Abstract: A television cable system includes a headend and a decoder coupled by an in-band communication link and an out of band communication link. The headend controller includes conventional transmission systems for providing a plurality of program channels to the decoder via the in-band communication link. In addition, the headend system includes a plurality of controller inputs which provide data to a download executive circuit which in turn organizes data and transfer it to a transmitter coupled to the out of band data link. Within the decoder, a pair of processors are operative via a communication link therebetween. One processor is of predefine capability and is used to operate a user keyboard as well as conventional tuning and signal processing and descrambling systems to provide television display. The remaining processor includes a memory manager coupled to an out of band transmission receiver which receives downloaded interpretive execution data.

Abstract: A biphase stable FPLL includes a polarity determination circuit that ascertains the lockup phase of the FPLL based upon the polarity of the pilot in the digital signal. A frequency lock circuit also determines from the recovered pilot when frequency lock has occurred and the polarity determination circuit is responsive thereto for inverting the phase of the incoming, or alternatively, of the outgoing signal, as determined in order to supply an output signal of predetermined polarity.

Abstract: A simplified trackball arrangement utilizes a single IR emitter-detector combination for determining the distance and direction of movement of a chopper wheel. The chopper wheel has a plurality of slots for interrupting the infrared path between the emitter-detector combination. The distance travelled by the trackball is a function of the number of slots interrupting the emitter-detector combination IR path. The slots are arranged in a distinctive 1-2-3 pattern such that the direction of rotation may be determined by a pattern detector sensing a 1-2-3 or a 3-2-1 pattern to the IR beam interruptions.

Abstract: A cable system includes a cable head end and a plurality of distribution sites having equipment for supplying subscriber station receivers with digital video cable signals from the cable head end. The digital video signal includes a robust data component that is receivable by distribution site receivers and cable subscriber station receivers under very poor carrier-to-noise conditions, that is, where the video signal itself is not usable. The cable head end has capabilities for interrogating distribution site receivers and subscriber station receivers which respond by transmitting designated information concerning differences between the received robust data component and the transmitted robust data component. At the subscriber station receivers, the robust data component is in the form of a training sequence of known characteristics that is compared with a received training sequence.

Abstract: A track ball mechanism is mounted on a cantilevered portion of a printed circuit board that is supported in a housing. A switch, mounted on the opposite side of the cantilevered portion of the printed circuit board, is operated when it engages a boss on the housing. The ball of the track ball mechanism is operated by a human digit in the usual manner and the switch is operated when pressure on the ball deflects the cantilevered portion of the printed circuit board which causes the switch to engage the boss. The boss is supported on a cantilevered portion of the housing which deflects under excessive loading to protect the switch and track ball mechanism.

Abstract: An AFC filter for an FPLL comprises a filter formed of a network of resistors and capacitors exhibiting a predetermined phase response characteristic. The phase response characteristic is limited with increasing frequency to a value of about 90.degree. during a start-up interval.

Abstract: A data receiver comprises a demodulator for recovering a received data signal comprising a stream of interleaved regularly spaced one-dimensional symbols of a phase invariant symbol constellation, each of the received symbols representing 3 bits, Z.sub.0, Z.sub.1, Z.sub.2 produced by convolutionally coding a first data bit X.sub.1 to derive bits Z.sub.0, Z.sub.1 and precoding a second data bit X.sub.2 to derive bit Z.sub.2. The received symbols are applied to a first decoder for estimating data bit X.sub.1 and a bit Y.sub.2, Y.sub.2 being applied to a postcoder for conversion to an estimate of data bit X.sub.2. The first decoder may comprise a Viterbi decoder or a 4-level slicer. In a preferred embodiment of the invention the received signal includes a plurality of regularly spaced synchronization intervals, each comprising a number of received symbols, and the second decoder is prevented from changing state during the synchronization intervals.

Abstract: A symbol to byte converter converts multilevel symbols into data bytes. The bits of each M level symbol are written to a parallel register and read out serially to a serial register under control of an 8 times symbol clock. Successive groups of eight bits are read out in parallel from the parallel register with a byte clock to form the data bytes.

Abstract: A television signal is formatted for transmission by arranging a plurality of encoded data symbols, representing a plurality of source data bytes, into successive data frames each comprising 313 data segments. One of the data segments of each frame comprises a frame sync segment of which the last 12 symbols comprise a copy of the last 12 encoded data symbols of the preceding data segment. The remaining segments of each frame comprise 12 interleaved subsegments A-L, each subsegment comprising a plurality of encoded data symbols representing a contiguous group of sources data bytes, with the first symbol of each of the first 4 subsegments A-D comprising a predetermined segment sync symbol. The received signal is decoded by independently processing the symbols of each respective subsegment to derive estimations of the source data bytes.

Abstract: A bi-phase stable FPLL is locked by a DC pilot component in a recovered data signal. The signal is formatted in repetitive data segments including sync characters and a DC pilot. A sign bit, indicative of the polarity of the recovered data, is developed from the sync characters and is used to augment the DC pilot to stabilize the lock up of the FPLL to produce the desired polarity of recovered data.

Abstract: A cathode ray tube electron gun (11) especially Well suited for projection-type cathode ray tubes is disclosed as having a main lens system where the upper end of the first accelerating electrode (21) fits through and within the lower end of the focus electrode (23) and the upper end of the focus electrode fits through and within the lower end of the second accelerating electrode (25). This construction and arrangement of the electrodes provides for larger apparent aperture(s) in both the decelerating lens gap and the accelerating lens gap or the main lens system which reduces spherical aberration to achieve a small spot size while providing increased grid separation for improved high voltage stability and an easily constructed gun.

Abstract: A television receiver includes a synchronous demodulator including a bi-phase stable PLL for controlling sampling of the received signal to produce data. A phase inverter reverses the phase of the data in response to a control signal. Data segment sync characters are recovered with a sync correlation filter that also yields a sign bit indicating polarity. If the sign bit is wrong for a predetermined number of data segment sync characters, a control signal is produced to operate the phase inverter.

Abstract: An ATV signal includes a field sync reference having a relatively long pseudo-random number symbol sequence followed by three relatively short pseudo-random number symbol sequences, with the middle of the three short pseudo-random number symbol sequences having inverted polarity in alternate fields.

Abstract: A television cable system includes a headend and a decoder coupled by an in-band communication link and an out of band communication link. The headend controller includes conventional transmission systems for providing a plurality of program channels to the decoder via the in-band communication link. In addition, the headend system includes a plurality of controller inputs which provide data to a download executive circuit which in turn organizes data and transfer it to a transmitter coupled to the out of band data link. Within the decoder, a pair of processors are operative via a communication link therebetween. One processor is of predefine capability and is used to operate a user keyboard as well as conventional tuning and signal processing and descrambling systems to provide television display. The remaining processor includes a memory manager coupled to an out of band transmission receiver which receives downloaded interpretive execution data.

Abstract: An ATV system encodes variable length elementary streams of data into a multilevel symbol signal comprising a plurality of multiplexed fixed length data packets without sync information. The fixed length data packets are arranged in fields of repetitive data segments, each of which includes a data segment sync and each field of which includes a field sync. The fields of data segments are transmitted as suppressed carrier VSB modulation. In an ATV receiver, the data segment sync is used to generate a timing signal that identifies the beginning of each fixed length data packet. In one embodiment, a packet sync signal is inserted into each recovered fixed length data packet for recovering the elementary streams of data. In another embodiment, recovery of the elementary streams of data is accomplished without inserting a packet sync signal.

Abstract: A combined condition access and transport demultiplexer circuit comprises a decryption device receiving a demodulated transport bitstream including a plurality of multiplexed conditional access (CA) and product (e.g. video, audio and data) packets, each CA packet being identified by a CA PID and each product packet by a respective product PID. A comparator is provided for comparing the PID of each received packet with a plurality of stored PID values representing the CA PID and selected product PID's. A routing manager is responsive to the comparator for routing received CA packets from the decryption device to a conditional access circuit which controls the decryption device and for routing received product packets to appropriate output ports for further processing.

Abstract: A digital advanced television (ATV) receiver includes a multi-tap feedforward filter for reducing NTSC co-channel interference in a received ATV signal. A complementary Tomlinson precoder is used to compensate the transmitted ATV signal for inter-symbol interference (ISI) created in the receiver by the feedforward NTSC rejection filter. Data components of the transmitted signal are non-linearly precoded while synchronization components are linearly precoded to improve sync recovery S/N performance in the receiver.

Abstract: A trellis coded modulation system comprises a first coder for convolutionally coding a first input data bit X.sub.1 for deriving first and second output bits Z.sub.0 and Z.sub.1. A second coder precodes a second input data bit X.sub.2 for deriving an output bit Z.sub.2. The output bits Z.sub.0, Z.sub.1 and Z.sub.2 are mapped into corresponding one-dimensional multi-value symbols, wherein the output bits Z.sub.0, Z.sub.1 identify respective subsets of the symbols, each of the subsets comprising two equally spaced symbol values, and the output bits Z.sub.1, Z.sub.2 identify respective pairs of the symbols, each of the pairs comprising two adjacent symbol values.

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 reference data segment which includes a reference field timing signal is developed at the receiver. A portion of each data segment is compared with the reference field timing signal 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 one having the field timing signal. A confidence counter stabilizes the identification of the one data segment. For terrestrial transmission, the video signals are precoded in modulo N form to enable NTSC co-channel interference rejection in the receiver by a linear filter.