Abstract: A method for selecting feedback constants for two echo cancellers in an adaptive 2-wire to 2-wire repeater. The repeater is connected to two networks and when signals are received from both networks, the signal having the greater energy level is identified. A feedback constant of the echo canceller associated with the greater signal is set independent of the feedback constant of the other echo canceller. The feedback constant of the other echo canceller is set as a function of a ratio of the signal energy level of a lesser of to larger of the two signals received from the networks.

Abstract: A telephone circuit, which may be monolithically integrated, for feeding a subscriber's telephone line which is coupled via the circuit to a supply voltage generator. The circuit supplies the line with an impedance having a first predetermined value up to a given value of the line current, beyond which is supplies the line with an impedance of a second value greater than the first. The circuit is electrically equivalent to a voltage generator, identical to the supply voltage generator, having circuit components solely of the resistive type connected in series therewith.

Abstract: A switched mode DC power supply circuit for a telecommunication line, including a switched converter for charging an output capacitor from a DC source. The converter is controlled by a periodic control signal having a variable duty cycle so as to maintain a selected direct voltage level across the output capacitor. However, due to common mode currents on the telecommunications line, the capacitor may become charged above the selected voltage level even when the duty cycle of the control signal is reduced to zero. Such excess charge is returned to the DC source, without heat dissipation, by providing a further switched converter for coupling the capacitor to the DC source and which is controlled by a second periodic control voltage which is activated when the duty cycle of the first control voltage has been reduced to zero.

Abstract: A circuit arrangement for a telephone station with earth connection to the central supply device for the purpose of post-dialing signaling, operates independently of whether the negative or the positive pole of the exchange battery is earthed. This is achieved by provided that, on the actuation of the earthing key, the earth connection of the telephone is connected to the unearthed pole of the exchange battery via a transistor network which functions differently in dependence upon the polarity of the exchange battery earthing. The circuit arrangement is universally suitable for PBX exchanges.

Abstract: A method is disclosed for measuring telephone dial pulse parameters independent of telephone subscriber line length. To avoid distortions resulting from varying subscriber line lengths, there is performed during the first pulse interval of a dial pulse series to be measured, a voltage measurement with results in a value that depends on the line length, and, in accordance with this value, the times measured for pulse interval and pulse duration of the dial pulse series are corrected.

Abstract: Telecommunication line circuit including a Herter bridge with a first pair of terminals coupled to a bidirectional 2-wire line, a second pair of terminals coupled to an exchange, and a third pair of terminals where longitudinal currents are eliminated from sensed signals, as well as a ringing generator that may be coupled across the second pair of terminals which is coupled to a receive leg of a 4-wire exchange circuit and, through switching means to a ringing generator while the third pair of terminals is coupled to a transmit leg of the 4-wire exchange circuit.

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 means disposed in the handset adapted to disable the transducers. The switching means 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.

Abstract: A high-speed modem that transmits and receives digital data on an ensemble of carrier frequencies spanning the usable band of a dial-up telephone line. The modem includes a system for variably allocating data and power among the carriers to compensate for equivalent noise and to maximize the data rate. Additionally, systems for eliminating the need for an equalization network, for adaptively allocating control of a channel, and the tracking variations in line parameters are disclosed.

Abstract: The invention relates to a method for the gain control of an intermediate amplifier used in two-wire connections of a dial telephone network. The invention is also concerned with an intermediate amplifier used in such connections, the direction of the gain of the amplifier being controlled in accordance with the signal strength. The method comprises measuring the amplitudes of signals coming from different transmission directions, comparing the measured amplitudes of signals coming from different directions with each other, and controlling the gain of controllable amplifiers (12, 22) on the basis of the difference value of the amplitudes by applying a control voltage to the controllable amplifiers (12, 22) through reversephase control adapters (13, 23).

Abstract: A telephone network interface enclosure adapted to interconnect incoming telephone wiring to subscriber premises wiring.

Abstract: A subscriber line interface circuit receives and twice inverts currents from a 2-wire subscriber line and returns the currents to the subscriber line so longitudinal input impedance is low. Any differential input current in the subscriber lines is bypassed by a capacitor, so differential input impedance is very high. The circuit also sends a signal current from one system having one ground to another system having a different ground through one current path, while sending another current, having a phase opposite and amplitude equal to the signal current, through another path. This effectively isolates the two systems having different grounds.

Abstract: An echo canceller designed to cancel an echo signal [g(t)] generated in a send path (7) by a signal [f(t)] applied to a receive path (1) contains a subtractor (9) whose positive terminal receives a signal derived from the echo signal and whose negative terminal receives the output signal from a transversal filter (10) provided with means (12) for adjusting the filter coefficients in such a way that the component due to the echo signal is cancelled at the output of the subtractor (9).This echo canceller comprises a delta encoder (14) for encoding at a sampling rate 1/T the signal f(t) entering the receive path (1) and for supplying at the input of the transversal filter (10) a delta-encoded signal (.DELTA.F.sub.n), a circuit (22) for forming at the sampling rate 1/T the difference signal (d.sub.

Abstract: An echo canceller according to the present invention includes means for storing an impulse response in a memory, the impulse response being indicative of the characteristics of a transmission line. It also includes a detector for detecting ranges of samples within the impulse response having relatively large distribution of echo energy, these ranges of samples of relatively large distribution of echo energy being indicative of echoes on the transmission line. An echo canceller includes a digital filter having a plurality of weighted taps, each of the weighted taps having an associated tap weight value. A tap allocation circuit establishes the tap weight values in response to said detecting means so that only taps within the regions of relatively large distributions of echo energy are turned on. The ranges of echo energy are detected coarsely by detecting ranges of samples having relatively high estimated average echo power.

Abstract: The protection device in accordance with the invention is connected in series with the line. It comprises either a circuit (1) for providing protection against voltage surges, or else a filter (2) for providing protection against radio frequencies, or else both said circuit and said filter. It protects terminal equipment (telephone set, data terminal, fascimile machine, etc.) against disturbances both in differential mode and in common mode. The device is mounted in a protection connector which may either be of the wall socket type or else of the removable adapter type for plugging into a conventional wall socket, and in either case the terminal equipment has a plug which plugs into a corresponding socket of the protection connector.

Abstract: A convertible handset device for telephone sets includes: a handset body with a handle portion in the middle having a cord groove formed therein, a first internal trough with a trough mouth at one end and a second internal trough with an end opening at the other end; a conductive cord electrically installed in said cord groove in connection with a telephone set; a receiving unit with a receiver portion at one end and a flexible link at the other movably disposed in said first internal trough and electrically coupled to the conductive cord in the cord groove, and a transmitting unit with a transmitter portion at one end and an adjustable link at the other movably arranged in the second internal trough and electrically connected to the conductive cord in the cord groove. Thereby, the handset device can be either held in one hand or worn over the head.

Abstract: High voltage electronic contacts (S, S') and associated devices including TRIMOS (MOS TRIacs) devices connected in anti-parallel fashion between two terminals (S.sub.1 /S'.sub.2, S.sub.2 /S'.sub.1). Each electronic contact (S, S') is controlled via a control terminal (S.sub.4) by two auxiliary electronic contacts (NA, NB) each able to establish a low or high impedance between the control terminal (S.sub.4) and one of the two other terminals (S.sub.1 /S'.sub.2, S.sub.2 /S'.sub.1), the impedance conditions of these auxiliary contacts (NA, NB) being opposed. A power protection circuit associated to the TRIMOS device allows the flow of a relatively high current through the electronic contacts (S, S') for the lower voltage range across it, and minimizes the power dissipation in the contacts in the higher voltage range, i.e. when abnormally high signals are applied to the contact.

Abstract: An elastic telephone handset support for supporting a telephone handset to the head of a person, thereby enabling him or her to carry on a telephone conversation while having both hands free. The elastic telephone handset support comprises an extendable elastic loop which may be placed around the head of the person to support the upper end of the telephone headset, and an extendable support rod which contacts the shoulder of the person to support the lower end of the handset. Both the elastic loop and the support rod are retractable into the interior of the handset.

Abstract: A communication system for use with a single pair of externally provided telephone wires and a single pair of in-house wires for the provision of full intercom services and/or PABX type features to a plurality of subsets includes a line interface module connected between the single pair of externally supplied wires and a single pair of in-house wires. In addition, each subset is provided with a station adapter module between it and the single pair of in-house wires.

Abstract: Hands-free two-way communication is achieved, without the necessity of selectively muting either the sent or received signal and without the generation of interfering acoustical feedback between the speaker and microphone at the hands-free station, by frequency offsetting the audio signal sent from the hands-free station. The audio signal is frequency offset by first modulating the audio signal at a first carrier frequency to produce modulated upper and lower sideband outputs. The modulated upper sideband output is filtered out, and the modulated lower sideband output is coupled to the input of a demodulator. The modulated lower sideband output is then demodulated at a second carrier frequency offset from the first carrier frequency by a predetermined amount. A demodulated upper sideband output and lower sideband output is thus generated. The demodulated upper sideband output is filtered out, and the demodulated lower sideband output is provided for transmission or broadcast in the two-way communication.

Abstract: Adaptive filter for producing an echo cancellation signal in a transceiver system arranged for digital communication in the duplex mode via one single pair of conductors, the filter comprising delay means (8) having N terminals for delaying the N most recently transmitted symbols, an addressing circuit (10) having M input terminals (M<N), each of which is coupled to the terminals 1 to M of the delay means, the addressing circuit forming from the signals applied to the input terminals an address for a memory (11) in which for each of these addresses always a first correction signal is stored; a weighting and summing arrangement (9) having N input terminals coupled to the N terminals of the delay means, the arrangement providing a second correction signal which is a weighted sum of all the signals at the input terminals thereof, means (12) for adding together the first correction signal and the second correction signal and an adaptive control loop (13).