Fundamentals of Repeaters
Marc Tarplee, Ph.D. NCE
What is a repeater?
• A repeater is a device that performs 3 basic
– It receives and demodulates an RF signal.
– It regenerates the audio information.
– It modulates and retransmits the audio on a new
• Amateurs experimenting with VHF/UHF in the
1930’s discovered that propagation was generally
limited to line-of-sight.
• The limited working range offset the advantages of
VHF gear for mobile/portable operation (small
antennas and light equipment)
• In the 1950’s, widespread availability of WWII
surplus 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 1970’s, standard offsets and FM were
Basic Repeater Components
Basic Repeater Block Diagram
DUPLEXER ID TIMER OPERATED
• Repeater antennas are almost always
vertically polarized and have an
omnidirectional azimuth pattern.
• Generally the same antenna is used for
transmitting and receiving.
• The antenna is mounted as high as possible
in order to have good line-of-sight
• A duplexer is a special type of filter that allows a
single antenna to transmit and receive
simultaneously on two closely spaced frequencies.
• A typical duplexer consists of two pairs of
– Two pass the transmit signal from the transmitter to the
antenna while rejecting the received power.
– The other two pass the receive signal from the antenna
to the receiver while rejecting transmitted power.
• Typical rejection is better than 70 dB, while
attenuating the desired signal less than 2 dB
• A repeater receiver must have good sensitivity and
excellent selectivity, in order to have adequate
rejection of the transmitted signal.
• The receiver will have at least two outputs:
– Audio output
– Carrier detect
• The audio output can contain both audio signals
and out-of-band control tones.
• A signal appears on the carrier detect line when an
RF carrier breaks the receiver’s squelch. (a
repeater use requests service)
Carrier Operated Relay
• The carrier operated relay turns on the
transmitter in response to:
– a carrier detect signal
– an ID transmit signal
• The transmitter should meet the following
– High spectral purity (to avoid unnecessary
– Highest possible output power (for greatest
• The ID timer performs basic ID
– Generating appropriate ID’s
– Tracking time between ID transmissions
• 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 carrier
operated relay is generally replaced by a repeater
• A repeater controller provides (at least) the
– Telephone line interface
– Voice ID and announcement capability
– Transmitter controls
– Special supervisory tones (courtesy beep, etc.)
– DTMF decoding
– CTCSS decoding
Types of External Control
• Via telephone
– The repeater operation is controlled through
DTMF tone groups sent through a phone line.
• Via RF link
– The repeater controller is accessed via a
separate simplex RF link (above 222.15 MHz)
– DTMF tones sent into the repeater are used to
control its operation.
• An autopatch is a connection between an amateur
repeater 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 cell
• A reverse autopatch is a connection from the
PSTN 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.
• All modern repeater controllers have an
autopatch capability. All that is required is a
connection between the phone line and the
• Cell phones may also be used to provide a
line for autopatch. If the line will also be
used to control the repeater, an older AMPS
cell phone is necessary.
• CTCSS is the “continuous tone coded
• A repeater using CTCSS will cannot be
accessed unless a user transmits a
subaudible tone with his audio information.
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
K4YTZ Repeater (Leroy)
147.03 MHz DETECT
TEMP SENSOR AUDIO
• 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 base
Internet Repeater Linking
• This type of linking uses VoIP (Voice over
Internet Protocol) to connect repeaters via the
• The repeater is connected to the Internet via a PC
running software such as Ilink, Echolink,
• 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
• Uses a dial-up link to connect two repeaters.
• Primary repeater’s controller makes an
autopatch call to the secondary repeater.
• The secondary repeater’s controller answers
the call and goes into reverse autopatch
• This type of linking is full duplex
Remote Base Linking
• A separate RF link is installed between the
primary and secondary repeaters.
• FCC rules require that this link operate above
• When the primary repeater is opened, its controller
routes audio to the RF link transceiver and puts it
into transmit mode.
• When the secondary repeater’s RF link transceiver
receives a signal, this signal is sent to its
controller, which retransmits the signal over the
• This type of linking is half-duplex (simplex)
Remote Base Linking
Some Notes on Repeater
• All transmission over a repeater should be in
accordance with FCC Rules.
• Amateurs have no “right” to operate on a repeater.
The repeater or his/her designee grants operating
privileges to amateurs.
• Wait for the courtesy tone!!!!
• The repeater should not be tied up by long
conversations – use a simplex frequency for a long
Useful DTMF Commands for the
Macro Command / Message Macro Command / Message
*<autodial> 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
• 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 on