Abstract: Binary digital data signal patterns containing either no transitions, periodically recurring transitions or both are randomized by constructing a key signal from a summation of selected stored digits of the data pattern and combining such key signal with the data signal to form a scrambled line signal for transmission. The line signal so constructed is free of signal energy concentrated at particular frequencies and provides signal transitions adequate in number to assure reliable recovery of synchronization information. Descrambling of the received line signal is accomplished by precisely the inverse of the scrambling operation. The system is self-synchronizing because the key signals constructed by each of the scrambler and descrambler are derived from the same line signal.

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.