DATE DUE

Sit! ft £"1 J 0 4 TO

GAYLORD PRINTED IN U.S A




Guide from the National Bureau of Standards
ACKNOWLEDGMENTS

This guide was prepared by the Law En- forcement Standards Laboratory of the

National Bureau of Standards under the

^direction of Marshall J. Treado, Program

'Manager for Communications Systems,

and Jacob J. Diamond, Chief of LESL

Its preparation was sponsored by the

National Institute of Law Enforcement and Criminal Justice, Lester D. Shubin, Standards Program Marrager.
FEB J

^ m

COMMUNICATION

SYSTEMS GUIDE

Prepared by

WINSTON W. SCOTT, Jr. Electromagnetics Division

and the Law Enforcement Standards Laboratory Center for Consumer Product Technology

National Bureau of Standards

Washington, D.C. 20234

For the

National Institute of Law Enforcement

and Criminal Justice Law Enforcement Assistance Administration

Department of Justice Washington, D.C. 20531

U.S. DEPARTMENT OF COMfVlERCE

Juanita M. Kreps, Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Issued January 1979
National Bureau of Standards

Special Publication 480-12

Nat. Bur. Stand. (U.S.), Spec. Publ. 480-12, 36 pages CODEN XNBSAV

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON, D.C. 1979

For sale by the Superintendent of Documents,

U S Government Printing Office, Washington, D.C. 20402

(Order by SD Catalog No. C13 10:480-12) Stock Number 003-003-02012-5,

Price, $1.60 (Add 25 percent additional for other than U.S. mailing).
CONTENTS

Foreword i Introduction 2

Communication Systems 3

Recent Developments 3

A System Overview 3

Major Sub-Systems 5

Computer-Aided Dispatch Centers 6

Computer-Controlled Communication

Systems & Information Files 9

91 1 Public Calling System 1

Emergency Medical Service 12

Digital Systems 12

Automatic Vehicle Location Systems 14

Voice Privacy Systems 17

Repeater and Voting Receiver Systems is

Scanning Receiver Systems 19

Public Transportation Safety Channels 19

Planning and Management 20

Principal Components 21

Transceivers 21

Antennas and Combiners 21

Control Consoles 22

Power Sources 22

Standard Interfaces 25

Telephone Interfaces 25

Lightning Suppression Equipment 26

Test Equipment 28

Cost Considerations 29

Purchase of Communications Equipment 29

References 30

FOREWORD

The Law Enforcement Standards Laboratory

(LESL) of the National Bureau of Standards

(NBS) furnishes technical support to the

National Institute of Law Enforcement and

Criminal Justice (NILECJ) program to strength- en 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 is a law enforcement equipment

guide developed by LESL under the sponsorship of NILECJ. Additional guides as well as

other documents are being issued under the

LESL program in the areas of protective equipment, communications equipment, security sys- tems, weapons, emergency equipment, investi- gative aids, vehicles and clothing.

Technical comments and suggestions concerning this guide are invited from all interested

parties. They may be addressed to the author or

to the Law Enforcement Standards Laboratory,

National Bureau of Standards, Washington, D.C. 20234.

Jacob J. Diamond

Chief, Law Enforcement

Standards Laboratory
INTRODUCTION

Communication organizations in public safety

and law enforcement in particular are rapidly ex- panding and improving their services. Authorized base station transmitters in public safety

communications have increased from about

63,000 in 1968 to about 114,000 in 1977 [1]*. Funding for law enforcement equipment and

programs by Federal, State, and local law en- forcement agencies is currently estimated at over 15 billion dollars and predicted to increase

to 25 billion in 1980 [2]. Many law enforcement agencies have found

additional funding sources for communications—such as those funding 911, the national

.emergency telephone number, and Emergency

^ Medical Service (EMS). Since the communica-^

tion needs of these services are common to law I enforcement, there may be advantages in^ centralizing efforts [3].

^ The intent of this guideline is to inform and aid

the reader in the selection of subsystems used

in law enforcement communications. Included is

\ a general discussion of both complex and rela-

*

tively simple operational and support subsys-"

terns. Sections on principal equipment, cost considerations, and purchasing suggestions are

J also included to assist the potential purchaser

and user of the equipment. i.
COMMUNICATION SYSTEMS

jlhe increase in population throughout this

\ country has brought with it an increase in the

! demand for services, particularly law enforcel^lment services. To comply with this demand, law

j'j enforcement facilities have been expanded and

h become more sophisticated. With added facili- \X\es, greater numbers of personnel and

j increased responsibilities, more departments

are improving their communication systems to deal with the increased requirements imposed

\on them.

jfTo provide for orderly growth, it has been found

jadvisable to initiate early planning of new com-

|munications and electronic facilities and equip- Iment [4]. A communications manager needs to

ibe aware of the latest Federal Communications

fCommission (FCC) rules and regulations.

iExisting assigned radio frequencies need protecftion from the effects of new intermodulation

iproducts, many public buildings and institutions jineed adequate communication facilities, and

hew equipment needs to be properly installed and operated. Properly planned systems help

promote increased manpower efficiency and

savings of public funds.

. Recent Developments

As law enforcement departments have grown,

the need for a centralized facility for dispatching

vehicles and personnel has been recognized

and recommended by many large agencies.

Dispatchers use radio communications to communicate with officers in the field. The functions

of telecommunications can be categorized into |three areas:

• Communications with the department

i (telephone).

i • Communications within the department (telephone and radio).

• Communications with other agencies

(telephone, radio, facsimile, high

j speed digital).

Each category is essential for the protection of a community and its citizens.

With the increasing emphasis on reducing

crime, there has been more financial support for

all phases of law enforcement, including communications. This increase in support has enabled

some departments to consider purchasing more

elaborate and improved communication sys- tems. Communications have improved considerably since the days of one-way broadcast band

dispatching. Recent developments include the

application of the computer to such things as in- formation storage, retrieval, and comparison.

The use of terminals equipped with keyboards

and display screens operating with the

computer can be a valuable aid to the

dispatcher. Integrated circuits have made

possible relatively inexpensive and compact tele- printers. Tone-coded squelch and digital-coding

techniques allow the listener to be more

selective in the messages he hears, thus

enabling him to cope with the excessive traffic on some channels. Personal and portable

transceivers have become more compact and

lighter; the battery is now the limiting factor in size and weight reduction. In an effort to conserve battery power as well as reduce inter- ference, digital techniques have been developed to allow the receiving station to judge the

quality of the incoming signal and to automatically cause the personal transmitter to increase

(or decrease) the radiated power.

Frequency congestion exists today for many

reasons, but proper planning can reduce

unnecessary congestion. Joint planning among

municipal departments in a city and among

adjacent suburban governments is often a

valuable approach [5]. Such efforts usually

reduce redundant actions and improve the infor- mation flow between such groups.

A System Overview

One way to study communication systems is to look at a very complex system and then break it

i 3
into sub-systems consisting of smaller amounts

of equipment. The complex communication sys- tem in figure 1 is shown as an illustrative example, and is not an operational system in use by any specific law enforcement agency.

Specific systems must be carefully planned

around the needs and limitations imposed by

population and local area topography.

Figure 1 is divided into two major parts. To the

left are control center functions; to the right are

field functions. This communication system

functions as follows: The public reports an

incident by telephone (91 1 or direct dial) or, in limited locations, by radio (public transportation

safety channels or CB radio). Law enforcement

officials have access through several telecommunication media to a variety of information

files. Officers on foot or in vehicles have a

variety of means to communicate with the

command center. These include the telephone

for routine reports, and the radio for more

NCIC

FILES

INFORMATION

FILES

(Regional,

State, or

Local)

EMERGENCY OR DISASTER

CENTER (State, City, Etc.)

SLOW-SPEED DATA LINKS

(i.e. Telephone, Teletype, Facsimile)

HIGH-SPEED SWITCHING

NETWORKS (NLETS, ALECS, Etc.)

OTHER AGENCY VOICE

COMMUNICATIONS

(Fire, Forestry, Etc.)

911 PUBLIC CALLING SYSTEM

OR DIRECT DIAL

PUBLIC TRANSPORTATION

SAFETY CHANNELS

REGULAR AND EMERGENCY

POWER SOURCES

MAINTENANCE AND

SERVICE SHOPS

TELEPHONE

Figure 1 SCHEMATIC OUTLINE

OF A COMPLEX

COMMUNICATIONS SYSTEM
urgent voice or digital messages. Digital sys- tems may include automatic vehicle location,

I communication terminals, printers, and status

reporting. In order to improve transmission or reception quality, repeater or satellite receiver

systems are often used. Most of the sub-systems shown will be discussed in further detail in

i subsequent sections.

Major Sub-Systems

There are several recent major innovations in systems affecting control, command, and communication operations. Computer and digital e- quipment are now available at reasonable

prices, and as their use expands, it Is expected

that the resulting advantages of increased

community service and personnel safety will be more apparent. Some of these sub-systems are

described, along with the advantages and problems in their implementation and operational

use.

MOBILE

REPEATER

DIRECT

AUTOMATIC

VEHICLE LOCATION DIGITAL

FACSIMILE

VOTING

PORTABLE

REPEATER

DIRECT

DIGITAL

VOICE

PRIVACY

VOTING

SCANNING

RECEIVERS

EMS

PERSONNEL

SELECTED PERSONNEL
Computer-Aided Dispatch Centers

Computer-aided dispatch (CAD) is having a

major impact in the solution of some of the

chronic problems of command and control in law enforcement departments. A properly

designed computer system allows a manually

operated system to become one which is fast, accurate, and tireless.

Figure 2 illustrates the basic components of a

computer-aided dispatch system. When a

complaint is phoned in, the complaint-board

operator keypunches information (such as name, address, telephone number, and

complaint) into the computer. The complaintboard operator also assigns a priority number to indicate to the dispatcher the degree of

urgency. The computer assigns a case number

and records the time the complaint was

received. It also verifies that the address exists

and is within the jurisdiction of the agency. It determines the area of law enforcement responsibility and which police units are available for assignment. If there have been any prior

complaints at that address or there is other

relevant information, the computer recalls it and

then places a one-line summary of the entire

incident on the dispatcher's display screen. Acting upon the information displayed, the

I,

Figure 2.

fee

'— >

" iT
dispatcher assigns a police unit and relays

essential information, either by voice or by

digital communication. The computer-stored in- formation is continually updated. For example,

upon assignment, the police unit status file is updated by the dispatcher, and the time of

assignment is logged automatically. Other inforj mation is also entered, such as time of arrival,

classification, how the incident is disposed of, and the time the police unit is again available

for assignment.

[Officers in the field may initiate computer

I processing by going through the dispatcher

instead of the complaint console. Queries to the

remote information files may be requested to check information such as vehicle status, wants

and warrants. Depending on the amount of this

activity, a separate console or even a separate

operator may be justified.

The functioning of a particular CAD system may

differ from this outline due to the type of equipment used, the allocation of duties among the

various operators, or the number and extent of the data files used. But that reflects operational

decisions by department managers and the e- quipment involved, rather than fundamental

conceptual differences.
Table 1 lists some of the advantages and disadvantages of a CAD system. One of the major

benefits is the near-real-time ability to generate

management reports without the necessity of tedious manual data transfer from dispatch

cards to computer tape. One major communication facility showed labor savings due to field and communication center operations of more

than $29,000 in the first year of operation of

their CAD system [6].

Another consideration is the ease with which

mobile digital communication capability can be

added. With this feature it is possible for the

dispatcher, when making an assignment to a

police unit by voice, to activate a printer in the - vehicle. The receipt of hard copy in the vehicle

minimizes the possibility of misunderstanding or

error.

As more complex systems or components are

procured, operational and maintenance problems are likely to increase. Good procurement

practices and planning are obviously needed. It has been said that obtaining a new electronic

capability is somewhat like becoming a parent

[7]. It is an expensive, almost irreversible process and the joys of ownership are tempered by the problems that surface.

Table 1. Summary of advantages and disadvantages of computer-aided dispatcii systems

ADVANTAGES

1 . Replaces awkward manual system for keeping track of incident reports

and status with computer memory and

analysis.

2. Ability to quickly and effortlessly

compile management information.

3. Automatic logging as items are typed

into the system.

4. Interfaces easily with mobile digital

communications.

5. Improved overall service to public

such as reduced response time and

fewer handling errors.

DISADVANTAGES

1 . Requires special selection and training of dispatchers for needed skills.

Requires large initial funding and much

planning to construct and initiate operations.

3. Additional physical facilities and

maintenance arrangements may be required.

4. Special uninterruptable power supplies are often required for the computer.

Professional help is required to

identify and debug problems within

the computer and software systems.
Several surveys have been made to categorize

CAD systems. One survey of ten operational

systems gives data on population, calls for service, number of switchboard operators and

dispatchers, types of internal information files, and extent of voice and digital communications

with field units. Work-load measurements and

analysis have also been performed for a major

metropolitan police department in order to

better understand dispatching requirements in a CAD system [8].

Figures 3-5 illustrate several types of communication centers which utilize computer assistance

and typewriter keyboard terminals for the

dispatchers and supervisors. Figure 6 illustrates a typical computer system used in a CAD sys- tem.

Figure 6. A typical computer system used in a computer-aided dispatch system.

Computer-Controlled Communication Systems

& Information Files

Computer technology has made possible the

gathering of crime records into electronic

storage units with provision for rapid recall as

Figure 4 Command and control center located in the Las Vegas Metropolitan Police Department.

Figure 5 Automated communications center located in the Hillsborough County (Florida) Sheriff's Department.

needed. There are a multiplicity of such sys- tems in use by local. State, and Federal agencies. The National Crime Information Center

(NCIC), one such organization, is administered

by the Federal Bureau of Investigation. Serving a telecommunications network that involves all

9
50 states, the District of Columbia, Canada and

Puerto Rico (see fig. 7), the NCIC computers

process as many as 210,000 transactions per

day, and yield about 1,000 positive responses

(hits) [9]. There are ten computerized

files: Wanted persons; stolen vehicles, license

plates, guns, securities, aircraft, boats,

snowmobiles, and miscellaneous identifiable

articles; and offenders' criminal histories. The

Computerized Criminal History (CCH) file is intended to be a national index of the criminal

history records of individuals arrested for serious offenses. This file shares information

among State and Federal jurisdictions in response to the substantial interstate travel of

criminals.

The National Law Enforcement Telecommunications System (NLETS) is a sophisticated

computer-switched communications network

linking all of the law enforcement agencies in the United States and Puerto Rico. Other State

and Federal agencies are also members,

including the Department of Corrections, Wild

Life Management, Secret Service, and Interna! Revenue Service. Besides the capability of

quickly interconnecting law enforcement agencies for telecommunication, there is direct access for computer interrogation of driver's license and motor vehicle files within each

state. NLETS is incorporated as a non-profit or- ganization and is controlled by the participating states. The heart of the system is a pair of computers located in Phoenix, Arizona, which

control interconnections among the individual

State computer networks. The routing of messages over local networks within each State is a

State responsibility. NLETS operates continuously, exchanging point-to-point administrative

messages and regional and national all-points

bulletins. It is important to realize that NLETS is only a routing and communication agency and

maintains no data files. The NLETS governing

board and each individual State determine

which data files within the State can be

NCIC POLICY BOARD REGIONS

4 „W«„.„S,„E,

Operational Terminal -- Computer/Telecommunications Switcher • Operational Terminal — Keyboard — Printer

iShaded portions represent areas having on-lrne access

to NCIC through metro or state computers/switchers)

10
accessed by the system. The system, as now

formed, is capable of handling a peak hourly

load of 1 3,000 messages, but has the capability

for expansion to 26,000 messages an hour [10].

There are many important regional and

statewide communication switching systems.

For example, the Automated Law Enforcement

Communications System (ALECS) serves Illinois and seven other midwestern States [11], while

the California Law Enforcement Telecommunications System (CLETS) serves California.

There are also many data-file systems maintained by the States. One example is the Law

Enforcement Agencies Data System (LEADS)

operational within Illinois. This system maintains

files entitled Stolen Vehicles, Wanted and

Missing Persons, Stolen and Recovered Guns,

Stolen and Lost License Plates, Stolen Articles,

Firearm Owners, Criminal Histories, Alias

Names, Stolen Securities, Highway Conditions,

Accident Victims, Stolen Boats, Towed or Impounded Vehicles, and Liquor License

Owners. LEADS utilizes about 360 remote

terminals located in State, county, and

municipal offices within the State. The remote

terminals are connected via communication

lines to the central computer located in

Figure 8. Comparison of times required to teleptione

for assistance.

Springfield. Other State systems include the

New York State Identification and Intelligence

System (NYSIIS), the Iowa Traffic Records and

Criminal Justice Information System (TRACIS),

and the California Automated Jail Information

System (AJIS) [12,13].

911 Public Calling System

Agencies are always striving to reduce the time

period between receipt of a call and the time

assistance arrives on the scene. In contrast, the

911 system reduces the time it takes a citizen to actually contact the agency. When 91 1 is the

primary emergency number in a community, the

citizen saves time in not looking up the correct seven digit number and dialing it (see fig. 8). In some cases, a telephone book may not be

available or the caller may not be able to see

the dial.

The 91 1 system requires considerable planning

to efficiently receive, route, and dispatch calls. The fact that several agencies and several jurisdictions may be involved in any given 911

reception center usually raises questions of

control and chain of command [14]. The degree

of success in implementing a 911 system

depends greatly upon the process chosen for

DIAL911- RELAY TO SEPARATE AGENCY OR JURISDICTION

DIAL 911 —

DISPATCH FROM

ANSWERING SERVICE DIAL"0' DIAL 7-DIGIT NUMBER

OCCURRENCE OF INCIDENT

RECOGNITION

DECISION TO CALL

DIAL 911

ANS. BY AGENCY

RELAY ANS BY 2iid AGENCY

' ON SCENE ^ TIME SAVED

OCCURRENCE OF INCIDENT

RECOGNITION

DECISION TO CALL

DIAL 911

ANS. BY AGENCY

ON SCENE ^ TIME SAVED

OCCURRENCE OF INCIDENT

RECOGNITION

DECISION TO CALL

DIAL 0 ANS BY TELCO OP. Whal Location? ^hal Kind of Emergency?

Look Up Number?

DIAL

ANS. BY AGENCY

ON SCENE ^ TIME SAVED \1

OCCURRENCE OF INCIDENT

RECOGNITION

DECISION TO CALL

What Jurlfdicllon? Whal Agency (•)? LOOK UP NUMBER

ANS BY AGENCY

11
handling calls for other agencies and jurisdic- tions.

The Federal and State Governments have

committed themselves to the 911 emergency

calling system. The Federal Government is actively encouraging local authorities to establish this system in both urban and rural areas [15]. Entering 1977, it had been

established in 665 jurisdictions, representing

communities of all sizes and serving slightly less

than one-quarter of the total population of the

United States [61]. However, in the 25 largest

cities, those with populations greater than

500,000, more than one-half the population had

911 service.

Emergency Medical Service

Another public service which is rapidly growing

and one which, it is predicted, will eventually

rank in importance with law enforcement and

fire, is emergency medical service (EMS) [16]. The statement has been made that "the

greatest threat to the average citizen is not the

fire in the home or the criminal in the street—

the greatest threat to the average citizen is the

inability to get emergency medical care at a

time when minutes mean lives" [17]. With thei,, anticipated growth in EMS will come a signifi-f'

cant growth in communication needs. Some

metropolitan areas will receive sixteen or more

radio channels to handle the expected emergency traffic. Much planning is necessary to put

such a system into operation, and it remains to be seen how the EMS system will interact with

law enforcement communications.

Digital Systems

Digital systems, where messages are encoded

into binary form prior to transmission and

decoded at the destination, are of growing

interest in law enforcement communication sys- tems. Because digital systems use the language

of the computer, they are very efficient when

communicating with crime information files such

as NCIC. A mobile unit can directly access computerized crime information files when suitable

switching arrangements are made at the base

station. Other advantages include the following:

• Digital communications offer a significant degree of privacy. Special equipment is necessary to decode these

messages.

• Messages in digital format can be

transmitted much faster than ordinary

voice transmissions. Frequently used

messages (including status reports

and acknowledgments) can be sent by pressing a button.

• Unlike voice transmissions, which

require an acoustically quiet environment, digital transmissions can be

received and sent without phonetic

errors. Messages can be automatically stored for a period of time until the officer has time to review them.

Some equipment can check messages for errors in transmission.

12
i' Digital communications impose special require-

! ments on the overall communication system

1 [63]. To avoid significant interference with voice

\ transmissions, it is recommended that digital

!j transmission be via dedicated radio channels

[8]. Also, electromagnetic interference can

!j cause significant error rates, requiring either

I retransmission of messages or the use of error detection codes [64]. Adding digital terminals to

'\ older voice transmitters which have long warm-

'! up requirements can produce delays in digital

transmissions.

I

I Reports and guidelines on digital communications are available to assist law enforcement a- gencies in selecting, evaluating, and developing

i operational plans for digital communications

! 18,63 . These documents provide further details

1 on digital communications such as requirement

l| analysis, system concept design, implementation planning, and performance and cost

modeling. A standard providing minimum perforj mance requirements and test procedures for mobile digital terminals has been developed

\ [62].

i'l i' Commercial systems often include provision for

j sending status messages from the vehicles,

thereby saving time and radio channel usage.

Since a vehicle identification code is automatically sent periodically to the dispatcher, it is a

simple matter to include additional status mesj sages, selected by push buttons in the vehicle.

I Typical status messages are AVAILABLE,

I ENROUTE, ACKNOWLEDGE, and AT SCENE.

Also, certain alarm functions are possible,

including an "officer in trouble" signal.

Mobile digital communication terminals allow

the patrolman in the vehicle to visually receive

the incoming message. Figure 9 illustrates a

mobile digital terminal which has eight lines with

capability for 256 characters on a solid-state

h dot-matrix panel.

One system uses a programmable communications computer (also called a processor) at the

base station facility to perform functions such

as communications control, format conversions

and buffering, in conjunction with the host

Figure 9. A typical mobile digital communications ter- minal.

computer. The processor is connected to the

base station communications equipment

through an appropriate encoder and decoder in- terface. The mobile terminal consists of a keyboard and display. The keyboard may

include both alphanumeric capability and

special function keys such as status, emergency and "canned" messages. The eight-line

displays allow officers to view entire incoming

messages at one time. One-line displays are

available that are more compact [8]. The

smaller displays require manual switching from

line to line while reading or preparing a message. Attention should also be paid to display brightness and the likelihood of screen washout in daylight. Glossy surfaces, such as

the keyboard, may reflect light directly onto the

screen. The size of the keys and keyboard

should be checked for adequate size and

spacing.

The FCC requires that digital transmissions on

voice channels be less than two seconds in length and that such transmissions not interrupt

voice communications. Channel sensing equipment to accomplish this latter task is available on all equipment marketed for this purpose. An

alternative is to use dedicated "digital-only"

radio channels in lieu of voice channels already

assigned.
Other equipment available for use in the vehicle

is a printer which provides a permanent copy.

Some printers are capable of being controlled

from the base station such that even if unattended, messages will be printed out. Very

quiet print heads are available.

Typical complaints against printers are that they

are slow and wasteful of radio transmission

time, and that the resulting received audio is highly distracting without tone-coded squelch.

Also, printers usually do not have acknowledgment features, meaning that the sender doesn't

know whether the message was received

correctly (or at all). Probably for these reasons, mobile printers have not been too popular for use in law enforcement systems. However, at least one manufacturer includes as an option

with its mobile digital terminal a printer that

effectively gets around these objections. For

example, by using the buffer in the mobile

digital terminal, the "air time" is only 1.5 seconds maximum for 224 characters, and error detection is provided.

Other accessories include devices for the

facsimile transmission of messages and documents such as maps and photographs.

Equipment of this type can be produced in compact and lightweight models suitable for mobile installation. A typical system receives at a rate of 10 cm per minute (four inches per

minute) with a resolution of 35 lines per cm (90

lines per inch). This equipment can be operated

automatically when controlled by signals from

the transmitter.

Automatic Vehicle Location Systems

Dispatchers, in order to dispatch patrol vehicles

efficiently, must have some knowledge of where

the vehicles are located. There are systems that

do this automatically, with a high degree of precision, known as Automatic Vehicle

Monitoring (AVM) or Automatic Vehicle Location

(AVL) systems. There are many different kinds

of vehicle location techniques [22]. One

method, a dead-reckoning system, makes use

of the odometer to measure distance traveled

and a gyrocompass to measure travel direction. A computer processes this information and

displays the vehicle's location on a computerdrawn map. The degree of accuracy may be as good as 15 meters (50 feet) with this system.

See figures 10 and 1 1.

Facsimile can play a vital role in disseminating

information within a complex communicationsystem. For example, a telephoned complaint

received at a central facility and written on a

card can be transmitted by facsimile transmitter

directly to appropriate district stations [20]. This

method is fast and accurate, when compared

with other systems such as teletype. Further in- formation on performance characteristics and

purchasing hints for facsimile systems are

available [21].

Proximity systems use specially equipped

"signposts," located throughout the area to be

covered. Each signpost contains a low-powered

microwave transmitter which transmits its location continuously. A vehicle passing by

receives the signal, stores it, and tranmits to the

dispatcher, on request, the location of the most

recently passed signpost. Claimed accuracy is 90 to 180 meters (300 to 600 feet) at a 95

percent confidence level. See figures 12 and

13.
Figure 10. In a dead-reckoning sys- tem, a data processor

{left) is used in con/unction with a transceiver

{riafit) to send location information to the computer at the base station. {Photograph courtesy of the Boeing Co. ).

Figure 11. Computer processed lo- cation information is pre- sented at the control

position on a computer

generated map. {Photograph courtesy of the Boeing Co.).

15
Figure 12. A representation of a law

enforcement vetiicle re- ceiving a weak signal

from a transmitter mounted on a signpost and

retransmitting tfie vehicle

location to tfie dispatcfier.

{Pfiotograpfi courtesy of Hoffman Electronics

Corp. )

Figure 13. A view of tfie dispatcfier

position sfiowing vefiicle location and status for a proximity system. (Pfio- tograpfi courtesy of Hoff- man Electronics Corp.

)
Voice Privacy Systems

The availability of low-cost receivers has

encouraged public listening to law enforcement

communications. Unfortunately, there are some

individuals who misuse the information obtained

from such eavesdropping. One method used to discourage such listening is to add voice privacy

equipment to the police communications sys- tem. These systems encode the voice at the

transmitting end and decode it at the receiving

end. It is desirable that the coding technique

I chosen have adequate voice security, minimum

degradation of received voice clarity, and

reasonable compatibility with other equipment.

I Figure 14 illustrates a typical voice privacy sys- tem in operation.

The cost of voice privacy equipment depends

on factors such as the technique used for

scrambling and the number of codes available.

Voice privacy systems are available from a number of manufacturers at costs ranging from

$250 to over $6,000. For advice in selecting

voice privacy systems, the reader is referred to another guideline [23].

Incompatibility am^ng the scramblers of

different manufacturers and even different models of the same manufacturer is not unusual

[24]. Scramblers must often be tailored to work

with specific communications equipment. The

additional electronics adds complexity, bulk and

weight, and has a tendency to reduce system reliability and increase maintenance requirements.

On portable equipment especially, it is usually

desirable to reduce bulk and weight as much as

possible.

Figure 14
r I

Repeater and Voting Receiver Systems

Each police officer in the field expects to have

reliable communications with the dispatcher.

The police officer on foot patrol utilizes handheld, battery-operated transceivers. These

devices are low-power units (usually 2 1 /2 watts

or less) of limited range. They can normally

hear the dispatcher because of the high-power

base station transmitter, but the dispatcher may

have difficulty hearing the lower-power handheld transmitter. In some cases even a mobile

unit may have difficulty talking to the dispatcher

Figure 15.

because of irregular terrain or long distances.

One method of solving this problem is to use a f voting receiver system.

'

A voting receiver system consists of a number

of "satellite" receivers and a comparator. The

satellite receivers are located at carefully

selected locations within the desired area of

coverage. A low-power field unit then has a

better chance of being heard by one of the

satellite receivers because of the shorter

distances involved. If several receivers hear the

signal from the field unit, the comparator selects

the best signal for the dispatcher. The satellite receivers are usually connected to the

comparator by wire, but radio links can also be

used. Figure 15 is a photograph of voting equipment at a large facility.

A field transceiver, either hand-held or mobile,

may have difficulty at a particular locality in both

receiving from and transmitting to a given base

station. Possible solutions to the problem

include relocating the base-station antenna,

increasing the antenna gain, increasing the

transmitter power, or installing a repeater sys- tem. The latter is often the best choice for reasons of effectiveness. A repeater is essentially an intermediary receiving and re-transmitting

station designed to automatically relay communications between base-station and field units. A

desirable repeater site is generally one which

has power already available, few powerful

nearby transmitters, few radiofrequency noise

sources, controlled road access, and good

height and "overlook" for the area to be served.

Control of the repeater can be either by wire

lines or radio links.

Figure 15. Receiver voting equipment including amplifiers, controls, and patching arrangements

at the Los Angeles County Communications I Radio Center. »

Figure 16. Part of the portable emergency radio system

in the Los Angeles County Sheriff's Department. {Photograph courtesy of L.A. i County Communications Department.)

18
I Repeaters need not be fixed permanently in location to be of service to a community. For

example, emergencies may require additional

communications on very short notice. Figure 16

illustrates a trailer-mounted system consisting of a repeater with control console for local basestation use and a 12 meter (40 foot) crank-up

j tower for the antenna system. Additional equipment with the trailer includes an auxiliary

j generator as well as mobile transceivers and

personal transceivers arranged for two-frequency operation in the 450 MHz band. Six mobiles

and twelve portables, complete with antennas

and batteries are provided, although twice that

number can be handled with the repeater if needed.

! Additional information for those who are contem-

{ plating purchasing repeater systems is available

, in a report and a standard [25,26].

j Scanning Receiver Systems

!

I Scanning receivers provide a relatively inexpensive means for monitoring traffic on several

channels. Equipment of this type is priced from

approximately $100 to $250 or more. Crystals (if

ii used) for the desired channels are additional

and may total more than $100. A scanning

receiver can be used at fixed locations or for mobile operation. The receiver typically scans

selected channels in rapid sequence until a

signal is detected. At that point the receiver

stops scanning and that channel is heard until the signal ends. Then the receiver starts scanning again.

Options available include variable scanning

rates, and channels that can be locked out and

not routinely scanned. A priority channel can be

designated such that traffic on it will supersede

all other listening, even to the point of

interrupting a lock on another busy channel.

Units are available with frequency synthesizers

that are programmable by coded punched

cards. Hand-held, portable scanning receivers

I are also available. A word of caution: do not expect the same performance from these

receivers that would be expected from more ex- pensive fixed frequency receivers. Do not

*j expect the same reliability, freedom of overload

from nearby transmitting sources, and lack of spurious responses that the more expensive

communication receivers provide. Perhaps the

proper place for scanning receivers is for situations where information of a general nature

is desired and not where critical reliance is sought.

Public Transportation Safety Cliannels

In order to improve the safety of the traveling

public there is presently a proposal before the

Federal Communications Commission (FCC) to provide three frequencies in the standard AM

broadcast band for the transmission of information to the traveling public by "Traveler

Informatiori Stations" [27].

In addition, an ad hoc committee has recently

studied whether the Department of Transportation (DoT) should allow, fund, or encourage law

enforcement and other public safety organizations to use citizens band (CB) radio to augment

their present communication systems [28]. The

committee supported the use of CB Channel 9 as a national emergency and motorist-aid channel. It also supported the encouragement of cooperation between CB users and the emer- gency response agencies.

19
The FCC has estimated that there are fifteen million citizens band transmitters now in use in the United States. Many of these stations are

located in vehicles, and several law enforcement agencies have found that communications

with trucks, for example, can be advantageous

[11]. The misuse and abuse of CB equipment,

overcrowding, and the technically inferior quality of some CB communications are problems,

however. Careful planning is needed before any

such concept can become workable and

practical.

Planning and Management

In order to assure an effective and smoothly

operating communication system, a great deal

of early planning and continuing good

management is required. In the limited space

available here, we can only hope to point out

typical problem areas and refer the reader to some excellent references that deal more

completely with the subject.

Special problems exist in making major modifications to existing communication systems, as opposed to implementing entirely new systems.

For example, that part of the system which is changed or added must be integrated with the

rest of the system so that total system performance is enhanced. Usually the entire system

cannot be shut down during modification. The

process of modification must satisfy both old

and new systems.

It is essential that someone has a thorough

grasp of the communication needs of the law

enforcement agency. Someone continually

needs to match needs with the means by which

the desired result may be accomplished. The I best results in new system design or modification can then be achieved. In designing a new

system, however, there is broader scope for in- tegrated planning of all operational and support

systems [20]. New public buildings and facilities should be

| planned with adequate conduit systems

provided to allow future deployment of communi

cations systems. This illustrates the need for

'

early planning of communication facilities. It is

[ important that management recognize the need

for someone to keep abreast of Federal

Communication Commission (FCC) Rules and

Regulations; to be aware of and utilize current

state-of-the-art communications; to effectively . use existing assigned frequencies; and to assure proper operation and utilization of the e- - quipment [4].

[ Most communication system managers have \ many areas of responsibility. For example, the

manager usually consults with department

heads to review and monitor their communication needs, and to provide recommendations.

He may need to determine that all systems and

equipment meet the needs of the department, i not only economically, but with good

engineering and operational procedures. He I may design new or additional communication : systems and plan long-range programs. The ; manager needs to make certain that the terms

of the FCC licenses are met and that the Rules li and Regulations are followed [4]. System i managers should keep supportive data, not only t to ascertain personnel requirements, but also to a provide accurate inputs affecting budget

decisions for those in the administration who i' have fiscal responsibilities [30].
PRINCIPAL COMPONENTS

j Once a communication plan has been devel-

' oped, there is need to identify the kinds of equipI ment necessary to accomplish those goals. The

I following sections discuss many types of comI munications equipment available for use in law

I enforcement. New equipment is continually

I being developed, and readers should query the

various manufacturers for the latest developments.

j Transceivers

Detailed descriptions of the principal types of

I law enforcement transceivers are given in three

i companion guidelines [31-33]. These discuss

personal/portable, base station and mobile

transceivers, and give information relating to the

various available options and suggestions for proper placement in service.

more transmitters are sharing a common

antenna, there must be provision to reduce

transmitter intermodulation. The most commonly used type of equipment to reduce these

effects is a combiner. The type of combiner

chosen depends upon a number of system

factors including frequency separation, number

of transmitters and/or receivers, and antenna

system gain [34]. When transmitters and receivers share a single

antenna and are in operation simultaneously, a

duplexer is commonly used to provide the

necessary isolation. The duplexer usually

consists of high Q filters combined so as to achieve the desired isolation. The filters may be

placed in series to act as a bandpass filter, or in parallel to act as notch (band-reject) filters, or in combination. A typical filter installation is shown

in figure 17.

Antennas and Combiners

The antenna system is an important link in any

communications chain. A well designed and

deployed antenna system, with low transmission

line losses and low standing wave ratios (SWR),

will often make the difference between good

and poor communications. Usually the same

antenna system is used to transmit and receive,

since antenna switching is often performed

within the communications transceiver. Therefore the time, trouble, and expense taken to improve the antenna system will pay dividends

in improved performance for both transmitting

and receiving. Additional information on anten- nas is available in other guidelines [31-33].

Multifrequency operation in a given band is not

at all uncommon in busy urban areas. What

then can be done to assure satisfactory

operation at a given location when reception is desired a few megahertz or even a few tens of

kilohertz away from the frequency of an active

transmitter? The problem is one of providing

receiver protection from transmitter noise and

receiver desensitization. In addition, if two or

Figure 17. A cavity resonator installation for 39 MHz.

{Photograph courtesy of Los Angeles County Communications Department.)

Ferrite isolators in combination with bandpass

cavities are commonly used at VHF and UHF to reduce transmitter-produced intermodulation

when the frequency separation between trans21
mitter frequencies are at adjacent channels. A

ferrite isolator is a three port circulator with a matched resistive load connected to port #3. It passes transmitter power from its input (port

#1) to its output (port #2) with a typical loss of

0.5 dB, but attenuates rf energy in the opposite

direction by typically 20 or 25 dB. One disadvantage is that a ferrite isolator may itself generate

harmonics and other noise. Therefore harmonic

low-pass filters are usually placed between the

isolator and the following system component.

This device has an added advantage in protecting the transmitters from open or shorted

transmission line or antenna conditions.

Control Consoles

A control console usually consists of a deskmounted, enclosed panel containing a number

of controls used to operate a radio station. The

control consoles can be combined in various

ways to form a communication control center of almost any desired level of complexity and

sophistication. A communication control center

is of prime importance in law enforcement.

Incoming information in the form of citizen complaints is processed and dispatched at this location. Activities of the field personnel are

also monitored, coordinated, and directed from

the control center. Figure 18 illustrates typical

control consoles within such a communication

control center.

Typical features of a control console include

audio controls (microphone, loudspeaker or earphones, volume control, compression

amplifier, telephone line balance control, tape

record controls), and rf controls (transmitreceive switch or voice operated control, : selective-calling controls for individual mobile

units, and frequency selector). Indicators

include a transmit indicator, and volume unit ' meter. Useful accessories include card files for i frequently used information, automatic time ' clock, and automatic dialing controls for tele- phones. In general, there is a lot of interest in well-designed control consoles and many manufacturers offer consoles that are both pleasing

to the eye and human engineered for use in law

enforcement communications.

Power Sources

Power sources for communication equipment

vary over a broad spectrum. Base stations

primarily use power from the commercial power

lines. Mobile units use power from the vehicle

alternator and battery. Personal and portable

transceivers use either primary or secondary

batteries. These power sources are well described in the literature and will not be

discussed further here [35,36]. However, special

power sources are occasionally needed. For

example, a remote repeater site may not have

commercial power available, and base stations
are subject to occasional power outages, often

just when service is needed to handle a critical situation.

: Equipment used in emergency situations include

battery and inverter systems and engine-driven

j generators. A battery-inverter system offers the

j advantages of instant availability, low mainteI nance (no moving parts), easy installation, high

reliability, and good performance and efficiency.

Unfortunately, a battery is limited in the amount

of energy it can deliver, and a power failure of

sufficient duration will cause such a system to

' fail. If it is suspected that the outage time or current demand may exceed the capacity of an

existing emergency batter, the purchase of a

small supplemental engine-generator system

rather than a larger battery should be considered. The engine-generator system may be pro- grammed to start automatically after a given time

I interval in order to recharge the battery or supplement the battery power [37].

Engine-generator systems are relatively expensive, and to assure reliability must be regularly

inspected. They are not capable of providing

instantaneous power and require some time

(seconds or even minutes) before they can be

safely used. The selection of the engine

depends upon various factors. Diesel engines

are heavier and more costly than the other

choices, but are more rugged and dependable

and are often the choice for continuous

operation. Fuel costs and fire danger are lower

than for gasoline engines. Gasoline engines are

useful for output powers up to 100 kw; they

start quickly and are relatively low in initial cost. However, their higher operating costs, due to

fuel cost and short time between overhaul, work

to their disadvantage. The storage and handling

of gasoline involves great hazard, and the user must be cautious. Natural gas and LP gas

engines are perhaps the most reliable after long

shutdown periods, because these fuels do not

deteriorate with time as do gasoline and diesel

fuel. Also, because of cleaner burning, engine

life is longer and maintenance is less. Initial costs are comparable with gasoline engines.

The local situation should be studied relative to the availability and dependability of alternative

fuel supplies, especially in emergency

situations.

Figure 18. Adams City (Colorado) Dispatch Control Center.
Another source of power is the thermoelectric

generator. This system converts heat energy to

electrical energy by the use of a thermopile.

Electrical energy is produced by burning

propane or butane and heating the hot junctions

of the thermopile. Models are available that

supply from 1 0 to several hundred watts. Prices

range from one to over three thousand dollars. Special enclosures are available for better

corrosion, insect, and environmental control in hostile climates. Figures 19-21 illustrate examples of the power sources mentioned

above.

Figure 19

Figure 19. A remote communications site with propane

supplying a thermoelectric generator that is mounted on a portable building (arrow

points to generator). {Photograph courtesy

of U.S. Geological Survey.)

Figure 20. A nickel-iron (or Edison) battery installation

for standby power for the computers in a computer-aided dispatch center.

Figure 21. A standby motor-generator installation for a remote communications site.

Figure 20 Figure 21
other sources of electrical energy that are

presently being developed which may soon fill the needs of emergency and standby power sys- tems Include the following [38]:

• Fuel cells which convert the energy of chemical reactions such as the

burning of hydrogen into electrical energy. High initial costs and the lack

of long-term reliability are the major

disadvantages of these cells.

• Photovoltaic cells which convert

radiant energy from the sun into

electrical energy. These cells have

very high reliability, which makes

them attractive for remote unattended

locations. The major disadvantages

are high cost and the large surface area required for even modest

voltage and power levels. A practical

system would include batteries for use during cloudy days and at night.

Standard Interfaces

There are several problems due to the lack of standardization of law enforcement communicali tions equipment. For example, the control head

made by one manufacturer has a squelch

control and a channel selector which operate

' counterclockwise, while another manufacturer

' uses the opposite rotation. One manufacturer

has chosen the left side of the control panel for

{ the squelch control and the right side for the

volume control, while another manufacturer has

these reversed. The result is that an officer who

must use patrol cars equipped with different

types of equipment may make unnecessary

mistakes in critical situations. These and similar standardizing problems are being resolved

[39,40].

Standardization at the local level has been

attempted for many years, and items such as

cable connectors, mounting hardware, and

control heads used in mobile transceivers have

j been prime candidates [41]. It is expensive and

! difficult to change from the equipment of one

; manufacturer to that of another. Not only do

cables and similar accessories not interchange,

j but entire subsystems usually are not

electronically compatible. This dissimilarity of

circuitry and parts among manufacturers places

additional training and inventory requirements

upon maintenance personnel.

While there would be significant advantages in the standardizing of certain equipment inter- faces, there could well be disadvantages in the

standardization of the equipment itself. Manufacturers frequently claim that the stan- dardization of equipment would decrease their

ability to provide improved products [42]. For

that reason, equipment standards should,

whenever possible, be performance standards

rather than design standards.

Telephone Interfaces

A large expenditure in the annual budget of nearly every large law enforcement agency is for telephone service. The telephone is used

conventionally for interoffice and external communications. In addition, dedicated telephone

lines are often used with base stations and

repeaters, and with satellite receivers spaced

advantageously within a community and

connected in a voting arrangement to the base

station communication equipment.

Adequate service is a necessity, and it is important that the telephone equipment be

sufficient to perform the mission of the department as economically as possible, while at the

same time providing a good "telephone image"

to the public. There is nothing as disturbing to a

caller as to be forced to wait for an extended

period for a line to clear. One agency improved

its service by adopting the following guidelines

[43]:

• Sixty seconds was to be the average

talk time for primary operators,

• Ninety percent of all incoming calls were to be answered within twenty

seconds.

In order to accomplish the first goal, additional

training was provided in telephone answering

procedures and questioning techniques. Tele-
phoned reports and other calls expected to take

longer than sixty seconds were transferred to secondary operators. The second guideline

helped to determine the number of telephone

lines and operators required.

Many law enforcement agencies use a Private

Branch Exchange (PBX). A PBX is a switching

system for interconnecting telephones with

other telephones on the same premises. The

older PBX's are manually operated; a switchboard attendant makes the connections and

controls the bell ringing. Dial PBX systems make

use of dial operated equipment to establish connections between stations while a switchboard

controls "external" connnections to the system.

With another type of Private Branch Exchange

called CENTREX, incoming calls can dial directly to any extension without the assistance of an

operator. Outgoing and internal lines are dialed

directly by the extension users.

A PBX can be either telephone company or customer owned. If telephone company owned,

there are certain monthly fees to be paid. If the

PBX is privately owned, the appropriate connection arrangements are furnished, installed, and

maintained by the telephone company [44]. A

monthly charge is made for the interface.

Although a privately owned PBX often has a

very attractive initial cost and may offer otherwise unobtainable features, one should carefully

consider the alternatives before renting or purchasing. Local experience should be sought

out and questions asked relating to local servicing of both the PBX and the interface.

Because of the high costs involved, the

specifier of such a system should also study the

available equipment options from the several

suppliers, training programs for the operators,

and the expansion capabilities of the systems

[45-47].

Lightning Suppression

Lightning is one of the hazards to which communication facilities are subjected. Figure 22

shows the average frequency of occurrence of thunderstorms within the United States. The

most active area is in Florida. There, one communication facility was knocked off the air six times in one summer [48]. Also, one wild night

there were 19 base stations and repeaters

struck by lightning.

Fixed antenna systems are usually placed at high locations, such as a hilltop or the roof of a

tall building, and are thus highly susceptible to

lightning strikes. While there is little that can be

done to reduce the occurrence of lightning,

there is much that can be done to minimize the

effects of a lightning strike. The physical

damage (and shock hazard) can often be

greatly reduced by the proper design and

installation of the tower and antenna system.

A lightning strike may involve several hundred

thousand volts and currents increasing at the

rate of several thousand amperes per

microsecond. These rapidly changing currents can create hazardous inductive voltages

between nearby equipment cabinets and other

metallic objects (see fig. 23). Proper bonding

and grounding can greatly reduce this type of

shock hazard to personnel. A variety of protection measures can be applied to help assure the

uninterrupted operation of communications e- quipment. The following parts of a communication facility are usually the most vulnerable:

• Antennas, towers, and supporting

hardware,

• Transmission lines from transmitter to antenna,

. • Communications equipment and atten- dant buildings, and

• Power lines, telephone lines, and

control cables.

For basic lightning protection and the automatic

reduction of smaller voltage discharges through

communications equipment, the use of "dcgrounded" antennas is recommended. Exam-

pies of these are folded dipoles and colinear

verticals. High gain antennas use multiple

elements but still are essentially self-protecting.

Details on the proper methods of grounding and

connecting arresters, protectors, and suppressors are already available and need not be

repeated here [49].

Test Equipment

A visit to a maintenance area where work on

communication equipment is performed may tell one a lot about the operational success of a communication system. Such success is dependent not only on knowledgeable and

dedicated personnel but also on adequate test equipment. A well-equipped and modern shop

saves a great deal of labor and even frustration at times. Much emphasis has been placed on

obtaining modern communication systems and

operational equipment. But too often the

tendency is to stay with the old familiar test e- quipment which may no longer be adequate.

For example, there has recently been a significant improvement in frequency-modulated (FM)

signal generators used to test receivers. All- solid-state generators are available that provide

digital readout of frequency. The more expensive ones (in the region of 4-5 thousand

dollars), offer output frequency stabilization in the order of 1-5 ppm using special phaselocked circuits and very stable crystal

references. In addition, signal generators can now be built that have very low noise output. *i Some generators are available that operate with

such characteristics to slightly above 1 GHz.

The interested reader is referred for details to a

rather extensive discussion comparing available

models and listing manufacturers [50]. ^.

In the testing of transmitters, a spectrum!

analyzer can be a very useful tool. A spectrum i analyzer uses a frequency-domain presentation ] instead of the time-domain presentation that an ] oscilloscope uses. As a result, certain measure-

ments and information can be more readily

obtained. For example, certain characteristics of

signal sources (such as the signal generators

discussed above) can be readily studied.

Because of typically large dynamic range—often

exceeding 70 dB—measurements comparing

spurious responses and harmonics with the

fundamental frequency may be readily seen at a

glance. Spectrum analyzers are also useful to

identify certain modulation problems of transmitters, to compare relative signal levels in a large i spectrum of frequencies, and (with a tracking | generator) to adjust filters for desired frequency

rolloffs. Spectrum analyzers typically cost from

about 4 to 8 thousand dollars.

For suggestions as to where to purchase

general test equipment, the reader is referred to the section below entitled Purchase of Communications Equipment.

i

28
COST CONSIDERATIONS

I In public-safety communications there is an

I obligation, indeed a requirement, to carry out

j the tasks with reasonable efficiency and

minimal costs to the taxpayers. Grants are

available, but these often require feasibility

I studies and system designs which may be too

I complex and technical for the smaller communi1 ties who have limited staffs [51]. In such cases

jj a communications consultant may be

I necessary.

1 Poor planning and procurement practices can

I result in a waste of purchasing dollars.

! Equipment costs can generally be best

t determined by competitive bids. It has been

'I charged that the "lowest bidder" procedure

'! results in waste, delay, inefficiency, and

unnecessary expense [52]. However, most

governments require a low-bid system to avoid

the abuses inherent in no bidding system at all [53].

After the initial purchase of communications e- quipment, the user is faced with other costs

including training, maintenance, and test equipment. As more fully discussed in another

guideline, maintenance costs can be high [51]. Some communication officers figure mainte- nance to entail a yearly cost of 1 0 to 20 percent

of the fixed investment [4]. Test equipment for the aligning or testing of communications gear

can, in itself, run into a significant investment.

Some precision signal generators, for example,

cost $10,000 or more.

I PURCHASE OF COMMUNICATIONS EQUIPMENT

According to the Electronic Industries Association (EIA), there will be more emphasis on the

part of law enforcement agencies in improving

communications equipment [54]. Much of the

support will come from LEAA grants. Not only

will older equipment be replaced with more

I modern state-of-the-art equipment using

I established radio frequencies, but the recent al- location of frequencies in the 900 MHz band is expected to encourage greater use of sophisti-

, cated communication systems. With the

l[ increase in the use of communications equipment, maintenance, alignment, and testing of

J communications equipment can also be

expected to increase. A corresponding need

would also exist for more specialized communications test equipment and service aids. What

resources are available to help the prospective

, purchaser?

There are several buyers' guides for the general

: electronic market that cover products from "A"

|| to "Z" [55-57]. Buyers' guides that specialize in

telecommunications are also available [58-60].

However, none comprehensively and accurately cover only the law enforcement communications market.

The reader should query manufacturers that

advertise in trade magazines and journals.

Trade shows and conferences are a popular

and convenient way of getting acquainted with

some of the larger manufacturers in the field.

One extremely important source of information

is the Equipment Technology Center of the

International Association of Chiefs of Police.

The lACP, with the technical support of the NBS

Law Enforcement Standards Laboratory, has

started a program to test important items of law

enforcement equipment for compliance with the

NILECJ/LESL or other appropriate standards.

Handheld transceivers are among the first items

to be tested under that program.
REFERENCES

1. "Two-Way Radio Takes Off," Communications

News, Vol. 14, No. 8, p. 29, (Aug. 1977).

2. "Law Enforcement," Frost and Sullivan Market

Research Study, p. 262, (1975).

3. Editorial, "The Communicator's Complaint," The

APCO Bulletin, Vol. 41, No. 6, p. 38, (June

1975).

4. Atkinson, J. H., "Communications and Electronic Planning for a Growing Problem," The APCO

Bulletin, Vol. 41, No. 2, p. 10, (Feb. 1975).

5. Key, W., "A Look Into the Future of Police Communications," Proc. Third National Symposium

on Law Enforcement Science and Technology,

Vol. 3, pp. 169-172, (1970).

6. "Computer-Aided Dispatch, Command and Control," The APCO Bulletin, Vol. 40, No. 11, p. 20,

(Nov. 1974).

7. Kavanagh, D., "But Daddy, All the Other Kids

Have One," The APCO Bulletin, Vol. 40, No. 12,

p. 8, (Dec. 1974).

8. Sohn, R. L., "Advanced Command and Control Systems for Public Safety Agencies," 41st Annual Conference, Associated Public-Safety

Communications Officers, Inc., Washington,

D.C., p. 32, (Aug. 11-14, 1975).

9. "NCIC—A Tribute to Cooperative Spirit," Federal Bureau of Investigation, Department of Justice,

reprinted from FBI Law Enforcement Bulletin of February 1972, (revised Mar. 1975).

10. "The NLETS Program in Phoenix," The APCO

Bulletin, Vol. 40, No. 1, p. 18, (Jan. 1974).

11. Bourne, K. M., "Illinois State Police Depend on

Total Communications Systems," Communications News, Vol. 12, No. 7, p. 24, (July 1975).

12. "Iowa State Builds Better Communications

System for Fraction of Cost of Turnkey

Purchase," Communications News, Vol. 12, No.

7, Harcourt Brace Jovanovich publisher, p. 36,

(July 1975).

30

13. Scully, D. P., "Los Angeles County: Computer

Aided Dispatch Wide Area System" The APCO

Bulletin, Vol. 40, No. 11, p. 12, (Nov. 1974).

14. "For Help Dial-911," Summary Report, National

Service to Regional Councils, 1700 K Street, NW., Washington, D.C. 20006, p. 14, (July

1970).

15. "911 The Emergency Telephone Number, A

Handbook for Community Planning," Executive

, Office of the President, Office of Telecommunications Policy, p. 52, (May 1973).

16. Editorial, "EMS Communications," The APCO , Bulletin, Vol. 40, No. 1, p. 30, (Jan. 1974).

17. Vogt, F. B., "Why Can't People Plan Communications for EMS Systems?," The APCO Bulletin, Vol. 40, No. 12, p. 20, (Dec. 1974).

18. Sohn, R. L., et al., "Application of Mobile Digital 1 Communications in Law Enforcement," JPL SP

43-6, Rev. 1, Jet Propulsion Laboratory, (May

15, 1975).

1 9. "Mobile Antennas," NILECJ-STD-0205.00, Superintendent of Documents, Government Printing

Office, Washington, D.C. 20402, Stock No.

| 2700-00250, (May 1974).

I 20. "Chicago Facsimile: Fast and Accurate," Thej^

APCO Bulletin, Vol. 41, No. 8, p. 20, (Aug.

1975).

21. Facsimile Equipment Guideline (to be published).

^

22. Fey, R. L., "Automatic Vehicle Location

Techniques for Law Enforcement Use," LESPRPT-0205.00, Superintendent of Documents, i' Government Printing Office, Washington, D.C.

[ 20402, Stock No. 2700-00282, (Sept. 1974).

23. Sugar, G. R., "Voice Privacy Equipment for Law

Enforcement Communication Systems," LESPRPT-0204.00, Superintendent of Documents,

Government Printing Office, Washington, D.C. 20402, Stock No. 2700-00260, (May 1 974).

'

24. Beasley, W. L., "Proceedings of a Conference on Speech Scramblers," Center for Urban Pro- j grams, Texas A&M University, College Station, Tex. 77843, p. 29, (June 26-27, 1973).
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LESP-RPT-0206.00, Superintendent of Documents, Government Printing Office, WashI ington, D.C. 20402, Stock No. 027-000-00288-9,

j (Oct. 1974).

j26. "FM Repeater Systems," NILECJ-STD-0213.00,

Superintendent of Documents, Government

I Printing Office, Washington, D.C. 20402, Stock

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