Patent GB-673805-A (GB)
Title: Improvements in or relating to electric signal communication systems
Inventor: EARP CHARLES WILLIAM
IPC: H04B14/04
Filed: 1950-12-20
Abstract: 673,805. Multiplex pulse signalling pulse circuits. STANDARD TELEPHONES & CABLES, Ltd. Dec. 20, 1950, No. 31024/50. Classes 40 (v) and 40 (vi). In a commimication system, at the transmitter an electrical wave is periodically sampled and single indices representing the samples ambiguously on a continuous scale are transmitted to the receiver where the wave is recovered unambiguously by means responsive to the rate and direction of drift of the indices. As described, the samples are first converted into primary pulses, which are time-position modulated by the signal over a relatively large range, and time-position modulated index pulses are transmitted, which represent ambiguously the time position of the primary pulses and which have a relatively small modulation range. In one embodiment, a time division multiplex system is controlled by the master oscillator 1, Fig. 1, operating at 10 kc/s. A synchronizing pulse generator 3, controlled thereby, produces one microsecond pulses 18, Graph A, Fig. 2, spaced apart by twenty-four channel periods. The apparatus for the seventh channel, for example, comprises a phase modulator 6, to which the 10 kc/s. wave is applied through adjustable phase-shifter 5, and the modulating channel wave from terminals 7, 8, through an integrating circuit 9. The phase-modulated wave is converted into a primary pulse train by generator 10, the pulse times of which are modulated between the limits 21, 22, Graph B. Each primary pulse is converted into a short train or " comb " of 0.1 microsecond pulses by opening up a blocked valve 13 to shock-excite a resonant circuit 14, tuned to 500 kc/s., and the output from which is converted into the pulse comb by generator 15. Thus an unmodulated primary pulse 20, Graph B, is converted into the pulse comb, Graph C, the middle pulse, approximately, of which, say 24, occurs during the seventh channel period defined by the two microsecond channel gating pulse 19 produced by generator 12. The modulated pulse 26 produces the shifted pulse comb, Graph D of which pulse 27 occurs during the channel gating period. The pulse combs and gating pulses are applied to the circuit 16 which selects one pulse from each comb for transmission to the outgoing line 4 as ambiguous index pulses. At the receiver, Fig. 3 (not shown), the channel index pulse train, after separation, is applied to a filter which selects the harmonic having a frequency of 500 kc/s., viz. that of the pulse combs at the transmitter. This wave synchronizes a local oscillator of the same frequency, the output of which is preferably frequency divided to pass a 125 kc/s. wave to a frequency discriminator which yields the differential of the wave fed to the phase modulator 6 at the transmitter, that is to say, the same wave as was applied to the terminals 7, 8. In a modification of the transmitter of Fig. 1, the channel wave frequency modulates an independent 500 kc/s. source, the output from which is converted to a pulse train which is fed to the gating circuit, the integrating circuit being unnecessary, Fig. 4 (not shown). In a further embodiment both positive and negative index pulses are produced which, if a radio channel is used, may frequency-modulate a carrier wave. The primary pulses are applied to a cut-off valve 48, Fig. 7, which conducts to shockexcite a 250 kc/s. resonant circuit 50 ... 54, the wave train from which is squared by valve 55 and differentiated by transformer 72. The square wave train, Graph E, Fig. 2, is thereby converted into trains of alternate positive and negative pulses, Graphs F, G, which are respectively applied from the ends of the centretapped secondary of transformer 72 to the control grids of valves 70, 71. The channel gating pulse 19 is applied in parallel to the suppressor grids of these valves which are normally cut-off. The output transformer 73 is connected in pushpull to the two valves and feeds a positive or negative pulse to the output terminal 63 depending upon which valve has a positive pulse at its control grid during the occurrence of the gating pulse. At the receiver, two cut-off valves 79, 80, Fig. 8, are connected in push-pull to the index pulse input terminal 84 through transformer 85. Positive and negative pulses respectively unblock valves 79, 80 to shockexcite the resonant transformer circuit 86, 87 in cumulative fashion, the resulting output wave being used to synchronize a local oscillator operating at 125 kc/s. The frequency discriminator 90 operates at half this frequency through a frequency divider 89. Specification 673,354 is referred to.