GB592412A - Improvements in electric pulse modulation systems of communication - Google Patents

Abstract

592,412. Multiplex wireless signalling; pulse modulation. STANDARD TELE. PHONES & CABLES, Ltd. June 2, 1944, No. 10680. Convention date, Feb. 6,1943. [Class 40 (v)] A receiving arrangement for selecting a particular one of a plurality of signal modulated electric pulse trains, the repetition frequencies of which trains differ slightly from one another. Comprises means for blocking the receiver against the undesired pulses and means for blocking the receiver also against the desired pulses for those periods during which the desired and undesired pulses overlap. Figs. 1 and 2 show an arrangement in which 10 is a source of pulses a, Fig. 2 (I), and 12 is a source of pulses b, Fig. 2 (II), the two-pulse frequencies being slightly different. The pulses a and bare transmitted on a common channel 14 which may be wired or a common carrier wave, and received by receivers 16, 16<1> which both receive both trains of pulses. Considering 16, the input will be as in Fig. 2 (III) showing at intervals varying degrees of overlapping of the a and b pulses. A blocking unit 20 producing pulses as in Fig. 2 (IV) blocks the first receiver 18 except during the a pulses, thus giving an output as in Fig. 2 (V) in which the b pulses are removed except where they overlap the a pulses to produce peaks. The peaks are taken off in a clipper 28 and inverted in a shaper 30 to be applied to a second receiver 26 to eliminate those parts of the a pulses which are overlapped, thus giving an output as in Fig. 2 (VI). The pulses are differentiated at 32 and demodulated at 36, and finally passed through a low-frequency rejection circuit 38 to remove the low beat note due to the periodic absence of pulses and clipped pulses in the waveform, Fig. 2 (VI). The output will be free from interference by b pulses. The receiver 16<1> operates in a similar way to eliminate the effect of a pulses. Any number of channels may be similarly treated. In a modification, Fig. 3 (not shown), the interfering pulses are eliminated at the carrier frequency stage. In this case, the second blocking pulse is made wide enough to cover the complete series of consecutive overlapped pulses and eliminate them to leave wider gaps in the resulting pulse train. The invention may be used to eliminate a jamming pulse which is not exactly synchronized with the desired pulse signal.