A payload is the part of the satellite that performs the purpose it was put in space for. There are many different types of satellite but communications satellites are the kind we are interested in here. The payloads on communications satellites are effectively just repeaters. They receive the signals that are transmitted to them and then retransmit them at a different frequency back to earth.

Modern satellites do more than this. They receive the signals and then demodulate them to access the data, the data can then be processed before being modulated and retransmitted. The data can be stored for later retransmission or modulated using a different method, even at a different data rate.

The accompanying picture shows an anatomy of a typical satellite. You can see the uplink receiver chain and the downlink transmit chain. The central area shown as 'Processing', is where the frequency is translated or any demodulation, processing and modulation would take place.

Related Pages : Anatomy of a Satcom Terminal, Satellite Broadcast Simulator