Amateur radio repeater

An amateur radio repeater is an electronic device that receives a weak or low-level amateur radiosignal and retransmits it at a higher level or higher power, so that the signal can cover longer distances without degradation. Many repeaters are located on hilltops or on tall buildings as the higher location increases their coverage area, sometimes referred to as the radio horizon, or "footprint". Amateur radio repeaters are similar in concept to those in use by public safety (police, fire, etc.), business, government, military, and more. Amateur radio repeaters may even use commercially-packaged repeater systems tuned into an amateur radio frequency allocation, but more usually amateur repeaters are assembled from various sources for receivers, transmitters, controllers, power supplies, antennas, and other components.

In amateur radio, repeaters are typically maintained by individual hobbyists or local groups of amateur radio operators. Many repeaters are provided openly to other amateur radio operators and typically not used as a remote base station by a single user or group. In some areas multiple repeaters are linked together to form a wide-coverage network, such as the linked system provided by the Independent Repeater Association^[1] which covers most of western Michigan, or the Western Intertie Network System ("WINsystem") that now covers a great deal of California, and is in 17 other states, including Hawaii, along with parts of four other countries, Australia, Canada, Great Britain and Japan.

Simplex repeater

A type of system known as a simplex repeater uses a single transceiver and a short-duration voice recorder, which records whatever the receiver picks up for a set length of time (usually 30 seconds or less), then plays back the recording over the transmitter on the same frequency. A common name for them is a "parrot" repeater.

Same-band repeater

Standard repeaters require either the use of two antennas (one each for transmitter and receiver) or a duplexer to isolate the transmit and receive signals over a single antenna. The duplexer is a device which prevents the repeater's high power transmitter (on the output frequency) from drowning out the users' signal on the repeater receiver (on the input frequency). A diplexer allows two transmitters on different frequencies to use one antenna, and is common in installations where one repeater on 2m and a second on 440MHz share one feedline up the tower and one antenna.

Most repeaters are remotely controlled through the use of audio tones on a control channel.

Repeaters can be setup as a "Link System" where transmitting on one repeater simultaneously transmits on all repeaters in the system. These systems are used for area or regional communications, for example in Skywarn.

Cross-band repeater

A cross-band repeater (also sometimes called a replexer), is a repeater that retransmits a specific mode on a frequency in one band to a specific mode on a frequency in a different band. This technique allows for smaller size and less complexity of the repeater system. Repeating signals across widely separated bands allows for simple filters to be used to allow one antenna to be used for both transmit and receive at the same time, avoiding the use of complex duplexers to achieve the required rejection for same band repeating. This type of system is used in the OSCAR repeaters.^[7]

Contrast with a transponder, which retransmits a range of modes and frequencies from one band to another.

Most dual-band amateur transceivers are capable of cross-band repeat..