Satellite communications

The term “satellite transponder” refers collectively to a transmitter-receiver subsystem on board the satellite that processes, amplifies and retransmits a range of frequencies (the transponder bandwidth) to another location/terminal/antenna on the earth .

The bandwidth allocated for C band service is 500 MHz , and this is divided into sub bands, one for each transponder. A typical transponder bandwidth is 36 MHz, and allowing for a 4-MHz guard band between transponders, 12 such transponders can be accommodated in the 500-MHz bandwidth.

In a transponder the transmit carrier frequency is derived from the received signal . The frequency linkage allows an interrogating ground station to recover the Doppler shift and thus infer range and speed from a communication signal without allocating power to a separate ranging signal.