Method and apparatus for scrambling and unscrambling communication signals

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