Digitally-controlled analog encrypton
US4389671A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Sep 29, 1980 |
| Grant date | Jun 21, 1983 |
| Priority date | — |
| Expiry date | Sep 29, 2000 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04N7/1675
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
An apparatus for scrambling a television signal in which horizontal lines of the transmitted television picture are selectively inverted in accordance with the state of a pseudorandom noise generator. In order to permit correction of the throughput gain as well as the throughput offset at the receiving end of the communication link so as to obtain a desired level of picture quality, particularly in a satellite communication system, an analog calibration signal representing both black and white levels is inserted into a horizontal line of the vertical retrace interval at the transmission end of the link. This calibration signal is then detected at the receiving end of the link and the signal levels are adjusted as needed. In addition, a randomly-varying key code signal for resetting the pseudorandom noise generator is randomly inserted into another horizontal line of the vertical retrace period to control scrambling. The audio portion of the television signal is also scrambled by randomly shifting the audio carrier between first and second offset frequencies.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.