- 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 radio or radar device that responds to a certain received signal by emitting a radio signal itself.
- 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.
- noun a receiving and transmitting device in a communication or broadcast satellite that relays the signals it receives back to earth
- noun a channel system on a satellite that allows it to send and receive many different signals simultaneously