Abstract: A multi-station telephone communication system in which there is designated a master station and several other stations. Each of the stations is capable of communicating with any of a large number of standard telephone lines and non-locking pushbuttons are utilized to select the lines connected to each station. Each station is capable of monitoring the active line on which any of the other stations is communicating. Additionally, the master station is capable of supervising the conversation in any of the other stations by an ASSIST LOOP connection, in which the master station can overhear the conversation, but communicate one way with only one of the parties in the two-way communication. Each station is provided with a turret having panels in which are mounted their respective displays for indicating the active lines which are in communication with the respective turret as well as the lines in active communication with the other stations.

Abstract: A monobus conference arrangement is disclosed for use in a key telephone system. A conference circuit is serially inserted on each line and is arranged with an impedance element common to all of the stations using the line. In addition, a monobus circuit replaces the conventional hybrid in each station set. To avoid the problem of having more than one such impedance element connected in a multiline conference, the system is arranged so that current flows in a first direction through the conference circuit associated with the first-connected line and in a reverse direction through subsequently connected line conference circuits. Under control of the reverse current flow, the common impedance elements associated with the reverse current line conference circuits are removed from the connection.

Abstract: In order to reduce the signal loss in a telephone line switching and conferencing system there is interposed between each line and the switching matrix a monobus port circuit arranged to convert a transmitted telephone signal into an equivalent current source. The currents from several monobus circuits are added in a bus resistor before distribution back to the individual monobus circuit as a voltage where the original signal is subtracted from the bus signal. The resultant signal is transmitted to the telephone receiver. When the switching matrix crosspoint resistance is negligible, the component of the bus voltage measured at the current source output which results from current generated from each line is equal and opposite in magnitude to the voltage generated in the line. In any given line these voltages cancel each other, thereby eliminating the feedback signal.

Abstract: In order to reduce the signal loss in a telephone line switching and conferencing system there is interposed between each line and the switching matrix a monobus port circuit arranged to convert a transmitted telephone signal into an equivalent current source. The currents from several monobus circuits are added in a bus resistor before distribution back to the individual monobus circuit where the original signal is subtracted from the bus signal. The resultant signal is transmitted to the telephone receiver. When the switching matrix crosspoint resistance is negligible, the component of the bus voltage measured at the current source output which results from current generated from each line is equal and opposite in magnitude to the voltage generated in the line. In any given line these voltages cancel each other, thereby eliminating the feedback signal.

Abstract: During echo suppression in a system utilizing a full echo suppressor, noise is typically inserted in the receive line of the near-end party to assure him that the line has not "gone dead". The need for a separate noise source for this purpose is eliminated in a digital system by using the existing coded incoming signals on the line. Thus, during echo suppression the bits of the coded incoming signal are altered to provide a random noise signal of normal background amplitude which is then inserted on the receive line. In an illustrative companded sign magnitude code embodiment, the sign bit is replaced by the least significant bit, the least and next-to-least significant bits are interchanged and the remaining bits are zeroed, thereby producing an unintelligible background noise signal of appropriate amplitude.

Abstract: A circuit for varying the amplification afforded to a-c signals transmitted through a transmission line in accordance with the a-c losses of that transmission line. Gain control circuitry is provided which varies the magnitude of amplifying voltages and currents inserted into the transmission line in accordance with the a-c losses of that transmission line. The gain control circuitry is comprised of a line resistance sensor which establishes a control signal which is a function of the a-c losses of the transmission line. This control signal is applied to the remainder of the gain control circuitry to vary the magnitude of voltages and currents inserted into the transmission line in accordance with that control signal. As a result, the gain control circuitry automatically adjusts the gain of a repeater in accordance with each transmission line connected thereto.

Abstract: A circuit for varying the amplification afforded to a-c signals transmitted through a transmission line in accordance with the length of that transmission line. Circuitry is provided which establishes a control signal which is a function of the a-c losses of the transmission line. This control signal is applied to an amplifying network which varies the amplification of signals transmitted through the transmission line in accordance with the magnitude of that control signal, and thereby automatically adjusts the repeater for operation with any transmission line to which it is connected.

Abstract: A remote monitoring apparatus adapted for use with a commercial or private telephone communication system for activating a condition monitoring mechanism and converting the measured output thereof into data signals. The data signals are transmitted by the apparatus to a remote receiving station from which a triggering signal is derived to initiate operation of the data signalling apparatus.

Abstract: A coupling circuit for a telecommunication system comprises a resistance bridge whose four arms consist each of two identical halves in series with each other, the resistive halves of one pair of opposite arms being of relatively high magnitude while the resistive halves of the other pair of opposite arms are of relatively low magnitude. A two-wire line is connected across a first bridge diagonal while a matching load impedance is connected across the other diagonal. A signal-transmitting circuit, including a microphone, is connected across the midpoints of the low-resistance arms whereas a signal-receiving circuit, including an earphone, is connected across the midpoints of the high-resistance arms.

Abstract: Two-wire telephone lines connecting between subscriber telephones and the central office telephone system are coupled to four-wire transmission lines within the central office by means of phototransistors and light emitting diodes. The use of the phototransistors and light emitting diodes provides two-wire to four-wire conversion between balanced two-wire lines.

Abstract: A two-wire line is connected via a resistive hybrid circuit to a high-impedance output of a transmitter amplifier, carrying outgoing voice signals originating at a microphone, and to a high-impedance input of a receiver amplifier, carrying incoming voice signals destined for an earphone. A biasing network, connected across the line in parallel with the hybrid circuit, includes a pair of cascaded complementary transistors whose collectors are interconnected through a low-ohmic voltage divider supplying operating voltage, balanced with reference to the line voltage, to the transmitter ampllifier and delivering a similarly balanced reference voltage to the receiver amplifier.

Abstract: Audio frequency signalling, from a central location in a telephone system to a remote location serviced by a particular telephone set, is accomplished by connecting an audio frequency amplifier, having a predetermined a.c. threshold voltage level, and a predetermined d.c. voltage level, across the telephone line at said particular telephone set. By concurrently applying a low frequency a.c. pilot signal of an amplitude greater than the a.c. threshold voltage level of the audio frequency amplifier and an audio frequency signal voltage of a lesser amplitude to the telephone line at the central location, when said particular telephone set is on-hook, said audio frequency amplifier is enabled by the low frequency a.c. pilot signal and supplied with operating current from the telephone line. The audio frequency amplifier, thus enabled and energized, attenuates the low frequency a.c.

Abstract: The invention comes within the field of four-wire telephony. To avoid the closing of a loop between the two unidirectional channels, a half-echo suppressor is provided for each terminal, which comprises mainly a speech detector for the emitting channel, said speech detector having two operational modes: the first sends out a speech indicator signal based on the characteristics of amplitude and sign change on the emitting channel whereas the second compares the amplitude on the emitting channel and the amplitude on the receiving channel and is effective when the receiving channel is active. The invention applies more particularly to a PCM network in combination with a concentrator which uses the inactivity periods of the circuits.

Abstract: Regeneration of distorted signalling pulses is obtained by means of a Schmitt trigger which is fired when the input pulse has varied by a preset value .DELTA.V the maximum voltage of said pulse being stored in a memory device so as to maintain the trigger in the present state. The trigger is switched back during the trailing edge of the pulse when the signal has varied by the same preset value .DELTA.V through inhibition of the memory device. The regeneration meets C.C.I.T.T. R2 regulation.

Abstract: This invention is a security system for computer terminals which system provides means for preventing the unauthorized access to digital computers from illicit terminals. The invention provides a local code unit which includes means for manually selecting a sequence of digits by means of a keyboard. When the selected sequence and the pre-set code in the local code unit are the same, the terminal equipment is connected to the transmission path. This prevents unauthorized personnel at an authorized terminal from gaining access to a transmission path. A second code, pre-set into the code transmitter by any suitable means such as switches, is transmitted over the transmission path to the code receiver. A code receiver at the other end of the transmission path connects the computer to the transmission path only when the second code is the same as the code pre-set into the code receiver.

Abstract: Conference call provisions are incorporated in a Time Division Multiplex (TDM) signalling exchange wherein the signals are summed energywise and transmitted to a receiving subscriber set without subtracting the signal from that subscriber set and any tendency toward regeneration is obviated by filtered signal reconstruction in conjunction with sample-and-hold signal reconstruction of the TDM signalling system. Simple low-pass, high-pass and band-shaping filters are adequate for the purpose.

Abstract: Disclosed is apparatus for automatically balancing the hybrid network in a telephone system having a bidirectional cable connected to a first preselected hybrid network port and a balancing network connected to a second preselected hybrid network port. In response to a test signal applied to a third port of the hybrid network, the disclosed apparatus develops control signals in response to the magnitude and phase of signals at the hybrid network's first and second ports. These signals adjust the impedance of the balancing network to effect hybrid network balance.

Abstract: A touch type dial digit selector to rotary type dial digit sender converts touch type dial input information to a rotary type dial output and includes a touch type selector pad having the ten digit selecting push buttons arranged in four rows and three columns and associated row and column switches, an encoder for converting the information represented by the operation of the row and column switches into a four-bit binary code, a storage and pulsing circuit for receiving the digit information, and providing at an output the series of pulses representative of the dialed number. The storage and pulsing circuit includes a strobe input for initiating the registration of the input information by the storage and pulsing circuit. Means responsive to the concurrent operation of at least one row switch and at least one column switch of said touch type selector provide a strobe pulse to said strobe input at the end of a predetermined time interval greater than N seconds.

Abstract: In a push button operated telephone set to be used in a telephone system designed for break/make impulsing an electronic circuit is used for converting the push button signals to break/make pulse trains. In order to supply power to the electronic circuit from the central battery through the subscriber's line even if the terminal voltage is low at the subscriber, a DC voltage converter is used in the set to multiply the terminal voltage. This converter includes a pulse oscillator which is also used as a timing pulse generator for the electronic circuit, controlling the frequency, make/break ratio and pulse sequence intervals of the dial pulse trains sent to the exchange.

Abstract: A multi-stage connection switch frame comprising crossbar switch lattices arrayed in at least three stages which are interconnected through links. Two adjacent stages of the multi-stage connection switch frame comprise a plurality of vertical groups each group comprising a plurality of upper part of verticals connected to each other by horizontals thereof in a multi-stage configuration and a plurality of lower part of corresponding verticals in all of the vertical groups being connected to each other by horizontals thereof in a multi-stage configuration, thereby to form the lattices in two stages which are coupled to each other through the verticals.