Page 270 - Satellite Communications, Fourth Edition

250 Chapter Eight

Figure 8.7 Standard-A (C-band 6/4 GHz) 32-m antenna.
(Courtesy of TIW Systems, Inc., Sunnydale, CA.)
2
heaters provide reflector surface heat of 40W/ft for the main reflectors
and subreflectors, and 3000 W for the azimuth wheels.
Although these antennas are used with geostationary satellites, some
drift in the satellite position does occur, as shown in Chap. 3. This, com-
bined with the very narrow beams of the larger earth station antennas,
means that some provision must be made for a limited degree of track-
ing. Step adjustments in azimuth and elevation may be made, under
computer control, to maximize the received signal.
The continuity of the primary power supply is another important con-
sideration in the design of transmit-receive earth stations. Apart from the
smallest stations, power backup in the form of multiple feeds from the
commercial power source and/or batteries and generators is provided. If
the commercial power fails, batteries immediately take over with no inter-
ruption. At the same time, the standby generators start up, and once
they are up to speed they automatically take over from the batteries.

8.6 Problems and Exercises
8.1. Explain what is meant by DBS service. How does this differ from the
home reception of satellite TV signals in the C band?