Codan Radio Radio Repeater Systems Training Guide

Radio Repeater
Systems

TRAINING GUIDE

www.codanradio.com

RADIO REPEATER SYSTEM | TRAINING GUIDE

Radio R epeater

System

Training Guide

Page i

TRAINING GUIDE | RADIO REPEATER SYSTEM

NOTE

DOCUMENT REVISION

DEFINITION

© 2013 Codan Limited.
No part of this guide may be reproduced, transcribed, translated into any
language or transmitted in any form whatsoever without the prior written
consent of Codan Limited.

CODAN™, NGT™, Easitalk™, CIB™ and CALM™ are trademarks of
Codan Limited. Other brand, product, and company names mentioned
in this document are trademarks or registered trademarks of their
respective holders.

Comshel © is a copyright name of Sinclair Radio Laboratories Ltd.
The maps used in this document are based on information taken from
the National Topographic System map sheets numbered 92-H, 92-I and
92-I/6 ©. Her Majesty the Queen in Right of Canada with permission of
Energy, Mines and Resources Canada..
Antenna and duplexer data are copyright catalogue reference material
used with permission of Sinclair Radio Laboratories Ltd.

The English version takes precedence over any translated versions.

Documentation uses a three-level revision system. Each element of
the revision number signifi es the scope of change as described in the
diagram below.

1-0-0

Major Revisions:

The result of a major change to

product function, process or requirements.

The result of a minor change to

product, process or requirements.

The result of typing corrections or

changes in formatting, grammar or wording.

Three-level revision numbers start at 1-0-0 for the fi rst release. The
appropriate element of the revision number is incremented by 1 for each
subsequent revision, causing any digits to the right to be reset to 0.

For example:
If the current revision = 2-1-1 Then the next major revision = 3-0-0
If the current revision = 4-3-1 Then the next minor revision = 4-4-0
If the current revision = 3-2-2 Then the next editorial revision = 3-2-3

Document revision history is provided at the back of the document.

Codan Radio Communications

43 Erie Street, Victoria, BC
Canada V8V 1P8
www.codanradio.com
[e-mail]

Toll Free Canada and USA:
Phone: [phone]
Fax: [phone]

International:
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Minor Revisions:

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TG-002
3-0-0
September 2013

Page ii

RADIO REPEATER SYSTEM | TRAINING GUIDE

On August 7th, 2012 - Codan Limited (ASX: “CDA”) announced
the acquisition of Daniels Electronics Limited, a leading designer,
manufacturer and supplier of land mobile radio communications
(LMR) solutions in North America. The acquisition of Daniels delivers
on Codan’s stated strategy of growing market share and diversifying
its radio communications product offering. Codan Limited designs,
manufactures and markets a diversifi ed range of high value added
electronic products, with three key business divisions; radio
communications, metal detection and mining technology.

Codan Radio Communications is a leading international designer
and manufacturer of premium communications equipment for High
Frequency (HF) and Land Mobile Radio (LMR) applications. We’ve
built our reputation for reliability and customer satisfaction over 50
years in radio communications, in some of the toughest conditions
on the planet.

For over 50 years Codan has provided customers in North America
and internationally with highly reliable Base Stations and Repeaters
that are environmentally robust to operate in rugged and extreme
temperature conditions where low current consumption (solar
powered) is a key requirement.

Codan is a pioneering member of the P25 Digital standard, for radio
system interoperability between emergency response governmental
organizations, providing enhanced functionality and encryption.
Our products operate between 29 - 960 MHz and are available in
a variety of Base Station and Repeater confi gurations for two way
voice and mobile data applications.

DANIELS ELECTRONICS
IS NOW CODAN RADIO
COMMUNICATIONS

ABOUT CODAN RADIO
COMMUNICATIONS

Our self-servicing customers range from Forestry and National Park
services through Police and Fire departments and on to Utility and
Transportation groups. Our products have been deployed in every
imaginable situation from the Antarctic to Hawaiian mountaintops to
Alaska, enabling respondents to Forest Fires, Ground Zero rescue
and routine patrols.

Codan is an industry leader in Analog and P25 radio systems design.
We offer modular rack-mounted Base Stations and Repeaters
capable of operating in Low Band VHF,VHF AM , VHF FM, UHF FM,
700 MHz, 800 MHz, 900 MHz

Pete Lunness is a member of the Applied Science Technologists
& Technicians of British Columbia, has a Diploma in Electronics
Engineering Technology from Camosun College and a Certifi cate in
Adult and Continuing Education from the University of Victoria.

Pete has been at Daniels / Codan since 1996, working in engineering,
sales and customer support, and has been instructing technical
training courses since 1998.

ABOUT THE AUTHOR

Page iii

TRAINING GUIDE | RADIO REPEATER SYSTEM

BIBLIOGRAPHY

(1) Bullington K., “Radio Propagation Fundamentals”, B.S.T.J.

36, pp. 593-625; May 1957

(2) Bullington K., “Radio Propagation for Vehicular

Communications,” in IEEE Transactions on Vehicular
Technology, vol. VT-26, No.4, November, 1977

(3) VHF and UHF Propagation, Datafi le Bulletin 10003-1,

Communications Products Department, General Electric
Company, Lynchburg, Virginia, July 1977

(4) Stewart Alex G., “Low-Current Repeaters Suit Remote Site

Needs”, in Mobile Radio Technology, Vol.8, Issue 9,
pp. 10-24; September 1990

(5) Peasland T.H.S., Stewart Alex G., “The Development of

Simple Wide Area VHF Radio Systems”, Unpublished
report to Communications Canada, 1983

(6) Peasland T.H.S., Stewart Alex G., Phillips J.M., “Radio

Repeater System Applications Manual”, Daniels
Electronics Instruction Manual, 1992

(7) Singer Edward N., “Land Mobile Radio Systems, 2nd

Edition”, Prentice Hall, Inc., 1994

One of your best sources of information is the various equipment
manufacturers. Most have prepared reference material for their
products.

In no event will Codan Ltd. be liable for direct, indirect, special,
incidental or consequential damages resulting from the use of any
information contained within this document.

Page iv

Contents

RADIO REPEATER SYSTEM | TRAINING GUIDE

Chapter 1: Repeater System Basics ......................................1

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

Determining Frequencies and Frequency Band(s) ....................................3

Coverage Area and Site Location .............................................................. 4

Chapter 2: Repeater System Confi gurations .........................9

Determining Confi guration .........................................................................9

Linked Repeater Systems ........................................................................ 11

CTCSS ..................................................................................................... 15

Other Confi gurations ................................................................................ 15

Chapter 3: Repeater System Equipment ............................. 17

Repeater / Base Station ........................................................................... 17

Antennas .................................................................................................. 20

Duplexers, Multicouplers and Combiners ................................................ 24

Power supplies ......................................................................................... 25

Accommodation ....................................................................................... 28

Chapter 4: Installation and Maintenance ............................. 31

Installation Hints and Techniques............................................................. 31

Maintenance ............................................................................................ 32

Lightning Protection ................................................................................. 33

Interference .............................................................................................. 34

Appendix A: Drawing Coverage Maps ................................. 35

Appendix B: Drawing Path Profi les ...................................... 39

Appendix C: Calculating Path Loss ...................................... 43

Appendix D: Calculating Signal Levels ................................ 45

Appendix E: Mobile Coverage Tests .................................... 51

Appendix F: Examples of Antenna Data .............................. 55

Appendix G: Examples of Duplexer Data ............................ 61

Appendix H: Examples of Cable & Connector Losses ......... 65

Appendix I: Blank Worksheets ............................................. 67

Appendix J: Glossary of Terms ............................................ 73

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Page vi

RADIO REPEATER SYSTEM | TRAINING GUIDE

CHAPTER 1: REPEATER SYSTEM BASICS

Guidelines to Plan and Implement a Simple, Effective and Reliable Radio Communications System

INTRODUCTION

This document will familiarize you with radio system design, focusing on repeaters and base stations.
This document gives you the basics to design simple radio systems. Professional help should be
obtained for more complex radio system designs.

Radio signals operate over line-of-sight paths. This implies that you must be able to see the radio
with which you wish to communicate. Actually, contact between radios slightly beyond line-of-sight
distances are often possible, owing to refl ection or refraction of the radio waves. Physical restrictions
of signal paths between radio users (such as mountains or buildings) can disrupt system operation.
Figure 1-1 shows the line-of-sight signal paths between the portables and from the portables to the
base station at the offi ce. At far right, note the restriction of signal path between the mobile and the
offi ce caused by the hill.

Portables

Office

Mobile

Figure 1-1: Line-of-Sight Signal Paths

Chapter 1: Repeater System Basics Page 1

TRAINING GUIDE | RADIO REPEATER SYSTEM

To extend this coverage, a radio repeater or a repeater system is required as shown in Figure 1-2. A
repeater is nothing more than a radio or combination of radios connected in such a way that it simply
passes on or “repeats” anything that it hears.

Repeater

Portable

Figure 1-2: Repeater for Extended Coverage

Mobile

Portable

When the distance becomes too long, or the coverage provided is too restricted for a single repeater,
more repeaters are added as shown in Figure 1-3. By establishing a series of repeater sites, a chain
can be linked together to provide radio coverage over a large area. Unfortunately, every time a signal
is “repeated”, some of the quality is lost, thus the number of repeaters that can be linked together in
any one line is limited.

Repeater 1

Portable

Figure 1-3: Repeaters Linked Together

Repeater 2

Office

There are many steps to designing a radio system, even a simple repeater system. First, the frequencies
and frequency bands to be used must be determined. The coverage area required by the radio
system must then be decided, and from that, the location of the site(s) should be chosen. The system
confi guration will be dependant on the location of the sites and the requirements of the end user. The
equipment (repeater, duplexer, antenna, batteries, etc.) must be determined and then installed and
tested. The operation of the radio system will depend on the end user, the location and amount of sites,
and the coverage area.

Chapter 1: Repeater System BasicsPage 2

RADIO REPEATER SYSTEM | TRAINING GUIDE

DETERMINING FREQUENCIES AND FREQUENCY BAND(S)

The fi rst step in designing a radio system is to decide the frequency band(s) to be used in the system.
Determining the proper frequency band to use could be limited to licensing, environmental or existing
system considerations. The frequency bands differ in noise levels, ranges, skip, and other factors.

VHF Lowband (29 to 50 MHz)
This band is subject to heavy skip – signals bounce off the ionosphere and travel great distances.
There are frequent dead spots, and the signal does not bounce off hills or buildings. It has the most
range and the highest noise level.

VHF Highband (132 to 170 MHz)
There is much less skip, less range, and less noise in this band than VHF lowband. This band also has
fewer dead spots than the VHF lowband.

UHF band (406 to 512 MHz)
This bands range is less than in VHF highband. The signal bounces off hills and buildings well and has
practically no skip interference. It also has fewer dead spots and noise.

800 / 900 MHz band (806 to 960 MHz)
The signal bounces off buildings and hills extremely well and presents little noise. The range is less
than UHF and there is more absorption by foliage.

Licensing requirements are the fi rst consideration in determining frequency band. The different
frequency bands available for licensing are determined by a government agency that usually covers site
licensing and frequency coordination. The FCC (Federal Communications Commission) and Industry
Canada are the government agencies in the United States and Canada respectively.

Frequency band selection can also depend on the environment in which the radio system will be
operating. VHF lowband is used in many industrial applications (eg. gas and oil companies) as well
as some law enforcement applications (eg. highway patrol). VHF highband is widely used in forested
or wilderness areas. UHF and 800 / 900 MHz is typically used in urban areas, and to link VHF sites
together. The government licensing agency can help you determine the proper frequency band if you
are unsure of which band to use.

If a radio system already exists, you must assess your existing radio equipment and frequencies. In
order to use the existing equipment with a repeater system, it must be type approved under your
governments’ regulations for use in a repeater system. Your existing equipment should be capable of
at least two frequency operation. The separation between the two frequencies will, to some extent,
dictate system complexity.

Chapter 1: Repeater System Basics Page 3

TRAINING GUIDE | RADIO REPEATER SYSTEM

COVERAGE AREA AND SITE LOCATION

One of the key components of radio system design is to determine the coverage area required and
the location of sites needed to cover that area. An existing radio system may not cover all of the
required area, and another repeater may be required. A new repeater can be “linked” to your existing
radio system to increase your coverage area. Depending on the location, a radio system can provide
coverage of an area with a radius of 5 to 50 kilometers (2 to 30 miles) or even further under ideal
conditions.

A repeater or remote base station is usually located at a high site to ensure that the radio system covers
all of the area required. The development of low power, high reliability, battery operated radio systems
has allowed radio repeaters sites to be located at remote mountain tops and other areas where roads
and power lines do not exist. If room is available at the site to erect a building to house the equipment,
and to safely land a helicopter, the site could be used for your radio system.

One key to good system planning is good mapping. Topographic (contour) maps 1:250,000 for coverage
(as demonstrated earlier), and 1:50,000 for profi les between sites are recommended.

The whole idea of using low-powered, automatic repeater stations (ARS) is to put them where they are
required for coverage, and not where it may be most convenient. You now must fi nd a site or sites that
will:

i) provide your missing coverage.

ii) provide a location from which a repeater will give a strong signal into your base station (if

required).

iii) be accessible by road, trail, or helicopter.

iv) be in a position that will be line-of-sight to the next site (if required).

v) if a second site is necessary, provide the coverage you need, yet not leave coverage overlaps

between sites; nor conversely leave an unusable gap in coverage between the two sites.

Whether you plan a remote controlled base station, a repeater, or two (or more) repeaters; mobile
coverage maps for each mountain-top site are suggested, as are profi les between sites, and profi les
from site(s) to base station(s).

Chapter 1: Repeater System BasicsPage 4

RADIO REPEATER SYSTEM | TRAINING GUIDE

If it looks like one repeater will provide your missing coverage you may wish instead to consider using
a remote controlled base station as shown in Figure 1-4. This may provide the required coverage but
the following items will have to be considered:

a) a site must be available that has power and telephone lines available and is in a location that will

provide your coverage needs.

b) there will be an ongoing expense for the remote control lines rented from your telephone company.

c) the phone and power lines may not be reliable.

d) such a site will probably already be occupied leading to possible future problems of access (road

closures and maintenance), radio noise and interference from other users (see sketch).

e) road access usually means that there will be a greater possibility of vandalism.

Power and telephone lines

Office

Figure 1-4: Remote Controlled Base Station

Multi-user mountain-top
site (base station).

Road access

Chapter 1: Repeater System Basics Page 5

TRAINING GUIDE | RADIO REPEATER SYSTEM

To determine if the site you have chosen will cover the required area, a coverage map should be drawn
for that site. A coverage map shows the areas that the proposed radio system will effectively cover
with line-of–sight paths. Mobile coverage maps are a bit of an “art form” because you have to use your
imagination. In spite of this, they end up being quite accurate, and are much less expensive than a fi eld
survey. In addition, if more than one site is required, prepare profi les of the path between the sites.
A coverage map and path profi le are shown in Figure 1-5. Detailed information about drawing coverage
maps is available in appendix A, and detailed information on path profi les can be found in Appendix B.

Phillips Creek

4000'

2000'

Office

4000'

3000'

3000'

Portable
Poor or no Signal

3000'

2000'

Obstructed Path

2000'

Line-of-sight (50 km)

1000'

Plan View

Obstructions

Office
2020'

1000'

Figure 1-5: Coverage Map and Path Profi le

Chapter 1: Repeater System BasicsPage 6

Line-of-sight

Hills Not Obstructing.
Signal O.K.

Elevation

RADIO REPEATER SYSTEM | TRAINING GUIDE

The propagation of radio energy from one point to another is affected by obstacles, both natural and
man-made. Much depends on whether the obstacle is totally blocking, or partially blocking the signal
path. In the latter case the refl ected signal from the obstacles takes a longer time to reach the receiving
antenna than does the direct ray. The result may be distortion, or even total cancellation, of the received
signal.

Appendix C details the method of calculating the path loss between sites. Once the path losses are
known, simple calculations of losses and gains will provide the signal level which should result on the
paths. Appendix D contains instructions for calculating the signal level on a path. Recommended
signal levels on your paths are suggested as follows:

i) between repeater sites - a minimum of 20 μV.

ii) repeater site to base station - a minimum of 10 μV.

Discussion with other local users and a trip to the proposed site may also be advantageous, particularly
if you also do some tests using a low-powered portable (at the proposed site) to a mobile in the
questionable areas. See instructions in Appendix E on mobile coverage tests.

There are other items for consideration, many other factors that are not easily measurable may affect
radio signals. Signals may be received beyond line-of-sight, and some obstructions may not completely
wipe out signals. On longer paths, you may also gain the advantage of refractive bending of the signal
beam which is allowed for by your use of 4/3 earth curvature graph paper. Note however, that as the
frequency is increased; refractive bending, although normally downward, will vary (even upward) by
atmospheric conditions such as temperature, pressure and relative humidity. At VHF and UHF below
800 MHz this is not normally a problem, although other weather conditions such as heavy sleet or ice
storms may reduce your signal levels by up to 20 dB.

Licensing your radio system for use does not automatically give you the legal authority to install equipment
on site. Leasing or buying the small plot of land is required. You may fi nd it necessary to work with
different governments (federal, municipal, county, state, etc.) to arrange all of your requirements. Most
authorities have additional specifi cations that you must meet if your repeater sites are within a specifi ed
distance of an operating airport. Painting and lighting of obstructions is one such specifi cation.

Equipment outages at a mountain top environment are often weather related. The equipment is
designed to be as reliable as possible and is thoroughly tested before installation but a lightning strike
nearby can negate all of that in an instant. Consider carefully before locating your repeater site on a
Lightning Peak, or; as we have done in the example, on an Iron Mountain. If not familiar with weather
patterns in the area yourself, talk to those that have local knowledge.

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Chapter 1: Repeater System BasicsPage 8

CHAPTER 2: REPEATER SYSTEM CONFIGURATIONS

DETERMINING CONFIGURATION

RADIO REPEATER SYSTEM | TRAINING GUIDE

Radio system confi guration is dependant on the frequencies available, location of repeater sites and
the end user’s operating requirements. Two frequencies are required for a single repeater system.
These frequencies are designated as F1 and F2. The separation between these two frequencies
determines the size of the duplexer used in the repeater.

Rx-F1
Tx-F2

Repeater

Tx-F1
Rx-F2

Portable

Figure 2-1: Two Frequency Repeater

Tx-F1
Rx-F2

Office

The repeater in Figure 2-1 shows an ineffi cient use of frequencies and would exhibit some unwanted
characteristics. For example, if the repeater went “off the air” users would not be able to communicate
with each other since all units are transmitting on one frequency and receiving on another frequency.

Chapter 2: Repeater System Confi gurations Page 9

TRAINING GUIDE | RADIO REPEATER SYSTEM

A more effi cient use of the two frequencies would be a talk-around repeater (or 2T1R) as shown in Figure 2-2. This system
uses 2 channel positions on the mobiles, portables and base station equipment.

Rx-F1
Tx-F2

Repeater

From other
locations

Portable

Ch.1 & 2

Figure 2-2: Talk-Around Repeater

Two advantages of this system are:

i) While two fi eld mobiles (or portables) are working (talking to) and monitoring (listening to) each

other on channel 2, an outside call (from the offi ce or mobile or another location) via the repeater
will still be received.

ii) The repeater is not operating (“on the air”) for all conversations thus reducing possibilities for

interference and battery drain at the repeater site.

Portable

Ch.1 & 2

Portables Ch.1: Tx-F1 Rx-F2 Through repeater

Ch.2: Tx-F2 Rx-F2 Talk around

Chapter 2: Repeater System Confi gurationsPage 10

RADIO REPEATER SYSTEM | TRAINING GUIDE

LINKED REPEATER SYSTEMS

There are various methods of linking (or chaining) repeaters together. An expression that is often used
to describe the repeater that connects to the mobiles and base stations is “drop”, or local coverage
repeater. The expression “linking” is used in preference to “trunking” because the latter is more often
used to describe a different technology. In the following diagrams the term “drop repeater” describes
a repeater that transmits and receives simultaneously and is used to talk to mobiles, base stations,
aircraft, etc. The term “switched link” describes a repeater that does not function simultaneously but is
switched to transmit or receive at any one time (controlled by incoming signals). It is used to connect
one site to another. The term “repeating link” repeater describes a repeater that transmits and receives
simultaneously, just like a “drop” repeater, but unlike a “drop” it is an inexpensive method of linking to
a number of other sites.

Figure 2-3 represents two repeaters linked together (two linked repeaters). Note that in this system
three pairs of frequencies are required.

To / From Mobiles and

Base Stations

REPEATER 1 REPEATER 2

Drop

Repeater

Tx-F1

Rx-F2

Figure 2-3: Two Linked Repeaters

Switched link

Repeater

Tx-F3

Rx-F4

To / From Mobiles and

Base Stations

Switched link

Repeater

Tx-F4

Rx-F3

Drop

Repeater

Tx-F5

Rx-F6

Chapter 2: Repeater System Confi gurations Page 11

TRAINING GUIDE | RADIO REPEATER SYSTEM

Figure 2-4 represents a Y confi guration. Star and Y confi gurations use repeating links as the center
site. Note that the drop repeater frequencies at (A) and (D) are the same. As the system expands,
three pairs of drop frequencies are usually adequate for re-use. Terrain will often provide enough
separation between mobiles using the repeaters so that interference between them is not an issue.
The strongest signal will normally be captured by the closest repeater. Note also that the antenna on
the repeating link at (C) will probably have to be multi-directional.

To / From Mobiles and

Base Stations

(A) (B)

Drop

Repeater

Switched link

Repeater

Tx-F1
Rx-F2

(D)

Drop

Repeater

Switched link

Repeater

Tx-F3
Rx-F4

To / From Mobiles and

Switched link

Repeating

link Repeater

Tx-F4
Rx-F3

Base Stations

Repeater

Tx-F3
Rx-F4

(C)

Drop

Repeater

Tx-F7
Rx-F8

Drop

Repeater

Tx-F5
Rx-F6

Tx-F1
Rx-F2

Figure 2-4: Y Linked Confi guration System

Chapter 2: Repeater System Confi gurationsPage 12

Tx-F3
Rx-F4

RADIO REPEATER SYSTEM | TRAINING GUIDE

Microwave equipment can be used to link repeaters together instead of radio links as shown in Figure
2-5. E&M is the typical standard used to interface the microwave with the repeater. With this type of
system your site locations are limited to sites where a leased microwave channel is available.

Drop

repeater

Tx-F1
Rx-F2

Drop

repeater

Tx-F3
Rx-F4

Interface Interface

Microwave

system owned

by others

Figure 2-5: Microwave Linked System

Dual-tone, multi-frequency (DTMF) equipment can be added to your repeater(s) to disable its operation
until it is activated by the mobile or base station as shown in Figure 2-6. In this way linking frequencies
are not used until needed, reducing power consumption and possible interference.

Link

Repeater

Repeater

Microwave

system owned

by others

Link

DTMF

Drop

Repeater

DTMF

Drop

Repeater

Mobile (A) Mobile (B) Mobile (C)

Figure 2-6: DTMF Controlled Link System

Without connecting the drops to the links via DTMF, mobile (A) and (B) (above) can communicate with
each other but not to mobile (C). Once both link repeaters are connected to their drops, all three can
communicate with each other.

Chapter 2: Repeater System Confi gurations Page 13

TRAINING GUIDE | RADIO REPEATER SYSTEM

Link

Repeater

Link

Repeater

Link

Repeater

DTMF

Drop

Repeater

Drop

Repeater

Drop

Repeater

Mobile (A) Mobile (B&C) Mobile (D&E)

Figure 2-7: Partial DTMF Controlled Link System

With the arrangement shown in Figure 2-7, mobiles (A), (B) and (C) are in constant communication.
Mobiles (D) and (E) can be communicating between themselves at the same time without interference
from the others. All mobiles will be in contact with each other by activating the DTMF switch.

Chapter 2: Repeater System Confi gurationsPage 14

RADIO REPEATER SYSTEM | TRAINING GUIDE

CTCSS

Where frequencies are congested, the authorities may require frequency sharing, in which case it will
be necessary to use some type of CTCSS (Continuous Tone Coded Squelch System) as shown in
Figure 2-8. In such a system all mobiles, portables and base stations are provided with a sub-audible
tone-encoder on the repeater channels. Each repeater uses a tone-decoder. These units are operating
continuously when your microphone transmit button is depressed. Another signal on the same VHF or
UHF frequency cannot activate the receiver at the repeater because it would be allocated a different
CTCSS tone. This gives the appearance of a quiet channel all of the time although there can still be
interference between users if both come on channel through their own systems at the same time.

Repeater A

Tx-F1

Rx-F2

Possible Interference

CTCSS
Tone A

Tx-F2
Rx-F1

Mobiles A Mobiles B

Figure 2-8: CTCSS Protected Repeater Systems

OTHER CONFIGURATIONS

Repeater B

Tx-F1
Rx-F2

CTCSS

Tone B

Tx-F2
Rx-F1

Another confi guration option for radio systems is telephone interconnects. Interconnects are usually
electrically located between the base station and the telephone company lines. They enable mobiles
to receive and initiate normal telephone calls.

Most authorities require that they be compatible with the telephone system, cause no electrical
interference, and be controlled by the mobile, not the telephone caller. From a repeater users’ point of
view, the most important requirement is that an interconnect has timing devices that enable its use and
control through one or more repeaters.

The ultimate test of which interconnect to purchase is whether it will work on your repeater system. By
entering the proper sequence of DTMF tones, the mobile user is able to dial either pre-programmed
telephone numbers or any other telephone number. Limitations on length of call, restrictions on use of
long distance numbers and other features may be programmed into the interconnect unit.

Chapter 2: Repeater System Confi gurations Page 15

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Chapter 2: Repeater System Confi gurationsPage 16

RADIO REPEATER SYSTEM | TRAINING GUIDE

CHAPTER 3: REPEATER SYSTEM EQUIPMENT

When determining your system components remember that RELIABILITY is the most important
consideration. Quality equipment is worth the extra cost, particularly in the long term.

You must also remember that changing a component in one part of the system may affect the other
parts. For example, replacing the antenna type at one end of your linking path may require a change in

antenna at the other end, and a change in antenna mounting and / or housing may affect .... In other

words, there is great inter-dependence among the components. Remember also, when purchasing
equipment, to compare the range of temperature that is expected at the site(s) to the component
specifi cations supplied by the manufacturer.

In this section we are going to examine the individual pieces of equipment that make up the system.

REPEATER / BASE STATION

A repeater simply repeats everything that it hears. Any signal that is heard by the repeater’s receiver is
transmitted by the attached transmitter. A Base Station simply passes on received signals to a console
and the transmitter transmits audio from a console.

Repeaters can be assembled out of almost any combination of receivers and transmitters but in the
context of low power, high performance repeaters, some of the details take on a special signifi cance.
When a unit is powered by batteries, low current circuitry must be incorporated in the repeater to
conserve battery life. Also, when a repeater is located on a snow covered mountain top, or in desert­like terrain, extreme temperature performance is important. A well designed grounding system is also
important since the radio equipment is exposed to lightning to a far greater extent when placed on
mountain tops. For greater coverage the repeaters can be connected in chains, so the cumulative audio
distortion must be low. Base stations are typically the center of a communications hub and need to
be of extremely high reliability for safety and continuity concerns, especially for law enforcement, fi re
departments and other public safety agencies.

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TRAINING GUIDE | RADIO REPEATER SYSTEM

Codan Radio Communications is a manufacturer of high reliabiltity repeaters and base stations. Codan
receivers and transmitters frequency stability is specifi ed as +/- 1 ppm over the temperature range of

-40 °C to +60 °C (-40 °F to +140 °F), a very wide range and very cold at the lower end. Low audio
distortion in the receivers and transmitters (typically less than 2%) allows the the system designer to link
several sites in a chain to provide extended coverage. Very low current draw on both the synthesized
and crystal controlled repeaters and base stations allows these units to run from solar powered battery
sites. Codan manufactures the repeaters and base stations in a modular confi guration, for ease of
troubleshooting and maintenance.

a) Receiver modules

The receiver squelch circuit also has a form of hysteresis that allows the squelch control to be set at
a level which eliminates noisy signals, but when a signal does open the squelch, the receiver goes to
full sensitivity to allow a fading signal to come through and not be chopped up by the squelch snapping
shut for each momentary fade.

As well as hysteresis squelch, the receiver response time can be modifi ed to suit particular applications.
Some applications require a very fast response to an incoming signal, such as when several repeaters
are linked into a chain. If each receiver was slow in turning on its attached transmitter, the delay over
the length of the chain would be intolerable. The opposite situation is where it is desirable to hold the
transmitter on the air for a brief period although there is no incoming signal. This arrangement allows
two stations to talk back and forth without the repeater dropping out between transmissions.

b) Transmitter modules

The transmitter modules are of an adjustable output power, typically 0.5 to 8 Watts at VHF and UHF.
The transmitters are rated at 100% duty cycle, meaning continuous operation at full output without
degradation over the full temperature range.

An adjustable time-out-timer built into the transmitters can shut down the transmitter after a preset
length of time (adjustable from 1 second to 8 hours). This will stop the transmitter from draining the
batteries when a stuck microphone condition occurs.

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RADIO REPEATER SYSTEM | TRAINING GUIDE

c) System Regulator modules

The system regulator is a module that incorporates voltage regulators, an audio output stage, and a
means of metering various stages of the receivers and transmitters mounted in the same subrack.

One special feature of the voltage regulation stage is an anti-latchup hysteresis circuit. This is a switch
that turns off at a selected voltage and turns on at a different voltage. This feature is particularly useful
when the repeater is powered by solar cells. In a standard installation, if the solar array does not recharge
the battery fast enough (not enough sunlight), the repeater will discharge the battery completely and
the repeater will stop operating. When the solar cells get some illumination they will start to charge the
batteries and the repeater will come back to life for a short time, at least until the battery’s output voltage
falls below the repeater’s operating point. With the hysteresis switch, the repeater is disconnected from
the batteries when their voltage falls below approximately 8 volts, and it remains disconnected until
the solar array has had a chance to charge the battery up to some higher voltage, usually around 11
volts. This differential arrangement prevents the repeater from turning on and off the air by allowing the
power supply to receive a signifi cant charge before having to power the equipment. These hysteresis
voltages can be changed if different voltage levels are required for turn-on and turn-off. (eg. 10 volts
turn-off, 11.5 volts turn-on).

d) Control Cards

Each system may have an audio control card that routes audio, muting and COR-PTT signals, or
a serial data control card that routes LVDS serial data and analog / digital COR-PTT signals. Each
control card is set up for the specifi c confi guration of the repeater / base station. Setting up the control
card with the specifi c confi gurations allows the transmitter and receiver modules to be swapped out and
replaced with other receiver / transmitter modules for maintenance and troubleshooting procedures,
without affecting the operation of the system.

e) Equipment Isolation

An important feature to consider is equipment isolation. By this we mean the amount of coupling between
the transmitter and receiver other than through the antenna and associated duplexers / multicouplers.
The amount of coupling between receiver and transmitter is highly variable and often causes problems
which only show up after the installation is complete. The low-power repeaters are compact, and it is
possible to arrange 2 receivers, 2 transmitters, a system regulator and the required control cards side
by side in a 19 inch rack. This close physical spacing between the various components can create
problems and so close attention must be paid to unit shielding. Each of the components (receiver,
transmitter, system regulator, etc.) is mounted in an extruded aluminum enclosure which provides
a continuous Radio Frequency Interference (RFI) tight seal. All leads entering these enclosures are
fi ltered to prevent RFI from either entering or leaving on an unintended path. Double shielded co-axial
cable between receivers, transmitters and duplexers is often used to enhance the isolation. With careful
selection of a duplexer it is possible to operate a transmitter / receiver pair at a frequency spacing of
less than 400 kHz, although this is not recommended.

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