A repeater is a combination of a receiver and a transmitter that receives a signal and retransmits it, so that signals can cover longer distances. A repeater sited at a high elevation can allow two stations, otherwise out of line-of-sight propagation range of each other, to communicate. In addition to amateur radio, repeaters are used in commercial and government mobile radio systems.

The repeater receives on one radio frequency (the "input" frequency), demodulates the signal, and simultaneously re-transmits the information on its "output" frequency. (When a single frequency is given for a repeater, it is the output frequency.) All stations using the repeater transmit on the repeater's input frequency and receive on its output frequency. Since the repeater is usually located at an elevation higher than the other radios using it, their range is greatly extended.

Because the repeater both transmits and receives the same time, isolation must exist to keep the repeater's transmitter from degrading its own receiver. If the repeater's transmitter and receiver are not isolated well, the transmitter will "desensitize" the receiver, causing the repeater to interfere with itself. The problem is similar to being at a rock concert and not being able to hear the weak signal of a conversation over the much stronger signal of the band. Typically, repeaters use sets of filters (called duplexers) to avoid this. Stations using the repeater do not need these expensive filters because they do not transmit and receive simultaneously.

Amateur repeaters in the 2 meter band, the most commonly used VHF band, usually use a 600 kHz (0.6 MHz) separation. In the 1.25-meter band (another VHF band, rarely used), a 1.6 MHz separation is used. In the 70 cm band, the most widely used UHF band, a 5 MHz separation is most common, and in the 902–928 MHz band, another UHF band, a 25 MHz separation is used.


PBARC Repeaters

Other Repeaters

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