GB634372A - Improvements in or relating to pulse modulation signalling systems - Google Patents

Abstract

634,372. Pulse signalling. PHILIPS LAMPS, Ltd. Aug. 30, 1946, No. 26164. Convention date, June 21, 1943. [Class 40 (v)] in a time modulated pulse signalling system, twin or multiple pulses are used, each consisting of two or more constantly spaced pulses, both or all of which are used at the receiver to produce single pulses which are transformed into intelligence signals. The arrangement avoids the risk of undesired pulses being produced by interference during reception. For transmission, the twin pulses may be produced by utilising two channels, one having a retarding circuit, or by means of a differentiating network, which produces two pulses of opposite polarity for each applied pulse, and then reversing the phase of one of these pulses. For reception, the signals are applied to a normal superheterodyne receiver 9-12, Fig. 4. After detection, the twin pulse signals are applied via a limiter and threshold valve circuit to a special pulse divider 15. This pulse divider comprises one channel with amplifier 21 and a parallel channel with a delay circuit 22 and an amplifier 20. The delay time of circuit 22 is chosen so that the retarded first pulse of the pulse combination is applied in like phase and simultaneously with the second pulse to threshold valve stage 23. Thus, only signals derived from the combination of two input pulses separated by the predetermined interval, will be applied from stage 23 to pulseshaping circuit 24 and thence through a filter to reproducing device 17. A circuit suitable for use as retarding circuit 22 is described in Fig. 5 (not shown), in which gas discharge tube 29 is rendered conducting by the input signals which are applied to the control grid and condenser 25 then discharges through inductance 29 thereby producing a rising voltage in coupled inductance 31 which is applied to the output terminals. The second pulse arrives while tube 29 is still conducting and thus has no effect. Fig. 7 shows a similar circuit in which an additional tube 291 and condenser 25<1> is also provided. In this case, tube 291 is sensitive to triggering impulses only when tube 29 is conducting, the discharge current from condenser 25 then modifying the cathode potential of tube 29<1>. If an input pulse is received during this period, tube 29<1> conducts, the resulting output from inductance 31<1> then being applied to the output terminals. Alternatively, a transmission line may be utilised for retarding circuit 22, the delay period then being adjustable. The use of multiple pulses as distinct from twin pulses, would involve similar arrangements, but would comprise a plurality of delay channels.