Abstract: The present invention relates to a multistatic sonar system having a particular mode of communication between the emitter base and the receiver bases responsible for detecting the sonar echoes. This system makes it possible in particular to circumvent the drawbacks occasioned by the use of radio communications or of satellite-based communications generally used. The signal emitted by the emitter base comprises an apprisal pulse conveying information pertaining to the mode of operation of the system according to the invention, in particular the instant of emission, and a sonar pulse proper. This system is especially intended for use by underwater vessels while diving, for detecting and locating surrounding objects or controlling the positioning of an autonomous underwater vehicle.

Abstract: The invention relates to towed acoustic transmitters forming an underwater vehicle which is itself intended for towing a linear acoustic receiving array (105). It consists in placing the vertical faired acoustic array (303) of such a transmitter at the very rear of the underwater vehicle, and in balancing the weight of this array by a faired ballast (313) situated at the very front thereof. These two parts are joined by a girder (310) of small cross-section, and the center of gravity of the whole is situated at the front of this girder and beneath it. The vehicle is towed by a cable (101) fastened to the vehicle by a hook (314) fixed to a swivel joint (315) above the center of gravity. It makes it possible to facilitate the operations of submersion and fishing-out of the whole while also achieving a greater depth of submersion.

Abstract: The invention relates to towed sonars. It consists in compensating electronically for the movement of the antenna in order to suppress the Doppler shift of the fixed echoes. In order to do that in a towed linear antenna (203) comprising N sensors (205), M (M<N) successive sensors are selected which are switched electronically in order to make them travel synthetically over the antenna in the direction opposite to the movement of the latter at a speed equal to twice the forward speed of the antenna. In order not to have too large a number of physical sensors, the signals from the latter are interpolated in order to obtain synthetic sensors which are sufficient in number to reduce the increment of the movement of the synthetic sub-antenna in such a way as to suppress the parasitic lobes due to the incremental nature of this movement. It makes it possible to increase the sensitivity of sonars without increasing their power. FIG. 2.

Abstract: A circuit for rapidly resynchronizing a clock with an external clock is disclosed. The clock to be synchronized is obtained at the output of a phase-locked loop by dividing the frequency of a reference clock in a frequency divider whose division factor is controlled by a phase controller which detects the deviation between the transitions of the two clocks to be synchronized. According to the invention, the pulses of the reference clock are applied to the phase-locked loop by means of a gate, with this gate being rendered nonconductive by means of the characteristic transition of the clock to be synchronized which follows the appearance of a resynchronizing control signal, and thereafter this gate is rendered conductive by means of a characteristic transition of the external clock.

Abstract: Digital echo canceler for a modem for data transmission by means of phase and, possibly, also amplitude modulation of a carrier, the ratio between carrier frequency f.sub.o and modulation rate 1/T having the form P/Q, P and Q being integers.The echo canceler receives the binary data to be transmitted for generating an echo copy signal. An echo canceler of a simple implementation is obtained in that the echo canceler comprises means responsive to each symbol configuration at each instant iT for generating at least a number depending on the amplitude allotted to the carrier at said instant iT and for applying this number to at least a given section of an assembly of adaptive digital filter whose output signals are combined for forming a digital version of the echo copy signal, the coefficients of these filters being adjusted by an assembly of adjusting circuits receiving said error signal in digital form and arranged for minimizing a predetermined function of said error signal.