Abstract: A gray-scale image is progressively transmitted over a narrow-band channel after the gray-scale values of all picture elements (pixels) have been formatted into a hierarchical structure of picture subdivisions of successive sizes from entire image down to basic element values. Each formatted value is encoded as an approximate average of paired values. Transmission involves sending the primary value, representing the overall gray-scale magnitude, and following with successively split image values so that the entire image can be reconstructed at a receiver in progressively finer detail until the ultimate image results. The coding is nonredundant and full reconstruction is accomplished by transmitting the same number of bits that are required to send the image pixel-by-pixel and line-by-line with the difference that an intermediate version can supply enough image detail for recognition.

Abstract: Disclosed is a helical scan video tape recorder having a flying sense head located upstream from a flying erase head and further upstream from a flying record/playback head. By employing a separate sense head to detect synch pulses, tension and relative speed of the video tape are controlled so as to eliminate synchronization errors in consequence of editing operations.

Abstract: A speech transmission system is improved in intelligibility and naturalness by separating voiced from invoiced speech segments prior to application to a transmission channel of restricted bandwidth. Voiced segments are combined without processing with discrete-frequency coded unvoiced segments processed in analog or digital fashion conformably with the limited channel bandwidth at the transmitter. Voiced segments are reproduced conventionally while unvoiced segments are simulated by noise sources triggered by decoded discrete frequencies at the receiver. The reconstructed speech signal can thus occupy substantially more than the limited channel bandwidth.

Abstract: Disclosed is a helical scan video tape recorder having a flying sense head located upstream from a flying erase head and further upstream from a flying record/playback head. By employing a separate sense head to detect synch pulses, tension and relative speed of the video tape are controlled so as to eliminate synchronization errors in consequence of editing operations.

Abstract: Disclosed is a bubble memory system adapted for construction on a single construction unit such as a pluggable card and for providing to prospective users a standard interface including an input data port, an output data port, a clear port, a store enable port, read and write enable ports, register select ports and a clock port. In the memory system, a plurality of bubble memory chips are interconnected in parallel with each of the chips being separately accessed for writing or reading purposes with the aid of the register select ports. Common control of the bubble memory chips is obtained through digitally generated control signals. Low voltage protection is provided by appropriately turning off the in-plane rotating field when the power source exhibits a low voltage condition, thereby protecting the stored data.

Abstract: An adaptive echo canceller for two-wire, simultaneous two-way data communication at full bandwidth uses Nyquist-interval, rather than baud-interval, processing to achieve independence from timing discrepancies between near-end and far-end terminals. The entire echo signal, and not merely baud-interval samples thereof, is suppressed. The echo canceller is preferably a transversal structure.

Abstract: Disclosed is an apparatus for telephone signaling comprising a burst detector connected across the line emanating from the central office and an amplifier, similarly connected, which is enabled with the output signal of the burst detector. In operation, the central office applies a succession of signal bursts of predetermined frequency and duration, followed by the desired alerting signal. When a signal burst is detected in the burst detector, the amplifier is enabled for a predetermined period of time following the signal burst. During the enabled time, the ringing signal applied by the central office is appropriately amplified to cause an alerting transducer to produce the desired sound.

Abstract: A signal distribution circuit subject to high-level reverse-current transients is protected by the combination of a reverse-current sensor and a controlled current shunt. The sensor detects a potentially damaging reverse-current current surge and sends a control signal to the current shunt. The current shunt then diverts the surge away from the distribution amplifier which consequently can have a low power rating. After the transient subsides, the circuit is automatically reset to allow continuation of normal signal distribution.

Abstract: An adaptive echo canceller for digital data transmission systems permits full duplex, i.e., simultaneous bidirectional transmission, operation at full bandwidth over two-wire transmission facilities. A transversal filter arrangement digitally synthesizes a cancellation signal for unwanted leakage, i.e., echoes, through hybrid junctions directly from the digital data input symbols, rather than from the analog transmitter output. An error control signal for correlation with tap signals on the transversal filter is derived from the output of the receiver, instead of its input.

Abstract: An adaptive equalizer and echo canceller jointly respond to a common error difference between the actual output and the quantized digital output of a data receiver in a two-wire digital data transmission system to achieve simultaneous full-bandwith full-duplex operation. Two-wire transmission channels are typically terminated in hybrid balancing networks which because of their fixed impedances permit "echoes" of the transmitted signal to interfere with reception of the much weaker incoming signal. Both the equalizer and canceller are adaptively adjustable transversal structures.

Abstract: A dual-speed, dual format full-duplex two-wire voiceband data transmission system provides automatic speed selection at the answering terminal responsive to a handshaking sequence which is compatible with existing systems operating at telegraph speeds. Existing systems provide asynchronous full-duplex serial data transmission in the speed range of zero to 300 bits per second using frequency-shift keying of tones in split frequency bands dedicated to the respective transmisson directions. Alternative full-duplex serial data transmission at 1200 bits per second using phase-shift keying of carrier waves in these same split frequency bands can now be provided from a common line protocol.

Abstract: A sample timing recovery arrangement for synchronous amplitude and phase modulated digital data transmission systems correlates present and delayed samples of received digital data signals to obtain a spectral line at the sampling rate using digital techniques. Conventional methods of timing recovery generally perform analog operations on the envelope of a received data signal.

Abstract: A cable is passed through a lubricant filled chamber comprising an open housing and first and second flexible, annular discs each having radial slits along its inner circumference. A third flexible annular disc adjacent to said second disc includes radial slits on its inner circumference rotatably displaced from said second disc slits. The inner circumferences of the discs deformably engage the cable whereby lubricant beads are deposited at the second disc, which beads are uniformly spread by the deformably engaged sections of the third disc.

Abstract: An error reducing arrangement is provided for a signal receiver wherein a sequence of received signals is divided into groups and each group is partitioned into subgroups. A signal representative of the deviations among the signals of each group and a signal representative of the deviations among the signals of each subgroup of said group are generated. Responsive to a subgroup deviation signal exceeding its group deviation signal, the subgroup signals are altered to reduce the subgroup deviations. In this manner errors are reduced without affecting error free signals.

Abstract: A modulator for differentially encoded phase-shift keyed digital data is implemented entirely by digital means. Baseband serial binary data are illustratively transformed into dibit pairs which are assigned discrete quaternary carrier-wave phase shifts. A "staircasing" shift register whose weighted outputs are combined to form a quantized phase-modulated carrier wave is advanced by a relatively high-speed counter through a frequency divider network. The division rate of the divider is selectively accelerated in each baud interval in accordance with the assigned dibit coding. The resultant quantized carrier wave is then lowpass filtered prior to application to a telephone transmission line. By controlling the division rate of the divider rather than the advancement rate of the shift register, gradual transitions are imparted to the output carrier wave with minimal harmonic distortion.

Abstract: Asynchronous character-oriented (start-stop) data are transmitted through a synchronous transmission channel at a rate which can exceed the synchronous rate. The excess data rate is accomplished in an input buffer at the transmitter by suppressing occasional stop bits in proportion to the difference between synchronous and asynchronous rates. An output buffer at the receiver detects start bits and thereafter monitors the presence or absence of stop bits. When a stop bit is absent, the output buffer restores it before delivering the character to the data user.Special control signals not organized into characters, such as, all-space signals are also monitored at both transmitter and receiver to insure that stop bits are not spuriously inserted.

Abstract: In a multipoint data communications system in which a central processing unit communicates with a plurality of remote terminals over a shared two-way communications facility, an automatic fault isolation circuit is provided to monitor energy levels originating at the several remote terminals. One or more energy level thresholds are incorporated into bridging locations through which incoming and outgoing address and message signals are distributed to, and collected from, remote terminals by way of the shared facility for the purposes of detecting noise buildups and isolating trouble conditions automatically without human intervention.

Abstract: An automatic and adaptive time-domain equalizer with a first transversal structure operating on received signal samples has its convergence properties improved by the addition of a second transversal structure operating on detected signal samples and having its tap-gain settings conjugate, i.e., reversed in time, with respect to those of the first transversal structure for effectively measuring the spread of tap gain values generated at the first transversal structure and a third transversal structure also operating on received signal samples but having its tap-gain settings determined by the spreading error. The matrix product of the spreading-error tap-gain values and received signal samples modifies the up-dating of the tap-gain values controlling the first transversal structure. The resultant faster convergence is particularly useful in the presence of severe amplitude distortion in the data transmission channel.

Abstract: A demodulator for differentially coherent phase-shift keyed data signals correlates samples taken in consecutive baud intervals. Received digital data signals are hardlimited to preserve zero-crossings only and samples of such hardlimited signals are temporarily stored in a delay structure. Polarity correlations are made between two pairs of samples relatively delayed by a baud interval less 45.degree., and a baud interval plus 45.degree., of carrier wave phase. These direct correlations control the counting direction of separate reversible counters. A further indirect correlation is made between the direct correlations and this third correlation is used to inhibit or not the operation of the reversible counters. The count-up, count-down and inhibit pattern constitutes ternary processing of binary data. The resultant counts are decoded at the end of each baud interval by observing whether the net count has been up or down. The counters are reset.

Abstract: A digital data transmission rate of three bits per cycle of bandwidth is achieved in precoded partial-response band-limited communication channels by partitioning binary digits into groups of three two-level digits and translating these binary groups of three into pairs of three-level digits prior to transmission. Correct pairwise association of received signals is accomplished by reserving a three-level digit pair for monitoring purposes. This reserved pair can validly occur only at a transition between allowable pairs. By monitoring the presence of the reserved pair, correct pairwise association of ternary digits is assured and binary digits are properly decoded without having to provide a special framing signal.