satellite communication

Transponders

A transponder is a type of communication device that can either send or receive signals (or both). With a special transponder in your car, you can drive slowly through a tollbooth while your toll is electronically collected. The term transponder is a portmanteau or a combination of two words into one in this case, it comes from transmit and respond. Airplanes have transponders that communicate with radar used by air traffic controllers on the ground, and race cars have transponders that help them time their laps accurately