Facsimile and static presentation processing – Facsimile – Specific signal processing circuitry
Patent
1983-12-21
1987-01-13
Buczinski, Stephen C.
Facsimile and static presentation processing
Facsimile
Specific signal processing circuitry
358124, 358122, H04N 7167, H04M 170
Patent
active
046368531
ABSTRACT:
A multi-mode audio scrambling system includes an all-pass filter and a 90 degree phase shift circuit for supplying balanced modulators with 90 degree phase displaced audio information and 90 degree phase displaced carriers derived from the horizontal line frequency of a television receiver for producing a single sideband, suppressed carrier audio spectrum. A plurality of offset frequencies are derived from the horizontal line frequency and are used to further modulate the resultant signal to produce a single sideband displaced audio spectrum. A logic circuit selects the offset frequency (mode) in response to vertical interval signals, video inversion signals and audio tone or data signals. The final output is thus scrambled in different modes with different offset frequencies. A complementary unscrambling system is also described.
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Forbes Ronald L.
Lund John A.
Buczinski Stephen C.
Wallace Linda J.
Zenith Electronics Corporation
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