LEARNING EVENT 8: SATELLITE COMMUNICATIONS SYSTEM CONCEPT
A communications satellite has been described as a "microwave radio repeater in the sky." This implies that the
satellite is a link in an existing communications system. A block diagram of an integrated communications
system including a satellite link is shown in Figure 1-1. Inclusion of a communications satellite as part of the
microwave radio link overcomes many of the obstacles experienced by long-distance HF radio communications.
Figure 1-1. An integrated satellite communications system.
1. Integrated satellite communications system. Figure 1-1 is a simplified diagram showing only one subsystem
of each type normally found in an integrated communications system. In practice, many subsystems of each
type may be used, as well as different combinations of equipment in the various subsystems. The system shown
in the diagram is designed to pass information in the form of teletypewriter, telephone, and facsimile traffic.
Frequency division multiplexing (FDM) subsystems are normally selected for this application so as to make
maximum use of the bandwidth available in each voice channel. This follows from the fact that analog signals,
varying in either frequency or amplitude, occupy far less bandwidth than digital signals for comparable amounts
of conveyed information.
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