Method and apparatus for scrambling and unscrambling communication signals
US4024576A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Sep 2, 1975 |
| Grant date | May 17, 1977 |
| Priority date | — |
| Expiry date | Sep 2, 1995 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04N2007/1739
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
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.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.