NBS

PUBLICATIONS AlllOP b315ti3

* tkh R.I.C.

Evaluation of Electronic Monitoring

Devices

Arnold G. Perrey

Barry A. Bell

Center for Electronics and Electrical Engineering

Electrosystems Division

Marshall J. Treado

Law Enforcement Standards Laboratory

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Gaithersburg, MD 20899

December 1986

Prepared for QQ nal Institute of Justice

2 QQ Department of Justice

lington, DC 20531

. U56

86-3501

1986

C.2

NBSIR 86-3501

EVALUATION OF ELECTRONIC MONITORING

DEVICES

Arnold G. Perrey

Barry A. Bell

MBS

RESEARCH ' INFORMATION CENTER

AJ-F..

Center for Electronics and Electrical Engineering

Electrosystems Division

Marshall J. Treado

Law Enforcement Standards Laboratory

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Gaithersburg, MD 20899

December 1986

Prepared for National Institute of Justice

U.S. Department of Justice

Washington, DC 20531

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director
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A
ABOUT THE TECHNOLOGY ASSESSMENT PROGRAM

The Technology Assessment Program is sponsored by the Office of

Development, Testing, and Dissemination of the National Institute of

Justice (NIJ), U.S. Department of Justice. The program responds to the

mandate of the Justice System Improvement Act of 1979, which created

NIJ and directed it to encourage research and development to improve

the criminal justice system and to disseminate the results to Federal,

State, and local agencies.

The Technology Assessment Program is an applied research effort

that determines the technological needs of justice system agencies,

sets minimum performance standards for specific devices, tests

commercially available equipment against those standards, and

disseminates the standards and the test results to criminal justice

agencies nationwide and internationally.

The program operates through:

The Technology Assessment Program Advisory Council ( TAPAC

consisting of nationally recognized criminal justice practitioners from

Federal, State, and local agencies, which assesses technological needs

and sets priorities for research programs and items to be evaluated and

tested.

The Law Enforcement Standards Laboratory (LESL) at the National

Bureau of Standards, which develops voluntary national performance

standards for compliance testing to ensure that individual items of

equipment are suitable for use by criminal justice agencies. The

standards are based upon laboratory testing and evaluation of

representative samples of each item of equipment to determine the key

attributes, develop test methods, and establish minimum performance

requirements for each essential attribute. In addition to the highly

technical standards, LESL also produces user guides that explain in

nontechnical terms the capabilities of available equipment.

The Technology Assessment Program Information Center (TAPIC)

operated by a grantee, which supervises a national compliance testing

program conducted by independent agencies. The standards developed by

LESL serve as performance benchmarks against which commercial equipment

is measured. The facilities, personnel, and testing capabilities of

the independent laboratories are evaluated by LESL prior to testing

each item of equipment, and LESL helps the Information Center staff

review and analyze data. Test results are published in Consumer

Product Reports designed to help justice system procurement officials

make informed purchasing decisions.

Publications issued by the National Institute of Justice,

including those of the Technology Assessment Program, are available

from the National Criminal Justice Reference Service (NCJRS), which

serves as a central information and reference source for the Nation’s

criminal justice community. For further information on how to order,

or to register with NCJRS, write to the National Institute of Justice,

National Criminal Justice Reference Service, Washington, DC 20531.

James K. Stewart, Director

National Institute of Justice
ACKNOWLEDGMENTS

This report was prepared by the Law Enforcement Standards

Laboratory of the National Bureau of Standards under the direction of

Lawrence K. Eliason, Chief of LESL. The laboratory work for this

project was carried out by staff members of the NBS Electrosystems

Division. The cooperation of the four manufacturers involved and the

loan of their equipment for testing is gratefully acknowledged. The

research was sponsored by the National Institute of Justice, Annesley

K. Schmidt, Research Analyst. The technical effort to develop this

report was conducted under Interagency Agreement LEAA-J-IAA-021-3

,

Project No. 8505.

11
FOREWORD

The Law Enforcement Standards Laboratory (LESL) of the National

Bureau of Standards (NBS) furnishes technical support to the National

Institute of Justice (NIJ) program to strengthen law enforcement and

criminal justice in the United States. LESL’s function is to conduct

research that will assist law enforcement and criminal justice agencies

in the selection and procurement of quality equipment.

LESL is; (1) Subjecting existing equipment to laboratory testing

and evaluation and (2) conducting research leading to the development

of several series of documents, including national voluntary equipment

standards, user guides and technical reports.

This document presents the results of a two-step program to

evaluate electronic monitoring devices that are intended for use in

monitoring the presence of individuals within a given area who are

responsible to the criminal justice system but not confined to

institutions. As some of the testing was conducted in 1985, the

manufacturers claim to have improved their equipment since then. In no

case does the testing of this equipment imply the recommendation or

endorsement of any product by the National Bureau of Standards, the

National Institute of Justice or any other government agency.

Technical comments and suggestions concerning this document are

invited from all interested parties. They should be addressed to the

Law Enforcement Standards Laboratory, National Bureau of Standards,

Gaithersburg, MD 20899.

Lawrence K. Eliason, Chief

Law Enforcement Standards Laboratory
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CONTENTS

Page

Foreword iii

Executive Summary vii

I. Introduction 1

II. Test Equipment 4

III. Description and Evaluation - 1985 Tests 5

A. System #1 5

B. System #2 22

IV. Description and Evaluation - 1986 Tests 36

A. System #3 37

B. System #4 40

V. Conclusions and Recommendations 47

V
COMMONLY USED SYMBOLS AND ABBREVIATIONS

A ampere H henry nm nanometer

ac alternating current h hour No. number

AM amplitude modulation hf high frequency o.d. outside diameter

cd candela Hz hertz (c/s) ohm cm centimeter i.d. inside diameter P- page CP chemically pure in inch Pa pascal

c/s cycle per second ir infrared pe probable error d day J joule pp. pages dB decibel L lambert ppm part per million dc direct current L liter qt quart “C degree Celsius lb pound rad radian »F degree Fahrenheit Ibf pound-force rf radio frequency

diam diameter Ibfin pound-force inch rh relative humidity

emf electromotive force Im lumen s second

eq equation In logarithm (natural) SD standard deviation F farad log logarithm (common) sec. section

fc footcandle M molar SWR standing wave ratio

fig- figure m meter uhf ultrahigh frequency

FM frequency modulation min minute uv ultraviolet

ft foot mm millimeter V volt

ft/s foot per second mph mile per hour vhf very high frequency g acceleration m/s meter per second W watt g gram N newton X wavelength

gr grain N-m newton meter wt weight

area = unit^ (e.g., ft^ in ^ etc.); volume = unit^ (e.g., ft^ m^ etc.) PREFIXES

d deci (10"') da deka (10) c centi (10“^) h hecto (10^) m milli (10-^) k kilo (10^) micro (10"‘) M mega (10*) n nano (10“’) G giga (10’) P pico (10“'^) T tera (10'^) COMMON CONVERSIONS

(See ASTM E380)

ft/s X 0. 3048(XX) = m/s

ftx0.3048 = m

ft-lbfXl.355818=J

grX0.06479891=g

inx2.54=cm

kWh X 3 600 (XX) =J

lbx0.4535924=kg

Ibfx 4.448222 = N

lbf/ftXl4.59390=N/m

Ibf-inX 0.11 29848 = N-m

Ibf/in^X 6894.757 = Pa mphX 1.609344=km/b

qtX 0.9463529 = L

Temperature: (T-f — 32)x5/9=r-c

Temperature; (TcX9/5) + 32= 7"-f

VI
EXECUTIVE SUMMARY

Through the use of electronic monitoring devices (EMDs), persons

convicted of certain crimes may be sentenced to home confinement,

thereby reducing both the cost and social implications associated with

institutional confinement. Accordingly, a strong case can be made for

the use of EMDs by many jurisdictions in this country. In view of

their possible widespread use, the National Institute of Justice asked

the National Bureau of Standards to develop a test plan and conduct

tests of these devices to measure (1) their advertised basic technical

characteristics, and (2) other operational characteristics such as

range, safety, compatibility between system components, and tamper

resistance

All known manufacturers of EMDs were contacted but only two

companies were willing to submit their systems for testing in 1985.

The systems (transmitter and receiver /monitor ) were tested in an open

field, wooden residence, metal building and a laboratory environment.

Both systems performed as advertised with respect to operating

freguency, range of operation, and waterproof characteristics.

Differences between the two were due primarily to frequency band

considerations. Both systems have relatively low effective radiated

output powers, making them susceptible to reduced operating range in

the vicinity of certain configurations of metal objects and broadcast

electromagnetic interference (EMI). Conversely, they were not bothered

by EMI from typical household products. Reduced operating range also

resulted when the individual wearing the transmitter shielded it from

direct line of sight to the receiver/monitor , substantially reducing

the received signal in one instance. Neither system was found to be

unsafe during these limited tests and, when called upon to do so,

transmitted a different signal than that for normal operation.

Two additional companies submitted equipment for testing in 1986,

and their transmitters and receiver/monitors were tested in a similar

fashion. Both of these systems also met their stated goals as to

operating frequency, range of operation, and waterproof

characteristics. Neither system was found to be unsafe during these

limited tests, and the one that had a tamper capability transmitted a

different signal when tampered with. Because of low effective output

power, both systems would be susceptible to interference in the

vicinity of broadcast transmitters. For additional information on the

test results for each of these four systems, please refer to the

summaries at the conclusion of each series of tests: page 20 for

system #1, page 34 for system #2, page 37 for system #3, and page 42

for system #4.

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Evaluation of Electronic Monitoring Devices

Arnold G. Perrey, Barry A. Bell,* and Marshall J. Treado

National Bureau of Standards, Gaithersburg, MD 20899

Electronic Monitoring Devices (EMDs) are used to monitor

the presence of individuals within a given area who are

responsible to the criminal justice system but not confined

to institutions. Several EMDs were tested to measure

operational characteristics such as operating frequency,

approximate range of operation, component capability, and

tamper resistance. Tests were conducted in an open field,

wooden residence, high rise metal building, and in a

laboratory environment.

Key words: early release; electromagnetic interference;

electronic monitoring; monitoring device; parole; receiver/

monitor; tamper resistance; transmitter.

I . INTRODUCTION

Several manufacturers have developed equipment that is intended to

be used to monitor the presence of individuals within a given area who

are responsible to the criminal justice system but not confined to

institutions. This equipment, referred to as Electronic Monitoring

Devices (EMDs), is intended to permit law enforcement agencies to

determine, on a timely basis, whether persons on noninstitutional

confinement are in compliance with the terms of their agreement.

Through the use of EMDs, persons convicted of nonviolent crime may

be sentenced to home confinement, thereby reducing both the cost and

social implications associated with institutional confinement.

Jurisdictions with a lack of space that elect to enter into an early

release program may also want to use EMDs to monitor the status of

parolees in such a program. A study by the U.S. Department of Justice

estimates that there are 1.827 M persons in the United States on

probation or parole, and it is further estimated that about 8 M people

nationally are convicted of misdemeanors at the state and local

government levels each year. Very few of these individuals ever serve

time in jail. Proponents of the use of EMDs by the criminal justice

system believe that certain monetary savings will result, as the cost

to monitor an individual will be significantly less than the cost to

house, feed, and rehabilitate the same person. There are also

projected savings in lost wages and productivity, as well as a decrease

in the need for additional correctional facilities. Thus, a strong

case can be made for the use of EMDs by most jurisdictions.

Electrosystems Division, Center for Electronics and Electrical

Engineering, National Engineering Laboratory.

"k k

Law Enforcement Standards Laboratory, National Engineering

Laboratory.

1
As the possible need for EMDs became apparent, several different

models were proposed and at least two were evaluated in typical

probation situations, one in New Mexico and Illinois, and a second in

Florida. Several other manufacturers have come forth in response to

written and verbal solicitations, saying that they intend to produce a

product capable of monitoring persons on noninstitutional confinement.

At the request of the National Institute of Justice (NIJ), the

National Bureau of Standards (NBS), through its Law Enforcement

Standards Laboratory (LESL) and the Electrosysteras Division, has

evaluated the performance of EMDs with an emphasis on the technical

properties and operational characteristics of the equipment. All known

manufacturers of EMDs were contacted to obtain information on the

technical characteristics of these devices and the results of any prior

testing of components or of complete systems. Typical systems usually

consist of three major components: a transmitting device worn by the

individual, the receiver/monitor device that plugs into household power

and transmits a signal via a standard telephone line, and a computer

terminal at the central headquarters location that receives and

displays this signal. A test plan, developed by LESL, was used to

measure the basic technical characteristics of the transmitter and the

receiver/monitor and to measure operational characteristics such as

safety, range, compatibility, and tamper resistance.

The EMD evaluation program was advertised in the Commerce Business

Daily and all known manufacturers were asked to send in equipment for

evaluation. The following two companies voluntarily submitted their

equipment for testing in 1985: Monitech Systems, Inc., 3269 South

Main, Suite 210, Salt Lake City, UT 84115, and Contrac Company, P.O.

Box 427, Key Largo, FL 33037. Two others. Correction Services, Inc.

(CSI), P.O. Box 2941, West Palm Beach, FL 33402, and Control Data

Corporation (CDC), 7600 France Avenue South, Edina, MN 55435, submitted

their equipment for testing about a year later. The CDC system is now

being handled by Boulder Industries of 6175 Longbow Drive, Boulder, CO

33402.

In the following report, the respective units are described and

documented by the order in which they were received. Hence, the

Monitech system (now known as Computrac) is referred to as system #1,

Contrac as system #2, CSI as system #3, and CDC as system #4. Tests

were conducted in four locations. The four locations are shown in

figure 1, which depicts the NBS Gaithersburg, MD campus:

1 In order to adequately describe the systems and experiments

discussed in this report, commercial equipment and instruments are

identified by manufacturer's name or model number. In no case does

such identification imply recommendation or endorsement by the National

Bureau of Standards, the National Institute of Justice or any other

government agency, nor does it imply that the material or equipment

identified is necessarily the best available for the purpose.

2
237

KDKMAGK[1IC

lAEORATORY 3

Figure

1.

Map

of

the

National

Bureau

of

Standards.
Test Locations T1 = Open field test area

T2 = Administration Building

T3 = Bowman House

T4 = Metrology Building

In analyzing the data in the tables, the reader should know that a 6

dB/]iV reduction in signal strength means a loss of approximately

one-half the transmitter output power and that a 1 dB/uV received

signal is considered marginal, i.e., not sufficient to guarantee

reception if atmospheric or environmental conditions change.

II. TEST EQUIPMENT

Five major items of test equipment were used in these tests. An

EMI/field intensity meter was used for all field strength tests. This

instrument can be used in a manual or programmable mode for measuring

electromagnetic interference (EMI) emissions within a frequency range

from 30 MHz to 1.0 GHz in accordance with specifications of MIL

Standard 461A. The direct peak pulse measurement mode was used to

evaluate the system performance. In this mode the instrument provides

a detector function that responds to the peak value of the input

signal. Since these systems transmit rather short pulses, a peak hold

duration of 0.05 s was chosen. The system bandwidth was limited to 0.1

MHz for satisfactory noise reduction.

A biconical dipole antenna was used to test system #1 which has a

carrier frequency just below 170 MHz. This antenna is a broadband,

horizontally-polarized antenna designed to cover the frequency range

from 25 MHz to 200 MHz, and is calibrated for a 50-Q load. The antenna

unit is specifically designed for measurement of radiated emissions and

meets MIL Standard 461A requirements.

A conical log periodic spiral antenna was used to test systems 2,

3, and 4 which have carrier frequencies in the range of 310-325 MHz.

It is a broadband antenna operating over the frequency range of 200 MHz

to 1 GHz. The antenna has a nominal 50-Q impedance and meets the

requirements of MIL Standard 461A. A log spiral antenna is circularly

polarized, assuring equal response to signals radiated in either the

horizontal or vertical plane.

A spectrum analyzer in an oscilloscope mainframe was used to

document the pulse signatures of the transmitters under test. The unit

is capable of operating over a frequency range from 1 kHz to 1.8 GHz.

In order to photograph the transmitted pulses, a custom-designed pickup

coil was used to connect to the spectrum analyzer input. This pickup

coil allowed close proximity coupling between the spectrum analyzer and

the transmitters under test.

An oscilloscope camera with Polaroid film was used to photograph

pulse waveforms and codes of the equipment tested. All pictures taken

were taken with a time exposure which varied from 10 to 50 s for

individual frames.

4
III. DESCRIPTION AND EVALUATION - 1985 TESTS

A. SYSTEM #1

The system #1 equipment consisted of:

1) Telemetry receiver #101884-1238

2) Digital processor #101884-186

3) Miniature transmitter #251

4) Miniature transmitter #264

A photograph of these components is given in figure 2. The test

equipment in the background is not part of the system.

The Equipment

1. Transmitters

A close-up photograph of the miniature transmitters is shown in

figure 3, and the physical dimensions of these devices are shown in

figure 4. This particular type of transmitter is worn around the neck

on a loop that is approximately 15 cm (6 in) in diameter. The loop

serves two purposes: a) physical support of the transmitter, and b)

electrical control of the transmitting mode. When an individual is

being outfitted with a transmitter, the loop has to be opened; then it

is closed around the neck by means of a pin contact feature. The loop

itself consists of 50 strand, 32-gage stainless steel wires that

electrically connect to the internal power source and the active

transmitting circuit.

The transmitter can be deactivated by attaching a small permanent

magnet to its case. It transmits a burst of radio frequency for a

predetermined time (-20 ms). The transmitter operates using two time

periods. The nominal time between bursts is either 1 s or 2 s depending on whether the attachment loop is electrically open or

closed.

Measured transmitting parameters differed

transmitters as indicated below:

slightly between

Transmitter #251 Transmitter #264

Operating frequency:

Toneburst duration:

Period 1 nominal:

Period 1 actual:

Period 2 nominal:

Period 2 actual:

168.922 MHz

~25 ms

1 s (open loop)

0.897 s

2 s (closed loop)

2.075 s

168.989 MHz

~24 ms

1 s (open loop)

1.251 s

2 s (closed loop)

2.414 s

2. Monitor

The monitor station as received consisted of two items, a receiver

which is ordinarily used for telemetry purposes, and a digital

processor. The physical dimensions and external features of these

items are shown in figure 4. A telephone interface was not provided.

Upon receipt of a signal from the transmitter, the receiver provides

5
6

Figure

2.

System

#1,

from

left

to

right:

1)

The

telemetry

receiver

#101884-1238,

2)

The

digital

processor

#101884-186,

3)

Transmitter

#251,

and

4)

Transmitter

#264.
7

Figure

3.

System

#1

Transmitters.

Left:

Transmitter

^251.

f

=168.922

MHz.

Right:

Transmitter

#264,

f^=168.898

MHz.

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TRANSMITTER,

SCALE
amplitude and frequency information to equipment such as the digital

processor. Its input impedance is 50 Q and it has a built-in speaker

which automatically disconnects when a headset is used. The headset

jack is also used as a means to connect the receiver to the digital

processor, in this application. Receiver tuning and level controls are

on the front panel along with the antenna connection, battery charge

input, and battery status indicator.

Upon receipt of the signal from the receiver, the digital

processor measures and stores it until the next pulse is received. The

stored level can be recorded or displayed as needed, as can the period

between pulses. Amplitude or period displays can be selected using the

mode selector switch. Amplitude is displayed as a current between 0-1

mA, while the period between pulses can range from 0.2 s to 9.999 s. The processor is battery powered, with a battery status indicator on

the panel. The battery is rechargeable.

Transmitter Testing

The following is the performance data for transmitters #251 and

#264 from measurements taken in locations T1 through T4 . The field

intensity meter and biconical dipole antenna were used for the tests in

all four locations. The antenna correction factor for these tests is

14.5 dB. Field strengths were measured in decibels referenced to one

microvolt (dB/y.V) and converted to microvolts per meter (y.V/m), taking

into account the antenna correction factor.

These data provide a baseline of information about the inherent

field strength of these two transmitters as a function of radial

distance from the transmitter. Table 1 gives the results of tests

conducted in the open field test site with the monitor placed on the

ground and each transmitter, in turn, moved to locations 10, 20, 30,

40, and 50 m ( 32.8, 65.6, 98.4, 131.2, and 164 ft) from the monitor.

Transmitters were worn by an individual facing the monitor at a height

of approximately 1.2 m (4 ft) above the ground. Any measurement of

approximately 1 dB/uV or less (about 40 m from the monitor, in this

case) is considered marginal (not reliable) reception.

Table 1. System //I measurements at the open field test site

Transmitter #251 Transmitter #264

Radius dB/|jV (jV/m Radius dB/pV pV/m

10 m +4.0 8.2 10 m +3.0 7.5

20 m +3.0 7.5 20 m +2.0 6.7

30 m +2.5 7.1 30 m +1.5 6.4

40 m +1.1 6.0 40 m +1.0 5.9

50 m -1.0 4.7 50 m -1.6 4.4

At a distance of 40 m (131.2 ft) an attenuation in field strength

of approximately 15 dB was measured when the person wearing the

transmitter turned his back towards the antenna. A 15 dB decrease in

field strength means that more than 3/4 of the signal level was lost.

This decrease is probably caused by body bulk or capacitance or both.

9
There was no interference from citizens band radios or police radios

operating at typical police frequency bands, nor was there any

interference from impulsive noise such as that generated by motor

brushes or automobile engines.

Tests were conducted with the monitor placed on the floor in one

section of the lobby of the Administration Building and each

transmitter, in turn, moved to locations 10, 20, 30, 40, and 50 m

(37.8, 65.6, 98.4, 131.2, and 164 ft) away at a height of approximately

1.2 m (4 ft) off the ground. Again, the transmitters were worn by an

individual who faced the monitor. See figure 5 for the layout of the

lobby floor of the Administration Building. The designation TP was

given to the test position, the location of the receiving antenna and

the field strength meter. Table 2 contains data taken at designated

distances along the straight line path from the test position.

Table 2. System //I measurements in the Administration Building

Transmitter //251 Transmitter #264

Radius dB/pV nV/m Radius dB/uV (jV/m

10 m +4.0 8.2 10 m +3.5 8.0

20 m +3.5 8.0 20 m +3.0 7.5

30 m +3.0 7.5 30 m +3.0 7.5

40 m +2.0 6.7 40 m +2.0 6.7

50 m +1.5 6.4 50 m +1.8 6.5

Third

Floor +1.0 5.9

Third

Floor +1.0 5.9

Compared to the open field data, the reception at this inside

(lobby) location is somewhat greater (about 0.5 dB/uV) for a given

radial distance from the transmitter. Entrance into an elevator

located approximately 10 m (32.8 ft) from the monitor resulted in a

complete loss of signal when the elevator door was closed. Reception

on a given corridor level, up to a distance of 50 m (164 ft), was about

the same as given in the table above. A measurement taken while the

transmitter was located on the third floor (two floors above the

monitor location) near the elevator shaft is given in the table.

However, reception with the transmitters located above the third floor

was marginal (<+l dB/uV). This is probably due to the amount of steel

in this building, as it has all metal walls, except as indicated in

figure 5. Strong interference from the NBS Security Communication

System located in the basement of the building (one floor below the

lobby) generated a field strength of 3 V/m at the test station. Total

masking of the signal from the low power transmitters occurred when the

security communication system was being used. The carrier frequency of

the NBS security system is about 168 MHz.

The Bowman House is located on the NBS campus and is surrounded by

tall oak trees. The building is of all wood construction and features

a typical residential layout (see fig. 6). The numbers indicate

successive transmitter positions relative to the test position.

Underlined numbers indicate basement locations. The data in table 3

indicate that maximum reception was obtained in locations 5 and 6 where

10
Figure 5. Layout of the lobby area, NBS Administration Building.

11
NBS

bowman

hods

iiI

r-(M

12

Figure

6.

NBS

Bowman

House.

Inside

locations 1

through

14

of

transmitter

relative

to

receiving

antenna

and

field

intensity

meter

at

the

test

position.
the fewest wall obstructions existed between the transmitters and the

receiving antenna/f ield strength meter test setup. Locations 11, 12 , 13 , and ]A in the stairwell and basement had decreased reception due to

heating and air conditioning ductwork, flooring, etc.

Table 3. System //I measurements at the Bowman House

(inside locations 1 through 14)

Transmitter #251 Transmitter //264

Location IB/mV nV/m Location dB/nV MV/m

1 +4.5 8.9 1 +4.0 8.2

2 +4.5 8.9 2 +3.0 7.5

3 +4.5 8.9 3 +3.0 7.5

4 +4.0 8.2 4 +3.5 8.0

5 +5.0 9.2 5 +4.0 8.2

6 +5.0 9.2 6 +4.0 8.2

7 +4.0 8.2 7 +3.0 7.5

8 +3.0 7.5 8 +3.0 7.5

9 +3.0 7.5 9 +2.0 6.7

10 +4.0 8.2 10 +3.0 7.5

11 +3.0 7.5 11 +3.0 7.5

12 +3.0 7.5 12 +2.0 6.7

13 +3.0 7.5 13 +2.0 6.7

14 +3.0 7.5 14 +2.0 6.7

The data in table 4 were obtained from readings taken outside the

Bowman House at successive locations, 15 through 18-2, relative to the

test position (see fig. 7). These positions represent the maximum

possible normal range of operation in the vicinity of the Bowman House

which is enclosed on three sides by a chain link fence and surrounded

by tall foliated trees.

Table 4. System #1 measurements at the Bowman House

(outdoor locations 15 through 18)

Transmitter #251 Transmitter #264

Location dB/pM |jV/m Location dB/MV pV/m

West 15 +2.0 6.7 West 15 +1.5 6.4

15-1 +2.0 6.7 15-1 +1.5 6.4

15-2 +2.5 7.1 15-2 +2.5 7.1

South 16 +2.5 7.1 South 16 +2.5 7.1

16-1 +2.5 7.1 16-1 +2.5 7.1

16-2 +2.5 7.1 16-2 +2.5 7.1

East 17 +2.5 7.1 East 17 +2.5 7.1

17-1 +2.5 7.1 17-1 +2.5 7.1

17-2 +1.0 5.9 17-2 +1.0 5.9

North 18 +2.5 7.1 North 18 +2.0 6.7

18-1 +2.5 7.1 18-1 +2.0 6.7

18-2 +2.5 7.1 18-2 +2.0 6.7

13
14iM

Figure

7.

Test

perimeter

locations

15

through

18

outside

of

the

NBS

Bowman

House.
Occasional interference at the level of about 20 uV/m was

encountered from the transmitter of the NBS Security Communication

System. No impulsive interference was detected. Position 17-2

provided the most attenuated reception point, probably due to the

effects of a chain link fence in that vicinity.

The data in table 5 , which were obtained through measurements in a corridor of the Metrology Building (see fig. 8), are very similar to

that obtained at test location T2, the main lobby of the Administration

Building. In both of these locations, the measured field strength was

approximately 0.5 dB/iiV greater than it was at the field test site, for

a given radial distance from the transmitter. The reason for this

enhanced reception is probably due to the metal walls acting to direct

the radiated signal towards the receiving antenna.

Table 5. System //I measurements in the Metrology Building

Transmitter #251 Transmitter #264

Radius dB/nV nV/m Radius dB/pV |jV/m

10 m +4.0 8.2 10 m +3.5 8.0

20 m +3.5 8.0 20 m +3.0 7.5

30 m +3.0 7.5 30 m +3.0 7.5

40 m +2.0 6.7 40 m +2.0 6.7

50 m +1.5 6.4 50 m +2.0 6.7

Immersion Testing

For the immersion test a laboratory sink, measuring 40 by 60 by 30

cm (16x24x12 in) was used. Approximately 50 L (13.2 gal) of warm water

constituted the immersion medium. The measurement antenna was

positioned 4 m (13.3 ft) from the sink.

As can be seen from the data in table 6, an attenuated reception

of about 1 dB/uV (about 11% reduction in range) occurs during

immersion. Both transmitters were apparently unaffected by the brief

immersion testing.

Table 6. System #1 immersion tests

Transmitter #251 Transmitter #264

Reference reading

Units immersed for

15 min (5 min

between readings)

Units removed (still wet)

Units removed (dry)

Radius dB/pV (jV/m

4 m +4.0 8.2

4 m +3.0 7.5

4 m +3.0 7.5

4 m +3.0 7.5

4 m +3.0 7.5

4 m +4.0 8.2

15

Radius dB/ pm pV/m

4 m +3.0 7.5

4 m +2.0 6.7

4 m +2.0 6.7

4 m +2.0 6.7

4 m +2.0 6.7

4 m +3.0 7.5
16

Figure

8.

Layout

of

building

220,

Metrology

Building.
Monitor Testing

The receiver and interfacing digitizer were used in conjunction

with transmitters #251 and #264. In general, these units functioned

very well and according to the manufacturer's specifications. This

monitor has been developed as a telemetry receiver and, as such, is

capable of discerning very small signal levels. The manufacturer

rates the minimum discernable input signal to be -150 dBm or 0.0007 y.V.

Such a sensitivity is really not required for a parole monitoring

system, since it would adversely extend the confinement area to be

monitored. It is understood, however, that a different design is

forthcoming.

The receiving unit converts an incoming radio frequency pulse into

an audible tone burst with a frequency of approximately 1000 Hz which

can be monitored with either headphones or with a loudspeaker. The

manufacturer uses the 8-Q audio output as a voltage source for the

second unit, the interfacing digitizer (digital processor). Standard

phone plugs are used to interconnect both units; however, the phone

plug connection was not quite reliable. Intermittent operation was

probably due to metal fatigue of the receptacle leaf contacts or

oxidation of the plug contacts or the ring and tip. Furthermore, a

separate voltage source, one not affected by volume control settings,

would be advantageous

.

The digital processor converts the tone burst into two different

data signals. The received pulse is measured and processed with each

received pulse and the data stored until the next pulse. The stored

output level is available as a 0 to 1 mA output for analog recording

and is called the amplitude channel. A second channel, the period

channel, is used to measure the period between transmitted pulses by

counting an internal clock. It also provides a 0 to 1 mA output. For

test purposes, and in order to document the logic and level codes of

the unit, the current outputs were converted to a voltage output by

means of 100-fi precision resistors.

The accompanying photographs, 9A through 9D, show the pulse period

and amplitude level functions under operational conditions. The

initial turn-on of the monitor is shown in figure 9A. The transmitter

was activated beforehand in order to have a signal available as soon as

the monitor became functional. The oscilloscope traces shown were

taken over a time period of 50 s. The upper trace represents the

period signal with an amplitude of 20 mV per division and a scan rate

of 5 s per division. The received pulses, one pulse every 2 s, can be

identified as small negative voltage spikes. The small step changes

between these pulses are caused by movement of the transmitter. The

lower trace shows the amplitude signal ; it is used to identify any

changes of transmitting or receiving characteristics. As shown in

figure 9A, the activation of the monitor takes the form of a multistep

change of the amplitude signal, after which an operating level of 1.5 V

is reached indicating normal or "transmitter - in-range" operation.

17
B

Figures 9A and 9B. Pulse period and amplitude level traces

under operating conditions.

18
c

D

Figures 9C and 9D. Pulse period and amplitude level

traces under operating conditions.

19
In order to show the normally-received pulse train and the period

change that occurs when the transmitter is tampered with, figure 9B was

obtained using an exposure time of 20 s. The left side of the picture

shows the normal signal--one pulse every 2 s. The right half of the

picture shows the occurrence of a period change on the upper trace (one

pulse every second), indicating that the transmitting loop has been

opened. Coinciding with the period change, the amplitude signal on the

lower trace steps from approximately 1.5 V down to a 1-V level, thereby

signaling the tamper mode. In figure 9C, the 1-s period pulse train

(indicating tamper mode) is still being received, but the transmitter

was then turned off near the center of the sweep. After a delay of

approximately 10 s, the period signal (upper trace) changes level by

about 20 mV. This change is indicative of a ’’no-signal-received"

condition. Ten seconds after the level change of the period channel,

the amplitude signal changes state and begins to transmit a multistep

output code (alarm signal). This continued pulsed output code can be

seen in figure 9D. No attempt was made to decode or interpret this

transmission.

The next set of pictures, figures 9E, 9F, and 9G show the radio

frequency tone burst from the receiver at the input of .the digital

processor, the spectral signature of transmitter #251, and spectral

signature of transmitter #264, respectively.

In figure 9E a radio frequency tone burst of approximately 20 ms

in duration can be seen. The signal level shown here is about 300 mV

peak to peak and was taken from the input of the digital processor.

The next picture, figure 9F, shows the spectral position of the emitted

signal (f -169 MHz) from transmitter #251 as well as its magnitude. In

figure 9G^the signal of transmitter #264 is shown (f -168 MHz). It can

be seen that the emitted signal from this unit is *^ower than that of

transmitter #251. A probable cause for this difference could be a

failing battery. However, this cause was not verified since the sealed

case of the transmitter does not allow access to measure the battery

voltage. In order to measure the pulsed transmitter output, a

specially-designed pickup coil was used in conjunction with the

spectrum analyzer. The transmitting/ attachment loop was used to

inductively couple the emitted signal to the spectrum analyzer by

closing the loop through the center of the coupling coil.

Summary

System #1 was tested on the grounds at NBS, Gaithersburg,

Maryland, in an open field test site, a high-rise building, a wooden

residence, and in a laboratory environment. In general, the system

performed as advertised. Range of operation measurements were made out

to 50 m (164 ft) at the field test site indicating use at that range

under optimum conditions. At a range of 20 m (65.6 ft), the field

strength measured through the walls of the wooden building was recorded

at 2.5 dB/uV, as compared with 3.0 dB/uV at the field test site,

indicating a very small drop in capability. When operated inside the

Administration Building, measured field strengths were slightly higher

than at the field test site. However, the signal would not penetrate a

steel enclosed elevator shaft at a distance of 10 m (32.8 ft).

20
21

Figure

9E

through

9G.

Radio

frequency

tone

burst

and

spectral

signature

of

transmitters
Transmitter effective radiated output power (~1 pW) , based on

received signal strength, and supply voltage (~3 V) were low enough to

be safe under all conceivable usage conditions. Transmitter design

does not permit normal access to the electronic circuitry and severance

of the transmitting loop automatically transmits a different signal.

Radiation from a citizens band radio, walkie-talkies operating at

police band frequencies and devices simulating the noise patterns of

electric hair dryers, shavers, and mixers did not interfere with the

operation of the system. Because the transmitter is hermetically

sealed, there was no way of measuring battery current drain without

breaking the seal. This system does not send a signal indicating a

transmitter or monitor battery low voltage condition. The necklace

connections had to be reinforced to handle repeated opening and closing

during testing.

The transmitter operated while immersed with a signal attenuation

of about 1 dB/uV at a distance of 4 m (13.3 ft) from its location.

There was no degradation in system performance after removal from the

water tank. The monitor portion of the system operates, off its own

internal 12-V power supply, allowing it to function independently of

the household power supply. The transmitters and monitor components

were electronically compatible, but the system, as received, was not

telephone-line compatible and thus will require additional equipment or

redesign to make it function as a complete system.

B. SYSTEM #2

The system #2 equipment consisted of:

1) Transmitter #1

2) Transmitter #2

3 ) Monitor Base Station

4) Digital Telephone Line Tester

5) Telephone Connection Hardware

A photograph of the components for this system is given in figure 10.

The Equipment

1. Transmitters

The transmitter dimensions are shown in figure 11. The casing

shown contains the battery power source, transmitter circuitry, and

radio frequency (rf) emitting device; the unit is hermetically sealed.

Both transmitting units operate at a carrier frequency of 316 MHz and

transmit very short rf bursts, approximately 6 ns wide, every 25 s. The transmitter casing is hermetically sealed to improve its

waterproof and tamperproof characteristics. The device is attached to

the subject by two straps to either forearm or ankle. However, straps

were not submitted for testing. The transmitter cannot be disabled

since transmission is continuously on and it has relatively low power

consumption.

22
ro

23

Figure

10.

System

#2,

from

left

to

right;

1)

and

2)

transmitters

#1

and

#2

(

f

^

316

MHz),

and

monitor

base

station.
MjIA

dOi

AA3IA

3Q1S

24

Figure

11.

Physical

dimensions

of

transmitter.

System

#2.
2. Monitor

Figure 12 shows the physical dimensions of the home monitor as

well as its external features. The areas marked 1 through 4 designate

circuit components as they likely have been packaged. Number one

probably is a power supply as it is located close to the power switch

and the incoming low voltage power line. Position two could contain

digital circuits and code storage devices, whereas in area three a

dialer and telephone interface could be located. Position four most

likely contains the radio frequency transmitter/receiver circuitry.

The monitor contents are sealed in a plastic briefcase-size package

with an external crimp seal.

3. Digital Telephone Line Tester

The digital telephone line tester was used to verify the

programmed telephone number and the stored activity code of the

monitor, as well as the unit identification digits. The telephone

number stored for the autodialer in the monitor electronics was 2729,

which is an internal NBS extension number. A unit identification code,

in this case code 111, was verified using the digital telephone line

tester. The telephone line tester also verifies the following

operational codes of the monitor:

1) phone line test: 111

111

- 3 - 3

2) out of range: 111

111

- 2 - 2

3) back in range: 111

111

- 0

- 0

4) monitor tamper: 111

111

- 1 - 1

5) low batteries: 111

111

- 8

- 8

All codes are indicated in pairs since they are transmitted twice

to the host computer for verification.

Transmitter Testing

The following is the performance data using transmitters #1 and #2

from tests taken in locations T1 through T4. The field intensity meter

and log periodic antenna were used for tests in all four locations.

The measurement setups at test sites T1 through T4 for testing system

#2 are the same as those for system #1. The antenna correction factor

for the log periodic antenna used in these tests is 17.2 dB.

During these open field tests there was no discernible

interference from any adjacent channel communication systems nor was

there any impulsive interference that could be detected. The data in

table 7A provide a baseline of information about the inherent field

strength of the two transmitters as a function of the radial distance

from the transmitter. Upon later examination, the data point at 20 m

(65.6 ft) appeared to be anomalous, as a smaller field strength was

measured at that location than at locations farther from the monitor.

Accordingly, a second set of measurements was taken at a later date to

25
QO

26
resolve this measurement discrepancy. This second set of measurements,

taken only with transmitter #1 as transmitter #2 had ceased to operate,

verified that the original 20 m value was incorrect and it should not

be treated as a valid data point. See table 7B for these measurement

results

.

Table 7A. System //2 measurements at the open field test site

Transmitter #1 Transmitter #2

Radius dB/pV pV/m Radius dB/pV pV/m

10 m +2.0 9.1 10 m +2.0 9.1

20 m^ +1.0 8.2 20 m^ +1.0 8.2

30 m +1.5 8.6 30 m +1.5 8.6

40 m +1.5 8.6 40 m +1.5 8.6

50 m +1.5 8.6 50 m +1.5 8.6

^Invalid data point. See text.

Table 7B. System #2 measurements at the open field test site

Transmitter #1

Radius dB/pV pV/m

10 m 1.2 8.3

20 m 0.96 8.0

30 m 0.8 7.9

40 m 0.65 7.8

50 m 0.53 7.6

Tables 8A and 8B give the measurement results obtained from

testing system #2 in the Administration Building. In this case, table

8A gives the data obtained from the straight line measurements and

table 8B from the around-the-corner path, as shown in figure 5.

27
Table 8A. System //2 straight line measurements in the Administration Building

Transmitter #1 Transmitter #2

Radius dB/nV nV/m Radius dB/uV nV/m

10 m +1.0 8.2 10 m +1.0 8.2

20 m +0.0 7.3 20 m +0.0 7.3

30 m +0.0 7.3 30 m +0.0 7.3

40 m -1.5 6.1 40 m -1.0 6.5

50 m -5.0 4.2 50 m -4.0 4.6

Table 8B. System #2 around-the-corner measurements

in the Administration Building

Transmitter //I Transmitter //2

Radius dB/MV nV/m Radius dB/uV MV/m

10 m +1 8.2 10 m +1 8.2

20 m 0 7.3 20 m 0 7.3

30 m -2 5.7 30 m -1 6.5

40 m -4 4.6 40 m -3 5.4

50 m -6 3.6 50 m -5 4.2

Reception and measurements at this location showed some signal

deterioration^ as the reception is progressively lower for a given

radial distance from the transmitter, compared to the open field data.

Also, normal transmissions made from other levels of the building could

not be received. Again, there was a complete loss of signal when the

transmitter was in the elevator with the door closed. On a designated

corridor level the reception was about the same as given in the table

above. The NBS Security Communication System (f of about 168 MHz) did

not interfere with this system. Also, no impulsive interference was

encountered.

During the Bowman House tests, transmitter #2 became intermittent

and ceased to provide reliable measurements. Therefore, no measurement

data for this transmitter were recorded. Also, at 8:00 p.m. on July 9,

1985, a strong, pulse-modulated CW signal interfered with the test.

The measured field strength of this signal was 185 uV/m. The signal

originated from a northeast direction, approximately 30 to 35 degrees

relative to the location of NBS. This signal could have originated at

the Montgomery County Air Park which is 8.3 km (5 mi) away at

approximately 35®. The data in tables 9 and 10 were obtained when

there was no interference from this source. These data show that the

reception from this transmitter is fairly uniform from all of the

locations throughout the house, and is enhanced (in the order of 1

dB/y.V) over that obtained in the open field.

28
Table 9. System //2

( inside

measurements at the

locations 1 through

Transmitter //I

Bowman House

14)

Location dB/pV |jV/m Location dB/pV |jV/m

1 +2.0 9.1 8 +1.5 8.6

2 +2.0 9.1 9 +1.5 8.6

3 +2.0 9.1 10 +2.0 9.1

4 +1.5 8.6 11 +2.0 9.1

5 +2.0 9.1 12 +2.0 9.1

6 +2.0 9.1 13 +2.0 9.1

7 +2.0 9.1 14 +2.0 9.1

Table 10. System //2 measurements at the Bowman House

(outdoor locations 15 through 18)

Transmitter #1 Transmitter #1

Location dB/nV [jV/m Location dB/pV ijV/m

West 15 +2.0 9.1 East 17 +2.5 9.7

15-1 +2.0 9.1 17-1 +2.5 9,7

15-2 +2.0 9.1 17-2 +2.5 9.7

South 16 +2.5 9.7 North 18 +2.0 9.1

16-1 +2.5 9.7 18-1 +2.0 9.1

16-2 +1.5 8.6 18-2 +2.0 9.1

Table 11 gives the results of tests conducted in an all-metal

environment as the corridor walls consist of forged sheet metal. No

interference of any kind was detected during this test. At this

frequency, the data obtained in this location are very similar to the

open field test data, indicating that the all-metal environment did not

particularly enhance the reception for this type of transmitter.

Table 11. System #2 measurements in the Metrology Building

Transmitter #1

Radius dB/pV nV/m

10 m +2.0 9.1

20 m +1.5 8.6

30 m +1.5 8.6

40 m +1.5 8.6

50 m +1.0 8.0

29
Immersion Testing

Table 12 gives the results for immersion testing of system #2.

The test setup was identical to that used to test system #1 and no

radio frequency or impulsive interference was detected during this

test

Table 12. System //2

Transmitter

immersion

//I

tests

Remarks Radius dB/nV |jV/m

Reference reading 4 m +2.0 9.1

Unit immersed for 15 min 4 m -4.0 4.6

(5 min between readings) 4 m -4.0 4.6

4 m -4.0 4.6.

Unit removed (still wet) 4 m -1.0 6.5

Unit removed (dry) 4 m +2.0 9.1

Considerable attenuation (about 6 dB/uV) occurs

transmitter under the immersion testing conditions used. Also, there

is about a 3 dB/iiV attenuated reception (about 29% reduction in range)

of the transmitted signal when the surface of the transmitter is wet.

Once dry, the transmitter was apparently unaffected by the brief

immersion testing.

Monitor Testing

The photograph of figure 13 shows the monitor and transmitters

with the monitor interfaced to the telephone system. Once the monitor

base station is connected to the telephone line and is turned on

(activated), it performs automatically. In order to document its

functions, such as line seizure, dialing, etc., an oscilloscope with a

Polaroid camera attachment was connected to the telephone line. In

order to photograph the trace perturbations, elapsed time exposure had

to be used. The exposure time for figures 14A through 14D varied from

10 to 50 s or 1 to 5 s per division. Figure 14A shows the monitor base

station telephone line output at a zero volt level (initial state).

Upon turn-on, a level change occurs after approximately 1.7 seconds.

This operational level is about 52 V peak and is held high for

approximately 10 s after which line seizure occurs (see fig. 14B).

Note that the voltage level reduces to about 12 V.

In figure 14B the automatic dialing process can be seen in detail.

Following the previously set 12-V level, a short zero level can be

seen; it is followed by another level change up to about 20 V.

Approximately 1.5 s after this change the dial pulse train appears.

The number 2729, an NBS extension number, can be recognized by counting

pulses. The next picture, figure 14C, shows a second identical dial

sequence followed by a 3-s end-of-message pulse (zero level). All

codes dialed are paired or transmitted twice for host computer

30
r

Figure 13. Monitor base station connected to the telephone line.

31
A

B

Figures 14A and 14B. Telephone line operational levels

and dialing pulse trains.

32
c

I

Figures 14C and 14D. Telephone line operational levels

and dialing pulse trains.

33
verification. Note that figure 14C has a 2-s per division time scale.

The following picture, figure 14D, is a 50~s time exposure and shows

that after check-in dialing, the telephone was in use for almost 14 s,

indicated here by a 10-V level. As the receiver was returned to the

cradle, the dc level changed to 20 V. Fifteen seconds later the level

changed back to the 52-V operational level.

In order to show the transmitted pulses of transmitters #1 and #2,

a spectrum analyzer with a frequency range from 1 kHz to 1.8 GHz was

used in conjunction with a specially-constructed pickup coil. This

coil has five turns of #13-gage copper wire; it is connected in series

to a 50-Q resistor and connects directly to the spectrum analyzer's

50-Q input. The coil diameter is about 5 cm (2 in) and permits

insertion of the receiver in order to inductively couple the received

signal to the input of the spectrum analyzer. Using this setup

provided the photograph of figure 14E, the emitted pulse from

transmitter #1 and its spectral position of f -321 MHz. Similarly,

figure 14F, shows the emitted signal from transmitter #2 at f -317 MHz.

One additional picture, figure 14G, shows a signal at abou^ 302 MHz

that was received whenever the home monitor station was activated. The

distance between home monitor and the pickup coil of the spectrum

analyzer was approximately 2.5 m (8.3 ft). The meaning of this signal

is not quite clear; however, it could be interpreted either as

undesired radiation from the local oscillator or, perhaps, as radiation

from a built-in feature used to control the lid tamper mode.

Summary

System #2 was tested on the grounds at NBS, Gaithersburg, MD, in

an open field test site, a high-rise building, a wooden residence and

in a laboratory environment. In general, the system performed as

advertised. Range of operation measurements were made out to 50 m (164

ft) at the field test site, indicating use at that range under optimum

conditions. Measured field strengths inside the Administration

Building were substantially less than those measured at the field test

site. However, field strengths measured through the walls of the

wooden building were similar to those originally measured at the open

field test site.

Effective radiated output power (- 1 pW)

,

based on measured field

strength, and supply voltage (-9 V) were low enough to be safe under

all conceivable usage conditions. The low transmitter duty cycle, one

short pulse every 25 s, also reduces the risk of injury to the wearer.

This transmitter has no "tamper" signal and the design of the case does

not allow normal access to the electronic circuitry or power supply,

and it has no protruding antenna. Placing a hand on the

receiver/monitor produced a "tamper" signal, as advertised. Radiation

from a citizens band radio, walkie-talkies operating at police band

frequencies, and devices simulating the noise patterns of electric hair

dryers, shavers, and mixers did not interfere with the operation of the

system. Because of the sealed case, there was no way to measure

transmitter battery current drain. The transmitter operated while

immersed with a signal attenuation of about 6 dB at a distance of 4 m

(13.3 ft) from its location and there was no degradation in system

performance after removal from the water tank and dried.

34
Figures 14E and 14F. Spectral signatures of transmitters.

35
The monitor uses standard household power for normal operations.

If household power is lost, an internal 12-V battery provides standby

power for an estimated 10 h of operation. Notice of impending loss of

power is transmitted automatically when the battery voltage level drops

to 11.5 V. The transmitter and monitor components were electronically

compatible, and system is telephone line compatible as it meets the

requirements for impedance, pulse rate, and transmission level. Pulse

dialing systems, although compatible with both rotary and touch-tone

dialing systems, are not as fast acting as touch-tone systems.

IV. DESCRIPTION AND EVALUATION - 1986 TESTS

The two systems received in 1986 were tested in the exact same

locations as those in 1985 with the exception of test site #2, the

Administration Building. The results obtained from testing in the

Metrology Building, which also has metal walls, were similar enough to

permit the elimination of tests at site #2. As requested by the

sponsor, a substantial number of measurements were made with the

transmitter worn at the ankle to better simulate the actual

human/ transmitter daily environment. Also, measurements were made with

the wearer's body directly between the transmitter and the receiver,

again to better simulate actual using conditions. These are the major

differences between the 1985 tests and the 1986 tests.

The test equipment used in the 1985 tests was again utilized, so

its description will not be repeated in this section of the report.

The same rationale will be applied to the functioning of the

transmitters and receiver /monitors . Systems 3 and 4 were designed to

work in the same general manner as the other two, so there is no need

to describe their operation herein.

36
Field strength measurements reported on in the tables for systems

3 and 4 are given only in one value, decibels referenced to a microvolt

(dB/uV). Conversion of these values to field strengths in microvolts

per meter can be easily done by those who desire it.

A. SYSTEM #3

Two transmitters and a receiver/monitor were received from the

manufacturer for these tests. System #3 operated at a frequency of

approximately 323 MHz as illustrated in figure 15, which shows the

spectral characteristics of the transmitted signal. For this system

the rf bursts occurred at approximately 58-s intervals. The

transmitters for this system appeared to have much greater output power

than those tested the previous year. This resulted in substantially

greater operational range measurements. The first pair of system #3

transmitters failed and had to be replaced before testing could begin.

Later, one of the replacement transmitters ceased to operate part way

through the testing, and the Bowman House and immersion tests were

conducted using only one test unit. It is the opinion of test

personnel that the results would have been similar if the second

transmitter had been available for these two tests. Although these

units were not dismantled, it is assumed that the inability to transmit

was due to an internal power supply or component failure.

Figure 15. Transmitter spectral signature for system #3.

Summary

System #3 was tested on the grounds at the National Bureau of

Standards (an open field test site), in a wooden residence, in a

building with metal walls, and in a laboratory environment. In

general, the system performed in accordance with the manufacturers

specifications. As shown in table 13, range of operation measurements

37
were made out to 75 m (246 ft) with one of the transmitters at the open

field test site indicating satisfactory use at that range under

line-of“Site conditions. Measurements were taken at the 4 ft high

positions, front and back, and with the transmitter worn on the ankle.

The front and ankle positions produced almost identical readings out to

a distance of 55 m (180.4 ft), with about a 6 dB/uV reduction in signal

strength occurring when measurements were made with the transmitter in

the back position.

Table 13. System #3 measurements at the open field test site

Transmitter //3 Transmitter y/4

Location Location

Distance Front Back Ankle Distance Front Back Ankle

( in m) (Field strength in dB/pV) ( in m) (Field strength in dB/pV)

10 35 30 35 10 42 38 42

20 32 26 32 20 36 31 36

30 24 22 24 30 31 26 29

40 21 13 21 40 27 19 26

50 18 11 18 50 21 16 20

55 16 10 16 55 18 13 18

75 4

At a range of 20 m (65.6 ft) , the field strengths measured through

the walls of the wooden building were 48-50 dB/iiV, as compared with 32

dB/uV at the open field test site, again demonstrating the ability of

transmissions at this frequency band to penetrate glass and wooden

structures. The difference in ground moisture content and terrain

irregularities near the building undoubtedly contributed to this

difference in received signal strength which is illustrated in table

14. Ankle measurements were again very similar to those taken at the

front position, and there was a 5 dB/iiV reduction in signal strength

when the wearer's body was between the transmitter and the receiver.

38
Table 14. System //3 measurements at the Bowman House

Transmitter //3 Transmitter //3

Location Field strength

(in dB/nV)

Location Field strength

(in dB/MV)

1 45 15 48

2 46 15-1 49

3 46 15-2 49

4 48 16 50

5 48 16 B/A 45/49

6 48 16-1 49

7 48 16-2 50

8 48 17 50

9 48 17-1 49

10 48 17-2 49

11 48 18 50

12 14 18 B/A 45/49

13 - 18-1 49

14 48 18-2 48

12 - Underlined numbers are basement locations

15 thru 18-2 - Outside locations

16 B/A, 18 B/A - Back and ankle measurements

As shown in table 15, measurements inside the metal building (see

fig. 8) produced a signal strength of 44 dB/iiV at 20 m (65.6 ft),

probably due to reflections from the walls and operation in a

climate-controlled environment. The reader should note the reduced

field strength levels for the cross corridor measurements.

Table 15. System //3 measurements in the Metrology Building

Transmitter #3 Transmitter #4

Location Location

Distance Front Back Ankle Distance Front Back Ankle

(in m) (Field strength in dB/MV) ( in m) (Field strength in dB/MV)

10 48 42 48 10 50 45 50

20 44 40 44 20 47 40 43

30 41 37 40 30 43 38 40

40 39 33 38 40 41 36 39

50 35 30 34 50 39 33 36

Cross Corridor 5 m 35 dB/nV Cross Corridor 5 m 37 dB/MV

10 m 30 dB/MV 10 m 32 dB/MV

The transmitter operated while immersed with a maximum signal

attenuation during the 15-min period of 6 dB/uV, which was expected at

this frequency band (see table 16). It returned to normal operation

39
after removal from the water tank. Radiation from household devices

did not interfere with the operation of this system and, in keeping

with its design, it does not send a signal when tampered with.

Table 16. System #3 immersion tests

Transmitter #3

Distance

( in m)

Field strength

(in dB/nV)

Reference 4 62

Unit immersed

for 15 min (5 min

between readings)

4 55

57

58

Unit removed

(still wet)

4 63

Unit removed 4 59

(dry)

B. SYSTEM #4

Two transmitters and a receiver/monitor were received from the

manufacturer for these tests. The transmitters seemed to have a

greater output power than those tested the previous year.

System #4 operated at a frequency of approximately 313 MHz, with

the modulation occurring at approximtely 50-s intervals. The spectral

characteristics of the system #4 transmitters are shown in figures 16A

through 16C. Figure 16A shows the narrowband spectrum of the

transmitter, with the carrier frequency at -313 MHz. Figure 16B gives

the wideband spectrum for this transmitter utilizing the maximum

bandwidth of the spectrum analyzer, 1.86 GHz, in order to show more of

the spectral content from the transmitter without modulation. The

marker frequency, -313 MHz, identifies the fifth spike from the left as

the carrier frequency. All other spikes are nominal sidelobe

frequencies generated by the transmitter. Figure 16C gives the

wideband spectrum from the analyzer showing amplitude modulation of the

sidelobes that occurs when the signal is pulse-width modulated in the

time domain.

40
I

Figure 16A. Narrowband spectrum of system #4 transmitter

without modulation.

Figure 16B. Wideband modulation of system #4 transmitter

without modulation.

41
Figure 16C. Wideband spectrum of the system #4 transmitter.

Summary

System #4 was tested on the grounds at the National Bureau of

Standards (an open field test site), in a wooden residence, in a

building with metal walls, and in a laboratory environment. In

general, this system performed in accordance with the manufacturers

specifications. As shown in table 17, range of operation measurements

were made at the open field test site out to 48 m (157 ft), with the

ankle readings only slightly lower than the readings taken from the

front. Back measurements were 4-5 dB/]iV less than those taken at the

other two positions.

Table 17. System //4 measurements at the open field test site

Transmitter #1231 Transmitter #1236

Location Location

Distance Front Back Ankle Distance Front Back Ankle

( in m) (Field strength in dB/pV) ( in m) (Field strength in dB/pV;

10 20 15 20 10 20 15 18

20 15 10 13 20 10 6 8

30 5 3 6 30 6 2 4

40 4 2 3 40 3 1 2

48 (max) 2 No

Reception

0 50 1 -2 0

42
At a range of 20 m (65.6 ft), the field strengths measured outside

of the wooden building were 18-20 dB/uV, compared to 10-15 dB/uV at the

open field test site. See tables 18 and 19.

Table 18. System #4 measurements at the Bovmian House

Transmitter #1231 Transmitter #1231

Location

Field strength

(in dB/pV) Location

Field strength

(in dB/|jV)

1 20 15 20

2 18 15-1 18

3 18 15-2 20

4 20 16 19

5 20 16 B/A 12/7

6 16 16-1 14

7 8 16-2 13

8 7 17 7

9 8 17-1 4

10 16 17-2 6

11 18 18 8

12 7 18 B/A 4/1

13 18 18-1 4

14 15 18-2 6

12 - Underlined numbers are basement locations

15 thru 18-2 - Outside locations

16 B/A, 18 B/A - Back and ankle measurements

43
Table 19. System #A measurements at the Bowman House

Transmitter //1236 Transmitter //1236

•cation

Field strength

(in dB/nV) Location

Field strength

(in dB/pV)

1 27 15 18

2 25 15-r 14

3 25 15-2 18

4 28 16 25

5 30 16 B/A 18/13

6 22 16-1 20

7 16 16-2 13

8 16 17 6

9 11 17-1 5

10 23 17-2 8

11 25 18 9

12 16 18 B/A 5/3

13 24 18-1 5

14 19 18-2 9

12 - Underlined numbers are basement locations

15 thru 18-2 - Outside locations

16 B/ A, 18 B/ A- Back and ankle measurements

Measurements inside the metal building produced signal strengths

of 20-23 dB/]iV at the same distance, as illustrated in table 20. All

of these test results are similar to those encountered with system #3,

except at lower field strength levels.

Table 20. System #4 measurements in the Metrology Building

Transmitter y/1231 Transmitter #1236

Distance Front Back Ankle Distance Front Back Ankle

( in m) (Field strength in dB/|jV) ( in m) (Field strength in dB/pV)

10 29 26 29 10 30 21 22

20 23 20 18 20 20 12 11

30 19 15 14 30 12 7 8

40 14 10 12 40 10 4 6

50 11 8 8 50 8 2 4

60 7 3 5 60 4 0 2

Cross Corridor 5 m 20 dB/pV Cross Corridor 5 m 15 dB/pV

10 m 12 dB/nV 10 m 9 dB/nV

The two transmitters operated while immersed in the water tank,

but at substantially reduced power levels. However, as seen in table

21, they both returned to full strength after being removed. Radiation

from typical household appliances did not interfere with the operation

of this system, and the transmitters sent a coded signal when tampered

44
with. The difference between the two digital signals is shown in

figures 17A and 17B. Figure 17A shows the pulses of the code word

during normal operation while 17B illustrates the transmission code

under tamper conditions.

Table 21. System //4 immersion tests

Transmitter //1231

Distance Field strength Distance Field strength

( in m) (in dB/pV) ( in m) (in dB/pV)

Reference 4 40 4 42

Unit immersed 4 34 4 34

for 15 min (5 4 31 4 19

min between

readings)

Unit removed

4 32 4

ii

17

(still wet) 4 42 4 40

Unit removed

(dry) 4 44 4 42

In summary, systems 3 and 4 are improvements over the two systems

previously tested. The transmitters are more powerful (-100 pW versus

~1 pW) and have much greater range. However, in one case, the system

was not able to function throughout the entire test period as three of

four transmitters failed. Interference from outside sources such as

other radio systems is still a problem. On several occasions testing

had to be delayed until higher-powered transmitters were not in use.

We cannot stress too strongly the need to pretest a given location

before installing low-powered EMD systems and expecting them to operate

as advertised.

45
Figure 17A. System #4 pulse code during normal operation.

Figure 17B. System #4 pulse code under tamper conditions.

46

t
V. CONCLUSIONS AND RECOMMENDATIONS

All four systems operated as advertised under optimum conditions.

The major differences between the systems were due to the selection of

a specific transmission frequency band. System #1, operating at a

lower carrier frequency than the others, had better transmission

through openings and along metal corridors and had less reduction in

signal level when immersed in water. The other three systems,

operating at a higher frequency, had a better overall range of

operation and better signal penetration through wooden structures. All

were subject to loss of range capability due to body bulk or

capacitance, when operated in the vicinity of broadcast transmitters

operating at the same general frequency, and when immersed in water.

Operation along metal corridors can produce an increase in effective

range along the corridor, whereas operation in the vicinity of metal

objects can also cause an attenuation in signal strength in certain

directions

.

Users of this equipment should be informed of the above

shortcomings, and potential areas of use should be checked out in

advance to prevent system installation in the vicinity of unmanageable

interference. Additional user testing of these systems under typical

residential conditions would be helpful in determining how widespread

the problem of interference might be.

47
NB5»n4A (REV. 2 -eo) U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See Instructions)

1. PUBLICATION OR

REPORT NO.

NBSIR 86-3501

2. Performing Organ. Report No. 3. Publication Date December 1986

4. TITLE AND SUBTITLE

Evaluation of Electronic Monitoring Devices

5. AUTHOR(S)

Arnold G. Perrev. Barrv A. Bell, and Marshall J. Treado

6. PERFORMING ORGANIZATION (If joint or other than NBS, see In structlon s)

national bureau of standards

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/Grant No.

8. Type of Report & Period Covered

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City, State, ZIP)

National Institute of Justice

U.S. Department of Justice

Washington, DC 20531

10. SUPPLEMENTARY NOTES

Document describes a computer program; SF-185, FlPS Software Summary, is attached.

11. ABSTRACT (A 200~word or less factual summary of most significant information. If document includes a significant

bi bl iography or literature survey, mention it here) Electronic Monitoring Devices (EMDs) are used to monitor the

presence of individuals within a given area who are responsible to the

criminal justice system but not confined to institutions. Several

EMDs were tested to measure operational characteristcs such as

operating frequency, approximate range of operation, component

capability, and tamper resistance. Tests were conducted in an open

field, wooden residence, high rise metal building, and in a laboratory

environment

e-a¥iY°reieaieT''etectr8tn^gh'etYc-"5i?er¥a't4»fc'er"'4T^iWSK

monitoring device; parole; receiver /monitor ; tamper resistance;

transmitter

13. AVAILABILITY

(2Q Unlimited

[31] For Official Distribution. Do Not Release to NTIS

331 Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402.

[^_] Order From National T echnical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

56

15. Price

$ 13.95

USCOMM-DC 6043-P80

1I