Method of providing sound privacy system compatible with mono and btsc stereo audio
US4956862A · kind A · utility
9Cited by
9References
16Claims
0Family size
Assignee
Inventors
Key dates
| Filing date | Feb 2, 1989 |
| Grant date | Sep 11, 1990 |
| Priority date | — |
| Expiry date | Feb 2, 2009 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04N7/167
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
In order to provide secure access to the audio portion of a television signal, the audio portion of a TV signal is modulated at a frequency that is offset from the standard carrier frequency. In the embodiment disclosed herein, the audio portion of the TV signal is modulated with a nonstandard 4.75 Mhz carrier that is offset from the standard 4.5 Mhz carrier. In order that a standard TV receiver cannot receive the offset audio signal, the TV signal further contains an unmodulated carrier signal at 4.5 Mhz to "blank" unauthorized reception.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.