TABLE OF CONTENTS The earth segment of a satellite communications system consists of the transmit and receive earth stations. The simplest of these are the home TV receive-only (TVRO) systems, and the most complex are the terminal stations used for international communications networks. Also included in the earth segment are those stations which are on ships at sea, and commercial and military land and aeronautical mobile stations.
As mentioned in Chap. 7, earth stations that are used for logistic support of satellites, such as providing the telemetry, tracking, and command (TT&C) functions, are considered as part of the space segment.
Planned broadcasting directly to home TV receivers takes place in the Ku (12-GHz) band. This service is known as direct broadcast satellite (DBS) service. There is some variation in the frequency bands assigned to different geographic regions. In the Americas, for example, the downlink band is 12.2 to 12.7 GHz, as described in Sec. 1.4.
The comparatively large satellite receiving dishes [ranging in diameter from about 1.83 m (6 ft) to about 3-m (10 ft) in some locations], which may be seen in some backyards are used to receive downlink TV signals at C band (4 GHz). Originally such downlink signals were never intended for home reception but for network relay to commercial TV outlets (VHF and UHF TV broadcast stations and cable TV head-end studios). Equipment is now marketed for home reception of C-band signals, and some manufacturers provide dual C-band/Ku-band equipment.
