Method and apparatus for scrambling and unscrambling communicati

Details Method and apparatus for scrambling and unscrambling communicati Method and apparatus for scrambling and unscrambling communicati

1975-09-02

1977-08-30

Buczinski, S. C.

Facsimile and static presentation processing

Facsimile

Specific signal processing circuitry

358120, 358121, H04N 144

Patent

active

040458148

ABSTRACT:
Method and apparatus for scrambling and unscrambling television video and audio signals in a subscription television system in which program selections of subscribers are known at a central transmitting site, and control signals encoded into vertical blanking intervals of the video signals are addressed to receivers authorized to receive unscrambled transmissions, to selectively control unscrambling at those receivers. In an unscrambler at each subscriber's receiver, the control signals are decoded, and, if addressed to the particular subscriber's receiver, operate to enable or disable the unscrambler, or to frequently vary its mode of operation, thereby greatly increasing the security of the system and deterring viewing of scrambled transmissions. Video scrambling and unscrambling are effected by inversion of selected horizontal lines of a transmitted television picture, and a technique is disclosed for inversion of alternate groups of equal numbers of line.

REFERENCES:
patent: 3081377 (1963-03-01), Watters
patent: 3440338 (1969-04-01), Walker
patent: 3527877 (1970-09-01), Walker
patent: 3777053 (1973-12-01), Wittig et al.
patent: 3789131 (1974-01-01), Harney
patent: 3801732 (1974-04-01), Reeves
patent: 3824332 (1974-07-01), Horowitz
patent: 3885089 (1975-05-01), Callais et al.

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