In
telecommunication, a
transponder is one of two types of devices. In
air navigation or
radio frequency identification, a
flight transponder is a device that emits an identifying signal in response to an interrogating received signal. In a communications satellite, a
transponder gathers signals over a range of uplink frequencies and re-transmits them on a different set of downlink frequencies to receivers on Earth, often without changing the content of the received signal or signals.