NBSIR 74-356

REPEATERS FOR LAW ENFORCEMENT

COMMUNICATION SYSTEMS

R.M. Jickling

J.F. Shafer

Electromagnetics Division

Institute for Basic Standards

National Bureau of Standards

Boulder, Colorado 80302

September 1973

Prepared for

National Institute of Law Enforcement and Criminal Justice

Law Enforcement Assistance Administration

U.S. Department of Justice

Washington, D.C. 20537

NBSIR 74-356

REPEATERS FOR LAW ENFORCEMENT

COMMUNICATION SYSTEMS

R.M. Jickling

J.F. Shafer

Electromagnetics Division

Institute for Basic Standards

National Bureau of Standards

Boulder,. Colorado 80302

September 1973

Prepared for

National Institute of Law Enforcement and Criminal Justice

Law Enforcement Assistance Administration

U.S. Department of Justice

Washington, D.C. 20537

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

NATIONAL BUREAU OF STANDARDS. Richard W Roberts Director

CONTENTS

Page

FOREWORD iv

ABSTRACT 1

1. INTRODUCTION 1

2. REPEATER SYSTEMS 2 2.1 Repeaters Under Local Control 2 2.2 Repeater Under Remote Control 4

2.3 Repeaters Using Single Antenna and Duplexer- 4

2.4 Repeaters Using Two Antenna Sites 6

2.5 Repeaters Using Voting Receivers 6

2.6 Vehicular Transceiver as a Repeater 8

2.7 Repeaters for Microwave Frequencies 8

3. REPEATER SYSTEM ANCILLARY EQUIPMENT 10

3.1 Transmission Line Components 10

3.2 Failure-Mode Protection Components 12

3.3 Selective Tone-Coding Applications 12

4. REPEATER SYSTEM MEASUREMENTS FOR VHF AND UHF 13

5. GLOSSARY OF TERMS 14

6. ACKNOWLEDGMENT 16

7. REFERENCES 17

8. BIBLIOGRAPHY 18

iii
FOREWORD

The National Bureau o£ Standards (NBS) has established

a Law Enforcement Standards Laboratory (LESL) for the National

Institute of Law Enforcement and Criminal Justice (NILECJ) of

the Law Enforcement Assistance Administration, Department

of Justice. LESL's function is to conduct research that will

assist law enforcement and criminal justice agencies in the

selection and procurement of quality equipment.

In response to priorities established by NILECJ, 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 guidelines, state-of-theart surveys and other reports

.

The Electromagnetics Division of NBS prepared this

report under the direction of Marshall J. Treado , Program

Manager for Communication Systems and Jacob J. Diamond,

Chief of LESL.

This document. Repeaters for Law Enforcement Communication Systems, describes the application of repeaters used in

mobile communication systems. It is intended to serve as a background reference or information guide for users and

prospective users of such repeaters.

iv
REPEATERS FOR LAW ENFORCEMENT

COMMUN I CAT I ON SY STEMS

ABSTRACT

This report is concerned with r£-type repeaters

used in land- mobile communications systems. Repeater

systems are described with emphasis on appropriate

antenna site selection, s ignal -re j ect ion techniques,

and specialized transmission-line components for the

transmission and reception o£ signals. Repeaters

using the vehicle transceiver are mentioned. Repeaters at microwave frequencies are described to

the extent that their use for control and as audio

links is pertinent. Measurement techniques that

are unique to land-mobile repeaters are discussed.

Key words: Duplexer; FxM transceiver; land-mobile

communications; law enforcement; repeater; and

vertical antenna.

1. INTRODUCTION

A repeater is a device which receives , amplifies , and

simultaneously retransmits a signal to provide improved communication range and coverage [1] . Even with a good base

station antenna site, it is possible that a hill, a building,

or other obstruction can cause a shadow region where received

signals are extremely weak. In such cases, rather than

attempting to improve the signal strength by increasing the

power radiated by the base station, an unmanned repeater

station can be located outside the shadow region to retransmit received signals into the region and vice versa [2].

Mountain tops, tall building roofs, and existing commercial

broadcast towers provide excellent sites for repeaters when

available. Othervv^ise, a special tower installation is

necessary

.

In its simplest form, a repeater consists of a receiver

on one frequency with its audio output connected to the audio

input of a transmitter operating on a second frequency. For

most law enforcement systems, the first frequency differs

from the second by a few hundred kilohertz to a few megahertz.
An operational system requires additional control features

which include carrier delays, failure -mode protection, and

positive repeater control. Because of the close frequency

spacing between received and transmitted signals, specialized

antenna transmission-line components are required.

2 . REPEATER SYSTEMS

Repeater systems provide a dependable technique for

increasing the signal strength in shadowed areas within the

service region. Use of repeaters will enhance mobile-to -mobile

coverage in terrain that would otherwise result in unsatisfactory communications. Personal transceivers, with their low

power and reduced antenna efficiency, will also benefit from

the increased signal strength provided by the repeater. The

equipment configurations described herein can provide reliable communications coverage over the required service area.

The transmitting and receiving capabilities of a repeater

should be in proper balance; that is, the service area for

transmitting and receiving should be as nearly identical as possible. Also, transmission and reception to the same

geographical areas will minimize interference with other

communication systems. For balance, a repeater working with

vehicular transceivers normally requires less transmitter

power than one designed to work with personal transceivers

because of the latter's reduced antenna efficiency. Systems

that frequently utilize personal transceivers usually require

additional hardware to improve the balance. This hardware

may include voting receivers, remote receivers, and directional antennas for improving the receiving capability of the

repeater receiver. Some factors determining the degree of

balance are the insertion loss of the duplexer at the recei^^er, the receiver desensit ization at the repeater site,

and the frequency separation.

2 . 1 Repeater Under Local Control

There are shadow regions caused by large buildings in

most metropolitan areas where both personal -to-personal transceiver and personal -to- base transceiver coverage is required.

Figure 1 illustrates the communication paths between personal

transceivers, A and B, by means of a local repeater (under

local control) using separate transmit and receive antennas.

Vertical separation between the antennas usually provides the

2
RECEIVE ANTENNA

3
isolation necessary to reduce receiver desensitizat ion for

vertically-polarized signals. The smaller the frequency

separation between receiver frequency and transmitter

frequency F2 , the greater will be the required vertical antenna separation. While this two-antenna installation

normally is less expensive than other systems, it lacks the

signal rejection capabilities of a single antenna with duplexer. The duplexer system can also be used with a local

repeater

.

. :' 2.2 Repeater Under Remote Control

The remote repeater, figure 2 , is equipped with a telephone line or radio link for control which can be used to

enable or disable the repeater in case of malfunction. This

line or link can also be used to provide audio to the transmitter, thus giving the dispatch center control in the event

of priority dispatch information. The remote repeater takes

advantage of 1 ine - of - sight coverage of the required service

area. Also, a remote site will likely be located well away

from sources of impulsive noise (mainly from automobile ignitions) which tend to limit receiver sensitivity. However,

a remote site which serves many users requires careful recording of all frequencies in use, including the local oscillators and other frequency mixing products. When interference problems arise, this record is essential for locating

sources of intermodulat ion of the transmitter or receiver,

excessive local oscillator leakage, and undesirable mixing

products. The availability of commercial power, telephone

lines, year-around access, emergency generator systems, and

delivery of fuel to the site are additional factors in site

selection

.

2 . 3 Repeaters Using a Single Antenna and Duplexer

Limited antenna space on existing towers may preclude

the use of two antennas. Use of a common antenna on either

a local or remote repeater has the advantage of identical

transmitter and receiver coverage if the repeater is also

balanced [3,4]. However, frequency pairs in the 150 MHz band

may not be ideally separated for repeater use. (The FCC

assigned frequency separation is five MHz in the 450 MHz

band.) If the assigned pair differs by only a few hundred

kilohertz, additional system hardware such as cavities,

crystal filters, and other rejection components are required.

Figure 3 illustrates the use of a single antenna interconnected

to the repeater by a duplexer.

4
COMMUNICATION DEPARTMENT

CONTROL

Figure 2. Block diagram of a repeater under remote control.

PERSONAL

TRANSCEIVER

Figure 3. Block diagram of a repeater using single antenna

and duplexer.

5
2 . 4 Repeaters Using Two Antenna Sites

A repeater can be arranged so that the horizontal separation o£ antennas yields sufficient isolation between the transmitted and received signals for satisfactory repeater performance.

If each antenna is in 1 ine -of - s ight view of the desired service

area with a hill or other obstruction between the two antennas,

isolation between transmitter and receiver can be achieved.

Wire lines or a radio link between sites interconnect the

receiver to the transmitter for the repeat function. This

approach to repeater siting is advantageous when the intermodulation products of other systems at the transmitter site

degrade the receiver performance. Figure 4 illustrates a twoantenna-site repeater system.

2 . 5 Repeaters Using Voting Receivers

An extension of the two-antenna-site repeater is shown

in figure 5. Multiple receivers are positioned such that

one or more will receive signals from a transmitter at any

location within the service area. These signals are relayed

to a comparator which selects the one signal with the highest

qual ity

.

There are three selection techniques used in available

voting equipment which are suitable for police communication

systems. The three techniques are audio quality selection,

rf signal level selection, and quieting level selection [2]

.

In the first system, the audio signals from the satellite receivers are processed for certain characteristics by

the selector to determine signal quality. Characteristics

considered are level, frequency distribution, syllabic rate,

and noise level during pauses in speech. In this system,

the satellite receiver requires no additional special circuitry and all of the selection equipment may be located at

a central position.

In the rf signal level selection system, the selector

compares the received radio frequency signal level from each

receiver and chooses the receiver with the highest level.

Measurements of received rf signal level can only be performed at the receiver, however, and the measurement information must be conveyed to the selector. Consequently,

each statellite receiver is equipped with encoder circuitry

which generates coded tone combinations which correspond to

various rf signal levels. The coded tones are sent along

with the receiver audio output to the selector, where the

tones provide the information required to choose the best

audio signal.

6
COMMUNICATION DEPARTMENT

CONTROL PERSONAL TRANSCEIVER

PERSONAL TRANSCEIVER

Figure 4. Block diagram of a repeater usin g two antenna

sites

MOBILE TRANSCEIVER

AUDIO #3

VOTING SELECTOR

OR COMPARATOR

TELEPHONE

LINE COMMUNICATION CENTER

Figure 5. Block diagram of a repeater using voting receivers

7
The third method is quieting level selection. In this

method, the selector compares the quieting levels on the lines

from the unsquelched receivers and chooses the receiver line

with the least amount of noise. It is necessary in this

system that the squelch status of the receiver be known at

the voting selector. This information is conveyed to the

selector by means of a tone or dc signal generated at the

satellite receiver when the receiver is squelched.

The audio portion of the selected rf signal is routed

to the repeater transmitter via telephone line. Voting

receivers are also used for base station operation in

the non-repeat mode. Reception at the dispatch center of

a signal from a remote receiver can be used to activate a transmitter in the vicinity of that receiver [5].

2 . 6 Vehicular Transceiver as a Repeater

The transceiver installed in a vehicle can be interconnected to perform the repeat function for personal transceivers as illustrated in figure 6. When the user leaves

the vehicle, the personal transceiver he carries may not

transmit to the base station satisfactorily because of poor

transmitting position or low transmitter power. By arranging the vehicular transceiver to function as a repeater,

the personal transceiver has the equivalent power of the

vehicular transceiver.

2 . 7 Repeaters for Microwave Frequencies

To conserve VHF and UHF spectra, information from communication centers to remote base stations is usually transmitted by microwave link. Microwave repeaters are sometimes

necessary to amplify and redirect signals when obstructions

are in the link path. Because directional antennas are

readily available at these frequencies, the energy is contained within a narrow beam between transmitter and receiver

antennas, thereby minimizing interference from other radio

services. However, multipath propagation, where the terrain

reflects part of the beam so that signals from more than one

direction and path length are received, can result in destructive interference. Space diversity is one technique for reducing the effects of multipath propagation caused by atmospheric conditions. Two receiving antennas can be mounted

8
BASE

STATION

Figure 6. Block diagram of a system using the vehicular radio

as a repeater

.

9
on the tower approximately 10 to 25 meters (30 to 80 feet)

apart, and a diversity switch will automatically select the

larger signal for the input to the receiver. Figure 7

illustrates a typical repeater in a microwave system. Multiple

input signals can be transmitted simultaneously using a frequency division multiplexer connected to the FM transmitter.

Highly directional antennas, usually reflectors 1 to 5 meters

(3 to 16 feet) in diameter, direct the signal to and from the

repeater. Multiple repeaters, at distances ranging from 15 to

60 kilometers (10 to 40 miles) , are used if required by the

terrain. For engineering economy of the communication system,

careful and well-planned site selection is important.

.

' 3. ; REPEATER SYSTEM ANCILLARY EQUIPMENT

Specialized transmiss ion - line components are required

in most repeater systems because of the close frequency spacing

between the transmitted and received signals. Undesired intermodulation products, generated in the non-linear elements of

both receiver and transmitter by the strong fields from other

nearby systems , will degrade the performance of a repeater [6]

.

The use of selective signaling, such as continuous sub-audible

tone equipment, will reduce co -channel and adj acent -channel

interference and reduce the voice traffic that must be monitored

by the user. Automatic equipment is available to provide call

letter identification of the repeater. Identification is

required by the FCC at 30 minute intervals or at the end of

a message group.

3 . 1 Transmission Line Components

Three critical factors to consider in the selection of

appropriate components for the transmission line system in

land-mobile repeaters are transmitter noise interference,

receiver desensitization , and intermodulat ion [7]. Their

effects can be minimized by the appropriate choice of transmission line components. When frequencies are closely spaced,

a duplexer can be used to reduce the transmitter noise delivered to the antenna. Many multiple antenna installations

require the use of an isolator or a ferrite circulator to

reduce transmitter noise. However, one should be aware that

the addition of a circulator or isolator may produce harmonics,

thus requiring a low-pass filter inserted after the isolator

or circulator to reduce harmonically related spurious emission.

10
IHPUT

FREQUDICt

DIVISION FH WDUUTOR

TQMMKIK

D£MODULATORj

RECEIVER ^

— RECEWER —

RECEIVER —TOWSHtTTER—

mmmm)

Division WLTIPLEXBI

FH

HODUlATOR

EOUIPHEH^

OUTPUT MICROWAVE REPEATER

OUTPUT

Figure 7. Block diagram o£ a microwave repeater.

11
When tower space is limited, a single antenna with a diplexer can serve more than one repeater. A good quality,

low-loss transmission line will help compensate for the

additional losses introduced by the diplexer [8]

.

Band-pass cavity filters can be installed in the transmission line to reduce interference from other systems. Since

band-pass cavity filters are broader in frequency response

than notch filters, they are ineffective when employed near

the user's frequency. The notch filter is a band-stop filter

with a rapid transition from pass to reject. This characteristic favors its use near the user's frequency. A crystal

filter in the receiver transmission line will minimize interference that is within a few channel spacings of the user's

frequency.

3.2 Failure-Mode Protection Components

Timing devices are used to limit the time that a transmitter can remain continuously in the transmit mode. The

timer, while designed to protect the equipment in the event

of a malfunction, also discourages excessively long communications. Many timers can be reset for another interval by releasing the press- to- talk switch momentarily. Thus, most users

prefer that timer reset be accomplished by the absence of a signal at the repeater receiver rather than the absence of the

repeater carrier which would include the carrier delay interval.

Timer intervals are usually adjusted for one to three minutes

(maximum allowed by FCC) at the discretion of the communications

officer.

Transmitter carrier delays are incorporated into a repeater

system to minimize the on-off cycling that can occur with a marginal input signal. Delay intervals are typically one-half

second to a maximum of five seconds.

3 . 3 Selective Tone -Coding Application s

To minimize the voice traffic that must be monitored

by a mobile unit, a repeater system can be designed so that

communications can be directed to specific groups within a department. Tone-controlled squelch systems may be utilized

effectively for this purpose. These systems minimize cochannel interference that can result from tropospheric

12
enhancement (ducting) between geographical regions. Tonecoding equipment, while minimizing the annoyance of interference from weak undesired signals, does not assure satisfactory operation if a strong undesired signal captures the

tone -controlled receiver. This capture can result in a lost

message. In areas where this capture problem exists, the use

of tone coding on voice-grade telephone lines to the repeater

receiver will insure that the repeater is always under the

control of the communications center.

4. REPEATER SYSTEM MEASUREMENTS FOR VHP AND UHF

NILECJ standards for receivers, transmitters, and antennas describe the measurement methods applicable to most

repeater components. While most repeater components are identical to the components used in base and mobile installations,

the demands on repeater equipment are more stringent. Because

of the simultaneous operation of the repeater transmitter and

receiver, as well as the proximity of other transmitters and

receivers, receiver desensiti zation caused by high level fields

can be a serious problem. Careful shielding is necessary to

provide isolation for the repeater from all other transmitters

and receivers at the site. Measurements of the receiver

sensitivity, with and without the transmitter in operation,

give a quantitative measure of the leakage and radiation

present [9,10].

Proper adjustment of audio signal levels in a repeater is

necessary to obtain reliable operation. One procedure that

provides satisfactory results is to connect an on-frequency

signal generator with 10 00 Hz modulation and ± 3 kHz deviation

to the antenna input of the repeater receiver. The audio output of the receiver is connected to the audio input of the repeater transmitter and the audio input level is adjusted to

produce ± 3 kHz of transmitter deviation. In addition, the

modulation limiting control of the repeater transmitter is

adjusted to limit the system to rated deviation as prescribed

by the FCC.

13
5. GLOSSARY OF TERMS

5.1 Continuous -Tone -Controlled Squelch System (CTCSS)

A form of selective signaling wherein the radio receiver(s)

are equipped with tone -respons ive devices which allow audio

signals to appear at the receiver audio outputs only when a carrier modulated with a specific tone is received. Said tone

must be continuously present for continuous audio output.

The transmitter emitting the carrier shall be modulated with

a continuous tone, whose frequency is the same as the tone

required to operate the tone -respons ive device in the receiver, in order to permit audio at the receiver output.

i

. :

. 5.2 Diplexer

A device permitting an antenna system to be used simultaneously or separately by two transmitters or receivers.

5.3 Diplex Operation

Simultaneous transmission or reception of two signals

using a specified common feature, such as a single antenna.

5.4 Duplexer

A device which permits a single antenna system to be

used for both transmitting and receiving.

5.5 Duplex Operation

For radio communication, the operation utilizing two

radiofrequency channels, one for each direction of transmission, in such manner that intelligence can be transmitted

concurrently in both directions.

5 . 6 Filter

A device for separating waves on the basis of their frequency by introducing relatively small insertion loss to waves

in one or more frequency bands and relatively large insertion

loss to waves of other frequencies.

14
5.6.1 Band-pass Filter

A filter which has a single transmission band, neither

of the cutoff frequencies being zero or infinite.

5.6.2 Band-stop Filter

A filter which has a single band of attenuation between two cutoff frequencies, neither one being zero or

infinite. The filter passes frequencies on either side of

this band.

5.6.3 High-pass Filter

A filter having a single transmission band extending

from some critical or cutoff frequency, not zero, up to

infinite frequency.

5.6.4 Low-pass Filter

A filter having a single transmission band extending from

zero frequency up to some cutoff frequency, not infinite.

5.6.5 Notch Filter

A filter designed to attenuate or reject a specific

frequency band with sharp cutoff at either end.

5 . 7 Mobile Repeater (Mobile Relay Station)

A base station established for the automatic retransmission of mobile service communications which originate on the

transmitting frequency of the mobile stations and which are

retransmitted on the receiving frequency of the mobile stations.

5 . 8 Repeater

A combination of apparatus for receiving communication

signals and automatically retransmitting corresponding signals

which are amplified.

15
5 . 9 Repeater Station

An operational fixed station established for the automatic

retransmission of radio communication signals received from

any station in the mobile service.

5.10 Selective Signaling

A general method for signaling mobile, fixed, or repeater

stations, or groups of stations selectively (rather than all

simultaneously) from a base or mobile station.

6. ACKNOWLEDGMENT

Electromagnetics Division staff members assisting in the

preparation of this report were Harold E. Taggart, project

manager, Winston W. Scott, Jr., and John J. Tary.

16
7. REFERENCES

[1] McMullen, T. , Ed., FM and Repeaters for the Radio Amateur,

(The American Radio Relay League, Inc., Newington, Conn.,

1972) .

[2] Police Telecommunications Systems, IIT Research Institute

[Associated Public -Safety Communications Officers, Inc.,

1971)

.

[3] Bryson, W.B., Design of high isolation duplexers and a new antenna for duplex systems, IEEE Trans, on Vehicular

Communications, VC- 14 , No. 1 (Mar. 1965).

[4] Tilston, W.V. , Simultaneous transmission and reception

with a common antenna, IRE Trans, on Vehicular Communications, VC-11 , No. 1 (Aug. 1962).

[5] McCormick, J., Better city-wide coverage with hand-held

portables. Communications, pp. 32-35 (June 1971).

[6] Radio - Frequency Interference (RFI) in Two-Way FM Radio

Systems (General Electric Datafile Bulletin No. 10002-2,

May 1972) .

[7] Trott, R.C., Introduction to notch filters. Communications,

pp. 22-25 (Mar. 196 9)

.

[8] Zinn, W.H., The passive device -- an antenna decongestant,

Communications, pp. 20-24 (July 1972).

[9] Standard Specifications for Land Mobile FM Communication

(U.S. Department of Agriculture, Forest Service,

Washington, D.C. p. 14, Oct. 1971).

[10] Hartwick, F.C., Mobile Communication Repeater Requirements (RCA Service Co., Cherry Hill, N.J., 1963).

17
8. BIBLIOGRAPHY

Hamsher, D.H., Communication System Engineering Handbook

(McGraw-Hill Book Co., Inc., New York, N.Y., 1967).

How To Use Duplex Operation Curves [General Electric Datafile

Bulletin No. 10007-4, May 1972).

Sessions, K.W., Jr., Radio Amateur's FM Repeater Handbook

(Editors and Engineer, Ltd., New Augusta, Ind., 1969).

Institute of Electrical and Electronics Engineers, IEEE Stand

ard Dictionary o£ Electrical and Electronics Terms, IEEE

STD-100 (Wiley- - Interscience , John Wiley and Sons, Inc.,

New York, N.Y. , 1972) . Report o£ the Advisory Committee for the Land Mobile Radio

Services, Federal Communications Commission, 2_y Parts

1^2 (U.S. Government Printing Office: 1967 0-281-850

^ 1967 0-281-851)

.

Technical Terms and Definitions for Law Enforcement Communica

tions Equipment, LESP-RPT-0203. 0 .

.

^Standard for Base Station FM Transmitters, NILECJ-STD-0201 . 00

^Standard for Mobile FM Transmitters, NILECJ-STD-0202 . 00

^Standard for Personal/Portable FM Transmitters, NILECJSTD-0203. 00

.

^Standard for Base Station FM Antennas, NILECJ-STD-0204 . 00

.

Standard for Mobile FM Antennas, NILECJ-STD-0205 . 00

.

^Standard for Base Station FM Receivers, NILECJ-STD-0206 . 00

.

^Standard for Mobile FM Receivers, NILECJ-STD-0207 . 00

.

^Standard for Personal/Portable FM Receivers, NILECJ-STD-0208

.

*Standard for Batteries (Personal/Portable Transceivers)

,

NILECJ-STD-0211. 00

.

^Glossary of Standard Terms and Definitions for Law Enforcement Communications, NILECJ-STD-0210 . 00

*To be published.

18
NBS-114A (REV. 7-73)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBSIR 74-356

2. Gov't Accession

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

"Repeaters for Law Enforcement Commvmication Systems"

5. Publication Date September 1973

6. Performing Organization Code

7. AUTHOR(S)

Robert M. Tickling and John F. Shafer

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS, BoulderLabs.

DEPARTMENT OF COMMERCE

Boulder, Colorado 80302

10. Project/Task/Work Unit No.

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

National Bureau of Standards

M. J. Treado, Div. 400.09

Law Enforcement Standards Laboratory

Washington, D. C. 20234

13. Type of Report & Period Covered LESP-RPT-0206, 00

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

LESL will review this document further and submit it to the National Institute

of Law Enforcement (NILECJ) for publication.

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

bibliography or literature survey, mention it here.)

This report is concerned with rf-type repeaters used in land-mobile communications systems. Repeater systems are described with emphasis on appropriate

antenna site selection, signal-rejection techniques, and specialized transmissionline components for the transmission and reception of signals. Repeaters using

the vehicle transceiver are mentioned. Repeaters at microwave frequencies are described to the extent that their use for control and as audio links is pertinent.

Measurement techniques that are unique to land-mobile repeaters are discussed.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons

)

Duplexer; fm transceiver; land-mobile communications;

law enforcement; repeater; vertical antenna.

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