Abstract: The modulating device reduces the number of electronic functions required for generating an SSB signal which is subjected to SSB peak-limiting in a transmitter which is selectively operable either on the upper channel or on the lower channel. By means of a mixer, the signal delivered by the peak-limiter is mixed with a signal whose frequency is double that of the local oscillator. By filtering the signal thus obtained by means of the filter which is symmetrical with the filter employed for carrying out SSB modulation, the signal to be transmitted on one of the channels is thus obtained. The signal to be transmitted on the other channel is obtained by reversing the position of the two filters.

Abstract: Prior to each voice activity period, the transmitter supplies a digital preamble for coding the speech signal levels and during these periods high frequency signals modulated in substantially constant amplitude, but transmits nothing other than said preamble and said periods. On reception, a signal detector and logic elements control a switch to obtain only speech signals at the input of an attenuator. The preamble decoding circuit controls the attenuation value of the attenuator in order to resupply to the receiver output signals of the same relative level as those applied to the transmitter input.

Abstract: The transceiver according to the invention is controlled by an automatic alternation device in order to permit transmission solely when voice signals are to be transmitted and when the receiver does not receive such signals. On transmission, the transmitter supplies constant amplitude-modulated, high frequency signals during voice activity periods and supplies nothing outside these periods. On reception, a detector for detecting the rapid amplitude transitions of the received signals and a logic circuit control the switching off of an electronic switch during the voice activity periods, so that the output of the receiver only supplies voice signals. The gain of the receiver amplifier is controlled by an automatic control loop. The value of the time constant of this loop is controlled so as to be low during the voice activity periods and high outside these periods.