General Instrument Corporation

Jerrold Division, General Instrument Corporation

John D Schilling

Clyde N Robbins

Daniel J Marz

Joseph Dolinski

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.

Method of providing sound privacy system compatible with mono and btsc

An automatic frequency control tracks a television signal before and after a period of interruption. The automatic frequency control comprises a voltage controlled feedback loop including a voltage controlled local oscillator and a mixer for mixing the output of the oscillator with the TV signal. The output of the mixer is filtered to remove unwanted components of the mixed signal and to equalize sidebands of the television signal. The output of the filter is supplied to a detector which is tuned to a component of the television signal, and produces a voltage corresponding to the frequency of the component. The output of the detector is supplied to the voltage control input of the local oscillator to track the television signal component. Circuitry automatically senses the absence of the TV signal component from the mixer, and automatically applies a reference voltage to the voltage control input of the oscillator when the TV signal component is absent. The detector is operative to detect the television signal component following the application of reference voltage to the oscillator so that when the television signal returns, the detector is capable of tracking it.

Automatic frequency control

A television signal distribution system protects outgoing programs from unauthorized reception; and marks or tags the conveyed signals with a digital word identifying the class of viewers authorized to receive the program ('level of service'). Basic encription is accomplished by effectively suppressing the horizontal and vertical synchronizing information. Horizontal sync information, and the program-characterizing level of service word which is interleaved in time with prescribed horizontal sync pulses, is distributed via pulse amplitude modulation of the audio carrier. At subscriber receiving stations, the sound carrier amplitude modulation is recovered to permit level of service authorization verification; and to reconstitute the video carrier to receivable form by an amplitude modulation which is the inverse of the sync-suppressing modulation of the head end. In accordance with one feature of the present invention, a further data channel may be employed to very subscriber service authorizations--as to permit pay-per-view billing.

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Dresher, PA, United States of America

John D Schilling