The quality of pictures sold to cable subscribers is of paramount importance. However, methods commonly used in cable to provide conditional access may worsen picture distortions caused by the cable plant. One such distortion, which we will refer to as scratch noise, is a result of an interaction between sync suppression scrambling and the automatic gain control of the television receiver.
This paper describes an innovative circuit design (patent application filed) to eliminate scratch noise. This circuit design produces a trade-off due to the effects of plant power supply hum on the cable signals. The paper concludes by presenting and evaluating one possible approach for dealing with hum.