Abstract: In a SLIC in which loop current is supplied via active circuits, feed resistances via which the active circuits are conventionally coupled to the line are constituted by bifilar resistance wire windings of a ferrite core transformer, which may include a third winding coupled to an input of the active circuits.

Abstract: A modem capable of simultaneously transmitting and receiving data signals over a single communication channel with a remote modem includes a transmitter for converting TX digital data into analog signals for transmission over the channel and a receiver for converting received analog signals into RX digital data. A mechanism identifies a remote echo returning to the modem corresponding to previously transmitted TX digital data. The identifiying mechanism is capable of identifiying a echo originating intermediate between the modem and the remote modem. Another mechanism substantially cancels the identified remote echo. The present invention also encompasses the method of identification and cancellation of remote echos. In addition, remote echo cancellation signals are not combined with received signals until local echo has been substantially cancelled.

Abstract: An echo canceller for cancelling a variable-phase echo signal is connected between two one-way send and receive paths coupled by means of a coupling circuit (6) to a two-way path. This echo canceller comprises an adaptive filter (92) cooperating with a phase shifter (95) for forming a replica of the echo signal, and a subtractor (72) inserted in the receive path for producing a difference signal between the echo signal and its replica. This canceller further comprises a suppressing circuit for suppressing a d.c. component (300) of the difference signal, which circuit is designed for supplying an adjusting quantity in the direction of the adaptive filter and the phase sifter.

Abstract: In order to deal with echoes having exceptionally long tails, such as are generated by 2B1Q signals in ISDN systems, an echo canceller comprises a first echo cancelling means, conveniently a transversal filter, operative over a first number of baud periods, and filter means, conveniently an infinite impulse response filter, operative over a later number of baud periods. The filter means responds to each symbol of the transmitted signal to generate a pulse response which decays exponentially according to a predetermined function. The echo canceller further comprises means for subtracting the outputs of the first echo cancelling means and the filter means, respectively, from the received signal. The filter means may have more than one tap, enabling the exponential decay function to be adjusted to give a closer approximation to the shape of the echo tail.

Abstract: A Protector device 20 connectable between a subscribers line pair and the telephone exchange includes a protector P1 comprising a pair of foldback diodes and fuses F1 and F2 in series with the respective lines which fuses incorporate an impedence/heater element 25. A pair of contacts S1, S2 with meltable insulation provides a fail-safe short circuit path following continued operation of the protector P1. The device 20 will deal with accidental contact with mains voltages that appear on the lines and will also handle short surges due to lightning strikes for example.

Abstract: An amplifier in a housing for receiving and detecting the presence of portable paging devices that produce an audible signal when activated. The amplifier allows the connection of a large capacity annunciator or visual alarm. Circuitry is provided to connect the output of the amplifier to the bell of conventional telephone sets without affecting its normal operation. The telephone set bell can be activated with a voltage signal different from the one it normally generates so that a user can distinguish the two calls.

Abstract: An enhanced amplifier for interconnecting a two-wire, bidirectional cable side transmission path and a two-wire bidirectional equipment side transmission path in a communication system includes a first hybrid splitter and a second hybrid splitter. The first hybrid splitter is formed of a cable-to-equipment voltage sense amplifier, a shunt current driver, and a series current compensator for generating a first simulated terminating impedance. The second splitter is formed of an equipment-to-cable voltage sense amplifier, the shunt current driver and the series current compensator for generating a second simulated terminating impedance. Other features disclosed include automatic gain adjustment circuitry for automatically setting the gain in gain/equalizer circuits to a fixed level. Further, auto-balancing circuitry is provided for adjusting automatically and continuously both equipment and cable side balance networks.

Abstract: A subscriber line circuit (1) is connected via a subscriber line (3a, 3b) to a telephone set (2). For a raised receiver the subscriber line (3a, 3b) is supplied with a line current (Is) by speech signal amplifiers (4), which are powered from a power source (VBB). The speech signal amplifiers (4) and their power supplying amplifiers (7,9, and 10) have large idling power, apart from the power fed to the subscribe line. To decrease this idling power, the subscriber line circuit (1) has auxiliary amplifiers (5) with low idling power for supplying the subscriber line (3a, 3b) when the receiver is cradled. When a call is in progress and the receiver is lifted, the line current (Is) has a relatively large value, and when the call ceases and the receiver is replaced the line current (Is) decreases. This current decrease is sensed via a resistor (R2) by a loop sensing circuit (13), which sends a signal (S1) to a control circuit (14).

Abstract: A shield device installable on a telephone handset to overlie the pushbuttons, thereby preventing unauthorized persons from making outgoing calls. The shield device comprises a flexible strap that tightly encircles a mid area of the handset to maintain the shield in place. A keylock is incorporated into the shield device.

Abstract: A frequency responsive selective ringing circuit detects a selected one of a plurality of frequency-distinctive ringing signals applied on either the tip or ring conductors of a telephone line, distinguishes between the respectively different frequencies on a rapid cycle-by-cycle basis, and either applies the ringing signal to telephone equipment to ring the telephone equipment if the ringing signal is one which is selected, or rectifies the ringing signal and applies the rectified DC signal to the ringing circuit of the telephone equipment. The rectified DC signal will not ring the telephone because the DC signal is not conducted through a capacitor in the ringing circuit of the telephone equipment.

Abstract: In a system (20) for transmitting voice and data signals, insulated metallic conductor pairs (44--44) which transmit data signals and insulated metallic conductor pairs (46--46) which are capable of transmitting voice signals are enclosed in a common sheath system of a single cable (40). User pickup of station apparatus (34) during the generation of a ringing voltage on a voice conductor pair causes that pair to become disturbing and to impart impulse noise to a closely coupled data pair. The data pair is designated a disturbed pair and the signals transmitted thereby may be affected adversely. This problem is overcome by providing a circuit (80) comprising in parallel a resistance and an inductance and being in series with the station apparatus. Such an arrangement reduces substantially that frequency content of any disturbing signal which appears on the disturbing pair and which is in the range of the data signal spectrum.

Abstract: A telephone includes a lamp pivotally mounted to the telephone housing. An inductive pick-up detects an incoming call on a telephone line and actuates a switching device to energize the lamp if the ambient light level adjacent the telephone is below a predetermined level as determined by a photosensor on the telephone housing. After disconnection of the call, a time delay circuit de-energizes the lamp after a predetermined time interval. The ambient light level at which the lamp will be illuminated and the time delay between call disconnection and lamp shut-off are programmable by a user. A manual override switch allows activation or deactivation of the lamp independently of detection of an incoming call or the ambient light level.

Abstract: A protection device is provided for a telephone having a two wire subscriber line and an earth line. The protection device comprises a single surge protection device connected between a bridge rectifier polarity guard and the remainder of the telephone circuitry, which is connected to the output of the polarity guard. Three diodes are used to interconnect the earth line and the pair of output lines from the polarity guard to the surge protection device in such a way as to prevent surges from being fed to the remainder of the telephone circuitry. The surge paths including one or two arms of the polarity guard.

Abstract: A telephone subscriber line is connected to a SLIC via contacts of an isolation relay. Line voltage on the line side of the relay contacts, and line current on the SLIC side of the relay contacts, are detected during opposite polarity half-cycles of an a.c. fault on the line, and the contacts are opened to protect the SLIC if the voltage and/or current is excessive. The interruption of current causes the line voltage to rise to maintain the protection for the duration of a fault.

Abstract: A method and apparatus for transmitting a byte-organized serial data stream from a transmitting station to a receiving station that may employ byte boundaries different than the transmitting station. The technique includes sending N different data streams from the remote terminal, where N is the number of different framing alignments that may be imposed on the unframed data stream by the network. The different data streams are chosen so that one will be framed by the network as the intended data stream regardless of which framing alignment is actually imposed.

Abstract: Telephone network interface apparatus including an enclosure providing a splice chamber for receiving a telephone network cable including a plurality of incoming telephone lines, and providing a terminal chamber having a plurality of telephone terminals mounted therein; a plurality of individual, replaceable subscriber line interface modules are mounted on the enclosure, each module includes an interface jack, a subscriber wiring bridge including a pair of subscriber terminals, an interface plug connected to the subscriber terminals for being removably received within the interface jack, and each module provides an internal space for receiving a telephone circuit, the interface jack is for being connected to one of the telephone terminals and thereby to one of the incoming telephone lines and the subscriber terminals are for being connected to a subscriber premises line, upon the interface plug being removed from the interface jack a demarcation point being provided between the one telephone line and the subs

Abstract: Apparatus and method for receiving and decoding the bursts of line current activity produced by rotary dial action in dialing a sequence of digits. In accordance with the apparatus of the present invention, a rotary dial pulse receiver counts the number of bursts of line current activity produced by a given telephone handset in dialing a standard test digit. A conversion means selects a conversion algorithm which is effective to express the relationship between the number of bursts counted and the value of the digit dialed and applies the selected algorithm to decode the value of subsequent non-standard digits dialed. In accordance with the method of the present invention, a method of converting the number of bursts in line current activity produced through rotary dial action in dialing a sequence of digits by selecting and applying a conversion algorithm is described.

Abstract: An interface circuit provides for coupling of communications signals between a conductor of a transmission path, and a key telephone system and provides for protection against electrical energies, as may be associated with transient electrical event occurrences along the transmission path. The interface circuit provides for coupling of some of these transient electrical energies from the transmission path conductor to an earth ground. The interface circuit includes a plurality of electrical components and a plurality of electrical conductors being fixed to either of first and second surfaces of a sheet of electrically insulating material. The electrical conductors are spaced apart from each other by at least a predetermined amount. Some of the electrical conductors connect the electrical components of the interface circuit in a workable arrangement whereby the communications signals may be coupled.

Abstract: A reciprocal impedance conversion network is disclosed. Such conversion network preferably is used in a reciprocal negative impedance repeater for the nonloaded cable facilities of a telephone system. Two independent voltage sources for generating reciprocal negative impedance are connected between a first port and a second port. The first port is operably connected to the first voltage source such that a series negative impedance appears at that port. This port is specifically connected to the switching equipment of the telephone system. The second port is operably connected to the second voltage source such that a shunt negative impedance appears at that port. The second port is specifically connected to the nonloaded cable facilities of the telephone system. The invention further provides a frequency dependent gain circuit which is useful for equalizing the losses along the nonloaded cable facilities.

Abstract: A security device for use with a telephone handset having a microphone and an ear transducer is disclosed. It is adapted to prevent eavesdropping while the handset is in an on-hook position. The security device is comprised of switching assembly disposed in the handset adapted to disable the transducers. The switching assembly is switched to a first state when the handset is placed within a first predetermined orientation corresponding to a secure mode and is switched to a second state when the handset is placed within a second predetermined orientation corresponding to an operative mode.