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: A modulator transmitting an analog data signal by variation of the frequency of an oscillator comprising an integrator (1, 2) and a bistable circuit with trigger hysteresis (8 to 13). The two-level voltage from the bistable circuit, taken to a terminal of a resistor network (6, 7, 30) connected to the input of the integrator, is formed from the potential O and the potential kU, which is lower than the supply voltage U, applied respectively to the inputs of two analog switches (12, 13) whose outputs are connected to the output of the bistable circuit. The data signal v.sub.e is applied to the input of a conversion circuit (17) arranged to supply voltages v.sub.e1 and v.sub.e2 varying linearly as a function of v.sub.e and symmetrically with respect to kU/2 and applied respectively to the inputs of two further analog switches (26, 27) whose outputs are connected to another terminal in the resistor network. The input and output signals of the inverter (9) of the bistable circuit are used to control the switches.