A transponder is a device for receiving and rebroadcasting a signal. Transponder on a television satellite receives a television signal beamed from large satellite uplink stations on the ground, then processes, encodes, amplifies and rebroadcasts the signal over a large area of the Earth's surface. Usually, TV signal is amplified by the transponder, and can be encoded or modified in other ways. The signal is encoded to ensure that only paying subscribers are able to access the signal.