Fundamentals of Repeaters

8/8/2019 Fundamentals of Repeaters

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Fundamentals of Repeaters

Marc Tarplee, Ph.D. NCE

N4UFP


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What is a repeater?

A repeater is a device that performs 3 basic

functions:

It receives and demodulates an RF signal.

It regenerates the audio information.

It modulates and retransmits the audio on a new

RF carrier.


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Some History

Amateurs experimenting with VHF/UHF in the1930s discovered that propagation was generallylimited to line-of-sight.

The limited working range offset the advantages of

VHF gear for mobile/portable operation (smallantennas and light equipment)

In the 1950s, widespread availability of WWIIsurplus electronics led to the creation of the first

repeaters on the West Coast. The repeaters were AM and used frequencies on

the 2 meter band.

By the 1970s, standard offsets and FM wereintroduced.


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Basic Repeater Components


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Basic Repeater Block Diagram

DUPLEXER

RECEIVER

CARRIER

OPERATED

RELAY

TRANSMITTER

f1

f2

CARRIER

DETECT

PTT

AUDIO

ID TIMER

CW

ID

ID

XMIT


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Antenna

Repeater antennas are almost alwaysvertically polarized and have an

omnidirectional azimuth pattern. Generally the same antenna is used for

transmitting and receiving.

The antenna is mounted as high as possiblein order to have good line-of-sightcoverage.


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Duplexer Diagram


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Duplexer Operation

Received Signals


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Duplexer Operation

Transmitted Signals


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Receiver

A repeater receiver must have good sensitivity andexcellent selectivity, in order to have adequaterejection of the transmitted signal.

The receiver will have at least two outputs: Audio output

Carrier detect

The audio output can contain both audio signalsand out-of-band control tones.

A signal appears on the carrier detect line when anRF carrier breaks the receivers squelch. (arepeater use requests service)


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Carrier Operated Relay

The carrier operated relay turns on the

transmitter in response to:

a carrier detect signal

an ID transmit signal


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Transmitter

The transmitter should meet the following

criteria:

High spectral purity (to avoid unnecessaryreceiver interference)

Highest possible output power (for greatest

coverage)


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ID Timer

The ID timer performs basic ID

housekeeping tasks:

Generating appropriate IDs

Tracking time between ID transmissions


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Repeater Simulation


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Important Upgrades


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External Control

The control operator (repeater trustee or his

designee) needs to be able to control the operation

of the repeater transmitter, in the event of: Electrical malfunction

Inappropriate use of the repeater

To implement the external control function as well

as some other desirable features, the carrieroperated relay is generally replaced by a repeater

controller


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Repeater Controller

A repeater controller provides (at least) thefollowing capabilitiesTelephone line interface

Voice ID and announcement capabilityLinking

Transmitter controls

Special supervisory tones (courtesy beep, etc.)

DTMF decoding

CTCSS decoding


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Types of External Control

Via telephoneThe repeater operation is controlled through

DTMF tone groups sent through a phone line. Via RF link

The repeater controller is accessed via aseparate simplex RF link (above 222.15 MHz)

On-the-AirDTMF tones sent into the repeater are used to

control its operation.


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Autopatch

An autopatch is a connection between an amateurrepeater and the PSTN that permits a repeater user

to make a phone call from his/her radio, provided

that the radio has DTMF capability.

The call made through the autopatch is subject to

all the restrictions of an amateur transmission.

The popularity and utility of of autopatch has

declined significantly with the advent of cellphones.


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Reverse Autopatch

A reverse autopatch is a connection from thePSTN to an amateur station through a repeater.

The call is originated by the PSTN subscriber, not

the mobile amateur.

The originator of the call should be an amateur

the call will be carried on amateur frequencies

Once again, the restrictions on amateur

transmissions apply to these communications.


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Implementing Autopatch

All modern repeater controllers have an

autopatch capability. All that is required is a

connection between the phone line and thecontroller.

Cell phones may also be used to provide a

line for autopatch. If the line will also beused to control the repeater, an older AMPS

cell phone is necessary.


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CTCSS

CTCSS is the continuous tone coded

squelch system

A repeater using CTCSS will cannot beaccessed unless a user transmits a

subaudible tone with his audio information.


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CTCSS Tones

67.0 69.3 71.9 74.4

77.0 79.7 82.5 85.4

88.5 91.5 94.8 97.4

100 103.5 107.2 110.9

114.8 118.8 123.0 127.3

131.8 136.5 141.3 146.2

151.4 156.7 162.2 167.9

173.8 179.9 186.2 192.8

203.5 206.5 210.7 218.1

225.7 229.1 233.6 241.8

250.3 254.1


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K4YTZ Repeater (Leroy)

DUPLEXER

RECEIVER

REPEATER

CONTROLLER

TRANSMITTER

147.03 MHz

146.43 MHz

CARRIER

DETECT

PTT

AUDIO

+

CTCSS

AUDIO

Line

Amp

AMPS

CELL PHONE

CABINET

TEMP SENSOR

OUTDOOR

TEMP SENSOR


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Repeater Linking


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Repeater Linking

Repeaters may be linked to increase the

coverage available to the users.

Linking methods:

Internet ilink, etc.

Telephone line

VHF/UHF link between repeaters (remote baselinking)


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Internet Repeater Linking

This type of linking uses VoIP (Voice overInternet Protocol) to connect repeaters via the

Internet.

The repeater is connected to the Internet via a PCrunning software such as Ilink, Echolink,

IRLP/Speak Freely

The software provides A/D conversion and

compression for the audio and transceiver control. The repeater may be accessed from the Internet by

users who have VoIP capability


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Telephone Linking

Uses a dial-up link to connect two repeaters.

Primary repeaters controller makes an

autopatch call to the secondary repeater.

The secondary repeaters controller answers

the call and goes into reverse autopatch

mode.

This type of linking is full duplex


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Remote Base Linking

A separate RF link is installed between the primaryand secondary repeaters.

FCC rules require that this link operate above 222.15MHz

When the primary repeater is opened, its controllerroutes audio to the RF link transceiver and puts itinto transmit mode.

When the secondary repeaters RF link transceiverreceives a signal, this signal is sent to its controller,which retransmits the signal over the secondaryrepeater.

This type of linking is half-duplex (simplex)


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Remote Base Linking


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Useful DTMF Commands for the

K4YTZ RepeaterMacro Command / Message Macro Command / Message

* Patch Autodial 410 Morning Net

# Patch Down 411 Evening Net

026 Time (male voice) 420 Skywarn Net

027 Time (female voice) 425 Meeting Week

029 Date 426 Meeting Tonight

400 Repeater Off 427 Breakfast

401 Repeater On 430 Outside Temperature

406 Patch Disable 431 Rack Temperature


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Closing Comments

FM Repeater operation is often the first type a

new amateur attempts, and is the main mode

for many amateurs All repeater users should be polite, courteous

and helpful to newcomers/visitors

The K4YTZ repeater is a reflection onYCARS

Documents

Fundamentals of Repeaters