Method and apparatus for modulating a separated television horizontal sync pulse as a subcarrier of audio information

A closed circuit television communication system for the transmission and reception of video signals over wires in which separated horizontal sync pulses of an original video signal are pulse width modulated by an audio signal, enabling the video signal to carry additional information which can be recovered on reception comprising:

• an original video signal containing horizontal sync pulses,
• means for separating said horizontal sync pulses from said original video signal,
• means for forming pulse width modulated pulses which vary with an audio input signal,
• said means for forming said pulse width modulated pulses includes means for producing stretched pulses which have a longer duration than said horizontal sync pulses of said original video signal, said stretched pulses being used to generate a linearly varying voltage with respect to time over a period of time determined by said stretched pulses,
• means for replacing said horizontal sync pulses of said original video signal with said pulse width modulated pulses while preserving the original video signal levels surrounding said pulse width modulated pulses thereby providing a reconstituted video signal,
• means for transmitting said reconstituted video signal over wire,
• reception means coupled to said wire for receiving said reconstituted video signal,
• sync separating means for separating said pulse width modulated pulses from said reconstituted video signal,
• means for demodulating said pulse width modulated signals to produce an audio signal output.