Abstract: A synchronous demodulator is controlled by a phase locked loop for tuning to a pilot in a television signal. A start-up interval is commenced upon initiation of tuning (either after power-up or a channel change) during which a substitute signal at the pilot frequency is supplied to the phase locked loop to rapidly bring the VCO close to its lock-up frequency. Thereafter the IF signal is supplied. The start-up interval is defined by an AFC Defeat signal from a microprocessor and controls an IF switch. The substitute signal is from a crystal oscillator.

Abstract: A television receiver includes a long loop frequency and phase locked loop (FPLL) in which the tuner voltage is controlled by the output voltage of the FPLL. A SAW bandpass filter couples the IF signal from the tuner to a synchronous demodulator and to the FPLL. An oscillator includes a SAW resonator that is formed on the same substrate as the SAW bandpass filter for supplying a reference signal to the FPLL and to the synchronous demodulator. The common substrate assures tracking between the IF SAW bandpass filter and the oscillator SAW resonator with temperature changes and processing variations.

Abstract: A digital video field identification system includes video signals formatted in blocks of video symbols in repetitive data segments with each data segment including a synchronizing signal character. One data segment includes a field timing signal. A field reference data segment which includes the field timing signal is developed at the receiver. Each data segment is compared with the field reference data segment and the number of symbol errors is accumulated for each data segment. The data segment exhibiting the least number of symbol errors is identified as the field timing segment. A confidence counter stabilizes the identification of said one data segment. The video signals are precoded in modulo N form to enable NTSC co-channel interference rejection in the receiver by a linear filter. The linear filter undesirably reduces the S/N ratio by 3dB.

Abstract: A television signal transmission system is used for transmitting an N-level video related data signal. The data signal is processed prior to transmission such that the majority of N-level symbols comprise a non-negative level for facilitating receiver lock-up. An in-phase pilot component may be added to the transmission by D.C. offsetting the processed signal to further facilitate receiver lock-up. The processed signal is precoded by a modulo-N filter and postcoded by a complementary linear filter in the receiver to reduce interfering NTSC components. In the absence of interfering NTSC components, a complementary modulo-N postcoding filter may be used in the receiver to provide improved signal to noise performance.

Abstract: NTSC co-channel interference is reduced in an HDTV receiver by developing an interference signal that is representative of the high energy components in the NTSC signal and subtracting the interference signal from the received HDTV signal to produce an enhanced HDTV signal for processing.

Abstract: A television signal transmission signal comprises a suppressed carrier, VSB signal having respective Nyquist slopes at the lower and upper edges of a 6 MHz television channel, the center frequency of the Nyquist slope at the lower edge of the channel being substantially coincident with the frequency of the suppressed carrier, and a pilot signal in quadrature relation with the suppressed carrier. The suppressed carrier is modulated by an N-level digitally encoded signal having a sample rate fs substantially equal to three times the NTSC color subcarrier frequency, with the frequency of the color subcarrier being less than the co-channel NTSC picture carrier by an amount equal to about fs/12. The received signal is demodulated by a synchronous detector in response to the received pilot signal and interfering NTSC beat components are attenuated by a linear filter having notches at fs/12, 5fs/12 and fs/2.

Abstract: A frequency stabilization circuit for a PSK data packet receiver includes a reference oscillator for supplying a continuous reference signal to a limiter that supplies feeds received data packets to a phase locked loop detection circuit including a voltage controlled oscillator. The frequency of the continuous reference signal is close to the carrier frequency of the data packets and maintains the frequency of the voltage controlled oscillator close to the data packet carrier frequency between data packets. During data packets, the reference oscillator signal is "swamped out" by the limiter.

Abstract: In a cable television system or other broadband cable communications network, improved throughput of inbound data communications by a plurality of transceivers transmitting on a predetermined frequency to a headend facility is provided by an apparatus and method for limiting the time period of the transmissions from failed transceivers. Transceiver failure in a transmitting mode can deprive effective access to the inbound channel to all of the aforesaid plurality of transceivers coupled to a system. In a preferred embodiment the transceiver modulator is disabled upon indication that the transceiver has been generating an inbound signal longer than a certain maximum time. Two protective stages are provided which respond to different indicia that an inbound signal is being generated and these stages then act on separate facilities of the modulator to prevent its operation. At least one protective stage is embodied in strictly passive circuit elements to improve reliability.

Abstract: A bit packet communication system includes a head-end having a software implemented 16 bit shaft register with a plurality of feed-forward taps and a different plurality of feed-back taps for simultaneously dividing and multiplying the input data bit packet to provide an output bit packet that is both encrypted and error protected. Dynamic encryption is provided by utilizing an initial preset for the software corresponding to a preset encryption key for the shift register. Authorized subscriber terminals are provided with memories and decryption keys are downloaded. The bit packets are assembled with a global bit packet encrypted with a global encryption key and subsequent individually addressed bit packets encrypted with address keys. The address keys and terminal addresses are permanently stored in the subscriber terminal memories. The global encryption keys are changed periodially.

Abstract: A television signal scrambling system scrambles by suppressing horizontal syncs and changing the phase of the video carrier during the horizontal intervals. Data is transmitted by using two different widths for the horizontal intervals. Framing code information is sent by means of long pulses of two different durations during the vertical blanking interval. Three filters are utilized for dynamic scrambling, with filters A and B defining one scrambling mode and A and C defining a second scrambling mode. Corresponding descrambling filters are included in subscriber terminals and the subscriber microprocessor controllers have information downloaded as to the filter pairs to be used for descrambling based upon the receipt of the first or second framing code and a mode definition. The mode definitions are in the form of encrypted data and are dynamically changed by downloading to the subscriber terminals.

Abstract: A television signal transmission system includes a cable head-end having a scrambler for scrambling a television signal and a subscriber decoder having an unscrambler for unscrambling the television signal in response to data signals from the transmitter. The unscrambler in the receiver is operated to unscramble the scrambled signal for authorized subscribers and to further scramble the scrambled signal for unauthorized subscribers.

Abstract: A bit packet communication system includes a head end having a software implemented 16 bit shift register with a plurality of feed-forward taps and a different plurality of feedback taps for simultaneously dividing and multiplying the input data bit packet to provide an output bit packet that is both encrypted and error protected. Dynamic encryption is provided by utilizing an initial preset for the software corresponding to a preset encryption key for the shift register. Authorized subscriber terminals are provided with memories and decryption keys are downloaded. The bit packets are assembled with a global bit packet encrypted with a global encryption key and subsequent individually addressed bit packets encrypted with address keys. The address keys and terminal addresses are permanently stored in the subscriber terminal memories. The global encryption keys are changed periodically.

Abstract: An FPLL circuit has a first low pass filter and a limiter having a delay that is less than one half the duration of a data bit for developing binary PSK data and a pair of multipliers, a first of which is operated in phase with and the other of which is operated in phase quadrature with an incoming RF signal. The second multiplier is connected to a third multiplier, which is also supplied with the limiter output for stabilizing the loop in the presence of data. The output of the third multiplier is supplied to a low pass filter that has a delay that is greater than the duration of a data bit and this output supplies an oscillator that develops the 90.degree. phase displaced signals for the first two multipliers.

Abstract: A television signal transmission system comprises a headend including a pair of SAW filters having equal delays, one filter having amplitude and normalized phase versus frequency response characteristics continuously varying between about -6 db and 180 degrees at the picture carrier frequency and zero db and zero degrees at the sound carrier frequency of the television signal, the second filter having substantially flat amplitude and normalized phase responses between the picture and sound carrier frequencies. An RF video signal is applied to both filters, the output of the first filter being selected for transmission during at least a portion of the horizontal blanking intervals of the television signal with the output of the second filter otherwise being selected for transmission. The transmitted signal is received by a decoder including a bi-phase stable phase modulation detector and third and fourth SAW filters having response characteristics complementary to the headend filters.

Abstract: A television signal data transmission system comprises means for transmitting a television signal in which the phase of the RF carrier is modified during a periodically recurring interval by a SAW filter having a varying phase response between the video and audio carrier frequencies of the signal. The periodically recurring interval is modulated between a first width and a second smaller width respectively representing complementary logic states of a data bit. The first width of the width modulated interval preferably extends between two points respectively located within the non-viewable, overscan portions of the video signal immediately adjacent and on either side of a horizontal blanking interval of the television signal. The transmitted signal is received by a decoder which includes a phase modulation detector for detecting the width modulated intervals and a pulse width discriminator responsive thereto for deriving the data bits.

Abstract: A PSK carrier recovery system has a frequency multiplier, a filter circuit and a limiter circuit for producing a double frequency signal from the incoming PSK signal. A pair of demodulators are supplied with the double frequency signal and with 0 and 90 degree phased reference signals of the same frequency to produce two output voltages representative of the phase of the incoming PSK signal. The output voltages are supplied through a pair of low pass filters at baseband frequency to a pair of remodulators which are also supplied with the reference signals. The outputs of the remodulators are added and applied to a filter, a limiter, a phase adjuster to compensate for processing delays and to a divide by 2 frequency circuit. The reconstituted signal has a frequency substantially equal to the incoming PSK signal and has a phase equal to one of the phases thereof. The incoming PSK signal is also supplied through a limiter to a demodulator circuit along with the reconstituted signal for demodulation.

Abstract: In a cable television (CATV) system improved upstream data communication is provided by the use of preferred frequencies. Harmonics of downstream video and audio carrier signals arising from cable discontinuities produce common mode nonlinear distortion. Cable discontinuities caused by a loose, defective or corroded connector operate as a downstream mixing diode. The cross- and intermodulation products thus produced are avoided in the present invention by the use of upstream frequencies displaced from these harmonics. In a preferred embodiment, two harmonically-related upstream carriers generated by a single signal source and centered between adjacent harmonic noise peaks provide reliable upstream data channels in a two-way CATV system. In another arrangement, each subscriber terminal transmits upstream in an alternating manner, first at one frequency and then at a second frequency, until an acknowledge signal is received from the CATV headend.