Apparatus for scrambling and descrambling communication signals
US4639777A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Dec 13, 1984 |
| Grant date | Jan 27, 1987 |
| Priority date | — |
| Expiry date | Dec 13, 2004 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04N7/1675
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
Of the scrambling systems used in CATV and direct satellite broadcasting systems, the invention pertains to the transmission of a keying signal for demodulation. The keying signal, as a carrier wave displaced 90.degree. in phase from a picture carrier wave, is superimposed on the conventional sync signal suppression period with no sound carrier wave being processed, thereby avoiding the generation of buzzing noise which would occur when the keying signal is superimposed on the sound carrier wave. With this invention, not only can the generation of buzzing noises be eliminated, but also even in multiplex sound systems the sound signal can be transmitted without the sound quality being adversely affected. Also, no synchronizing signal can readily and easily be detected and, therefore, subscription TV programs can not be viewed by unauthorized persons.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.