Zenith Radio Corporation

Zenith Electronics Corporation

Melvin C Hendrickson

Richard G Merrell

Johnny Collins

James W Ensinger

Richard W Citta

Dennis M Mutzabaugh

Robert L Sproston, Jr

A technique for toggling the coding mode in a television signal encoder comprises establishing a rectangular window defining a relatively small and substantially centrally located portion of the field image intervals of the television signal. The coding mode of the encoder is toggled whenever the APL of the television signal occurring during the window exhibits a change for successive video fields exceeding a predetermined threshold level.

Technique for toggling coding mode in a television signal encoder

An encoded television signal is transmitted in the form of an inverted video component amplitude modulating an RF carrier to a selected percentage of modulation and characterized by inverted reference black and white level components. At the receiver, a decoding signal equal in frequency to and 180 degrees out of phase with the RF carrier is generated and combined with the received signal to provide a decoded television signal. The level of the decoding signal is controlled in response to the difference between the peak detected reference level signals such that the percentage of modulation of the decoded television signal is the same as that characterizing the encoded signal.

Television signal scrambling system

A suppressed sync television decoder includes a phase locked horizontal oscillator for controlling operation of a suppressed sync detector which supplies a circuit for restoring suppressed sync in a television signal. The restored sync is coupled to the phase locked oscillator and to a first four bit counter. A second four bit counter is supplied with the horizontal oscillator signal and inhibits counting in both counters when it counts 16. A reset signal corresponding to the end of the vertical interval initializes both counters. If the number of sync pulses counted by the second counter is less than 16, an error signal is produced. Thirty-two error signals result in generation of a defeat pulse to unlock the oscillator.

Decoder lockout defeat circuit

A subscription television system includes means broadcasting a scrambled television signal encoded with p-bit program and subscriber authorization codes and m-bit memory write and read codes. Each subscriber is provided with a decoder having (2.sup.m) p-bit memory locations, the decoder being operable for storing a broadcast p-bit subscriber authorization code in a memory location defined by the broadcast m-bit memory write code for updating the decode authorization status of the subscriber and being operable for comparing a broadcast program code with a subscriber authorization code stored in a memory location defined by the broadcast m-bit memory read code for developing a decode authorization signal to effect unscrambling of the broadcast television signal.

Memory select system for an STV decoder

A remote control system for a television receiver includes a transmitter and a receiver, the transmitter being adapted for transmitting a single word multibit code identifying a selected function of the television receiver. Each bit of the transmitted multibit code comprises a first occurring data signal representing a selected logic state followed immediately in time succession by a second occurring data signal representing the complementary logic state, the first and second data signals comprising a single pulse representing a first logic state or a grouping of at least two relatively closely spaced pulses representing a second logic state, whereby each transmitted bit comprises the same number of pulses. The remote control receiver includes apparatus for testing the parity relationship of the first and second occurring data signals of each bit of the received multibit code and for controlling the selected function in response to each tested bit being characterized by a condition of parity.

IR Remote control system

A decoder is responsive to a decode authorization signal for unscrambling a broadcast RF television signal having randomly suppressed horizontal blanking and synchronization pulses. The decoder comprises a tuner having a gated automatic gain control circuit and a video detector responsive thereto for developing a baseband video signal corresponding to the broadcast television signal. The decoder further comprises a sync restoration circuit developing a standard horizontal synchronization pulse in response to each suppressed horizontal blanking pulse of the baseband video signal, the standard horizontal synchronization pulses being continuously combined with the baseband video signal for operating the automatic gain control circuit and being coupled for unscrambling the baseband video signal only in response to the decode authorization signal.

Subscription television decoder

A remote control system for a television receiver includes a transmitter and a receiver, the transmitter being adapted for transmitting a multibit code identifying a selected function of the television receiver wherein the data bits forming the multibit code each comprise a single pulse representing a first logic state and a grouping of at least two relatively closely spaced pulses representing a second logic state. The remote control receiver includes a self-clocking detector for converting the transmitted pulses to a binary logic signal and decoding means responsive to the logic signal for operating the selected television receiver function.

A television receiver includes a frequency synthesizer phase lock loop operated in a time multiplexed manner to provide two tuning signals for tuning a received television signal. The two tuning signals are developed at the outputs of first and second voltage controlled local oscillators alternately operated in response to a phase detector which is reset at the beginning of each alternate operation.

Television receiver having multiplexed phase lock loop tuning system

A system for selectively addressing a plurality of television receivers, each of the receivers being identified by a unique n-bit address code, comprises means for transmitting a prefix code which is common to the p most significant bits of a group of address codes during a first horizontal scanning line of the vertical interval of a broadcast television signal. A plurality of suffix codes, each comprising the n-p least significant bits of a different one of the n-bit address codes of the group, are transmitted during each of a series of subsequently occurring horizontal scanning lines of the vertical interval for completely identifying the address codes of the group. Each television receiver includes a decoder for identifying when its associated address code has been transmitted in the form of a corresponding prefix and suffix code.

Stv Subscriber address system

A television window tuning system has duty cycle adjustment means for selectively varying the duty cycle of the tuner associated local oscillator signal. Increasing the duty cycle of the local oscillator signal effectively shifts the tuning window in frequency space in one direction while decreasing the duty cycle shifts the window in the opposite direction. In one embodiment of the invention, the duty cycle adjustment means is set for producing a 0% duty cycle oscillator signal for deriving a tuning window particularly adaptable for use with conventional AFC systems.

Apparatus for shifting a tuning window

A television tuner system includes a varactor diode as the frequency determining element and means lacking a fine tuning control for addressing the varactor. In the addressing means, a plurality of DC potentials, each defining the band edges of one of the 82 standard broadcast television channels, are selectively accessible for deriving a nominal tuning voltage defining a frequency near the center of a selected channel and a pair of control voltages defining a restricted range of frequencies about the channel center frequency. The nominal tuning voltage is initially supplied to the varactor for tuning to the channel center frequency and is subsequently decoupled therefrom wherein tuning is maintained within the restricted range of frequencies by confining the voltage supplied to the varactor between the pair of control voltages. Automatic frequency control means are used to tune the varactor to a received signal within the restricted range of frequencies.

82 Detent manual varactor tuning system

An electronic all channel television tuning system has a presettable counter for deriving the number of the receivable television channel by counting, on a continuing sample basis, the varactor diode tuner local oscillator frequency. The derived channel number is supplied as an input of a comparator which includes separate tens and units channel number comparison sections. A channel number selector supplies an encoded desired channel number to another input of the comparator and to a frequency band decoder which establishes appropriate preset information for the counter. The system local oscillator frequency is varied by a voltage ramp circuit having two pairs of matched current sources and sinks of different capacity for supplying current, through respective transmission gates, to charge or discharge a tuning capacitor at different rates. A difference in the tens section of the comparator activates the transmission gates for both the larger and smaller capacity source-sink pairs, producing the high ramp speed. After equality in the tens digits only one of the small capacity source-sink pair is activated, under control of the units section of the comparator, to produce the low ramp speed.

Growing community of inventors

Elmhurst, IL, United States of America

Melvin C Hendrickson