hoffmann%marie@mc.lcs.mit.edu (Ron M. Hoffmann) (01/08/86)
The use of circular polarization is television broadcasting has been, as far as I know, restricted to certain subscription stations operating in the UHF band. By transmitting with, for example, right-hand circular-polarization and equipping the receivers with a similar antenna, they can effect considerable attenuation of odd-number reflection ghosts, since these would have opposite polarization sense. And actually, it is really just the first reflection that is a problem, second, third... bounces are usually too far attenuated to create a visible problem. Actually, the visual aspect of the problem is only secondary to the technical problem of decoding suppressed- synch type scrambled transmissions. Multipath makes decoding a stable image more difficult. Now, in the case of broadcast FM stations, some proportion of the carrier is transmitted in both the horizontal and vertical planes. This is mostly as a concession to mobile receivers that commonly posses vertical whip antennas.