure 1, with the 3-axis field probe positioning shown in Figure 2 produced 

the following successful results with less than 3 dB variation across the 30 cm by 30 cm square.

Antenna E, as described in Table 3, was used in this test. Figure 7 shows the contour plot of the 

uniformity results. As in the 462 MHz case, data for the measurement pattern in Figure 3 were not 

collected.

Figure 7. Uniformity results for 915 MHz antenna showing less than 3 dB variation across 30 cm by 30 cm 

square.

2.3.3 2.4 GHz

We determined the field uniformity at 2.4 GHz using the approaches given in Figure 1 and Figure 

3 with several different antennas shown in Table 2. This was necessary to determine the tradeoff 

between the maximum antenna gain and the field uniformity performance. In general, while high 

antenna gain is desirable, the uniformity suffers due to the narrowing of the main antenna beam.

The first measurement case follows the data collection pattern and contour plot calculation, as in 

the previous sections. 

In addition to the two data collection patterns, three different antennas were tested. These different 

antennas were mounted to the top of the chamber and the electric field was measured at the 

platform as shown in Figure 1. Patch A, Helix, and Patch C were tested. The antenna efficiency of 

the three antennas is not known.

Table 3 shows the various test configurations and conditions to verify field uniformity. Table 4

explains each test. Table 2 describes the parameters for each antenna used in Table 3. Because the Side Opposite Bulkhead(cm)

Front Face (With Door) (cm)

Relative Power (dB)

Selected data points Minimum power point

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helix passed uniformity tests for the 2.4 GHz band, it was used in the development of the test 

methods described in future sections.

Table 3. Various antennas and test configurations.

Test was performed and the field uniformity exceeded 3 dB variation.

 Test was performed and the field uniformity met the uniformity requirements.

Table 4. Uniformity test descriptions.

2.3.3.1 Uniformity Testing with 13 Collection Points

The 3-axis field probe is placed on the platform according to Figure 2 and Figure 4. The results 

are shown in Figure 8 through Figure 10 in the form of contour plots. In test 8, and only for the

2.4 GHz frequency, an aperture of dimensions 22.23 cm by 22.23 cm was made from a 47 cm by 

47 cm piece of RF absorbing foam lens with depth 12.61 cm to reduce the interaction of the 

antenna’s radiated signal and reflections from the walls of the chamber.

Antenna 

Name

Antenna Type Test 

1

Test 

2

Test 

3

Test 

4

Test 

5

Test 

6

Test 

7

Test 

8

Patch A Patch N/A N/A N/A N/A

Patch B Patch N/A N/A N/A N/A N/A N/A N/A

Patch C Patch N/A N/A N/A N/A N/A

Horn Dual Ridged 

Horn N/A N/A N/A N/A N/A N/A

Helix Spiral Helix N/A N/A

Test 

Number

Description

1 Uniformity field strength data with 13 collection points.

2 Improvement upon bracket security with 13 collection points.

3 3 inch solid foam added to raise field probe with 13 collection points.

4 Add RF absorber to top of chamber with 13 collection points.

5 Uniformity field strength data with 25 collection points.

6 Different physical antenna used (same model) with 25 collection 

points.

7 90 degree mount rotation of antenna with 25 collection points.

8 Add RF absorber to top of chamber with 25 collection points.

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Figure 8. Uniformity results for Test 1 at 2.4 GHz.

2.3.3.2 Uniformity Testing with 25 Collection Points

The initial testing [2] was based on the collection of 13 data points and the computed contour plot. 

In order to simplify the verification of the field uniformity, we consider a different measurement 

process where we collect more data points, but only require a subset of those points to have less 

than 3 dB of variation. For the 25 point collection process, the 3-axis field probe is placed on the 

platform according to Figure 3 and Figure 4. The goal here was to have 75% of the points on the 

platform within a 3 dB variation. This means up to six points can be removed, and if the remaining 

(b) Patch A

(c) Patch C (d) Helix

(a) Uniformity setup

Selected data points Minimum power point

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points are within 3 dB then the field uniformity can be considered successful. The following graphs 

show how many points would need to be removed in order for the remaining points to be within 3

dB variation. Many of the following figures show that more than six points would need to be 

removed to meet specifications. Only if six or less points are removed will the configuration pass 

the uniformity test.

Figure 9. Uniformity results for Test 5 at 2.4 GHz. Note that more than 6 points would have to be 

removed in all cases. These configurations will not pass the uniformity test.

(a) Patch B (b) Patch C

(c) Horn (d) Helix

Selected data points Minimum power point Removed data points

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Figure 10. Uniformity results for Test 8 at 2.4 GHz. Note that the Helix with the RF absorbing lens is the 

only configuration that requires less than 6 points to be removed and thus will pass the uniformity test.

2.3.4 Conclusion 

Based on the series of measurements described above, we concluded that for the tests throughout 

this report, the Patch D would be used for the 450 MHz frequency range, the Patch E would be 

used for the 900 MHz frequency range, and for the 2.4 GHz range the helix antenna with the RF 

(b) Patch C

(c) Horn (d) Helix

(a) Uniformity Setup

Selected data points Minimum power point Removed data points

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absorbing foam lens would be used as the transmitting antenna at the top of the anechoic chambers. 

The latter is shown in Figure 10 (a). The following section provides an uncertainty analysis for the 

chosen (helix) antenna.

2.4 Field Uniformity Measurement Uncertainty Analysis

This section provides estimates of the uncertainties in the field uniformity measurements for a 

2.4 GHz helix antenna (one of the selected antennas for future tests). We performed this 

uncertainty analysis using a 3-axis field probe, helix antenna, signal generator, and amplifier. This 

analysis could be conducted by other labs to find the uncertainty in their field uniformity 

measurements. 

Following the convention stated in [7], the uncertainties are broken into two categories, Type A 

(evaluated by statistical means), and Type B (evaluated by non-statistical means). Throughout this 

section are several graphs and tables showing components of the uncertainty analysis. Figure 11

shows repeat measurements of field uniformity test data in histogram form. Figure 11 (a) shows 

all data from Test 8 (described in Table 4). Figure 11 (b) shows all data from Test 4 (described in 

Table 4). Figure 11 (c) shows data within the region of interest for Test 8. Figure 11 (d) shows data 

within the region of interest for Test 4. Figure 11 (e) shows combined data from Test 4 and Test 8. 

Figure 11 (f) shows combined data from the shared points (5 points in each test) in Test 4 and Test 

8. Table 5 shows the mean, standard deviation, and relative uncertainty of the data plotted in Figure

11. Table 6 shows the different types of uncertainty contributions present in the field uniformity 

experiment. Figure 11 (f) was chosen as the most relevant experiment because it focuses on the 

region of interest for two separate experiments with common field measurement locations. The 

standard deviation and mean used in Section 2.4.3 are calculated from the data in Figure 11 (f).

2.4.1 Type A Uncertainties

Specifications on equipment (provided by the manufacturer) and measurement precision are 

considered Type A uncertainties and are found in Table 6. Two independent measurements (Tests 

4 and 8 found in Table 4) were taken to find the field levels at various locations on the test platform 

within the anechoic chamber. This setup is shown in Figure 1.

2.4.2 Type B Uncertainties

Specifications on equipment utilized in the setup (not provided by the manufacturer) are

considered Type B uncertainties, and are found in Table 6. For the configuration tested here, the 

uncertainty contributions due to the repeatability of the signal generator, amplifier, and cable are 

considered Type B uncertainties because the uncertainty was approximated from the difference in 

the average of two data sets.

2.4.3 Combined Uncertainty 

Both types of uncertainties are combined to determine the total uncertainty in the field uniformity 

measurements. The calculation of relative uncertainty in Table 5 uses the following equation:

urelative (dB) = 20 × log10 (1 ±

σ

μ

), (2)

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where σ is the standard deviation and μ is the mean.

Figure 11. (a) Test 8 (b) Test 4 (c) Test 8 Region of Interest (d) Test 4 Region of Interest (e) Test 4 and 

Test 8 Region of Interest (f) Shared Points of Test 4 and Test 8 

Calculations in Table 5, excluding urelative, use (3):

u (dB) = 20 × log10 (

linear value

1v

m

) (3)

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Table 5. Mean (μ), standard deviation (σ), and difference of mean, for subplots shown in Figure 11. 

Note that relative uncertainty (u), is not symmetric about the mean because of the log conversion 

process. 

Subfigure (a) (b) (c) (d) (e) (f)

μ (V/m) 40.3 32.3 41.8 32.5 38.5 37.0

μ (dBV/m) 32.1 30.2 32.4 30.2 31.7 31.4

σ (V/m) 3.8 1.7 2.9 1.9 5.3 5.3

urelative (dB) +0.78 

-0.86

+0.45 

-0.47

+0.58 

-0.62

+0.49 

-0.52

+1.12 

-1.29

+1.16 

-1.34

Calculations in Table 6 use (4):

μ, σ (dB) = 20 × log10(linear value + 1) (4)

Table 6. Description of measurement uncertainties with associated values.

Type Variable Name Uncertainty 

Description

Method of Estimate Values 

(Linear)

Values 

(dB)

A uprecision

Precision in 

Measurements

Relative uncertainty from the 

standard deviation of

measurements from Test 4 and 

Test 8 (see Table 4).

0.17 +1.16 

-1.34

A uprobe

EMC Field 

Probe Specified by manufacturer. 0.1 +0.9 -0.9

B usignal generator

Signal 

Generator,

Amplifier,

Cable

(μ5a − μ5b) + (μ5c − μ5d)

2

Where μ5ais the mean dB value 

listed in Table 5 referring to 

Figure 11 (a) etc.

0.26 2.0

The linear values in Table 6 are used in the following equation to determine the combined 

uncertainty. 

 ucombined = √uprecision

2 + uprobe2 + usig gen unit2

 (5)

We combine these uncertainties using root-sum-of-squares addition on the linear values and then 

converted back to decibels. The combined uncertainty converted to decibels is 2.48 dB, which is 

within 3 dB, where 3 dB is the threshold for field uniformity specified in NFPA 1982.

3. Multipath Test and Reverberation Chambers

3.1 Introduction 

This section covers the basics of calibration, setup, and measurements for electromagnetic 

reverberation chambers to simulate a fireground response scenario in which the incident command 

station is outside a structure and a portable unit is inside a highly-reflective structure such as an 

oil refinery or factory. As in [1], both the base station and the portable device are tested under freefield conditions and, to simulate building penetration, ~100 dB of average path loss is included 

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between the two units. The intent is to provide the reader with a basic methodology on how to 

carry out measurements of wireless systems wherein one of the communication nodes is a wireless 

device located in an electromagnetic reverberation chamber (RC) and the other is located in an 

anechoic chamber (AC). The reverberation chamber in this test and others throughout this 

technical note is 147.32 meters (58 inches) high, 118.11 cm (46.5 inches) long, and 149.86 cm (59 

inches) wide. Chambers with other dimensions can be used so long as they are rated for the 

frequency of the device under test. Any high efficiency antenna, such as a Helix, can be used in 

this multipath test because the reverberation chamber averages out the antenna pattern. This means 

the antenna pattern will not affect the result. Figure 12 shows the basic test setup. An implicit 

assumption in this discussion is that the wireless system utilizes integrated or non-removable 

antennas on the RF PASS. The wireless system and the RF PASS may also have limited, if any, 

self-diagnostic capabilities. Further, in-depth discussion on key RC parameters can be found in 

the supplied references.

Throughout this section there are many equations used with variable descriptions that can be found 

in Table 7.

Table 7. Variable descriptions.

Variable Description

LAC

SG Loss of Cable Connected between the Signal Generator and Anechoic 

Chamber

LAC

Tx Loss of Cable Connected between the Transmitting Antenna and the 

Anechoic Chamber

LRC

Rx Loss of Cable Connected between the Receiving Antenna and the 

Reverberation Chamber

LRC

SA Loss of Cable Connected between the Spectrum Analyzer and the 

Reverberation Chamber

Ltot Total cable Loss

eTx,Rx Antenna Efficiency between Transmitting and Receiving Antenna

mTx,Rx Mismatch Loss between Transmitting and Receiving Antenna

PSA

ref(i) Peak Spectrum Analyzer Measurement for each paddle position (i)

GCC Chamber-to-Chamber Gain

PSG

ref Power Setting of the Signal Generator

PSA

ref Power Measurement from the SA

GAMP Gain of the Optional Amplifier

〈∙〉 Average of Measurements across all Paddle Positions

PLTarget Target Average-Total-Attenuation

LVAR Variable Attenuation loss

GTx Gain of Transmitting Antenna

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Figure 12. General multipath test setup showing linked anechoic and reverberation chambers. The RF 

PASS unit is located on a solid foam platform to ensure a minimum of a 1⁄2 λ separation from any of the 

chamber walls or floor. Note the Rx antenna in the RC is only used during the calibration setup discussed 

below; the Rx antenna and cable are left in the RC, but disconnected from the bulkhead during testing of 

the RF PASS.

An important focus of the discussion below is on the use of a signal generator and spectrum 

analyzer in the calibration process. Vector network analyzers are often used to calibrate RCs as 

well. The calibration here offers another option when use of a vector network analyzer is not 

feasible. This calibration process is intended for use in setting up the multipath test environment 

inside a RC. 

3.2 Background

The basic theory behind RCs is well established [8, 9], and RCs are used in several wireless 

technology measurements such as electromagnetic compatibility (EMC) testing [6] and total 

radiated power (TRP) of single-frequency [10][11], and modulated-signal [12][13] systems. The 

application discussed here focuses on use of the RC to create a rich multipath environment to 

emulate expected conditions when deployed in settings that provide a significant amount of 

electromagnetic scattering and reflections (e.g., factory floors, oil refineries, etc [14][15]). A key 

consideration relevant to wireless system testing is that the RC is considered a statistical RF 

environment. This means that statistical analysis techniques are required to interpret measurement 

results from a measurement process that makes use of a RC. The calibration process is discussed 

below and will demonstrate how statistical analysis techniques apply to RCs. 

Reverberation chambers operate under a proposition directly counter to that of an electromagnetic 

anechoic chamber, namely, that nearly all the energy is reflected back from the chamber walls and 

into the testing area or volume. In an anechoic chamber, the absorbing material on the walls 

prevents (or at least significantly attenuates) any electromagnetic reflections scattered from the 

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wall surfaces. Additionally, in a RC, the mixing of the electromagnetic fields by “stirring” via 

rotating paddles or position changes creates a rich multipath environment. 

3.3 Quality of the Reverberation Chamber 

The RC test setup requires a calibration process to ensure accurate results are achieved during 

testing. This calibration process assumes the RC is “well-stirred”. A well-stirred chamber implies 

that the chamber supports statistically uniform and isotropic electric and magnetic fields, (in all 

orthogonal field components), and that these field components vary sufficiently in amplitude (e.g., 

a coefficient of variation of one [16]) and over a sufficient dynamic range in level (e.g., greater 

than 20 dB) during the mixing process. (Note that henceforth we will discuss RC behavior with 

respect to the electric field or power since those are two quantities that are often measured in a 

RC.) 

In [16], the concept of a good or well-stirred reverberation chamber is discussed along with three 

measurements or checks that can be used to evaluate the quality of the RC setup. The three 

measurements are all statistical in nature, namely the maximum-to-average ratio, the maximumto-minimum ratio and the coefficient of variation. Achieving “good” values for these three 

measures does not guarantee a well-stirred chamber setup. If the results from these tests are not 

acceptable, the RC setup should be reworked and re-evaluated as needed. Manufacturers of RCs 

typically provide a range of frequencies over which the RC is considered well-stirred. For the 

purposes of the multipath test described below, ± 3 dB variation in electric field is considered wellstirred. However, we need to recognize that, while a nearly empty RC may perform quite well, 

when objects such as test equipment, antennas, and the RF PASS are placed in the RC, the stirring 

quality can degrade quite significantly. A detailed process for determining the quality of the RC 

setup is described in [6].

3.4 Calibration Process

This test procedure begins with a determination of the Ltot in which a known source such as a 

signal generator (SG) and a receiver such as a spectrum analyzer (SA) are used to find the gain 

between a transmitting source and the receiver. This is the gain of the chamber-to-chamber 

environment, and in this context, a negative gain value (in dB) represents a loss. Since a RC is 

one chamber of the system, a stirring paddle is turned between measurement samples to produce 

statistically uncorrelated samples, which are then averaged. (Note that uncorrelated samples imply 

independence between those samples in a well-stirred RC.) The procedure follows below. All 

equipment that will be located in the RC as part of the test should be present in the RC during the 

calibration process. This includes the inactive (powered down) RF PASS.

Additional Calibration Considerations

We need to first observe the RF PASS waveform as well as the base station waveform to find the 

appropriate hold time and measurement bandwidth for the spectrum analyzer. If the signal utilizes 

a narrow frequency band, for example less than 25 kHz, calibrating the chamber based on the 

center frequency of the band is sufficient. In general, the spectrum analyzer should be set at a 

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frequency step and resolution bandwidth between 10 kHz and 250 kHz for communication systems 

operating below 6 GHz. For larger bandwidths, a larger frequency step can be used. The minimum 

frequency step should be smaller than the carrier (or subcarrier) frequency spacing.

This calibration process does not determine the coherence bandwidth of the RC. In an AC, the 

coherence bandwidth is essentially the usable frequency range of the AC. By contrast, the 

coherence bandwidth in an unloaded RC, such as that used here, is generally quite narrow, e.g., 

often less than 1 MHz. For this particular multipath test, the environment essentially represents the 

worst-case scenario in which many reflections are present. A process for determining the RC 

coherence bandwidth based on vector network analyzer measurements is discussed in [12] and

[17]. 

3.5 Multipath Testing of an RF PASS System

For RF PASS testing, the configuration for the multipath test consists of an AC connected to a RC. 

In this case, the calibration process should include all elements used in the actual testing. In 

addition, the RF PASS is placed in the RC so that the loading effects on the chamber-to-chamber 

gain are included. The variable attenuation is set to 0 dB, in other words, no additional attenuation 

is added during the calibration process. Throughout this section various components are referred 

to as having gain, or loss. A component has loss if the signal strength decreases after traveling 

through the component (e.g. cables). A component has gain if the signal strength increases after 

traveling through the component (e.g. amplifier). 

Step 1. Setting the Calibration Source

The first step is to set up the overall system so that average total attenuation between the testing 

plane of the anechoic chamber and the RF PASS in the reverberation chamber is set to the desired 

target level, which in this NFPA test is 100 dB. The first step in the process is to directly connect 

the signal generator (SG) to the spectrum analyzer (SA) through the cables that will be used to 

connect to the antennas used for calibration (see Figure 13). Note that there are two sets of 

antennas; those used to link the two chambers and those used for the calibration process.

Figure 13. Initial step in establishing multipath test setup. The signal generator (SG) is directly connected 

to the spectrum analyzer (SA) through the cables used in the next step of the calibration process.

An important consideration is that the dynamic range between the SG and the SA must be at least 

120 dB. The dynamic range is the difference (in power) between the output power of the SG and 

the noise floor of the SA. Thus, we may need to include an amplifier directly after the SG. For 

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example, if the SG output is +10 dBm and the SA noise floor is -100 dBm, the dynamic range is 

110 dB. In order to achieve 120 dB of dynamic range, 10 dB of gain is added from the optional 

RF amplifier. The optional attenuation may be necessary to lower the resulting output power from 

the amplifier in order to protect the SA input during the initial setup in steps 1.1 and 1.2 below; 

this optional attenuation is not used when connected via the two chambers discussed below. For

variable definitions see Table 7.

1.1 Connect all the cables in the path between the signal generator and the spectrum analyzer (i.e., 

connect the cable connecting the transmitter and anechoic chamber directly to the cable connecting 

the transmitter and reverberation chamber), omitting the Tx and Rx antennas.

1.2 Measure the total cable loss Ltot between the SG and the SA. The loss value is negative (in dB) 

quantities, or between 0 and 1 (linear). Ltot[dB] = LAC

SG [dB]+LRCSA [dB] + LACTx [dB] + LRCRx [dB] = 

total cable losses in dB or in the linear scale, Ltot = LAC

SG LRCSA LACTx LRCRx

.

Step 2. Chamber-to-Chamber Gain Measurement for a Signal Generator and a Spectrum 

Analyzer

The second step requires connection between the two chambers. Figure 14 shows the calibration 

setup with the two chambers. Initially, the variable attenuation is set to 0 dB.

Figure 14. The calibration setup with the SG connected to the Tx antenna in the anechoic chamber and the 

SA connected to the Rx antenna in the reverberation chamber. The optional amplifier is necessary if the SG 

cannot supply adequate signal power. The cables in this figure are the same as used in Figure 13.

Within the RC, connect two antennas, one to the cable connecting the AC and the RC, and one to 

the SA. The main beam of the antenna patterns should point away from each other, and the main 

beam of the RC to AC antenna (in Figure 14) should point towards a stirrer. The goal in setting 

up the orientation is to minimize coupling (i.e., direct electromagnetic interactions) between the 

antennas. Typically, the antennas are placed at least 2 λ apart.

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Place the RF PASS (powered down) in the RC chamber to determine the effects that its presence 

has on the RC gain.

Determine the antenna efficiencies (eTx,Rx) and mismatch loss (mTx,Rx). These parameters may 

be provided by the manufacturer or measured with industry accepted measurement techniques. If 

the antenna efficiencies are not known, we can preferably use an antenna, well-accepted by the 

wireless testing community such as a dual ridged or standard gain horn, which will typically have 

high-efficiency values. 

Collect the peak SA measurement PSA

ref(i) for each paddle position, i, across the frequency band 

of interest. As discussed in [14], [11], the number of paddle positions impacts the uncertainty 

analysis. For this particular test, between 70 to 100 independent paddle positions provide a 

reasonable level of average field uncertainty. 

Calculate the chamber-to-chamber gain GCC for the desired configuration, as discussed below:

The equation used to calculate GCC as a function of frequency is

GCC(f)[dB] = −Ltot(f)[dB] + 〈PSA

ref(f)[dB]〉 − PSGref(f)[dB] − G(f)AMP[dB], (6)

where 

PSG

ref = power setting of the SG; 

PSA

ref = power measurement from the SA ;

GAMP[dB] = gain of the optional amplifier;

〈 〉 denotes an ensemble average

The mean chamber-to-chamber gain over the band of interest is found by averaging GCC(f) over 

frequency. If the cable losses are considered constant over the frequency band of interest, and the 

power supplied by the signal generator is constant over that frequency band, then only the received 

power PSA

ref(f) is a function of frequency. 

An alternative way to express (6) is

GCC[dB] = 10 × log10 [

〈PSA

ref〉

PSG

ref ×

1

Ltot

], (7)

where the cable losses and power levels are power losses expressed on a linear (rather than log) 

scale. The frequency dependence is not explicitly indicated in (7).

Refined Chamber-to-Chamber Gain Measurement

In order to improve the measurement accuracy, the antenna efficiencies and mismatch 

characteristics can be included, if known. This may be particularly beneficial if the mismatches 

are high or the efficiencies are low (or both). The mismatch and efficiency of the Tx antenna will 

reduce the transmitted power introduced into the chamber, while the mismatch and efficiency of 

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the Rx antenna will reduce the amount of power measured by the spectrum analyzer. Rewriting 

(7) to include the antenna and mismatch corrections, we now have:

GCC[dB] = 10 × log10 [

〈PSA

ref〉

(PSG

ref)

×

1

eTxeRx mTxmRx

×

1

Ltot ]. (8)

The various terms in (8) are defined as follows:

eTx,Rx = antenna efficiencies (values are between 0 and 1),

mTx,Rx = impedance mismatches of the antennas connected to the SG and SA

 (values are between 0 and 1).

Step 3. Setting the Target Average-Total-Attenuation

Once GCC is determined, the variable attenuation is adjusted to the desired overall attenuation, or 

target average-total-attenuation, between the base station in the AC and the RC. The target 

average-total-attenuation is set according to the process described in [1], [3] with the following 

change: the AC containing the RF PASS is replaced with the RC. The field uniformity at the plane 

containing the base station (or Tx antenna in Figure 32) is verified as described in [1]. The equation 

that describes the overall attenuation is

PLTarget(dB) = GTx(dB) − GCC(dB) + LVAR(dB). (9)

In the case of the NFPA multipath test, the variable attenuation is set as needed to achieve the 

targeted average attenuation of 100 dB. Thus, the average-total-attenuation from the plane (or 

table top) supporting the Tx antenna in the AC to the testing volume in the RC is set to 100 dB. 

The target average-total-attenuation can then be verified by redoing steps 1 and 2 above, and 

recalculating the PLTarget, as in (9).

Step 4. Carry Out Multipath Test

After establishing the target attenuation condition, the SG and SA are disconnected from the AC 

and RC, and the Tx antenna and connecting cable are removed from the AC. The base station (e.g., 

laptop with base station software and USB-port connected antenna) is placed in the AC, where the 

Tx antenna was previously located. The Rx antenna and connecting cable is left in the RC during 

the testing. The bulkhead which connects the cable and Rx antenna is terminated with a 50 Ω load. 

Figure 12 shows the setup with a base station and RF PASS unit.

A stepped movement of the paddle is used during the calibration process. However, during the 

multipath test, the paddles are turned continuously. As the paddle is moved, the multipath 

conditions change within the chamber, and thus the speed of rotation or movement can impact the 

measurement results. Based on [17] and laboratory testing during the development of this 

multipath test methodology, the paddle rotation is set for between 1 to 6 revolutions per minute.

In the latest revision of the standard the revolutions per minute is set to 3. 

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3.6 Results

The intent of this test is to verify the RF PASS system performance while operating in a rich 

multipath environment. Thus, the pass/fail criteria should reflect intended operations when the 

system is deployed. There are two pass/fail criteria: 1) the reception of the motion alarm at the 

base station within 30 seconds of initiation by the RF PASS, or 2) the reception of the evacuation 

signal at the RF PASS within the 30 seconds of initiation at the base station. As discussed above, 

the paddle is moving while these signals are being sent, and thus the signal level changes due to 

multipath during the test. This is different than a point-to-point attenuation test, where the channel 

applies a fixed amount of attenuation through a single path between the base station and the RF 

PASS. 

Figure 15 shows the motion alarm multipath results for units from four RF PASS manufacturers

in histogram form, where repeat measurements (y axis) were conducted for the RF PASS systems 

for various levels of introduced path loss (x axis). The path loss threshold above which the RF

PASS must operate (100 dB according to the Multipath Test in NFPA 1982) is indicated by the 

line at the 100 dB mark. The red color shows the introduced path loss value beyond which the pass 

criteria were not met. Due to the different frequencies and technologies of each manufacturer, 

failure occurs at different attenuation levels depending on the manufacturer.

Figure 15. Motion alarm test results for all manufacturers of RF PASS for the Multipath Test.

Figure 16 shows the evacuation alarm multipath results for three manufacturers, again in histogram 

form. There are no results for manufacturer four because a human would have to be introduced 

80 90 100 110 120 130 140 150 0

1

2

3

4

Total Path Loss (dB) Repeats

Manufacturer 1

109 dB Pass Fail

80 90 100 110 120 130 140 150 0

1

2

3

4

Total Path Loss (dB) Repeats

Manufacturer 2

122 dB Pass Fail

80 90 100 110 120 130 140 150 0

1

2

3

4

Total Path Loss (dB) Repeats

Manufacturer 3

129 dB Pass Fail

80 90 100 110 120 130 140 150 0

1

2

3

4

Total Path Loss (dB) Repeats

Manufacturer 4

109 dB Pass Fail

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into the chamber to send the evacuation alarm which would disturb the RF signals. Note that the 

RF PASS devices for each manufacturer successfully operate at the required attenuation levels. 

The point of failure as a function of introduced path loss is again indicated by the red color.

Figure 16. Evacuation alarm test results for all manufacturers of RF PASS for the Multipath Test. Results 

for manufacturer 4 were unable to be produced due to logistical reasons. 

The results of the NIST tests of the four RF PASS systems indicate that these systems would all

likely pass the Multipath Test given in NFPA 1982. However, NIST is not a certified NFPA test 

lab and official results may vary.

4. Configuration Considerations for Point-Point, MultiHop, and Interference Testing

The following sections discuss the setup and calibrations that were performed for three tests that 

involve anechoic chambers: the Point-to-Point, Multi-Hop and Interference (Low- and HighPower) Tests. These tests use a variety of equipment including, but not limited to, power 

combiners, spectrum analyzers, signal generators, anechoic chambers, and reverberation 

chambers. Many of the configurations discussed in Section 4 are applied in the Point-To-Point, 

Multi-Hop, and Interference testing described in Section 5.

80 90 100 110 120 130 140 150 0

1

2

3

4

Total Path Loss (dB) Repeats

Manufacturer 1

116 dB Pass Fail

80 90 100 110 120 130 140 150 0

1

2

3

4

Total Path Loss (dB) Repeats

Manufacturer 2

137 dB Pass Fail

80 90 100 110 120 130 140 150 0

1

2

3

4

Total Path Loss (dB) Repeats

Manufacturer 3

120 dB Pass Fail

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4.1 Path Loss Measurements for Anechoic Chamber

Path loss refers to the reduction in signal strength that occurs when a signal travels between the 

transmitter and receiver. If there is too much path loss between the firefighter and the base station,

the distress signal might not activate in a timely manner or at all. The main focus of the following 

procedures is to determine an appropriate test setup to verify the RF PASS performance under path 

loss conditions ranging from below 100 dB to in excess of 250 dB. The data presented in this 

section illustrate validation of the proposed setups. 

We determined from results of the uniformity study of Section 2.4 that Patch D would be used for 

the 450 MHz frequency range, Patch E would be used for the 900 MHz frequency range, and that 

the helix antenna with the RF absorbing lens produced the most uniform electric field for the 2.4 

GHz systems. For a path loss measurement in each band, these antenna types are mounted at the 

top interior of each chamber. Various antennas are placed on the test platform (at the bottom of 

the chamber) to transmit and receive signals from the top antenna. 

In Section 4, we present an example where the anechoic chambers are configured and measured 

to determine path loss at 2.444 GHz. Several equations throughout this section are used to detail 

the verification procedure. The variables used in these equations are explained in Table 8.

Table 8. Variable descriptions for equation use.

Term Description

GA Gain of Antenna

GRx Gain from Receiving Antenna

GTx Gain of Transmitting Antenna

LC Cable Loss

LCo Connector Loss

LFSC Free Space Chamber Loss

LFSC

AC Free Space Chamber Loss of Anechoic Chamber

LFSC

RC Free Space Chamber Loss of Reverberation Chamber Average

LPC Power Combiner Loss

PL2

1 Path Loss from Chamber 1 to 2

PL3

1 Path Loss from Chamber 1 to 3

PL3

2 Path Loss from Chamber 2 to 3

PL4

3 Path Loss from Chamber 3 to 4

PLA3

1 Power Loss with Added Attenuation from Chamber 1 to 3

PLmeas Measured Path Loss

PLtot Total Path Loss

AA Added Attenuation

MV Measured Value

PA Power Amplifier

SGI Signal Generator Input

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4.1.1 Measurement of Cable Loss for an Individual Anechoic 

Chamber Setup

When configuring the chambers to measure the total path loss (PLtot) through an anechoic 

chamber, the first step is to measure the loss of the coaxial cables and other connectors that would 

contribute to PLtot. The different components that need to be accounted for include four coaxial 

cables and a 20 dB attenuator. For the 2.4 GHz set-up, the same RF absorbing foam lens shown in 

Figure 10(a) is also used throughout this section. Figure 17 below shows the set up.

Figure 17. Set up for the path loss measurement calibration.

A 2.444 GHz continuous wave (CW) signal with 0 dBm amplitude was sent through this series of 

cables and connectors and was received by the spectrum analyzer to read -25.4 dBm. The cables 

and connectors contributed to 5.4 dB of loss.

4.1.2 Determining Antenna Type for RF PASS Testing Configuration 

For each AC setup, the target path loss values are determined by use of an antenna mounted to the 

top of the chamber (already determined for each frequency in Section 2.3.4) and a second 

calibration antenna placed on the measurement platform. An antenna with low path loss is ideal 

because it allows more flexibility in the path loss of other components. The goal of this section is 

to determine which calibration antenna will yield lowest path loss through an anechoic chamber. 

Once the cable loss was measured, the helix was mounted to the top of the chamber and different 

antennas were individually placed on the reference plane, as shown below in Figure 18. The goal 

was to determine which antenna created the lowest path loss while maintaining field uniformity at 

the table top. Measurements were taken for the path loss within the chamber and LFSC was then 

calculated according to (10) (see next page), where the variable descriptions are given in Table 8.

The results of all trials are summarized in Table 9 and Table 10. The descriptions of each antenna 

can be found in Table 2.

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Figure 18. Setup for the path loss measurement data collection.

Table 9. Spectrum analyzer measurements for each 2.4 GHz antenna and trial. The helix antenna is 

mounted as the transmitting antenna.

Patch A 

(dBm)

Patch B 

(dBm)

Patch C 

(dBm)

Patch C With 

Lens (dBm)

Trial 1 -38.7 -37.6 -32.1 -30.3

Trial 2 ------ ------ -32.2 -30.3

Trial 3 ------ ------ -32.1 -30.3

Table 10. PLtot for each 2.4 GHz antenna and trial. The helix antenna is mounted as the 

transmitting antenna.

Patch A 

LFSC (dB)

Patch B 

LFSC (dB)

Patch C 

LFSC (dB)

Patch C

LFSC With Lens (PLtot) (dB)

Trial 1 51.3 50.2 43.7 41.9

Trial 2 ----- ------ 43.8 41.9

Trial 3 ------ ------ 43.7 41.9

Patches A and B were the same type of antenna but with opposite polarizations. This should have 

caused one of the antennas to cross polarize with the transmitting antenna resulting in a higher

path loss. Because of the small difference between these two antennas’ results, we determined that 

patches A and B were poor quality antennas. Patch C had at least 5.5 dB less path loss compared 

to patch A or B which was favorable. For each trial, the receiving antenna was disconnected,

reconnected, and repositioned on the platform.

LFSC = PLmeas − LC + GRx + GTx (10)

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A helix antenna identical to the transmitting antenna was placed at the reference plane. With the 

RF absorbing lens in place, PLtot of the helix was found, see Table 11. This loss was within 1 dB 

of patch C, as shown in Table 10. 

This same process was repeated with a horn antenna (with specifications found in Table 2) on the 

reference plane. Because the antenna is linearly polarized, there were two orientations 90 degrees 

apart that were tested. Three trials were tested for each orientation. The antenna was disconnected, 

reconnected and placed on the platform for each trial. Results are shown in Table 11.

Table 11. PLtot measurements for three 2.4 GHz antennas. The helix antenna is mounted as the 

transmitting antenna.

The results showed that patch C yielded the lowest path loss. 41.9 dB is the LFSC within the 

anechoic chamber before taking out the 10 dB gain from the helix. Therefore PLtot within the 

chamber is 31.9 dB.

4.1.3 Path Loss between Two Anechoic Chambers

The purpose of this section is to determine the path loss from test platform to test platform through 

two anechoic chambers. This value is then used to determine how much added attenuation will be 

needed to achieve 100 dB path loss between test platforms. A value of 100 dB of path loss between 

devices located on test platforms in two anechoic chambers is required for several test methods, 

including the point-to-point, coexistence, multipath, and multi-hop methods. 

For some tests, a power combiner is used between chambers. For this, the insertion and isolation 

values are determined. A basic power combiner setup is shown in Figure 19. One port was 

terminated with a 50 Ω load while the other two were connected to a signal generator and spectrum 

analyzer to determine the insertion and isolation loss. The insertion loss was 3.5 dB and the 

isolation loss was 24.2 dB.

Patch C

With Lens LFSC (dB)

Helix With 

Lens LFSC (dB)

Horn With Lens 

LFSC Position 1 

(dB)

Horn With Lens 

LFSC Position 2 (dB)

Trial 

1

41.9 42.8 45.7 42.7

Trial 

2

41.9 ---------- 45.7 43.0

Trial 

3

41.9 ---------- 45.9 42.8

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Figure 19. Power combiner and labeled ports.

4.1.3.1 Chambers 1 and 2

Below are the experimental results for path loss between two anechoic chambers; we again used

the 2.4 GHz frequency band as an example. Two antennas were used in the following experiment 

for comparison. As decided in Section 2.4, the helix will be the top antenna for any subsequent 

tests. A helix and a horn were used to send the signal from the identical antenna in the reference 

plane in chamber 1 to the reference plane in chamber 2. This reference plane is shown in Figure 

18; that is, a signal traveled from a horn antenna to a horn antenna or a helix antenna to a helix 

antenna through the helix antennas at the top of the chambers. In the setup shown in Figure 20,

the antenna on the reference plane in chamber 1 transmits, and the antenna on the reference plane 

in chamber 2 receives. Because the horn is linearly polarized, two orientations with 90 degree 

rotations were measured. The cable loss was measured to be 7.5 dB. Figure 20 shows the setup. 

Table 12 shows the results collected by the spectrum analyzer and Table 13 shows PLtot.

Figure 20. Setup for chambers 1 and 2 with the power combiner.

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Table 12. Spectrum analyzer measured values for system calibration from chamber 1 to 2 with power 

combiner. The helix antenna is mounted to the top of the chamber as the transmitting antenna. 

We then calculated PLtot for each antenna, using [3]:

PLtot = abs(MV − (SGI + PA) − (GTx) − (GRx) + LC).

(11)

See Table 8 for the definition of the variables. For example, with the 2.4 GHz helix antenna on 

the reference plane in both chambers, PLtot can be calculated as follows: 

PLtot = −55.0 dBm − (−50 dBm + 55 dB) − 10 dBi − 10 dBi + 7.5 dB = 72.5 dB.

Table 13. PLtot of receiving antennas at 2.4 GHz, the helix is the transmitting antenna.

These data show that the helix and horn provide similar values of path loss. 

4.1.3.2 Chambers 1 and 2 with Added Attenuation 

The setup for the point-to-point test between chamber 1 and 2 with added attenuation differs from 

the other experiment only by adding a variable attenuator in series between chambers to achieve a 

value of path loss from test platform to test platform that is as close to 100 dB as possible. The 

input consisted of a -50 dBm signal and a 55 dB gain amplifier. The measurement results are shown 

in Table 14. PLtot was then calculated for each antenna with (8) and the results are listed in Table 

15.

Table 14. Antennas and their respective added attenuation and measured values for 2.4 GHz.

Table 15. Antennas and respective PLtot with added attenuation for 2.4 GHz.

Antenna on Reference Plane PLtot

Helix 99.8 dB

Horn Position One 99.5 dB

Horn Position Two 99.0 dB

Antenna on Reference Plane Measured Value

Helix -55.0 dBm

Horn Position 1 -65.1 dBm

Horn Position 2 -64.8 dBm

Antenna on Reference Plane PLtot

Helix 72.5 dB

Horn Position One 74.6 dB

Horn Position Two 74.3 dB

Antenna on Reference Plane Measured Value Added Attenuation

Helix -82.3 dBm 27 dB

Horn Position 1 -90.0 dBm 24 dB

Horn Position 2 -89.5 dBm 22 dB

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4.1.4 RF PASS Performance between Two Anechoic Chambers

After attenuation was added to configure the chambers for 100 dB path loss, the devices were 

placed on the test platforms in the anechoic chambers. The setup shown in Figure 21 is similar to 

that of the point-to-point RF test in [1]. The difference in the following setup from the existing 

point-to-point test lies in the power combiner and 20 dB attenuator that allow the system to be 

connected to other chambers for the multi-hop test.

Figure 21. RF-PASS-device-to-base-station configuration for two anechoic chambers.

4.2. Reverberation Chamber Calibration and RF PASS 

Stirrer Speed Dependency 

One use of a reverberation chamber is in the multipath test, as previously discussed. Another use 

for this type of chamber is in the multi-hop test which will be discussed in a later section. The 

calibration for the cables and components throughout the reverberation chamber is similar to that 

described in Section 3. However, for the multipath test, the calibration of the reverberation 

chamber is performed by connecting it to an anechoic chamber, whereas for the multi-hop test the 

path loss of the reverberation chamber alone is found. Then, in the four chamber multi-hop test,

each individual chamber is added into the total system’s path loss. We must verify that the stirrer 

speed of the reverberation chamber does not alter the time it takes for the base station to receive 

the motion alarm, nor the RF PASS to receive the evacuation alarm. While the exact values may 

change based on reverberation size, reflectivity, etc., the following procedure should be performed 

to determine the effects of stirrer speed on the alarm timing. 

4.2.1 Reverberation Chamber Calibration

The setup for the reverberation chamber calibration is shown in Figure 22.

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Figure 22. Calibration for reverberation chamber.

Laptop 1 is connected to the spectrum analyzer and collects/saves data at a user-specified interval. 

Laptop 2 controls the motor that sets the rate at which the paddle rotates. Two laptops were used 

only because each contained different software. One laptop with all necessary software would 

perform the same tasks as stated above. For the multipath and multi-hop tests, the paddle is rotated

at 0.2 revolutions per minute and data are collected every three seconds. In this way, power 

measurements of 100 paddle positions over 360 degrees are collected and averaged to determine

the path loss of the chamber. 

4.2.2 Stirrer Speed Dependency 2.4 GHz Manufacturer 3 RF PASS

We performed the calibration illustrated in Figure 22 using the helix antenna. The average path 

loss within the reverberation chamber for this system was 45.2 dB, where the path loss was found 

as in Section 3.5 equation (6), but with Ltot[dB] = LRC

SG [dB]+LRCSA [dB] + LRCTx [dB] + LRCRx [dB]. At 

2.4 GHz, there was 3.8 dB loss from the cables and the input was -20 dBm resulting in 21.4 dB 

average path loss in the reverberation chamber. The free space loss in the reverberation chamber 

will be taken as 21.4 dB. 

The goal was to achieve 100 dB average path loss between the reverberation and anechoic 

chambers. The path loss from within the anechoic chamber was 31.9 dB as found in the previous 

section, and the path loss from within the reverberation chamber was 21.4 dB. To achieve 100 dB 

average path loss, 46 dB attenuation was added in line between the two chambers.

Figure 23 shows the setup to determine how the stirrer speed affects the connection between the 

base station and RF PASS with the added attenuation in line. 

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Figure 23. Two segments of the Multi-Hop test between reverberation chamber and anechoic chamber.

For all RF PASS manufacturers, the RF PASS was placed inside the chamber on a piece of solid 

foam to keep the device at least one wavelength’s distance away from all chamber surfaces

(including the floor). A dielectric rod was attached to the device to keep the RF PASS device

moving to ensure the motion alarm did not go off until desired. The amount of time it took for the 

base station to receive the motion alarm from the RF PASS device was recorded in Table 16 for

different paddle rotation speeds.

Table 16. Time recorded for base station to receive motion alarm from RF PASS device with 46 dB 

added attenuation in line. 

From these results, we can conclude that the speed at which the paddle rotates within a range from 

one to six revolutions per minute does not significantly affect the time it takes to send the motion 

alarm from the RF PASS.

4.2.3 Stirrer Speed Dependency 900 MHz Manufacturer 1 RF PASS

We repeated the process in Figure 18, using patch E as the receiving and transmitting antennas. 

The path loss within the anechoic chamber was 32.8 dB. A 9 dB antenna gain was subtracted from 

this number to arrive at 23.8 dB path loss within the anechoic chamber. The same process shown 

in Figure 23 was repeated to find the path loss within the reverberation chamber with the 900 MHz 

Manufacturer 1 device in place. At 900 MHz, there was 18.5 dB path loss within the reverberation 

Revolutions/Minute Receive Time (sec)

1 11.56 

2 11.63 

3 11.76 

4 11.48 

5 11.22 

6 11.28 

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chamber. This yielded 42.3 dB path loss between the anechoic chamber and reverberation 

chamber, so 58 dB attenuation was added to achieve 100 dB total path loss. For each trial, the 

cables were disconnected to test for proper isolation by ensuring the base station and portable RF 

PASS device could not connect wirelessly before proceeding with the test. The results are 

summarized below in Table 17.

Table 17. Stirrer speed dependency results for 900 MHz Manufacturer 1 PASS systems showing time 

until motion alarm was received.

Revolutions/Minute Trial One Results (sec) Trial Two Results (sec)

1 9.30 8.64

2 8.47 9.25

3 5.98 11.61

4 12.70 10.55

5 8.35 8.61

6 9.80 7.30

Trial one shows that there is little consistency in the time it takes for the motion alarm signal to 

reach the base station. Comparing trial one and trial two shows there is little dependency on the 

stirrer speed. 

4.2.4 Stirrer Speed Dependency 900 MHz Manufacturer 2 RF PASS

The RF PASS of Manufacturer 2 was also a 900 MHz system so the same antennas (patch E) were 

used. The same 23.8 dB path loss within the anechoic chamber was used to determine the added 

attenuation needed to achieve 100 dB path loss. The RF PASS device of Manufacturer 2 was 

placed in the reverberation chamber and the process in Figure 23 was repeated to yield 17.8 dB 

path loss within the reverberation chamber. For this system, the two chambers had to be physically 

separated to achieve proper shielding. An additional cable with 3 dB loss was added to the system. 

Without this cable, we would have needed to add 58 dB to the system; with this cable, only 55 dB 

was added in line, to achieve 100 dB total path loss. After each test, without opening the 

reverberation chamber, the cables were disconnected, the base station motion alarm 

acknowledgement was reset, and the system was tested for proper isolation by ensuring the motion 

alarm was not received by the base station. The results can be seen in Table 18.

Table 18. Results for stirrer speed dependency with Manufacturer 2 showing time until motion alarm 

was received.

Revolutions/Minute Trial One Results (sec)

1 1.09

2 0.55

3 0.70

4 0.68

5 0.63

6 0.86

For each case the motion alarm was received almost instantly. 1 revolution per minute varied more 

than the other trials merely because the timer was stopped a little late. As explained above, there 

was little dependency on stirrer speed for any of the three manufacturers. 

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4.3. Path Loss across Four Chambers

This procedure determines how much added attenuation is needed when all four chambers are

connected in series for the multi-path test. The path loss between each chamber was calculated by 

factoring in individual connections, cables, and free space losses of the particular chamber. The 

same RF absorbing lens used in Figure 10(a) for the 2.4 GHz tests was used in each of the four 

chambers shown in Figure 24, although it is not shown.

Figure 24. Path loss set up for four chambers.

4.3.1 Path Loss Calculations

For the Multi-hop test, the total path loss from the test platform in Chamber 1 through the 

reverberation chamber and through two additional anechoic chambers should be 260 dB. Because 

this is difficult to measure directly, we found this value by adding together the path loss between 

pairs of chambers. PLtot was calculated between different chambers and is shown below in (12), 

(13) and (14) for the 2.4 GHz system. Variable descriptions can be found in Table 8.

PL2

1 = LFSC

AC

– GA + 3LC + 2LCo + LPC + LFSC

RC = 61.35 dB (12)

PL3

2 = LFSC

RC + 3LC + 2LPC + 2LCo + LFSCAC − GA = 63.6 dB (13)

PL4

3 = 2(LFSC

AC − GA

) + 3LC + 4LCo + LPC = 69.65 dB (14)

The superscript refers to the first chamber and the subscript to the second chamber in each chamber 

pair, as shown in Fig. 24. For all of these calculations, 31.9 dB was used as the path loss value for 

each anechoic chamber (including antenna gain), as found in Section 4.1.2. This value was based 

on a measurement obtained with Patch C in a single chamber. However, when measuring the path 

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loss between two chambers, a horn was used. To fix this discrepancy, the LFSCwithin the anechoic 

chamber will be taken as 44.3 dB, the average of the two free-space loss horn position values found 

in Table 11. Using this value and the same equations above, we calculate the new path loss values

between chambers. The corrected results are then

PL2

1 =63.75 dB

PL3

2=66 dB

PL4

3=74.45 dB

These values, as expected, resemble their measured counterparts in Section 4.1.2. The measured 

values for the PL4

3

(Section 4.1.2) obtained with the horn in position one was 74.6 dB, and in 

position two was 74.3 dB. These are compared with the calculated PL4

3

value stated above at 74.45 

dB with a horn position in between the first and second. 

5. Point-to-Point, Multi-Hop and Interference Testing

In this section, we describe the Point-to-Point, Multi-Hop, and Interference Test methods using 

pieces of the calibrations discussed in Section 4. 

5.1 Point-to-Point Motion and Evacuation Alarm Test

5.1.1 Description

The Point to-Point Motion Alarm and Evacuation Tests are designed to create a channel with a 

known path loss between the RF PASS device and its base station. After conducting a set of field 

tests and analyzing the data for various types of buildings encountered by firefighters, a value of 

100 dB path loss between the portable unit and the base station was deemed to be a representative

amount of attenuation for which point-to-point communication should be reliable [4, 18]. By 

isolating the RF PASS device from the base station, determining the path loss between chambers, 

and then adding the remaining attenuation to the channel, we were able to test the systems at the 

100 dB mark. If a motion alarm was received by the base station within 30 seconds, the system 

passed. If the evacuation test was received by the RF PASS within 30 seconds, the system passed.

An example setup based on a 900 MHz system is presented, followed by NIST results for four 

manufacturers: e.g., one at 450 MHz, two at 900 MHz and one at 2.4 GHz.

For the setup configuration, first the cable loss was measured with a signal generator and spectrum 

analyzer (see Section 4.1.1). The input on the signal generator was set to 0 dBm, the spectrum 

analyzer read -2.1 dBm. This leads to a cable path loss of 2.1 dB. Next, the PLtot within the 

anechoic chambers was measured with 0 dB external attenuation (see Section 4.1.3.1). 

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To configure the chambers to provide 100 dB between RF PASS and the portable base station, the

calibration in Section 4.1.3.2 was performed. Figure 25 shows the calibration setup.

Figure 25. Setup for the Point-to-Point motion and Evacuation Alarm test calibration with circularly 

polarized receiving and transmitting antennas. The spectrum analyzer was configured to sweep from 900 

MHz to 930 MHz. The signal generator was set to 0 dBm.

As an example, at 900 MHz, the spectrum analyzer read -33.6 dBm, so the path loss of cables = 

33.6 dB. Using (15) we can obtain the total path loss from the location of the PASS device to the 

location of the base station. The antenna gain was 9 dBi (see Table 2, Section 2.2).

PLtot = MV − LC + 2GA = 49.5 dB. (15)

This leads to a value of roughly 51 dB external attenuation needed to generate a total 100 dB path 

loss between the PASS device and base station.

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For the point-to-point test, we achieved the desired path loss using external added attenuation, as 

described in Section 4.1.3.2. Then the PASS device was placed on the test platform in one chamber 

and its base station was placed on the test platform in the other chamber. A connection was

established between the two. The doors were closed and a timer was set immediately after the 

audible motion alarm sounded on the PASS device. If the base station received the motion alarm 

from the PASS device within 30 seconds of the alarm being sent, the device passed the test. The 

test setup is shown in Figure 26.

Figure 26. Set up for the Point-to-Point Motion and Evacuation Alarm tests with use of circularly polarized 

antennas. The evacuation alarm test uses the setup as shown, with an additional dielectric rod inserted into

the RF PASS chamber and attached to the portable device. The operator moves the dielectric rod to keep 

the motion alarm from activating.

5.1.2 NIST Tests: Point-to-Point Motion Alarm Results

Figure 27 through Figure 30 show the results of the Point-to-Point Motion Alarm test for four

different manufacturers of RF PASS. Positions one and two use the portable unit vertical and

rotated at zero and 90 degrees. Positions three and four are horizontal and rotated at zero and 90 

degrees. The line at 100 dB shows the threshold path loss value. Several repeats were conducted 

for each test.

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Figure 27. Point-to-Point Motion Alarm test for Manufacturer 1.

Figure 28. Point-to-Point Motion Alarm test for Manufacturer 2.

80 90 100 110 120 130 140 150 0

1

2

3

4Repeats

Manufacturer 1 Low Attenuation Motion Alarm

Pos 1

104 dB Pass Fail

80 90 100 110 120 130 140 150 0

1

2

3

4Repeats Pos 2

97 dB Pass Fail

80 90 100 110 120 130 140 150 0

1

2

3

4Repeats Pos 3

102 dB Pass Fail

80 90 100 110 120 130 140 150 0

1

2

3

4

Total Path Loss (dB) Repeats Pos 4

98 dB Pass Fail

Manufacturer 1 Point-to-Point Motion Alarm 

80 90 100 110 120 130 140 150 0

1

2

3

4Repeats

Manufacturer 2 Low Attenuation Motion Alarm

Pos 1

117 dB Pass Fail

80 90 100 110 120 130 140 150 0

1

2

3

4Repeats Pos 2

117 dB Pass Fail

80 90 100 110 120 130 140 150 0

1

2

3

4Repeats Pos 3

120 dB Pass Fail

80 90 100 110 120 130 140 150 0

1

2

3

4

Total Path Loss (dB) Repeats Pos 4

120 dB Pass Fail

Manufacturer 2 Point-to-Point Motion Alarm 

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Figure 29. Point-to-Point Motion Alarm test for Manufacturer 3.

Figure 30. Point-to-Point Motion Alarm test for Manufacturer 4.

Note that each subplot within the figures contain results for the four different orientations of the 

PASS devices. This indicates that the position of the PASS device has an effect on performance. 

In the Point-to-Point Motion Alarm test, the position makes a difference as to whether the motion 

alarm is received within 30 seconds with 100 dB total path loss. The importance of these tests was 

80 90 100 110 120 130 140 150 0

1

2

3

4Repeats

Manufacturer 3 Low Attenuation Motion Alarm

Pos 1

119 dB Pass Fail

80 90 100 110 120 130 140 150 0

1

2

3

4Repeats Pos 2

118 dB Pass Fail

80 90 100 110 120 130 140 150 0

1

2

3

4Repeats Pos 3

113 dB Pass Fail

80 90 100 110 120 130 140 150 0

1

2

3

4

Total Path Loss (dB) Repeats Pos 4

115 dB Pass Fail

Manufacturer 3 Point-to-Point Motion Alarm 

Testing Stopped at 105 dB. Unit assumed to fail at 

some point past 112 dB.

Testing Stopped at 105 dB. Unit assumed to fail at 

some point past 112 dB.

Pos 2

Pos 4

Manufacturer 4 Point-to-Point Motion Alarm 

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to ensure there was a margin of successful operation past 100 dB. Manufacturer 4 showed 

successful operation in positions 2 and 4 up to 105 dB, meeting this 100 dB requirement. Because 

the requirement had already been met, we did not need to continue any further, and testing stopped 

after 105 dB for position 2 and 4 shown in Figure 4.

5.1.3 Evacuation Alarm Test Results

For the Evacuation Alarm Test, we needed to maintain intermittent movement of the portable RF 

PASS unit so that the motion alarm does not engage. One method to do this is to insert a dielectric 

rod through the chamber wall to be attached to the RF PASS. This enables the operator to shift the 

device slightly every 30 seconds or less. When in motion alarm mode, the RF PASS device is 

unable to receive the evacuation alarm signal because of the priority the motion alarm takes. 

One method to enable the operator to send the evacuation alarm signal after the chamber door is 

closed is with simple timed mouse-click software, installed on the computer that is used with the 

base station. This software may be used for the 900 MHz and 2.4 GHz systems. The 450 MHz 

system does not require the mouse-click software because there is no computer. For the 450 MHz 

system, a second operator may stand in the large anechoic chamber that houses the base station 

and manually send the evacuation alarm signal with the door closed. Figure 31 through Figure 33

show the results of the Point-to-Point Evacuation test for the first three manufacturers. 

Figure 31. Point-to-Point Evacuation Test for Manufacturer 1. 

80 90 100 110 120 130 140 150 0

1

2

3

4Repeats

Manufacturer 1 Low Attenuation Evacuation

104 dB Pass Fail

80 90 100 110 120 130 140 150 0

1

2

3

4Repeats

107 dB Pass Fail

80 90 100 110 120 130 140 150 0

1

2

3

4Repeats

104 dB Pass Fail

80 90 100 110 120 130 140 150 0

1

2

3

4

Total Path Loss (dB) Repeats

103 dB Pass Fail

Manufacturer 1 Point-to-Point Motion Evacuation 

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Figure 32. Point-to-Point Evacuation Test for Manufacturer 2. 

Figure 33. Point-to-Point Evacuation Test for Manufacturer 3. 

5.1.4 Point-to-Point Test Uncertainty Analysis

This section uses information from the field-uniformity uncertainty results in Section 2.4.3 to 

create an uncertainty analysis for the Point-to-Point Test. The Point-to-Point Test utilizes the setup 

80 90 100 110 120 130 140 150 0

1

2

3

4Repeats

Manufacturer 2 Low Attenuation Evacuation

120 dB Pass Fail

80 90 100 110 120 130 140 150 0

1

2

3

4Repeats

117 dB Pass Fail

80 90 100 110 120 130 140 150 0

1

2

3

4Repeats

122 dB Pass Fail

80 90 100 110 120 130 140 150 0

1

2

3

4

Total Path Loss (dB) Repeats

125 dB Pass Fail

Pos 2

Pos 1

Pos 3

Pos 4

Manufacturer 2 Point-to-Point Motion Evacuation 

80 90 100 110 120 130 140 150 0

1

2

3

4Repeats

Manufacturer 3 Low Attenuation Evacuation

118 dB Pass Fail

80 90 100 110 120 130 140 150 0

1

2

3

4Repeats

120 dB Pass Fail

80 90 100 110 120 130 140 150 0

1

2

3

4Repeats

121 dB Pass Fail

80 90 100 110 120 130 140 150 0

1

2

3

4

Total Path Loss (dB) Repeats

125 dB Pass Fail

Pos 2

Pos 1

Pos 3

Pos 4

Manufacturer 3 Point-to-Point Motion Evacuation 

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in Figure 26, which requires consideration of the uncertainty in the field at each of the test platform 

surfaces and the performance of the inline attenuator. The uncertainty in measurement of the 

variable attenuator is considered a Type A uncertainty because manufacturer specifications are 

provided. The overall uniformity uncertainty calculated in Section 2.4.3 used Type A and B 

methods. As such, the overall uniformity uncertainty is a Type B uncertainty. The following 

calculations utilize equation (4).

5.1.4.1 Combined Uncertainty 

Calculations to find mismatch loss in Table 19 use equation (16):

Mismatch Loss (dB) = −10 × log10 (1 − [

VSWR−1

VSWR+1

]

2

). (16)

Table 19. Description of uncertainties for Point-to-Point Test.

Type Variable Name Uncertainty 

Description

Method of Estimate Values 

(Linear 

Scale)

Values 

(dB)

A uvariable attenuator

Uncertainty in 

mismatch 

losses of 

variable 

attenuator

Mismatch loss calculated 

based on SWR (1.15) 

given by manufacturer.

< 0.5 % 0.02

B uuniformity uncertainty

μcombined

from Section 

2.4.3.

μcombined from Section 

2.4.3. 0.33 2.48

ucombined =

√uuniformity uncertainty platform 1

2 + uvariable attenuator2 + uuniformity uncertainty platform 22

.

This results in an estimated uncertainty of 3.35 dB. This is 0.35 dB higher than the 3 dB in the 

uniformity test which is to be expected since two separate chambers have been connected. Note

that although the uniformity uncertainty is considered twice, the overall uncertainty increased by 

much less than a factor of two (i.e., 3 dB). 

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5.2 Multi-Hop Test 

The purpose of the Multi-Hop Test is to verify that an RF PASS device can relay information to 

another RF PASS device through two repeaters under a certain amount of path loss and multipath. 

This test is designed so that the signal from RF PASS A must travel through each of the repeaters 

B and C, to reach the base station. We performed the Multi-Hop Test using two different RF PASS 

systems. At NIST, the same RF absorbing lens used in Figure 10(a) was used in the Multi-Hop 

Test setup, which is shown in Figure 34.

Figure 34. Setup for connection of Multi-Hop Test with four chambers.

5.2.1 Description

For Manufacturer 2 and Manufacturer 3, the stirrer in the reverberation chamber was rotating at 3 

revolutions per minute in all test cases. To test that the RF isolation between chambers was 

sufficient to force signal relay through the repeaters, the cables between chambers were 

disconnected and reconnected. The RF PASS in chamber 1 and repeater in chamber 3 were each 

placed horizontally or vertically to create four different position combinations. The repeater in 

chamber 2 was consistently horizontal. When disconnected, the RF PASS communication link to 

the base station failed, and when reconnected, it was reestablished. The chamber containing device

B was then disconnected and we verified that B and A both were unable to connect, then when the 

cables were reattached, the connection was successful. Lastly, the chamber containing device C 

was disconnected from the system and all three devices failed, then reconnected when the cables 

were reattached. These results prove that the isolation between chambers will force the signals 

through the designated cable paths.

After verifying isolation, the multi-hop test began. The motion alarm was permitted to activate and 

the time it took for the base station to receive the motion alarm signal was recorded. If the base 

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station received the RF PASS motion alarm within 30 seconds of the alarm being sent, the system

was considered to pass. For the evacuation alarm test the evacuation alarm was timed to go off by 

the automated click software 1.5 minutes after the chamber door was shut. A dielectric rod was 

used by the operator to prevent the motion alarm from going off. Then, once the evacuation alarm 

was sent, the time until the RF PASS received the alarm was recorded. If the evacuation alarm was 

received by the RF PASS within 30 seconds of the alarm being sent from the base station, the 

system was considered to pass. 

For all frequencies, there was a minimum 85 dB PLtot between the reverberation chamber and 

anechoic chamber. Between chambers 3 and 4 there was 100 dB PLtot. The 85 dB is the highest 

attenuation for which the devices could maintain contact with the repeaters. The added attenuation 

between chambers 1 and 2, and between 2 and 3, was increased in 1 dB increments to gather the 

point-of-failure data shown in Figure 35 and Figure 36. Based on these results, we determined that 

only 80 dB of attenuation was required between the reverberation chamber and anechoic chamber 

for an overall PLtot of 260 dB. As shown in the graphs below, there are never any failures for a 

total path loss of 260 dB. 

5.2.2 NIST Results

All results are shown in Figure 35 and Figure 36.

Figure 35. Aggregate point-of-failure results for the motion alarm test for Manufacturers 2 and 3. Dashed

lines represent the total path loss required by [1] for the Point-to-Point and Multi-hop Tests, respectively.

90 110 130 150 170 190 210 230 250 270 290 310 330 350 0

5

10 100 dB 260 dB Trials

Motion Alarm Test Results Manufacturer 2

302 dB Pass Fail

90 110 130 150 170 190 210 230 250 270 290 310 330 350 0

5

10

15

20

25 100 dB 260 dB

Total Path Loss (dB) Trials

Motion Alarm Test Results Manufacturer 3

271 dB Pass Fail

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Figure 36. Aggregate point-of-failure results for the evacuation alarm test of Manufacturers 2 and 3.

Dashed lines represent total path loss required for Point-to-Point and Multi-hop tests, respectively.

5.3 Low-Power Interference Testing

5.3.1 Introduction 

The RF Low-Power Interference Test is designed to introduce into the RF propagation channel 

the types of interference that may be found in environments where firefighters are deployed. This 

test, which was previously discussed in [3], focuses on replicating conditions for large building 

structures such as office buildings, factories, convention centers, and apartment buildings. Certain 

wireless transmissions that may cause interference are commonly found within these structures. 

For example, in offices and apartment buildings, the use of wireless local-area networks (WLAN) 

or wireless personal-area networks (WPAN) is common. In warehouses and factories, the use of 

RFID technology is common. 

Wireless systems such as WPAN and RFID operate in the unlicensed Industrial, Scientific, and 

Medical (ISM) frequency bands, with frequencies and power levels specified by the FCC. Because 

many RF PASS units also operate within these unlicensed frequency bands, in-band interference 

is possible. Consequently, the RF Interference Test is designed to test systems that operate in 

similar frequency bands by use of commonly encountered transmission protocols.

The interfering source in this test method will operate at approximately the same output power as 

the RF PASS; that is, at the maximum power allowed by the FCC. Higher-power signals that are 

transmitted either within the same band as the RF PASS (for example, signals that operate in the 

900 MHz frequency band that are licensed for land-mobile radio operations) or at frequencies 

90 110 130 150 170 190 210 230 250 270 290 310 330 350 0

5

10 100 dB 260 dB Trials

Evacuation Alarm Test Results Manufacturer 2

296 dB Pass Fail

90 110 130 150 170 190 210 230 250 270 290 310 330 350 0

5

10

15

20

25 100 dB 260 dB

Total Path Loss (dB) Trials

Evacuation Alarm Test Results Manufacturer 3

273 dB Pass Fail

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other than the RF PASS system (for example, broadcast radio or cellular telephone operations) are 

not considered in this test method.

As shown in Figure 37, the interfering signal is introduced into the test chamber that contains the 

user-worn RF PASS. This configuration is tested to simulate the condition where a firefighter is 

indoors in the presence of some other radio system. Because we expect that the firefighter will 

typically be some distance from the RF interfering source in this test method, the output power of 

the interferer is reduced by the free-space path loss corresponding to a 1.25 m distance. This 

distance was chosen as the closest expected proximity between a firefighter and another wireless 

device. Note that this distance falls within the range of distances proposed in similar work on 

medical device RF interference testing discussed in [19] [20]. 

Figure 37. A typical RF Low-Power Interference Test set up for RF PASS. The RF interference source is 

connected via a power combiner to the antenna located at the top of the chamber containing the RF PASS 

portable unit.

As with the Point-to-Point Attenuation Test, this test method is designed to allow free-field testing 

of a complete RF PASS system without the use of conducted measurements or removal of the 

antennas. Free-field testing allows the system to be characterized with any unusual antenna 

radiation pattern intact. 

Finally, we point out that interference testing has been reported in prior literature: for the 900 MHz 

ISM band, see [19][21] and for the 2.4 GHz ISM band, see [20][22][23]. In addition, [23] 

performed laboratory based coexistence testing in the 2.4 GHz ISM band for medical applications. 

All of the aforementioned work utilized several elements similar to those of the test method we 

RF PASS

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describe here, such as the use of an anechoic chamber to control the test environment and the use 

of commercial wireless devices as representative interference sources. In the future, it may be 

possible to merge some of the testing concepts, such as the channel occupancy (discussed here) 

and the transaction “breakdown” (discussed in [23]).

5.3.2 The Target Value of Interference

The interference tests described below focus on two primary frequency bands and transmission 

formats. These target values of interference are detailed in Table 20. The transmission formats 

used in this test (including power level, modulation, encoding schemes, and signal bandwidth) 

have been designed to replicate those of commonly-found wireless devices. As designed, the 

interference source is active 50 percent of the time in either frequency band (e.g., over the 

902 MHz—928 MHz band), or the initial channel of operation (e.g., over one of the six IEEE 

802.11b/g 20 MHz channels, numbered 1, 3, 5, 7, 9, 11).

Because the anticipated channel usage by the interferer in an actual deployment will vary from 

instant to instant, we statistically verify the target value of interference used in testing. We define 

50 percent channel usage such that a spectrum analyzer measurement over a 30-second period will 

detect the presence of the interference source 50 percent of the time, with the remaining samples 

measuring a clear or interference-free RF channel. In addition, over any five-second interval, the 

interference should be active between 25 and 75 percent of the time. Figure 38 shows an example 

based on the specified criteria for a 2.4 GHz interference source.

Table 20. Interference sources for RF PASS testing in the 900 MHz and 2.4 GHz ISM bands.

Frequency 

Range

Transmission Format or 

Modulation Scheme

Subcarrier or Channel

Bandwidth Output power and FCC part

902-928 

MHz

Frequency Hopping 

Spread Spectrum (FHSS) 100 kHz subcarrier

1 W peak power (30 dBm) into 

antenna (w/ max 6 dBi gain), FCC 

Part 15.247 [24]

2.4-2.472 

GHz

Direct Sequence

Spread Spectrum

(DSSS)

20 MHz (IEEE

802.11 channels)

63 mW peak power (18 dBm) into 

antenna, FCC Part 15 (See example 2 

[24] for determination of correction 

factor.)

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Figure 38. An example measurement showing 50 percent channel usage over a 30-second interval. The 

sampling rate was approximately 190 ms, and the 5-second intervals delineated by the dashed lines indicate 

active interference between 40 and 60 percent of the time within the interval. The measurement of a “noise” 

value means that the channel is clear of interference.

The channel usage percentage is measured with a spectrum analyzer and data acquisition software 

that samples the spectrum at the rate described above. In our case, the spectrum analyzer sweeps 

across the frequency band of interest in less than 3 ms; the data acquisition software captures the 

spectrum with a sampling rate of 225 ms ± 50 ms, and searches for the maximum value within the 

captured spectrum. Only the interference source is active when determining the interference 

channel usage; that is, there is no RF PASS communication activity. To arrive at the statistics for 

the target interference, a minimum of 500 samples are collected over approximately two minutes 

of data acquisition. The power threshold was 15 dB. The resolution bandwidth should be as low 

as possible while still achieving a 3 ms sweep time. In our case, 110 kHz and 180 kHz resolution 

bandwidth was used for the 900 MHz and 2.4 GHz frequencies, respectively. The ratio of 

interference signal samples to the noise samples provides the channel usage percentage. As 

discussed above, the channel usage percentage may vary in any five-second interval between 25 

and 75 percent. The test configuration for the RF interference source based on the use of standard 

commercial wireless products is included in the measurement description that follows.

5.3.3 Measurement System

Figure 39 shows a typical RF Interference Test set up. Two anechoic chambers provide shielding 

between the portable unit and the base station. The total path loss (or gain) associated with the 

environmental elements simulates the path loss experienced by personnel carrying RF PASS 

within a building or structure when the base station is located outside. The value of the external 

attenuator is adjusted in a calibration step described in the section entitled “System Calibration: 

Target Path Loss.” For the example results shown below, a 100 dB total path loss was inserted 

between the base station and portable RF PASS. Note that the attenuation path now includes the 

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power combiner, and so the external attenuator value must be changed from that used in the Pointto-Point Attenuation Test. 

The interferer is connected to the test chamber containing the user-worn device through a coaxial 

cable connected to the power combiner. The loss due to the coaxial cable and power combiner 

must be added to the nominal output power specified in Table 20, above. 

5.3.4 Specific Interference Test Configurations for 900 MHz and 2.4 

GHz Systems

This section provides specifics on setting up the interference sources used in testing the RF PASS 

devices. Note that in both the 900 MHz frequency-hopping, spread-spectrum (FHSS) and 2.4 GHz 

direct-sequence, spread-spectrum (DSSS) interference tests, the RF data rates are intentionally 

low in order to create high usage of the RF wireless channel by the interfering device. Most 

wireless systems are designed to maximize data throughput while minimizing the usage of the 

wireless channel to the greatest extent possible. This optimization is achieved, in part, by choosing 

a modulation format that allows the system to transmit the most data for the detected signal-tonoise ratio. The lower the signal-to-noise ratio, the lower the data throughput. If a lowerthroughput modulation format is chosen, the transmission will require more time, and thus occupy 

the channel longer while transmitting the same amount of data. Here, we are intentionally 

inefficient in our usage of the RF wireless channel in order to mimic high-usage conditions. The 

amount of wireless-channel activity in terms of RF transmission power levels and duration is 

important here, not the amount of data transferred over the wireless link. 

Table 21 provides specifics for the 900 MHz frequency-hopping interference test. The interference 

source is a wireless development board that utilizes industrial wireless transceivers, and is 

intended to represent a typical interference source that may be encountered during the deployment 

of an RF PASS system. As shown in Table 21, the key parameter for varying the interference duty 

cycle is the hop duration, or time that the interfering signal lingers on a particular frequency. A 

19 ms hop duration creates the 50 percent channel usage with the statistical behavior described 

above. The 900 MHz interference source used here is a DNT900 series wireless development 

board from RF Monolithics, Inc. previously employed as an RF interference source in [19]. 2

Table 21. Parameters for the 900 MHz interference source.

 

2

 Disclaimer: Mention of any company names serves only for identification, and does not constitute or imply endorsement of such a company or of its products by 

NIST. Other products may work as well or better.

Fixed Parameters Hop Duration (ms) Interferer Channel Usage (percent of time)

RF channel bandwidth = 100 

kHz

RF data rate = 38.4 kb/s

Serial data rate = 38.4 kb/s

Power level = 30 dBm

16 57

18 53

19 50

20 47

22 45

24 39

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The 2.4 GHz DSSS interference set up differs slightly from the set up shown in Figure 37. In this 

case, the interference source is established by connecting two wireless access points and then 

passing data between the two devices. The combined output power constitutes the RF interference 

source, which is connected to the chamber containing the portable RF PASS device in the same 

manner as in the previous configuration. Figure 39 shows the interference test set up that utilizes 

two access points. 

In these tests, the access points were devices that can operate in multiple IEEE 802.11 

configurations. The devices are set up in a bridging mode to allow “ping” packets between the two 

access points. Use of two access points in bridging mode and at equal distances from the RF PASS 

allows the maximum testing range (up to near 100 percent channel usage), and thus supports 

testing of the RF PASS to failure, if so desired. This also allows testing for lower channel-usage 

values, such as the proposed 50 percent, which simulates the channel usage of multiple wireless 

devices connected to a single wireless access point on the same channel. 

The devices are given unique IP addresses on the same subnet, and the security filters are set to 

allow the connection between the two devices. The computer is connected via an Ethernet port 

to one of the access points, which then repeatedly “pings” the other access point with the 

“continuous ping” option set. The ping packet size is adjusted to achieve the desired channel

usage with the packet size option in the ping protocol. Table 22 lists the parameter settings for 

various interference channel usage values. A ping packet size of 28 kb/s corresponds to the 

50 percent channel usage described above. The results provided here are based on D-Link® DAP2553 access points [25].

5.3.5 Measurement Procedure for Interference Testing 

The previous section provided details on how to configure commercial wireless devices to create 

the desired RF interference behavior. Testing of the RF PASS system is carried out in almost the 

same manner as the Point-to-Point Attenuation Tests, but with the addition of the appropriate 

interference source.

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Figure 39. RF interference testing set up for the 2.4 GHz frequency band. Two access points are connected 

together through a power combiner. The combined signal is then connected to the power combiner that 

feeds the chamber containing the portable RF PASS unit.

Table 22. Parameters for the 2.4 GHz interference tests with two access points.

Access Point Settings Ping Packet Size 

(kb/s) Interferer Channel Usage (percent of time)

Mode = Wireless Distribution

System/Bridging (WDS)

Physical layer = IEEE 

802.11b/g 

RF Channel = 1 Mb/s

Power level = 18 dBm

20 35

22 38

24 42

26 45

28 50

30 53

The test is conducted for any of the four Attenuation Test positions of the portable RF PASS 

device under the assumption that the system has successfully passed the Attenuation Test. The 

base station is again positioned with its antenna lying horizontally on the table. This orientation is 

designed to maximize the signal level received by the antenna at the top of the chamber.

The test method is conducted as follows: A wireless link is established between the base station 

and portable RF PASS device. The doors are then closed and the interfering source is turned on. 

The test administrator simply waits 30 seconds until the motion alarm automatically triggers. The 

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test is passed if the base station receives the alarm within 30 seconds, during which the interference 

source is active, as determined by an audible alarm emitted from the base station. 

5.3.6 NIST Results 

Interference testing was performed on products from three different RF PASS manufacturers. One 

system operated in the 2.4 GHz ISM band with a DSSS modulation approach; the other two 

systems used FHSS modulation in the 900 MHz ISM band. The 50 percent channel usage of each 

interference source allows a basic comparison of the systems. 

In Figure 40, the first two RF PASS manufacturers use FHSS in the 900 MHz band. The top graph 

indicates that the first manufacturer consistently fails to successfully transmit the PASS motion 

alarm when the interference source is active more than 40 percent of the time. However, as shown 

in the middle graph, the second manufacturer successfully transmits the motion alarm with active 

interference present 80 percent of the time. As shown in the bottom graph, the third manufacturer, 

who uses DSSS in the 2.4 GHz band, successfully transmits PASS motion alarms with interference 

channel usage up to approximately 60 percent. This system experiences intermittent failures with 

between 65 and 80 percent channel usage, and it experiences complete failure when the channel 

usage is 90 percent or more of the time. 

Figure 40. RF Interference Test results based on the channel usage (occupancy) criteria. RF PASS 

manufacturers 1 and 2 both operate in the 900 MHz band with a frequency-hopping, spread-spectrum 

modulation format; RF PASS manufacturer 3 operates in the 2.4 GHz band with a direct-sequence, spreadspectrum modulation format.

The test results clearly indicate that (1) successfully transmitting RF PASS motion alarms under 

the specified interference conditions is possible; (2) the RF Interference Test provides a 

quantifiable measure of performance for systems that use different modulation schemes and 

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

1

2

3

4

5Repeats

Manufacturer 1 Interference

37dB pass Pos 1

fail

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

1

2

3

4

5Repeats

Manufacturer 2 Interference

pass Pos 1

fail

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

1

2

3

4

5Repeats

Manufacturer 3 Interference

65dB pass Pos 1

fail

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frequency bands; and (3) the test can determine whether manufacturers may need to change their 

designs for more effective alarm communication in the presence of RF interference.

5.4. High-Power Interference Testing

This test uses a high-power wideband signal to interfere with an RF PASS device that is attempting 

to send a motion alarm to the RF PASS base station. In this test, we verify that there will be no 

lasting damage done to the RF PASS devices after the high-power interference has been turned 

off, and that when the interference is turned off the motion alarm will reach the base station.

5.4.1 Creating the Interfering Signal

The interfering signal selected for this task is a flat-spectrum broadband signal that covers 200 

MHz. The broadband nature of this signal ensures that the entire ISM band for all four frequencies 

used by the manufacturers of RF PASS are covered. Two signal generators within a single PXI 

chassis were used to create two 100 MHz broadband signals. The center frequency of each signal 

was placed to slightly overlap the other so as to resemble one 200 MHz broadband signal.

5.4.2 Setup, Procedure, and Test

The High-Power Interference Test uses two broadband signals whose center frequencies are 

chosen such that there is a slight overlap to achieve a 200 MHz span of interference. This span 

covers the entire U.S. ISM band for each frequency we are working with. The ISM bands and 

centers are listed in Table 23.

Table 23. ISM bands and centers.

ISM Band Start ISM Band End ISM Band Center

433.05 MHz 434.79 MHz 433.925 MHz

902 MHz 928 MHz 915 MHz

2400 MHz 2483.5 MHz 2441.25 MHz

5725 MHz 5875 MHz 5800 MHz

The center frequencies of each of the two broadband signals that are used to create the 200 MHz 

broadband signal are given in Table 24.

Table 24. High-Power Interference Test: Center frequency of each broadband signal.

Spectrograms, a specific type of spectrum analyzer plot which shows power levels in relation to 

function of time and frequency, were acquired at the overall center for each band to show that at 

the center where the bands meet there is consistent interference with no time or frequency gaps. 

The SA settings can be seen in Table 25 and the plots can be seen in Figure 41 through Figure 42.

Signal 1 Center Frequency Signal 2 Center Frequency 

382.425 MHz 485.425 MHz

863.5 MHz 966.5 MHz

2389.75 MHz 2492.75 MHz

5748.5 MHz 5851.5 MHz

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Figure 41. Spectrogram plots at the center of the four frequency bands with 1 s time resolution.

Figure 42. Spectrogram plots at the center of the four frequency bands with 10 s time resolution.

Frequency (MHz) Time (s)

433.925 MHz Center: 1 s 

420 430 440 450

20

25

30

35

40 Magnitude (dBm)

-100

-80

-60

-40

Frequency (MHz) Time (s)

915 MHz Center: 1 s

900 910 920 930

15

20

25

30 Magnitude (dBm)

-100

-80

-60

-40

Frequency (MHz) Time (s)

2441.25 MHz Center: 1 s

2430 2440 2450 2460

30

35

40

45 Magnitude (dBm)

-100

-80

-60

-40

Frequency (MHz) Time (s)

5800 MHz Center: 1 s

5780 5800 5820

30

35

40

45 Magnitude (dBm)

-100

-80

-60

-40

Frequency (MHz) Time (s)

433.925 MHz Center: 10 s

420 430 440 450

20

25

30

35

40 Magnitude (dBm)

-140

-120

-100

-80

-60

-40

Frequency (MHz) Time (s)

915 MHz Center: 10 s

900 910 920 930

15

20

25

30 Magnitude (dBm)

-140

-120

-100

-80

-60

-40

Frequency (MHz) Time (s)

2441.25 MHz Center: 10 s

2430 2440 2450 2460

25

30

35

40 Magnitude (dBm)

-140

-120

-100

-80

-60

-40

Frequency (MHz) Time (s)

5800 MHz Center: 10 s

5780 5800 5820

30

35

40

45 Magnitude (dBm)

-140

-120

-100

-80

-60

-40

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Table 25. Spectrogram settings for the two different captures shown in Figure 41 (1 s) and Figure 

42 (10 s).

Capture 1 Capture 2

Span: 40 MHz Span: 40 MHz

Resolution BW: 3.76 kHz Resolution BW: 381.94 kHz

Resolution BW Mode: Arbitrary Resolution BW Mode: Arbitrary

Resolution BW Couple: Fixed Resolution BW Couple: Fixed

Window Type: Flat Top (ampl acc) Window Type: Flat Top (ampl acc)

Frequency Points: 801 Frequency Points: 801

Main Time Length: 1.015625 μs Main Time Length: 10 μs

Max Overlap: 90% (Av off) Max Overlap: 90% (Av off)

Max Overlap 0 % (Av On) Max Overlap 0 % (Av On)

Average Type: Off Average Type: Off

The setup for the High-Power Interference Test is detailed in Figure 43.

Figure 43. High-Power Interference Test setup.

Procedure

1) Turn RF PASS on, place on test platform, close all doors, keep pack in motion with 

dielectric rod.

2) Verify base station has received portable unit’s “normal operation” signal (e.g., green 

icon), disconnect from base station chamber to ensure proper shielding, reconnect, and 

verify green.

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3) Introduce interference, wait 30 seconds.

4) Allow motion alarm to go off (stop moving pack).

5) Check that interference level is sufficiently high to disrupt the RF PASS system by 

verifying that no motion alarm is detected by the base station (wait 2 minutes).

6) Remove/turn off interference.

7) Count seconds until base station again registers motion alarm test. 

Initially, results of this test showed that the interference did not disrupt the motion alarm. That is, 

the motion alarm continued to get through to the base station. We then inserted a broadband power 

amplifier into the setup and repeated the tests and verified that the motion alarm was disrupted as 

described in Step 5.

5.4.3 Signal Generation

5.4.3.1 Background

In this section, we describe in detail how to generate a wideband interference waveform suitable 

for testing wireless devices operating within the ISM bands. This work is in support of the NIST 

effort to establish a general framework for testing new wireless products used by the public-safety 

community. A necessary component of the tests should be an evaluation of how the wireless device 

responds and performs to external RF interference. Any device operating within the ISM bands 

may be subjected to a wide variety of channel interference scenarios. Of major concern is the 

possibility that the RF safety device has to operate under the condition of an elevated noise floor 

due to a uniformly-congested wireless channel. Thus, the motivation for developing the 

methodology presented in this technical note came from a need to subject the transceivers used by 

first responders to an interference signal which is persistent in both time and frequency across the 

entire ISM band.

5.4.3.2 Theory

A random process, or signal in our case, is classified as a white noise process if it has a constant 

power spectral density. The signal may be further categorized by its distribution; for example, a 

uniform distribution or a Gaussian distribution may both produce valid white noise processes. To 

generate a discrete white noise sequence, simply take independent random samples of a given 

distribution. If each sample is taken from the same distribution and all are mutually independent, 

this sequence is known as an independent and identically distributed (i.i.d.) random process. 

Another way of thinking about this sequence is as a realization of a vector of random variables 

which all have the same distribution. Furthermore, the mean and covariance of this sequence will 

not vary with respect to time which means this sequence is wide-sense stationary (WSS). In the 

frequency domain, the power spectral density function Sxx(f) of the random process is given by 

the following equation: 

, (17)

where Rxx(τ) is the auto-correlation function of the random process. Applying the WeinerKhintchine Theorem, we find that the power spectral density of the white noise process is constant 

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across the entire frequency spectrum. The value of the constant will be equal to the variance of the 

random process:

 . (18)

Given that the power spectral density of a Gaussian white noise signal is constant for all 

frequencies, we may apply a digital filter to the white-noise signal to create an interference 

waveform of arbitrary spectral shape. The resulting complex IQ data are then uploaded to an 

arbitrary signal generator with the capability to up-convert and transmit IQ data.

5.4.3.3 Method

1. First we generate complex IQ vector as the sum of two independent zero-mean Gaussian 

distributions:

Z = X + iY,

where X and Y are random vectors generated with the MATLAB command randn. The 

associated covariance matrix of X and Y should be very close to the ideal [

1 0

0 1

]. Figure 

44 through Figure 47 show various forms of the 100 MHz wide interference signal. 

L=1*10^6; % Define Length of IQ Vector

IQ_complex = randn(L,1) + 1j*randn(L,1);

2. Define the parameters of the arbitrary signal generator and the desired interference 

waveform attributes. 

BW = 120; % Define system BW (MHz)

Fp = 50*10^6; % Define filter cutoff freq (Hz)

Fs = 2*BW*10^6; % Sampling rate (Hz)

t = (0:L-1)*(1/Fs); % Time vector

N = 100; % FIR filter order

Rp = 0.00057565; % Corresponds to 0.01 dB peak-to-peak ripple

Rst = 1e-5; % Corresponds to 80 dB stopband attenuation

3. Generate and apply digital filter to IQ vector. There is a lot of freedom in choosing which 

filter to apply but, for our purposes, we chose a constrained equiripple finite impulse 

response (FIR) filter which may be designed with the MATLAB command firceqrip.

NUM = firceqrip(N,Fp/(Fs/2),[Rp Rst],'passedge'); % NUM = vector of coeffs

IQ_time_filt = filter(NUM,1,IQ_complex);

4. Save filtered IQ data in file format appropriate for arbitrary signal generator. 

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IQ_save = [real(IQ_time_filt),imag(IQ_time_filt)];

dlmwrite('noiselong1.txt',IQ_save,'delimiter',',','newline','pc');

5.4.3.4 Plots

Figure 44: Bivariate histogram of Gaussian white noise 

data corresponding to a vector of length L = 10

6

.

Figure 47: Magnitude response of a power amplifier to a 

200 MHz wide interference signal.

Figure 46: Measured spectrum of 100 MHz wide 

interference waveform.

Figure 45: Realization of 100 MHz wide interference 

waveform.

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5.4.4 NIST Results

5.4.4.1 Manufacturer 3, High-Power Interference Test Results

Tests were performed at NIST and results can be seen in Table 26 through Table 28.

Table 26. Manufacturer 3, High-Power Interference Test results for Pack 1.

Pack 1

Trial Number Response Time (sec)

1 27.58

2 28.56

3 22.83

4 26.46

5 16.10

6 13.51

7 11.98

8 7.15

9 21.00

10 36.03

Table 27. Manufacturer 3, High-Power Interference Test results for Pack 2.

Pack 2

Trial Number Response Time (sec)

1 35.58

2 26.05

3 28.79

4 15.53

5 29.41

6 19.00

7 29.75

8 30.08

9 12.05

10 30.93

Table 28. Manufacturer 3, High-Power Interference Test results for Pack 3.

Pack 3

Trial Number Response Time (sec)

1 12.49

2 20.71

3 8.31

4 31.16

5 180+

6 14.93

7 19.60

8 17.73

9 33.00

10 16.78

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5.4.4.2 Manufacturer 1, High-Power Interference Test Results

Tests were performed at NIST. Settings are shown in Table 29 and results can be seen in Table 30

through Table 32 and Figure 48.

Table 29. Manufacturer 1 High-Power Interference Test settings.

Center Frequency of Interference 1 863.5 MHz

Center Frequency of Interference 2 966.5 MHz

Level -20 dBm

Amplifier 50% Gain

Table 30. Manufacturer 1, High-Power Interference Test results for Pack 1.

Pack 1

Trial Number Response Time (sec)

1 5.88

2 6.45

3 9.23

4 5.40

5 4.60

6 7.38

7 6.25

8 5.96

9 6.28

10 3.99

Table 31. Manufacturer 1, High-Power Interference Test results for Pack 2.

Pack 2

Trial Number Response Time (sec)

1 7.60

2 5.83

3 8.81

4 6.16

5 4.45

6 8.56

7 6.91

8 7.08

9 10.48

10 8.75

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Table 32. Manufacturer 1, High-Power Interference Test results for Pack 3.

Pack 3

Trial Number Response Time (sec)

1 5.71

2 7.85

3 7.71

4 5.84

5 8.61

6 5.78

7 5.78

8 7.55

9 7.75

10 11.03

Figure 48. Histogram of High-Power Interference Tests for Manufacturers 1 and 3. The 180+ trial is not 

shown in the histogram (as seen in the table).

6. Conclusion

We described the development of test methods designed to aid standards bodies with the 

evaluation of wireless technology used in firefighter, public-safety, and other applications where 

communications are utilized. The test methods described here were designed to be as costeffective as possible so that, not only test laboratories, but manufacturers and even end users can 

reproduce them for design, test, and evaluation purposes. 

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We anticipate that, as more and more wireless electronic-safety equipment becomes available, the 

test methods described here will be used for testing those systems as well. 

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