Abstract: Apparatus for protecting low voltage lines of a telephone system and including a jack block which may be mounted on a circuit breaker means having separable contact blades and such jack block has protecting elements including a plug with a plurality of contact studs that may be selectively inserted between the contact blades of the circuit breaker means.

Abstract: A solid state pulsing circuit and an adapter connector for pulsing the counting and register advance terminals of the L-(line) relay of an originating register in accordance with the digit nature of received DTMF signals is disclosed. The pulsing circuit includes a pair of solid state switches adapted to be alternatively actuated and the adapter connector connects the pulsing circuit to the counting and register advance terminals of the line relay without affecting the normal operation of the relay. Complementary MAKE and BREAK signals derived from the serial pulse output of a DTMF receiver operate the solid state pulsing circuit such that the pulsing circuit alternately pulses (opens and grounds) the counting and register advance terminals of the line relay in accordance with the production of pulses by the DTMF receiver. Other relay terminals (i.e.

Abstract: A dial signal receiver for receiving and decoding telephone digit signals in either dual-tone multifrequency (DTMF) or rotary dial pulse form is disclosed. DTMF digits are accepted, if, simultaneously, both the high and low frequency components, derived from a band-split filter, repetitively pass a short term check; and each component passes a long term check once. The short term checks comprise repetitively measuring the period of two consecutive cycles of each component of the input signal. The long term check comprises measuring the period of a number of cycles of each component of the input signal. The number of cycles for each component is dependent on the nominal frequency determined by the short term check of that component. At the end of a cycle related period, a "window" is opened for a time interval related to the expected frequency, as determined by the short term check. If a short term check pulse occurs during the open window period, the related component is accpeted as valid.

Abstract: The telephone system includes N line paging lockout printed circuit cards, where N is equal to an integer greater than one. Each of the paging lockout cards includes a first relay controlled circuit to lockout (N-1) of the paging lockout cards from a paging amplifier if any of the (N-1) of the paging lockout cards attempts to initiate a paging operation a fraction of a second after one of the N paging lockout cards has initiated a paging operation. A second relay controlled circuit applies a busy tone to a telephone subset associated with each of the (N-1) of the paging lockout cards attempting to initiate a paging operation after the one of the N paging lockout cards has initiated a paging operation.

Abstract: An echo cancelling system, in which a pseudo-echo is provided by producing an impulse response of an echo path, reversed in phase and then applied to a subtractor of the echo path to cancel an echo. A low level reference signal, such as random noise or an artificial random signal, is continuously applied to the echo path and successively delayed by a sampling period to obtain a plurality of delayed reference signals, which are multplied by the output of the subtactor to obtain a plurality of multiplied outputs. The multiplied outputs are integrated by integrators and then amplified by high gain amplifiers to be employed for producing the psuedo-echo. As a result of such construction of the adaptive control loop, the convergence time for cancellation is effectively improved.

Abstract: An electrical apparatus for use with telephone equipment to extend the effective length of an electrical circuit such as a subscriber loop or the like. The disclosed apparatus includes a variable resistance in shunt across the loop between the central office and a subscriber station, and also includes a sensor which senses the level of current in the loop and varies the shunt resistance in response thereto. When installed with the central office telephone switching equipment, the disclosed apparatus supplements the sensed current level in the loop, thereby increasing the distance from which subscriber station stations may be connected to the central office or enabling the use of telephone loops having greater internal resistance.

Abstract: A repeater for a submarine cable installation which allows remote control of amplifier gain, equalizer losses and oscillator frequency. A control signal of selected frequency is transmitted to the repeater and converted to a d.c. control signal to adjust the selected component. The signal from the remote control may be in the form of pulses of a desired frequency or signals of longer duration.

Abstract: An unconditionally stable impedance matching network for matching a nonloaded voice frequency transmission line to the standard impedance of a repeater on said line is provided.

Abstract: The disclosed T-type line compensation circuit reduces the gain and return loss variations when customer equipment is connected to a central office or PBX over telephone lines of various lengths. A linear resistor of a first series leg is thermally coupled, as a heat source, to a positive temperature coefficient (PTC) resistor of a second series leg. The shunt leg consists of a series connection of a bilateral zener diode, linear resistor, and varistor. The resistance value of both the second series leg and the shunt leg of the line circuit vary automatically with the direct current in the line to minimize gain variation due to telephone line length variation. The thermal feedback to the PTC resistor varies automatically with the direct current in the line to minimize return loss variations seen by the customer equipment.FIELD OF THE INVENTIONThis invention relates to a line circuit for compensating telephone loop line and return loss variations due to variations in line lengths.

Abstract: A telephone switch control clip adapted for attachment to a conventional telephone instrument of the type having a hand-held receiver that is electrically connected to a cradle which functions to receive and support the receiver when not in use. The hand-held receiver is of the type that includes a push button for opening and closing the telephone circuit. The button is normally biased to an extended position for closing the telephone circuit. The positioning of the receiver onto the cradle moves the push button to a retracted position to terminate or to open the telephone circuit. The clip comprises a member having a contour closely following the peripheral shape of the grip portion of the receiver.

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: The invention relates to terminal equipment for a carrier current multiplex system with a half echo-suppressor and a channel modem. The attenuator which is inserted in the transmission chain is disposed after a first modulation stage, thereby taking advantage of the propagation time of the filters of the modem to reduce the apparent reaction of the attenuator.

Abstract: A loop extender for adding a series-aiding boost voltage to a subscriber loop of a telephone system and having a d.c. boost voltage supply, an amplifier circiit having an active device connecting the voltage supply in series with a conductor of said loop for applying to the loop a magnitude of boost voltage that is dependent upon the gain of the amplifier circuit, and a further circuit, including a feedback for the amplifier circuit, for controlling the gain of said amplifier circuit in such a way that said gain is increased to cause an increase in the applied boost voltage in response to a rise in the magnitude of the loop current to a first predetermined threshold and/or in such a way that said gain is decreased to cause a decrease in the applied boost voltage in response to a decrease in the magnitude of the loop current to a second predetermined threshold.

Abstract: The subject echo canceller includes a controller, which uses a feedback arrangement to improve speech detector performance, for providing an improved multistate control signal responsive to which adjustment of the estimate is inhibited or not inhibited. For example, a first state of the control signal is provided when the value of a first function of the error signal exceeds the value of a second function of the error signal, the second function being an average of first function values. One first function may be the algebraic square of the error signal as normalized with respect to the energy detected in a far end signal, while the second function is the average of the normalized signal where the averaging is done over a predetermined time interval. The predetermined time intervals may be those time intervals during which near end speech is absent.

Abstract: A circuit for the reciprocal transmission of signals through transmitting channels. The circuit has amplifiers therein for amplifying the signals being transmitted in opposite directions along the line. A pair of electronic hybrid circuits are provided so that the signals which are emitted by one amplifier and which must be transmitted in one direction do not overdrive the input of a further amplifier which is provided for amplification of signals to be transmitted in the other direction. A circuit is provided in each of the electronic hybrid circuits for the continuous production of a reference signal which is fed to a comparator circuit connected to the input of the amplifier so that the signals arriving at the amplifier can be compared with the outgoing signals that are being transmitted in the opposite direction.

Abstract: In a voltage boost circuit, for telephone systems where reverse battery supervision is employed, optically coupled semiconductor devices are used to control both the polarity and the charge on a nonpolar capacitor. This capacitor is powered from a DC to DC converter and the capacitor serves the dual functions of a rectifier filter capacitor and a voice frequency (VF) bypass capacitor. The voltage boost circuit charges the capcitor so that it aids the central office battery, thus extending the normal operating range of the central office. Whenever the current in the loop drops below a predetermined threshold level, the voltage boost is removed by a rapid discharge of the aformentioned capacitor. When the loop is closed, the capacitor is quickly chared to the full boost voltage with a polarity so as to aid, or increase, the current in the loop.

Abstract: An echo canceller in a telephone circuit for minimizing a residual echo obtained by subtracting a pseudo-echo reproduced from an impulse response of an echo path from a true echo, in which the inpulse response is corrected by the use of the product of the residual echo and received input. A variable coefficient circuit is provided between a multiplier for obtaining the product and a circuit for correcting the impulse response. A control circuit is provided for reducing the coefficient of the variable coefficient circuit in accordance with the lapse of time of the duration of the received input exceeding a predetermined threshold level after receiving a circuit connection completion signal of the telephone circuit.

Abstract: A telephone set includes a unified internal chassis having individual cup portions for accommodating a transmitter and receiver. Each of these transducers is captured within its associated cup portion by a retaining member that is disposed about the perimeter of the transducer and the perimeter of the cup portion. A dial, which is mechanically and electrically separate from telephone network circuitry contained on a printed circuit, is secured to the chassis by fasteners, and the securing of the dial to the chassis serves to electrically connect the dial to the proper conductive paths of the speech network circuitry. The printed circuit and the components soldered thereto are only supported on the chassis by means of fastening devices and therefore the printed circuit is also readily disassembled from the chassis.

Abstract: A digital repeater for the regeneration of partial-response signals having improved noise immunity which basically comprises an equalizer followed by a regenerator. A band limiting filter disposed between the equalizer and regenerator transforms the partial-response signal to a modified form having the same or fewer levels and concurrently reduces the total power of the noise interference. A second filter disposed after the regenerator and having an inverse transfer function replicates the partial-response signal at its output so that the repeater appears transparent to the transmission line.

Abstract: A digital echo attenuation circuit for a two-wire-four-wire local telephone circuit in which each digital sample of the transmit and receive signals is compared directly and the results used to augment an accumulator. Once the accumulator reaches a certain threshold level, its output controls a digital pad to attenuate the receive signal and thereby prevent severe distortion and near singing effects.