A low cost system for encoding and decoding the picture and sound signals on CATV channels is described. A simple encoder is connected to the modulator for each encoded channel and an all-channel set top decoder can decode all channels--standard and non-standard. No modifications to the cable system are required.
The heart of the system is the patented "gray blank" method of encoding video by replacing the synchronizing and blanking components of the composite video signal with a steady voltage midway between black and white. The color reference burst is superimposed on the steady voltage. Proper synchronization on a normal television receiver is lost because the receiver attempts to lock on the blackest portions of the video signal. The sound is encoded by positioning the FM sound carrier 1 MHz below the video carrier. Pulse signals that are used to restore the video to normal are amplitude modulated on the repositioned sound carrier. Decoding is accomplished without demodulating the video or audio.