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Chapter 15:
Earth Stations: Types, Hardware, and Pointing
Abstract
Earthstations are the mundane side of satellite communication. In the old days, they were typically huge, expensive, remote dishes that served as gateway points between the satellite systems and the public-switched telephone network, the PSTN. In the dawning days of satellite communication, they were so expensive that it was thought that each country would probably have only one or two (remarkably paralleling the predictions a century and a quarter ago that each city might have only one telephone!). The very first commercial communications satellite, Telstar, was not in geostationary orbit. Thus, the huge antennas had to track the satellite accurately from horizon to horizon in less than half an hour to maintain communications through it. Requiring a dish to track a satellite greatly raises the cost of the dish. The faster the satellite moves across the sky and the more accurately the dish must track it, the more expensive the dish. Thus, the industry migrated to geostationary satellites a few years after Telstar to make the dishes cheaper and simpler. This brings up what might be called the fundamental economic law of satellite telecommunications: Every dollar a satellite costs gets divided by the (potential) number of users on the ground, while every dollar a terminal costs gets multiplied by the number of users. This leads to designing more expensive satellites and less expensive terminals, a trend that has continued for more than three decades.
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CHAPTER 15
19 PAGES


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