Radio Repeater

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A Radio Repeater is a combination of a radio receiver and a radio transmitter that receives a weak or low-level signal and retransmits it at a higher level or higher power, so that the signal can cover longer distances without degradation.

In dispatching, amateur radio, and emergency services communications, repeaters are used extensively to relay radio signals across a wider area. With most emergency (and some other) dispatching systems, the repeater is synonymous with the base station, which performs both functions. This includes police, fire brigade, ambulance, taxicab, tow truck, and other services. The civilian GMRS service in the United States and UHF CB service in Australia also use repeaters in much the same fashion as amateur radio operators do; however, the Canadian GMRS service is an expansion of the Family Radio Service and is designed to operate simplex-only.

A duplex repeater uses two radio frequencies; an "Input" frequency, which it monitors for signals, and an "Output" frequency, on which it retransmits the received signals at a higher power or higher altitude.

Normally, the input and output frequencies are quite close (for example, 600 KHz apart in VHF and 5MHz in UHF). This requires the use of special hardware called a duplexer so that the transmitter portion (output) of the repeater does not overwhelm the receiver portion (input) with too much power. However, a new method of repeating called cross-band is gaining popularity because it eliminates the need for expensive and bulky duplexers. By using a frequency in one band (such as UHF) for the input and another band (such as VHF) for the output, the two frequencies are very different so the transmitter is much less apt to interfere with the receiver.

Cross-band repeating is becoming a popular feature in newer mobile (mounted in an automobile) radios, because it allows a nearby user with a low-power handheld radio to relay transmissions via the more powerful mobile transmitter sometimes called a replexer -- thus increasing effective communications range dramatically.

Radio repeaters are typically placed in locations which maximize their effectiveness for their intended purpose:
-"Low-level" repeaters are used for local communications, and are placed at low altitude to reduce interference with other users of the same radio frequencies. Low-level systems are used for areas as large as an entire city, or as small as a single building.
-"High-level" repeaters are placed on tall towers or mountaintops to maximize their area of coverage. With these systems, users with low-powered radios (such as hand-held "walkie-talkies") can communicate with each other over many miles.

Radio Repeater

See also