Those components of the satellite installed expressly to accept, route, amplify, and translate the frequency assignment to/from the satellite. There are 24 transponders on a satellite.
A device aboard an aircraft for transmitting data to an air traffic control radar system. Each time the transponder is queried by the radar, it responds with a numeric code and the aircraft's altitude. The code may be selected by the pilot. In radio terminology, the transponder is referred to as "Squawk". For example, a controller may tell a pilot to "squawk 0347". That means that the pilot is to set the code to 0347 and turn on the transponder.
the portion of a satellite which transmits and receives radio signals in a prescribed frequency range, from ground stations or other satellites (transmitter/responder).