Sound masking in phase reversal TV scrambling system
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United States of America Patent
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Jan 31, 1989
Grant Date -
N/A
app pub date -
Feb 26, 1987
filing date -
Feb 26, 1987
priority date (Note) -
Expired
status (Latency Note)
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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.
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