GB652366A - Improvements in and relating to electric, pulse-signalling systems - Google Patents

Abstract

652,366. Pulse modulation multiplex pulse signalling ;. pulse shaping circuits. GENERAL ELECTRIC CO., Ltd., and LEVY, M. M. April 30, 1947, No. 11613. [Classes 40 (v) and 40 (vi)] Interference, in a receiver for a modulated pulse train, is reduced by generating a second pulse train of substantially the same waveform as the first but reversed in sign, and combining the two trains with a time displacement between them. Considering one pulse P of a time-modulated train, it is raised together with the base line, to a level p<SP>1</SP> by the interference voltage. It may, alternatively, be lowered, Fig. 2 (not shown). A corresponding inverted pulse D<SP>1</SP>, delayed by a time t, is produced by the reflection of pulse P<SP>1</SP> in a delay network, Fig. 4 (not shown), or by passing pulse p<SP>1</SP> through a matched delay network to a further amplifying valve which effects the phase reversal, Fig. 5 (not shown). On adding pulses p<SP>1</SP>, D<SP>1</SP> the wave (c) is produced, and the voltages due to interference (of a period long compared with the duration of the pulses) cancel. Demodulation is effected by clipping between L<SP>1</SP>, L<SP>2</SP> and selecting the steepened trailing edge of the pulse. The delay time t may vary from half the pulse width to several times the pulse width Fig. 3 (not shown). The factors governing the choice of this value are discussed. In a multi-channel system, cross talk between channels may be reduced by these means. A pulse with two steepened edges can be produced by combining with the signal pulse two inverted pulses, one suitably advanced, the other delayed. Both steepened edges may then be used for demodulation. The invention is also applicable to width modulated pulses, Fig. 6 (not shown). Specifications 641,982 and 652,353 are referred to.