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: A counting circuit is disclosed which generates an electrical representation corresponding to the number of pulses in a plurality of pulse trains, each pulse train containing at most ten pulses. The circuit does not start to count the number of pulses in individual pulse trains until a first pulse train with more than a preselected number of pulses is received. The circuit then counts each pulse in subsequently received pulse trains for a preselected number of pulse trains. The circuit is particularly useful in key telephone dial pulse signalling apparatus as a register circuit which is not responsive to false pulses generated by lifting the handset.

Abstract: A column mounts on a base housing and mounts a lever for pivotal movement between an "off-hook" and an "on-hook" position. A portion of the lever is an arm of a fanciful character which holds a telephone handset. The column attaches the character to it and the base housing. The lever has a collar in receipt of the column and an actuation tab from the collar for sliding contact with a nose of a finger of an actuator. The actuator transmits off-handset and on-handset signals to a hook switch in the base housing. A pivot bracket mounts the lever on the column diametrically opposite the finger and character arm and outwardly and away from the column. The lever moves through a comparatively small angle for a comparatively large displacement of the end of the lever represented by the arm of the character. A platform of the pivot bracket bears against laterally extending ribs of the column and attaches to the column by a fastener and hook-and-slot engagement.

Abstract: A modular connector, to be assembled with other such connectors into a switching frame designed to interlink incoming and outgoing lines of a telecommunication system, comprises a flat prismatic housing of generally rectangular outline with a bank of input terminals and a bank of output terminals fitted into a pair of recesses on its opposite longitudinal edges. Leads extending from the two terminal banks within the housing are bent to emerge at a major housing surface overlain by a printed-circuit board whose conductor strips connect them with two further sets of leads emerging from the same major surface adjacent one of its transverse edges, the leads of these letter sets extending into a junction box attached to the housing along that transverse edge. Within the junction box, normally closed by a hinged door, contacts tied to the two sets of leads can be selectively interconnected or, if desired, extended to testing equipment.

Abstract: The system receives subscriber station address information in the form of dial pulses transmitted from a calling station along a common intercom circuit and selectively accesses a called subscriber station having a corresponding station address in order to produce a call indication ring-out thereat. The system includes a hook condition detector circuit which controls multiple system functions with respect to the on-hook and off-hook status of the calling station, and further includes a dial pulse detector circuit which effects additional control with respect to completion of dialing by the calling station. The system is suitable for use with ten or varying numbers of subscriber stations and may include, for applications having more than ten subscriber stations, appropriate transfer and associated output control circuitry for double digit operation.

Abstract: This invention comprises a telephone hybrid circuit having two opto-coupler arrangements for transferring voice signals from the two-wire line to a port of the switching system on one hand and from a port of the switching system to the two-wire line on the other hand. In addition, a pair of feeder circuits in the form of current sources comprising active elements are provided for feeding a constant positive direct current to one wire of the two-wire line and a negative direct current of equal magnitude to the other wire of the two-wire line. Each of the current sources includes control circuitry for maintaining a constant ratio between the current furnished by the current source and a control current common to both current sources. A control current path is connected to the output of one of the opto-coupler arrangements for generating a common control current in response to a dc signal and a superimposed voice signal received from a port of the switching system.

Abstract: A control point driver circuit for use in a telephone exchange for energizing and deenergizing a control element such as a control relay in response to set and reset input pulses. The control point driver circuit comprises a transformer having a centertapped primary forming set, reset, and common inputs for receiving the set and reset input pulses and a secondary coupled to a constant control voltage. The control point driver circuit also includes a comparator having a first input coupled to the transformer secondary, an output coupled to the control relay to be energized and de-energized and a second input coupled to the comparator output for receiving first and second reference voltages which are related in magnitude to the constant control voltage to maintain the comparator in the set state or reset state indefinitely until a reset or set input pulse is received.

Abstract: A quick-release, snap-in bracket assembly for mounting telephone dials within a telephone housing is disclosed. The assembly allows dials of the same or different types to be rapidly mounted within or removed from a telephone housing through use of a pair of mounting members suitably dimensioned and disposed on opposite sides of the dial. Upstanding support members formed within the telephone housing are used to engage the interchangeable mounting members and the related dial attached thereto.

Abstract: The disclosure relates to a key telephone system intercom line circuit which uses only three leads to connect plural telephones and an intercom line control circuit. These leads comprise two talking circuit leads and one control lead. Exclusion circuits in each of the telephones are controlled by signals applied on the single control lead (1) to allow a telephone to seize the intercom line circuit when it is in an idle state, (2) to allow a called telephone (signalled via a separate pair of calling leads) to answer without being excluded and (3) to exclude all other telephones from the intercom line circuit after the calling telephone has seized the intercom line circuit.

Abstract: The disclosure is for key telephone system line control circuitry which provides telephone station line status signals for central office ring, busy, idle and station hold conditions by means of a single control line.

Abstract: A switching arrangement by which a telecommunication subscriber station selection unit is connected into the central office line is described. The selection unit involved is of the key-operated type wherein key actuation produces a specific surge current corresponding to the specific key depressed. Semiconductor elements form impulse contacts which are operated by a key-controlled pulse generator. A bistable relay is provided for disabling the station's speech circuit during the dialing phase, and at the same time maintains a transmission and feeder circuit, of which the selection unit forms a part and which is completed by actuation of a key. The operation of the bistable relay is influenced via a parallel circuit which offers a high impedance to the transmission and feeder circuit, so that the bistable relay can be rendered inoperative if it is erroneously in an operative state. Depression of a key is required to close the transmitter and feeder circuit, and when this occurs, i.e.

Abstract: Apparatus for enabling a blind person to determine the status of a plurality of telephone lines from the illumination condition of signal lamps associated therewith which respectively indicate the "ON", "OFF", "RING" or "HOLD" status of each line. Photosensors sense the illumination condition of each lamp and provide first signals in response thereto. The apparatus sequentially and repetitively scans the photosensors and the resultant sequentially appearing first signals are serially and repetitively converted to digitally coded signals which are serially read-into storage means. Means are provided for sequentially and repetitively generating a plurality of audio tone signals respectively having progressively different frequencies, each tone signal corresponding to a particular line. The coded signals are serially read-out of storage at the rate of the tone signal generation and are serially decoded.

Abstract: An extension telephone system in which a main equipment and each of a plurality of key telephone sets are connected together through paired information conductors and paired control conductors. The key telephone system can perform various functions such as answering to an incoming call from a single central office line, holding of the single central office line, transferring the incoming call from the single central office line from one key telephone set to another key telephone set, keeping the central office line in secrecy, incoming call indication, line busy indication, line holding indication and individual paging with electronic sound or voice by variation and polarity reversal of a DC voltage applied between the paired control conductors by the main equipment and utilization of the information conductors for a central office line communication, internal communication and individual paging control.

Abstract: In PCM transmission, it is well known to transmit 24 voice-grade channels at a bit rate of 1.544 Megabits per second (Mb/s). The number of channels which may be transmitted in about the same bandwidth is doubled by the use of correlative level coding, such as the modified duobinary technique. Because of the degradation experienced by the modified duobinary signal in passing over cable pairs, periodic regeneration of the signals is required for effective transmission. The present invention is directed to a regenerative repeater which equalizes, amplifies, reshapes, and retimes the received modified duobinary signal so as to provide a regenerated signal which is nearly identical with that originally transmitted.

Abstract: An end-office repeater accepts a high-speed bipolar signal, converts the bipolar signal into a unipolar signal, scrambles the unipolar signal, and encodes the scrambled unipolar signal into a modified duobinary signal for transmission over a cable pair. Before cable loss would severely degrade the duobinary signal, line repeaters and/or inter-office repeaters are installed at predetermined intervals so as to equalize and regenerate the modified duobinary signal. By so doing, the signal is recovered with acceptable phase jitter, which permits recovery of the original high-speed bipolar signal at the distant end of a repeatered span line. The receiving-end office repeater equalizes and regenerates the modified duobinary signal, decodes the signal to obtain a unipolar signal, descrambles the unipolar signal, and converts the unipolar signal into a bipolar signal.Detection of errors in the modified duobinary signal may be obtained without adding redundant digits.

Abstract: Hybridless bidirectional transmission networks typically include telephone line coupling transformers and unidirectional amplifiers for enhancing outgoing and incoming signals. Unwanted signal components in the outgoing direction, caused by cross coupling via the transformer of incoming signals, are minimized by employing a canceller network in circuit with the incoming and outgoing amplifiers. The canceller network has a complex transfer characteristic to compensate substantially for complex impedance components of the coupling transformer and 2-wire transmission facility and to generate a signal which is substantially a replica of the unwanted outgoing signal components. The replica signal and unwanted signal components are algebraically combined in the outgoing amplifier effectively to eliminate the unwanted signal components from the outgoing path.

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: The echo path of an echo signal subjected to a time-varying phase shift is bridged by echo cancelling apparatus including a variable phase shifter and an adaptive echo canceller connected in series. The variable phase shifter includes an adaptive control loop whose operation is compatible with that of an adaptive echo canceller. The phase-shifter control loop derives a control signal from the output signal synthesized by the echo cancelling apparatus and the residual echo produced by subtracting this output signal from the echo path signal. The control signal is used to produce a variable phase shift on the signal passing through the variable phase shifter in the echo cancelling apparatus. The echo canceller adaptively synthesizes a replica of the echo signal produced by the linear dispersive portion of the echo channel, while the variable phase shifter is adapted to impart a time-varying phase shift corresponding to the time-varying phase shift encountered by the echo signal in the echo path.

Abstract: Two sets of line terminals in a pair of PCM head stations are interconnected by a set of transmission channels via a number of cascaded relay stations each including a line repeater for each channel. A service link extends from an address generator in one head station to a monitoring unit in each relay station, the monitoring unit including a regenerating circuit for throughgoing address codes and further including a discriminating network which, upon detecting an address code identifying that relay station, sends a sinusoidal priming signal to all the associated repeaters. A predetermined PCM test code, e.g. one containing a certain number of consecutive zeroes, is simultaneously transmitted from the same head station over the channel containing a selected repeater to be checked which, upon coincidence of the test code with the priming signal from the associated monitoring unit, closes a loop for feeding back the test code to the originating line terminal.

Abstract: A wall bracket for a one-piece telephone which has a transmitter in a flat base and a receiver at the end of an upright portion extending upward from the base includes a shelf and a roof member which can straddle the telephone. The shelf has a depth such that the center of gravity of the telephone when on the shelf is outward beyond an edge of the shelf so that the telephone if not further supported would rotate about the edge. The roof member extends obliquely toward the shelf and is separated therefrom by a distance such that when the telephone is upright it can pass between the shelf and roof member but thereafter when the telephone rotates about the edge of the shelf the roof member acts as a stop for the receiver end of the upright portion to prevent further rotation and locks the telephone in place.