Abstract: This arrangement is intended to control the operation of the coefficients adjusting circuit (12) of an echo canceller and of the operation of a center clipper (15) inserted in the send path (7) of a four-wire circuit at the output of the subtractor (13) of the echo canceller for suppressing there, when it is set to its active state, the signals whose amplitude is lower than or equal to a clipping threshold. The control arrangement operates on the basis of the signal in the receive path (2) of the four-wire circuit, the level N.sub.REC of this signal and the levels N.sub.AV and N.sub.AP of the signals before and after the subtractor (13). It comprises a controller (21) for comparing the level N.sub.AV to two fixed thresholds N.sub.AV0, N.sub.AV1 and for comparing the ratio N.sub.AP /N.sub.AV to a threshold a which is capable of varying as a function of N.sub.AV, the center clipper being only set to its active state when the level N.sub.AV is comprised between N.sub.AV0 and N.sub.AV1 and the ratio N.sub.AP /N.

Abstract: D.C.-fed ringing signal generator for a group of subscriber lines comprises a cascade arrangement of a digital signal generator controllable by a control signal to produce a signal corresponding either to the ringing signal or to a signal having zero value,a digital-to-analog converter,a capacitively-coupled class-A amplifier, anda direct-coupled class-B symmetrical power amplifier to produce the output signal of the ringing signal generator.

Abstract: A self-adaptive equalizer for use in a data modem for correcting in the baseband a received data signal. The equalizer comprises a difference circuit for determining the difference between a received signal and a correction signal formed at a sampling frequency by a transversal filter having adjustable coefficients, and which produces a corrected signal which is applied to a decision circuit which recovers the data signal. The output of the decision circuit is applied to the transversal filter, the coefficients of which are adjusted so as to minimize the mean-square value of an error signal. The error signal at each actual sampling instant is formed by deriving the algebraic difference between the value of the corrected signal at that sampling instant and the value thereof at a previous sampling instant, the latter value being first multiplied by the ratio between the value of the recovered data signal at the actual sampling instant and the value thereof at the previous sampling instant.

Abstract: Method and apparatus for measuring the delay of the distant echo in an echo ancelling arrangement comprising a near echo canceller, a delay line and a distant echo canceller using the steps oftransmitting, by modulation of a carrier, a data sequence having a periodic autocorrelation function with sidelobes of negative or zero value, this sequence having a duration at least equal to the maximum value of the delay to be measured and a number of elements determined by the accuracy desired for measurement of the delay;calculating the correlation function between the data of a next transmitted sequence and the data formed by demodulating the received signal and storing calculated samples of the correlation function in a memory; and determining, among the samples stored, the sample corresponding to the maximum of the correlation function and the rank of that sample.

Abstract: An FSK modem transmission circuit which includes a modulator adapted to sctably produce pairs of low and high frequency carrier waves in any combination of up to five frequencies specified in international and U.S. standards. The modulator circuit includes a regenerative feedback loop which generates a triangular carrier wave at a frequency determined by the resistance of a resistor network having five different settings selected by switches therein controlled by the data signal and by logic control signals. The transmission circuit also includes a filter which modifies the waveform of the transmitted carrier wave to suppress odd harmonics thereof, thereby isolating the carrier wave from the modem receiver circuit which is coupled to the transmission circuit by a hybrid coupler.

Abstract: Method and apparatus for reducing the convergence time of an echo canceller including a transversal filter having N adjustable complex coefficients comprises the following steps:transmitting a complex training signal constituted by data d(n) transmitted at instants nT, where T is the data interval, having a period LT at least equal to NT and having the following two properties: ##EQU1## for every integer i such that 1.ltoreq.i.ltoreq.N-1, and ##EQU2## for every integer i such that 0.ltoreq.i.ltoreq.N-1; after the transmission of N data, calculating the coefficients C of the transversal filter from the sequence formed by the next L data transmitted, in accordance with the expression: ##EQU3## where C.sub.o represents the N initial coefficients,e.sub.R (n) is the difference signal between the received signal and the real output signal of the transversal filter,D.sup.* (n) represents the complex conjugate value of the last N data entering the transversal filter, and.sigma..sup.

Abstract: In an asynchronous transmission mode, the bit synchronization arrangement receives data signals in the form of binary pulse trains (at A). It includes an oscillator (3) whose output signal (at C) has a frequency F.sub.OS approximately equal to twice the binary rate of the pulse trains and a transition detector (1, 22) which supplies a calibrated voltage pulse (at B.sub.2) at each data signal transition. The oscillator supplies a triangular internal signal (at D) at the frequency F.sub.OS and a phase correction circuit (2) is provided to reduce the algebraic value of the slope of this signal during each calibrated pulse so as to produce a predetermined constant advancing or delaying phase shift according as the calibrated pulse occurs during a negative or a positive ramp of this signal.

Abstract: In this transmission system using differential PCM, the local decoder, inporated in the loop of the encoder, and the remote decoder comprise identical filters (5) and (15) each constituted by a cascade arrangement of several filtering sections (F.sub.1 -F.sub.N) of the first and/or of the second order; each section may have one or two controllable coefficients, which are modified at each sampling instant by a modification term which depends upon the product of the difference signal (e) produced in the encoder and the gradient of the difference signal (e) with respect to the controllable coefficient. When the filtering sections (F.sub.1 -F.sub.N) are recursive, the gradients are obtained by applying a signal corresponding to the difference signal (e) to identical recursive sections (F'.sub.1 -F'.sub.N). When non-recursive filtering sections (H.sub.1 -H.sub.L) are used, the gradient calculation sections (H'.sub.1 -H'.sub.L) are recursive with a transfer function inverse to that of the sections (H.sub.1 -H.sub.

Abstract: An electroacoustic transducer apparatus which prevents oscillations as a result of acoustic coupling between an acoustic-wave transmitter and a receiver. The transmitter and receiver each comprise an electro-acoustic transducer network. The transducers in each network are arranged so that the phase and amplitude of the signals applied to the transmitter transducers and the signals supplied to an adder circuit by the receiver network transducers (25) to (30) of the receiver network are such that in the oscillation frequency band the radiation pattern of the transmitter network and the directivity pattern of the receiver network are zero in at least one direction. The two networks are arranged relative to each other so that the directions of minimum radiation and directivity correspond to the directions of maximum coupling between the transducers of the two networks.

Abstract: The system for transmitting information between a central station (SP) and sub-stations (SS1, SS2, SS3) operates, for the transmission from the sub-stations to the central station in accordance with a method (TDMA method) which consists in providing time slots in each of which only one sub-station can transmit, the arrangement of these time slots being determined by a synchronizing signal transmitted via a link from the central station to the substations; this system is characterized in that it comprises at the sub-station ends delay adjustment means (MR1, MR2, MR3 . . .

Abstract: An off-hook detector for use in subscriber line interface circuits to indicate status of the subscriber line, or loop, exhibits reduced sensitivity to common mode or longitudinal currents. A central signal from the exchange switches the transmission bridge for the subscriber line from a balanced to an unbalanced condition. In the balanced condition a difference detector indicates loop status. In the unbalanced condition, a comparator compares the voltage on one side of the transmission bridge to a reference voltage to indicate loop status.

Abstract: "Hands free" telephone sets in which there is connected in parallel with the terminals (A) and (B) of a first path (C.sub.1) comprising the coupling circuit of the telephone set in series with a controllable amplifier (11) of the receiving path (6), a second path (C.sub.2) comprising a controllable amplifier (12) which is controlled by a linear regulator (13) which keeps its output signal constant. The gains of the two amplifiers (11) and (12) respond to each other. A device is provided so as to ensure that the gain in the second path remains higher than the gain in the first path. A third controllable amplifier (5) is provided between the microphone (4) and the input terminal (A) which is used in common by the first and second paths; the said means (14) are adjusted in such a way that the electro-acoustic loop which is closed by the second path (C.sub.2) is permanently the source of non-annoying oscillations.

Abstract: A transmission path between two terminal stations for transmitting digital information signals at a predetermined rate in one direction via a forward path and in the other direction via a return path. The transmission path comprises regenerative repeaters. A system for tele-location of these repeaters comprises in one of the terminal stations a transmitter for transmitting tele-location commands to the repeaters via the forward path, carrier signals of the said rate being on-off modulated in this transmitter by an amplitude modulator in accordance with output signals of a command sequence generator, and further comprises in every repeater a loop circuit between forward and return paths having an associated control circuit which cooperates with a detector for detecting the presence of carrier signals in the return path and for receiving tele-location commands.

Abstract: In this subscriber line interface circuit which comprises a pair of amplifiers whose outputs are connected to the subscriber's line, the input terminals of these amplifiers receive by means of negative feedback voltages having opposite phases depending on the transversal current I produced by the line interface circuit and independent of the longitudinal currents I accidentally produced on the subscriber's line. The two load impedances, which are connected between the supply terminals of the amplifiers and the terminals of a d.c. voltage supply source are controlled by means of their control terminals by voltages which have the same characteristics as the voltages applied to the input terminals of the amplifiers but which in addition have been shifted with a certain shift voltage V.sub.z. Consequently, the amplifiers of the line interface circuit operate completely independent of the longitudinal currents.

Abstract: This arrangement comprises a controllable attenuation circuit of the voice signal received, a pulse-duration modulator which produces pulses the duration of which is modulated by the voice signal supplied by the controllable attenuation circuit, an overshoot detection circuit which produces from the modulated pulses a compression pulse each time it is detected that the amplitude of the modulated voice signal reaches a certain threshold, the compression signal produced by the said overshoot detection circuit being applied in the attenuation circuit to an integrating circuit which produces the attenuation control signal. The amplifier of the loudspeaker receives the modulated signal.

Abstract: High-pass, low-pass and band-pass filters are obtained by combining switched-capacitance integrating networks.

Abstract: This system comprises an encoder in which the differential PCM signal to be transmitted is formed as the difference between the incoming linear PCM signal and a prediction signal produced by a prediction filter comprising a local decoder receiving the said differential PCM signal. According to the invention the local decoder and the remote decoder are constructed in an identical manner by means of one or several filtering sections arranged in cascade, each filtering section being of the purely recursive or non-recursive type with one sole coefficient differing from zero and having been provided with its own roundoff (or truncation) device having a step size equal to the quantizing step of the differential PCM signal, the incoming linear PCM signal being rounded (or truncated) in the same manner. This construction enables the cascade arrangement of encoders and decoders without any further degradation of the signal then the degradation produced by the first coding.

Abstract: For feeding a telephone subscriber's line without the use of a transformer, this junctor comprises a symmetrical amplifier whose two input terminals receive two negative feedback voltages derived from a weighted sum current of the currents entering and leaving the subscriber's line. To form this weighted sum current, use is made of a current mirror whose summing and input terminals are connected respectively to one terminal of the supply source and to the corresponding supply terminal of the amplifier, and a voltage divider connected between the output of the current mirror and the other terminal of the supply source and whose intermediate terminal is connected to the other supply terminal of the amplifier. The voltage ratio of the voltage divider is equal to the current ratio of the current mirror. The voltage at the ends of the voltage divider is applied to a voltage follower which is regulated to provide the weighted sum current with the desired amplitude.

Abstract: Apparatus for detecting the closure of a subscriber's telephone line in the presence of an alternating ringing voltage superimposed on a direct voltage comprises circuitry for producing a unidirectional current from the combined alternating and direct voltages. When the line is open no direct current will flow and hence the peak value of successive half cycles will be equal whereas when the loop is closed and direct current flows the peak values of successive peaks will be different. A capacitor (26) is charged by a voltage (U.sub.1), which is proportional to the combined voltage, through a transistor (24), provided that the voltage (U.sub.1) is greater than the voltage across the capacitor, and discharged through a resistor (27). The time constant of the discharge circuit is selected so that when the line is looped the smaller peak is lower than the voltage to which the capacitor is discharged and hence charging current flows into capacitor (26) on alternate peaks of the voltage (U.sub.1) only.

Abstract: A subscriber's connecting network comprising a symmetrical power amplifier which is formed by two pairs of complementary transistors. Resistors having the same values are arranged in collector circuits of the transistors of the symmetrical amplifier for limiting the current in the subscriber's line. In addition, means are present for making the base voltage dependent on the collector voltage of this transistor so that a predetermined voltage is present between these two electrodes in the normal direction of operation. Finally a by-pass capacitor for the speech currents in the subscriber's line is arranged between two input terminals of the symmetrical amplifier. The invention is particularly suitable for a network in which binary signals are used for the generation of ringing signals and metering signals in the subscriber's line.