Telecommunications Radioelectriques Et Telephoniques T.r.t.

Emmanuel Lefort

Gilbert M Ferrieu

Francoise Moliere

Maurice Georges Bellanger

Jean-Louis Jeandot

Tuan K Duong

Roger B Hamel

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.

Acoustic feedback cancelling electro-acoustic transducer network

An anti-Larsen circuit for a telephone station in which the listening channel comprises an automatic listening level control circuit, suitably of the type comprising a variable attenuator circuit, a pulse-width modulator and a threshold detector which supplies compression pulses. The transmission channel comprises a circuit for rendering the transmission channel operative or inoperative and also a control circuit. Actuation takes place above a sound-level threshold S.sub.1 and a de-activation below a sound-level threshold S.sub.2 which is smaller than S.sub.1.

Anti-larsen-effect arrangement in a telephone station equipped with a

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.

Automatic sound level control of telephone station

A balancing amplifier comprising a pair of transistors arranged as a differential amplifier and a negative feedback network including a transistor voltage follower as a part of the load circuit of each transistor of the pair of transistors. Owing to the negative feedback network high level signals can be balanced. The amplifier provides output signals in phase opposition from a single-ended input signal.

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Montigny le Bretonneux, France

Emmanuel Lefort