Communication Payload & Supporting Subsystems:
The physical principle of establishing communication connections between remote communication devices dates back to the late 1800s when scientists were beginning to understand electromagnetism and discovered that electromagnetic (EM) radiation (also called EM waves ) generated by one device can be detected by another located at some distance away.
By controlling certain aspect s of the radiation (through a process called modulation , explained in Section 4.4), useful information can be embedded in the EM waves and transmitted from one device to another.
The second major module is the communication payload, which is made up of transponders. A transponder is capable of :
Receiving uplinked radio signals from earth satellite transmission stations (antennas).
Amplifying received radio signals
Sorting the input signals and directing the output signals through input/output signal multiplexers to the proper downlink antennas for retransmission to earth satellite receiving stations (antennas).