Improvements in or relating to secret signalling systems

Abstract

Abstract 776,129. Optional signalling systems. TOUVET, G. Nov. 2, 1955, No. 31292/55. Class 40(3). In a secret signalling system using optical radiation the intensity of the optical radiation is modulated in accordance with the intelligence to be transmitted, the overall amplitude of the intensity being kept constant. As shown (Fig. 4), radiation from a source 8 of constant intensity such as a filament lamp or an arc is focused by a lens 9 on an electro-optical modulating device 10 such as a Kerr cell in which the intensity of the light source is modulated. The modulating device is controlled by the output of an oscillator 14 modulated at 13 with the intelligence to be transmitted. The modulation may comprise (a) two components of different frequencies whose amplitudes are complementarily modulated so that the amplitude of one increases as the other decreases; (b) a single frequency modulated component the amplitude of the frequency modulated carrier being maintained constant; (c) a single-phase modulated component; or (d) a frequency shift telegraph system in which an oscillator is keyed between two alternative frequencies one of which represents marks and the other spaces. The effective strength of the source is kept constant while the frequency changes. In the arrangement of Fig. 5 (not shown), two different light sources are used the modulation being of the kind referred to at (a) and (c) above. In the arrangement of Figs. 1 and 2 (not shown), the intensity of the source itself is modulated. Specification 774,471 is referred to.

Inventors

No inventors recorded.

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