Introduction to Repeaters Ron Milione, Ph.D. CETma W2TAP w2tap@arrl.org ron.p.milione.ctr@us.army.mil

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.

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 introduced.

Basic Repeater Components

Basic Repeater Block Diagram

Antenna 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 coverage.

Duplexer 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

Receiver 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

Transmitter The transmitter should meet the following criteria: High spectral purity (to avoid unnecessary receiver interference) Highest possible output power (for greatest coverage)

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 controller

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.

Autopatch 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 phones.

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 controller. 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 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

W2VL Repeater Block Diagram

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 linking)

Internet Repeater Linking This type of linking uses VoIP (Voice over Internet Protocol) to connect repeaters via the Internet. 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 mode. 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 Operation 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 QSO.

Useful DTMF Commands for the a Repeater as an example 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 W2VL repeater is flagship repeater of LIMARC 146.850- W2VL 1288.00- 147.375+ W2KPQ 224.820- 449.125- W2KPQ PL for all is 136.5