receiving and transmitting radio device installed at intermediate points in radio communications links, designed to amplify received signals and then retransmit them farther along the link. The intermediate point may be mobile, as a communications satellite, or stationary, as a relay tower. An active repeater consists of an antenna or several antennas, a radio receiver, a radio transmitter, equipment for remote control of repeater operation, and a power supply. The active repeater usually uses solid-state devices; vacuum tubes are used less frequently. The output stages of the radio transmitter usually incorporate traveling-wave tubes.
In contrast to a passive repeater, an active repeater is capable of providing service only to a limited number of links in a communications network. In order to eliminate mutual interference during simultaneous reception and transmission of radio signals, active repeaters use frequency-division, time-division, and coded squelch. Mutual interference is also eliminated by maintaining the signal level within predetermined limits and by protecting the transmitter against overloads (the total power of all transmitted signals must not exceed the permissible loading of the transmitter). Active repeaters often have standby equipment that can be switched in automatically.