Title: Method and apparatus for scrambling and unscrambling communication signals

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 or non-inversion in a preselected sequence, as determined by synchronized logic at the receivers and the transmitting site.

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Inventors: Hartung, Albert F. (Woodland Hills, CA, US)
Lehan, Frank W. (Santa Barbara, CA, US)
Barooshian, Charles T. (Pacific Palisades, CA, US)
Zacharski, Edward J. (Malibu, CA, US)

Application Number: 609577
Filing Date: 1975-09-02
Publication_date: 1977-05-17
Assignee: System Development Corporation (Santa Monica, CA)
Primary Class(es): 380/235 380/226, 380/262
Other Classes:
US Patent Ref:

3081377	Mar, 1963	Watters	178/5.
3440338	Apr, 1969	Walker	178/5.
3527877	Sep, 1970	Walker	178/5.
3777053	Dec, 1973	Wittig et al.	178/5.
3789131	Jan, 1974	Harney	178/5.
3801732	Apr, 1974	Reeves	178/5.
3824332	Jul, 1974	Horowitz	178/5.
3885089	May, 1975	Callais et al.	178/5.

Other Refs:
Primary Examiner: Wilbur, Maynard R.
Assistant Examiner: Buczinski, S. C.
Attorney: Fulwider, Patton, Rieber, Lee & Utecht