Ghost Reduction System for Television Receivers

Ghost images on television pictures are a common problem near tall buildings. Many investigators have studied this problem and succeeded in developing some ghost reduction systems. But due to the complexity of the ghost mechanism, there are no systems which cancel ghost images completely. There are two methods for ghost reduction at the receiver. The first is an antenna method, the second is a signal delay method. Directional antennas which have very narrow half power angles,---few tens of degrees,---or diversity antenna systems which have more than two antennas were app ied to several ghost reduction systems. (1) This method is simple and useful in many places but cannot cancel ghost signals which come from the same directions as the desired signals, still more, the antennas become large for good performance. For this reason the antenna method cannot be a perfect ghost reduction system. On the other hand, the signal delay method can cancel any ghost signal with several delay devices in a television receiver. But, because no long continuous delay devices were available this method has not been developed. There are two problems to be solved in the signal delay method. First is to develop the continuous variable delay devices. Second is to control the RF phase difference between the ghost and desired signals.(2)