Sound masking in phase reversal TV scrambling system
US4802213A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Feb 26, 1987 |
| Grant date | Jan 31, 1989 |
| Priority date | — |
| Expiry date | Feb 26, 2007 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04N7/167
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
A TV scrambling system includes means for scrambling a TV signal by phase reversing the carrier at a horizontal rate. A sound masking circuit includes a phase locked loop which operates at five times the horizontal frequency. The program sound signal is used to frequency modulate the VCO in the phase locked loop and the output is added to the regular program sound for modulation onto an RF carrier to create an interfering sound signal. Detection of the program sound signal in an unauthorized receiver is accompanied by beating between the 5 H harmonic of the phase reversal frequency and the interfering sound signal, which masks the program sound.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.