Abstract: A power line communications filter has an input terminal, an output terminal, and a common terminal. A transformer has primary and secondary windings, each having one end connected to the respective input and output terminals, and another end connected to a common connection. The windings are wound on a high permeability magnetic core in such a way as to promote flux leakage and with a winding polarity such that flux cancellation occurs when current flows through the windings in series. A capacitor is connected between the common terminal and the common connection of the primary and secondary windings. The capacitor has a large impedance at low frequencies such that low frequency current flows through both the windings in series and flux cancellation occurs.

Abstract: A communication switching system for routing digital voice and data signals and message signals between a plurality of peripheral circuits disposed in one or more peripheral subsystems and a main controller. Each peripheral subsystem is comprised of a peripheral switch matrix controlled by a peripheral control processor for switching the voice and data signals between predetermined peripheral circuits and the circuit switch matrix. The voice, data and message signals are transmitted through a circuit switch matrix of the main controller on predetermined time slot channels. The message signals are transmitted via communication controllers associated with the main controller and each of the peripheral subsystems according to a bit oriented data link protocol. The message signals are transmitted asynchronously during a predetermined one or more dynamically allocated time slot channels of the circuit switch matrix. The data link protocol guarantees error-free transmission of a plurality of message signals.

Abstract: A circuit for detecting a first plurality of status signals on a multiplicity of telephone lines and generating a second lesser plurality of control signals, less than the first plurality, in response thereto. Predetermined ones of the control signals are transmitted via a multiplexing circuit to a comparator circuit. A digital-to-analog converter generates analog threshold voltages for application to the comparator circuit in response to receiving command signals from a microprocessor. The comparator circuit generates a third lesser plurality of output signals, less than the second plurality, indicative of the status of a multiplicity of remote trunk circuits connected to the telephone lines. The circuit is inexpensive and occupies little circuit board area.

Abstract: A constant current line circuit for connection to balanced tip and ring leads of a telephone line and unbalanced transmit and receive leads of a PABX. A differential amplifier receives and applies incoming audio signals carried by the tip and ring leads to the unbalanced transmit lead, and detects D.C. loop current flowing through the tip and ring leads and generates a D.C. signal in response thereto. A voltage controlled feed current supply, connected in a circuit to the differential amplifier, generates a constant current D.C. voltage to the tip and ring leads in response to receiving the D.C. signal, and an integrator circuit is connected in a feedback path from the output of the differential amplifier to a voltage control input of the supply, for filtering audio signals received by the differential amplifier and regulating the generated D.C. signal to a quiescent value of approximately zero volts. The line circuit provides simultaneous bidirectional signal translation and constant D.C.

Abstract: A circuit for transmitting both voice and data at the same time between a subscriber's set and a switching exchange via a bidirectional two wire link. The invention is comprised of a subscriber's set adapted to generate and receive baseband voice signals and data signals, a circuit for 100% amplitude modulating the generated data signal on a carrier signal having its lowest sideband after filtering above the voice signal base band, a circuit for applying the voice signals and modulated carrier to a two-wire subscriber's line, a circuit for separating the voice signals and modulated carrier, and a circuit for demodulating the digital signal and applying the digital signal to control circuits of a switching exchange. Voice signals are applied to voice handling circuits such as the voice switching circuits of the switching machine.

Abstract: A circuit for receiving voice and data signals on a balanced line, the data signal being an amplitude modulated form of a carrier signal having a frequency at least twice as high as the highest frequency in the voice band. The circuit matches the input impedance thereof to a first nominal balanced line impedance with respect to voice signals and a second nominal balanced line impedance with respect to data signals, applies the data signals to an unbalanced data output terminal, and applies the voice signals to a terminal connected to a bidirectional unbalanced input/output lead of a PABX.

Abstract: A control apparatus for providing added service telephone features for stations of a multiple party line. Features provided are automatic number identification, party line privacy, fully selective ringing, remote station verification and disconnect and revertive calling. Apparatus to provide these features includes as the control logic, a conventional microprocessor acting on external logic and buffer memory interfacing with the line conductors. The external logic and buffer memory sense the input condition changes and provide signals indicative of these changes to the processor. The external logic and memory maintain a condition and monitor the line for condition change.

Abstract: Disclosed is a key telephone system using a line concentrator and a form of TDM signalling. A single data and supervisory control pair of wires connects a station instrument to the system to effect all switching and supervisory controls for all lines to which the station has access, regardless of the number of these lines. Each station instrument also has a pair of speech wires which are switched within a station-line matrix under the control of a memory unit as directed by the data transmitted. Lines are grouped into groupings of up to five lines accessible to each station, there being a matrix and memory for controlling the switching of the matrix within each grouping. More than five lines may be accessible from a station instrument, such instrument having connections to multiple groups through a station circuit individual to that station. Within the system, many added features, such as speech pair security, restrictions on allowed service, and the like may be readily incorporated.