Satellites orbiting the earth are used to receive and retransmit signals for
telephone, television, radio, and data communication. The basic relay device in
satellites, the transponder, has seen tremendous increases in efficiency thanks to
advances in compression technology. A communications satellite system comprises the
satellites and the ground stations for transmitting and receiving the signals. Direct
broadcasting satellites, which are geostationary, transmit radio and TV services that
consumers can receive through a cable redistribution network or a personal domestic disc
antenna. Recently a digital satellite radio system was inaugurated using satellites over
Africa, the Middle East, Asia, and Latin America. Signals from these
satellites—including distance education programs that are planned—will be able
to be received directly on special portable radio receivers.
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