Zenith Radio Corporation

Zenith Electronics Corporation

Michael Tentler

Wayne E Bretl

Gregory A Williams

David L Walker

An addressable subscription television decoder includes an input stage including an IF amplifier for converting a scrambled RF television signal to a composite baseband video signal. The baseband video signal comprises either a nominal sync component or a sync component having suppressed horizontal sync pulses during video fields and having non-suppressed sync pulses during vertical intervals, the vertical intervals also including selected encoded data signals. An AGC voltage for controlling the gain of the IF amplifier is developed by a circuit exhibiting a relatively short time constant whenever the composite baseband video signal is characterized by nominal level sync pulses, the time constant being increased in response to suppressed horizontal sync pulses. The sync pulses produced during the vertical intervals of the composite baseband video signal are thereby not subjected to excessive IF gain for facilitating processing of the data signals by the decoder.

STV Decoder with improved data signal recognition capability

A decoder includes an oscillator supplying a decoding signal to the control input of an RF modulator for decoding a sine wave encoded television signal. The decoding signal developed by the oscillator is randomly phase locked in either of two states with the output of a horizontal sync separator operated in response to the detected output of the RF modulator. In the first phase locked state, the decoding signal is in antiphase relationship with the encoding modulation resulting in a properly decoded baseband video signal. In the second phase locked state, the decoding signal is in phase alignment with the encoding modulation so as to constructively combine therewith. The second phase locked state is detected and broken each time it is assumed allowing the decoder to eventually assume the first phase locked state wherein a properly decoded video signal is produced.

Sine-wave decoding technique

A pulse interference detector is disclosed for use in a capacitance electronic disc player (CED). A relatively short-duration, high-amplitude periodic interference pulse, such as a radar pulse, is detected. The video carrier signal of the CED has a first envelope aberration in the form of a relatively long peak-to-peak duration amplitude modulation component, and a second envelope aberration in the form of the interference pulse. The CED incudes a defect corrector for inserting, when triggered, preceding unblemished display line information into a current display line void. The pulse interference detector receives and processes the video carrier signal and also detects the interfering radar pulse. The detector comprises a first signal path responsive only to the amplitude modulation component, and includes a resistor-capacitor network for producing a reference component substantially representing an average of the envelope excursion of the component. A second signal path is responsive only to the interference signal, and includes a transistor for triggering the defect corrector upon occurence of the interference pulse. A threshold of triggering response is established outside the maximum excursion of the envelope formed by the amplitude modulation component of the video carrier signal.

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Prospect Heights, IL, United States of America

Michael Tentler