Abstract: A multiphase communication system for simultaneously transmitting plural binary digits employs one or more error-check bits which perform an encoding on the conveyed information over a plurality of digit intervals. The information and error check digits are then communicated via a transmission channel--as by amplitude modulating phase-orthogonal carriers.Upon reception, the incoming information and error check digits are decoded, and supplied to error syndrome circuitry which corrects errors which may arise from time to time during data transmission.

Abstract: Communications apparatus includes one-for-n modem redundancy for a plurality of typically contiguously disposed modem modules. The modem modules comprise n active units each illustratively operating in a different frequency band and a redundant (spare) modem of electronically adjustable frequency. The on-line (active) modem modules each include a multiplexer which normally connects user terminal equipment associated with the module to the frequency translating and data and control signal processing circuitry in the module.When a fault is detected in one of the modems (sensed, for example, by negated module "data valid" or "clear to send" levels for receive and transmit modems, respectively), a hierarchal control network and related apparatus automatically sets the redundant modem to the proper operating frequency and substitutes the spare for the failed unit via the appropriate multiplexer.

Abstract: A full duplex data modem for general application, e.g., cable system signal distribution, terrestrial or satellite radio link, or the like includes transmit and receive portions for permitting reliable communications between plural stations coupled to the common communications link.In accordance with the present invention, a fixed value is applied to a modem adapted in a test mode to speak with itself, and the number of transitions counted at the modem receiver output, to measure the error rate of an entire system.

Abstract: A bilateral digital signalling network couples a master station and plural remote, or satellite stations via a common communications link--as by way of an MATV coaxial cable. Any data/control signals may be interchanged by the system stations--for example sensor station and closure latches in an apartment complex security system multiplexing security signals on the MATV video program disseminating cable.The system employs sequential multi-mode remote stations. In accordance with varying aspects of the present invention, encryption verification is required and performed on transmission address and data fields; satellite stations revert to a predetermined secure state if not polled frequently enough by a master station; and structure is provided to prevent a station from failing in a "talking" condition which blocks (masks) all upstream transmission.

Abstract: A system including a data modem having transmitter and receiver sections. The modem transmitter includes a multi-level data encoding system, a stable carrier generator and a selected transmission frequency, and a double sideband suppressed carrier modulator to modulate the multi-level signals on the carrier. All filtering to shape the signals in the transmitter section is done prior to modulation and, in the receiver section, after demodulation. Signals from several modem transmitters, each occupying its own assigned band, are multiplexed with two pilot carriers spaced by a predetermined frequency difference. The modem receiver includes a circuit to separate one of the carriers from the received band and mix that carrier with signals in a limited part of the band to shift the frequency of signals in the limited part of the band to an intermediate frequency (IF) band. A desired signal can be selected by frequency-shifting the IF signals so that the carrier frequency of the desired signal is at zero.