Patent GB-655697-A (GB)
Title: Multichannel electric pulse communication system
IPC: H04J3/04
Filed: 1948-09-10
Abstract: 655,697. Multiplex pulse code signalling. STANDARD TELEPHONES & CABLES, Ltd. Sept. 10, 1948, No. 23838. Convention date, Sept. 17; 1947. [Classes 40 (v) and 40 (vi)] In a multi-channel pulse communication system of the kind described in Specifications 627,462, 651,088 and 651,115, in which the pulse code represents changes of signal amplitude, two electronic distributers are provided, the second of which produces the control voltages of the respective channels and applies them to corresponding elements of the first, which has means for scanning these elements to produce pulses indicative of the control voltages for transmission. In one embodiment, Fig. 1, the channel pulses are produced in a cathode-ray distributer 11 when the beam causes the emission of secondary electrons from the dynodes 17, swept thereby, the common collecting electrode 18 having a low impedance 19 across which the pulses are developed. The pulses are shaped in circuit 14 and fed to the radio transmitter 2, 3, 4. The dynode 17 for each channel is supplied with a control voltage from the comparator 7 through a limiting amplifier 12. The comparator 7 comprises two triodes 40, 41 having a common cathode load resistance 43 and the grids of which are fed in opposite senses with the modulating signal, from source 5, 6, and the output of a demodulator 8, respectively, the demodulator being fed with the appropriate channel pulses from shaper 14, through a delay device 10 and cathode-ray distributer 9, which is fed from the same scanning potential source 1 as the distributer 11. When the demodulated signal amplitude from circuit 8 exceeds the modulating signal the comparator 7 produces a positive output which prevents the dynode 17 from producing an output pulse. As long as the modulating signal amplitude exceeds the demodulated signal the dynode continues to develop a pulse for each revolution of the cathode-ray beam. The pulses fed to the demodulator are widened in a flip-flop circuit 32 and fed to the grid of valve 36 to charge condenser 37 connected in the common anodecathode circuit of valves 35, 36. Valve 35 is so biassed to discharge condenser 37, during the interval between two successive channel pulses, that half the charge is lost which is gained from valve 36 during an applied pulse. The demodulated signal voltage across condenser 37 is fed through amplifier 39 to the comparator valve 41. A longer synchronizing signal pulse is derived from the dynodes 22, 23, 24, the pulses from which are made to overlap by defocusing the beam or using inductances 25 in series with the first two. At the receiver, Fig. 2, the pulse output from the radio receiver 45 and shaper 47 is applied to the channel distributer 50 feeding demodulators 66 similar to circuit 8, Fig. 1, followed by low-pass filters 67 and reproducers. The long synchronizing pulses are selected by valve 51 feeding an integrator 52, 53, 54, the diode 54 preventing integration of successive signal pulses and ensuring a sharp trailing edge to the voltage wave across the condenser 53. The synchronizing pulses are now of greater amplitude than the signal pulses and, after separation by clipping in valve 56, are differentiated in circuit 58, 59, the positive trailing edge pulses being selected by diode 60 and applied to valve 62. The high-Q tuned circuit 63 in the anode circuit of valve 62 is excited by the pulses to produce sinusoidal oscillations which provide the scanning potentials for distributer 50. In another embodiment, Figs. 3 and 4 (not shown), each transmitter channel uses two of the distributer dynodes so that a pulse is transmitted for every cycle of the distributer, the timing of which depends upon which of the two comparator output conditions obtain. At the receiver, a flip-flop circuit produces a positive or negative pulse depending on the timing of the received pulse, and the demodulating condenser is charged through one valve by the positive pulses and discharged through a second valve by the negative pulses reducing the condenser voltage by half that added by each positive pulse.