Abstract: In a digital mobile system, to avoid distortions and fadings due to multiple propagation and the doppler shift, adaptive gain of the amplifier of a demodulator must be controlled with information derived from the signal at a high frequency. This is accomplished without the use of intermediate frequency selection filters by first demodulating the signal to base band, filtering out the desired signal and remodulating the desired signal to a higher frequency. From this remodulated signal the adjustable gain is controlled.

Abstract: A telephone exchange communicates with a number of scattered local stations via radio links extending from a central terminal to respective peripheral installations each comprising a radio transceiver coupled via a repeater to the line loop of an associated local station. The repeater includes a constant-current generator, combined with a polarity inverter, which is controlled via a logic network in response to signals from the exchange and from the local station (detected by a sensor in the line loop) to reverse the flow of direct current for the transmission of binary pulses to the local station. In the case of a private subscriber, these pulses may be an intermittent square wave generating a ringing signal; in the case of a public pay station they may constitute commands for the collection of tokens or coins.

Abstract: A subcarrier frequency-modulated with a message signal is heterodyned with a carrier from a crystal-controlled oscillator in a mixer whose output is fed to a filter eliminating one of the resulting sidebands. In order to compensate temperature-dependent fluctuations of the carrier frequency, a function generator produces a corrective signal which is added to the message signal in the input of the frequency modulator traversed by the subcarrier. The corrective signal varies as a quadratic or a cubic function of temperature, depending upon the type of cut used on the quartz crystal controlling the carrier oscillator, with a polarity determined by which of the two sidebands is passed by the filter.