• noun a device in an aircraft for receiving and automatically transmitting radio signals so that an air traffic control station can identify the aircraft
  • A device or system which incorporates both a transmitter and a receiver, and which emits the appropriate signals automatically when the specified trigger signals are received. Used, for instance, in satellite communications, or in radars. Also called responder (1).
  • In a communications satellite, a unit which receives a signal from one location, processes and amplifies it, and retransmits it to other locations. A single satellite may have many transponders. Also called satellite transponder.
  • synonym transmitter-responder

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