Patent GB-618770-A (GB)
Title: Pulse type multiplex communication system
IPC: H04J3/00
Filed: 1945-12-04
Abstract: 618,770. Multiplex pulse signalling pulse delaying circuits. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Dec. 4, 1945, No. 32802. Convention date, July 17, 1943. [Classes 40 (v) and 40 (vi)] In a multiplex pulse communication using interlaced time-modulated or durationmodulated interlaced channel pulse trains, the transmitter has a common pulse generator 14, Fig. 1, and means 21, 22, 23, &c. in each channel to delay the channel pulse trains for interlacing, gating means being provided at the receiver in each channel circuit to render it responsive to the appropriate received pulses. The channel pulse modulators 15, 16, 17, &c. precede the delayers 21, 22, 23, the outputs of the latter being combined and passed to a radio transmitter 10 ... 13. An unmodulated synchronizing channel train is provided by a delay circuit 20. The delay circuits may comprise a normally conducting triode 30, Fig. 2, the pulses being applied in a positive sense to the grid from transformer 31. The grid circuit includes a condenser 35 shunted by a resistance 36 which may be varied to adjust the delay time, anode current being fed through a resistance 32 and output transformer 33 and a condenser 34 being connected between their junction and earth. On applying a pulse to the grid the anode current is substantially unaffected but grid current flows to charge condenser 35 negatively and bias the valve to cut-off. Condenser 34 then becomes charged positively and later discharges through valve 30 to produce the output pulse when the charge on condenser 35 has leaked away through resistance 36 to render the valve once more conducting. In other similar delay circuits tetrode valves, e.g. 30<1>, Fig. 7, are used, the condenser producing the output pulse being connected to the screen grid, or two condensers being connected to anode and screen respectively. An extra diode may be used to charge the control grid condenser, and the output pulse may be sharpened by an inductive feed back from anode to grid circuit. Modulating circuits.-The pulse train may be modulated in time by supplying amplitudemodulated pulses to the pulse delay circuit. In one such arrangement, negative pulses from circuit 51 and the modulating signal from circuit 52 are applied in parallel to the grid of triode 50, 'Fig. 7, so that when the valve is cut-off by the pulses the energy stored in the anode inductance 54 is dependent upon the modulating signal input to the valve. The delay time, due to the circuit of the following tetrode 30<1>, is dependent upon the amplitude of the pulse output of inductance 54 when valve 50 is cut-off. In another embodiment, Fig. 8 (not shown), duration-modulated pulses are produced by modulating the amplitude of triangular pulses in the pulse delayer, and subsequently clipping the pulse in a limiter valve. Receiver synchronizing and gating.-At the receiver, a sawtooth blocking oscillator 92, Fig. 10, sends gating pulses through output coil 113 to the channel separators through suitable delay circuits. The oscillator is synchronized by pulses from the synchronizing channel, the incoming R.F. pulse train being fed to valve 75, which is gated to select said channel, and its output rectified at 91 and applied to the grid of valve 92. Specification 552,482 is referred to.