GB591884A - Pulse communication systems - Google Patents

Abstract

591,884. Multiplex pulse signalling. STANDARD TELEPHONES & CABLES, Ltd. April 13, 1945, No. 9320. Convention date, April 20, 1944. [Class 40 (v)] Two pulse trains of the same periodicity are modulated by the same signal source, but in phase opposition, and interlaced to form a single pulse train, the latter being modulated by a second signal source for masking the first signals or to convey further intelligence. In one embodiment, the transmitter comprises a sine wave generator 4, Fig. 1, of half the radiated pulse recurrence frequency, feeding a wave shaper 8, producing square waves 10, followed by a differen. tiator 16, producing pulses 20. The positive pulses are modulated in amplitude in tetrode V1 to the screen grid of which is applied the modulating signal from one end of the secondary of transformer 28, producing pulses 30. The wave shaper 8 also feeds an inverter 12 producing a square wave 14 of opposite polarity to wave 10 which is differentiated at 18 producing pulses 22. The positive pulses are amplitude modulated in tetrode V2 by the modulating signal from the other end of the secondary of transformer 28 to produce pulses 32. Pulses 30 and 32 are mixed to produce pulse train 36 which is converted into a train of radio frequency pulses, in translator 38. Curves a and b, Fig. 2, represent the unmodulated pulses from V1 and V2 respectively. In curve c, 45 is the modulating wave applied to V1, and 47 is that applied to V2, the resultant pulse outputs being shown at d and e and their combination at f. A masking wave, curve g or a second signal may modulate all the pulse amplitudes by superposing it on the common H.T. supply voltage of valves V1, V2 from the generator 43, Fig. 1. The resulting doubly modulated pulse output is shown in curve h, Fig. 2. At the receiver, Fig. 3, valves 70, 72 are gated to pass the odd and even pulses respectively by voltages from the anodes of valves 60, 64 of a multivibrator 62 which is synchronized to half the pulse recurrence frequency by the output of a tuned circuit 56 energized by a valve to the grid of which are applied the incoming pulses. The modulation envelopes of the pulse outputs of valves 70, 72 are obtained in the outputs of filters 82, 84 respectively and after one has been phase reversed in circuit 76, they are combined in circuit 78, to add the two versions of the first signal and cancel out the masking or second signal. Alternatively the first signal may be cancelled out and the second produced in the output by shifting switch 85 to contact 87 to byepass the inverter stage 76. An embodiment of the invention using push-pull time modulation of pairs of the pulses is also described, Figs. 4, 5, 6 (not shown). The two modulators are of the cusper type and each demodulator is arranged to generate a demodulating wave of harmonic frequency by frequency division of the output of a tuned circuit, shock-excited by the incoming pulses and then multiplication to produce an odd harmonic.