Fundamentals of Repeaters by mercy2beans113

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									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
    RF carrier.
              Some History…
• 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
                f1                             CARRIER
                       RECEIVER                DETECT


                                  ID        CARRIER
     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
  resonant cavities.
   – 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
Duplexer Diagram
Duplexer Operation
 Received Signals
Duplexer Operation
Transmitted Signals
• 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
    receiver interference)
  – Highest possible output power (for greatest
               ID Timer
• The ID timer performs basic ID
  housekeeping tasks:
  – Generating appropriate ID’s
  – Tracking time between ID transmissions
Repeater Simulation
Important Upgrades
               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 carrier
  operated relay is generally replaced by a repeater
           Repeater Controller
• A repeater controller provides (at least) the
  following capabilities
  –   Telephone line interface
  –   Voice ID and announcement capability
  –   Linking
  –   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)
• On-the-Air
  – 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
           Reverse Autopatch
• 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.
      Implementing Autopatch
• 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
  squelch system”
• A repeater using CTCSS will cannot be
  accessed unless a user transmits a
  subaudible tone with his audio information.
        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
K4YTZ Repeater (Leroy)
       147.03 MHz                    DETECT

                       TEMP SENSOR


                      TEMP SENSOR     AUDIO

        146.43 MHz

                                              CELL PHONE
Repeater Linking
           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 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,
  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
          Telephone Linking
• 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
  222.15 MHz
• 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
  secondary repeater.
• 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
           K4YTZ Repeater
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
          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 on

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