Image Number 7 for United States Patent #6009172.
A technique for improving the scrambling concealment of a video signal and the like when displayed on a television set or monitor, includes the pulse width and/or pulse position modulation of a horizontal sync pulse in a horizontal blanking interval by time shifting the leading edge of the sync pulse while maintaining the trailing edge thereof stationary, by shifting the leading and/or trailing edge of the pulse, or by position modulating a sync pulse of specialized width. In modifications to the pulse width and pulse position modulation overlay techniques, the negative edge of the end of video lines may be modulated in the same way that the leading edge of the sync pulse is modulated, with the two edges locked together or modulated independently. Thus, the amount of position modulation of the horizontal sync pulse or its edge(s) is maximized so that the pertinent circuits of all television sets will always detect, and thus lock onto, the modulated or wobbling pulse width or pulse position modulated sync pulse. The embodiment in which the negative edges of the ends of video lines are modulated along with the sync pulses, insures that all television sets will lock onto a wobbling edge. This insures the concealment of the video signal, or equivalent signal, in all possible situations and for all types of television sets or monitors. An associated technique also is disclosed for descrambling the scrambled video signal when authorized.