GB369934A - Improvements in high frequency signalling systems - Google Patents

Abstract

369,934. Wireless signalling. STANDARD TELEPHONES & CABLES, Ltd., Columbia House, Aldwych, London.- (Tournier, M. C. ; 46, Avenue de Breteuil, Paris.) Dec. 23, 1930, No. 38665. [Class 40 (v).] The modulated wave of a highfrequency signalling system is applied to one or more electro - mechanical resonating d e - vices, such as p i e z o - electric crystals, adapted to attenuate the carrier wave while leaving one or both sidebands unaffected, the attenuation being carried to such a point that whilst saving power at the transmitter the receiver is still able to receive the carrier wave and to subject it to amplification independently of the side bands. The carrier is generated in a source O, Fig. 3, and is modulated by a signal source S in a modulator M. The modulated wave passes to the resonator R which attenuates the carrier wave, and thence to an amplifier A and transmitter T. The degree of attenuation of the carrier may be adjusted by varying the air gap between the absorbing crystal and its electrodes. At the receiver, Fig. 4, the received signals are amplified at A, and are then separated into two channels. In one, the pure carrier wave is selected by the resonator R and highly amplified by the amplifier Ac. In the other the carrier and sidebands are passed through a flatly tuned amplifier Ab. The two channels recombine in a detector D feeding a signal receiver R. If desired, one of the side bands may be suppressed at the transmitter. The received waves may be changed in frequency by the superheterodyne method before they are divided into the two channels. Specifications 294,177, [Class 40 (v), Wireless signalling &c.], and 344,869 are referred to.