Patent GB-663086-A (GB)
Title: Improvements in and relating to pulse signalling systems
Inventor: LEVY MAURICE MOISE
IPC: H01J31/06
Filed: 1948-08-11
Abstract: 663,086. Multiplex pulse signalling. GENERAL ELECTRIC CO., Ltd. July 21, 1949 [Aug. 11, 1948], No. 21192/48. Class 40 (v). In a pulse multiplex system using interlaced channel trains of amplitude or duration modulated pulses, the anodes of a cathode-ray demodulator-distributer at the receiver are associated with capacitances which are charged to a voltage dependent upon the amplitude or duration of the corresponding channel pulses and discharged shortly before the application of a fresh charge, the channel modulations being derived from the voltages across said capacitances. In one embodiment, the incoming pulse train at terminal J, Fig. 2, is applied to the grid of the distributer tube D1 through a delay network F. The pulse trains for each channel are separated at anodes A, the circuit for one channel being shown. The capacitance C is negatively charged by each pulse applied to anode A, to a voltage dependent on the amplitude or duration of the pulse and remains charged for most. of the pulse recurrence period, which voltage is applied to the grid of valve V1 and thence to the lowpass filter LPF by which the modulation is extracted. The biassed diode B is rendered conducting to discharge condenser C, just before the beam reaches anode A to recharge it. For this purpose a second cathode-ray distributer D2 is supplied with the pulses from terminal J through a limiting circuit LM and the scanning of the two tubes is so phased by phase shifter PS that a limited pulse reaches anode A1 of tube D2 just before the modulated pulse reaches anode A of tube D1. The pulse at A1 causes the current LC to ring and the first positive peak of the resultant wave renders the diode B conducting to discharge capacitance C. The anodes A are in the form of buckets to ensure that the amount of secondary, emission therefrom is less than the beam current. The distributer tube D1 may be arranged to convert time-modulated pulses into amplitude modulated pulses in known manner. In a modification, the beam in tube D2 remains switched on, the delay network F and limiter LM being omitted. Positive pulses are generated at the anodes A1, by arranging them to be secondary emitting, and the ringing circuit is replaced by a resistor. In another modification the anode A, Fig. 3, and capacitance C are connected to the cathode of a triode V2. The control grid of V2 is connected to the anode A1 through condenser C1, the anode being connected through inductance L to earth. A grid resistance R shunted by diode B1 acts as a self-biassing circuit for valve V2. When capacitance C is charged negatively by a pulse the valve V2 remains non-conducting. A pulse at anode A1, shock-excites the tuned circuit L and stray capacitance C2 and the first positive half cycle of the resulting wave renders valve V2 conducting to discharge capacitance C and allow current to flow in diode B1 to recharge C1. In another embodiment, a single tube of the type described in Specification 652,400 is used both to charge and discharge the capacitance C at the appropriate times, Fig. 4 (not shown).