Polarotor Control

0I The polarization of satellite TV signals is defined as horizontal (H) or vertical (V) with respect to the equator below the subsatellite point, and not, as is often wrongly assumed, with respect to the horizon on earth. Depending on the lo- cation of the receiving system on earth and the satellite"s geosynchronous pos- ition, a horizontally polarized signal may have some offset with respect to the horizon. As a rule of thumb, the lower the dish elevation for a particular satel- lite, the greater this polarization offset angle. The difference between horizon- tal and vertical is, however, always 90°. Most commercially available polariza- tion rotation units (polarotors) used for selecting between horizontally and ver- tically polarized transponders on board a TV satellite incorporate a small servo motor whose direction of travel is con- trolled automatically by the channel selection circuitry in the indoor unit, or simply by a switch. The servo motor rotates an angled probe fit...