| 摘要 |
An apparatus and method is provided wherein a television signal being transmitted may be modified by multiplexing in a digital information-bearing signal in a manner that binary pulses are encoded upon horizontal synchronizing pulse windows contained within the composite video signal. The apparatus comprises two primary subsystems, an encoder and a decoder. The encoder is further composed of four components (1) a horizontal synchronous pulse detector, (2) a pulse position modulator, (3) a digital signal conditioner, and (4) a mixer. The decoder consists of three components: (1) a horizontal synchronizing detector, (2) a pulse position demodulator, and (3) a digital signal conditioner. Functionally, the video/digital data multiplexer is a pulse position (PPM) digital communication system which utilizes the leading edge of the horizontal synchronizing pulses of a composite video signal as a marker denoting the location where a pulse will be inserted. Specifically, the video/data multiplexer inserts a 1-microsecond pulse into each valid horizontal synchronizing pulse window. The position of the 1-microsecond pulse in either one of two locations within the horizontal synchronizing pulse window is then determined by the input binary signal from the digital signal conditioner. Consequently the video signal becomes a carrier for binary (digital) information bearing signals.
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