The functions of an earthstation and the electronics that accomplish those functions may be conveniently grouped under three major tasks:
• Contacting the satellite using the assigned frequencies in the radio-frequency band;
• Signal processing, which may operate at one or more intermediate frequencies;
• Interfacing with the sources and destinations of the signals at whatever baseband or broadband frequencies are inherent to the nature of the communication.
A small, single-purpose terminal will have a lot less complexity than a hub or gateway station. (Hubs are earthstations that serve to control and route traffic in networks.) Small, usually single-purpose earthstations and large gateway stations operate quite differently because of the different quantity of information they handle in the signal. In a small station, the electronics are simpler and usually less demanding in terms of noise and signal processing. Gateway stations, because they handle perhaps hundreds of thousands of signals of various types simultaneously, are more complex and need higher-quality equipment.
In this chapter, we will examine how signals flow into, through, and out of some typical earthstations. We will see how some of the electronics are used to accomplish these tasks, and we will elucidate the important ways that the electronics work together with the dish gain to allow links with the satellite.
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