Patent GB-633730-A (GB)
Title: Pulse multiplex communication system
IPC: H04J3/00
Filed: 1947-05-21
Abstract: 633,730. Multiplex pulse signalling; pulse generating circuits; thermionic distributers. RADIO CORPORATION OF AMERICA. May 21, 1947, No. 13686. Convention date, June 1, 1946. [Classes 40 (v) and 40 (vi)] [Also in Group XL (b)] In a receiver for a pulse multiplex system, which uses interlaced channel pulse trains and a synchronizing pulse train, each synchronizing pulse produces a plurality of waves which control a step wave generator, the step wave having a number of risers corresponding to the number of received pulses between the synchronizing pulses and being applied in common to all the channel separating circuits which are thus rendered responsive in turn to signal pulses. Step-wave generator.-In the embodiment described, the synchronizing pulses from the video output B, Fig. 2a, of the radio receiver are separated in the valve 1, Fig. 3a, an output differentiating circuit, and the biassed-back valve 2, which responds only to the trailing edge of the differentiated synchronizing pulse C. The output D from the cathode of valve 2 is applied to the normally non-conducting valve 3, the output E of which is applied after shaping, curve F, to the grid of the normally conducting valve 4. The anode pulse G is applied to the normally non-conducting valve 5 to produce pulse H at its cathode. This pulse is applied to a phasing trigger circuit 6, 7 and over lead 100 to the step-wave generator. The trigger circuit 6, 7 is a flip-flop multivibrator giving waveform I at the anode of valve 6 and waveform J at the common cathode point. The latter has a positive peak, the timing of which can be adjusted by a variable tap on the anode resistor of valve 7. This positive peak causes valve 8 to pass current K, Fig. 2b, and shock-excite the tuned circuit 8<1> to produce, for example, nine oscillations L for each driving pulse. These oscillations are rectified by valve 9, the output M from its cathode being fed to the peaker valve 10 to produce a peaky wave N, the negative portions of which are caused by reaction from the stepwave generator coupled thereto. The positive peaks of wave N cause valve 12 to conduct to charge condenser 44 in steps P. The pulses H from valve 5 are applied to valves a, b, c which are normally non-conducting, but which are caused to conduct thereby. Valve c discharges condenser 44, and valve a prevents valve 12 from conducting during this period while valve b discharges the load capacity connected to the cathode of the output valve 13. Valve 11 is normally non-conducting but conducts to restore the coupling condenser 43 to its original condition after each input pulse to valve 12. Channel separation and demodulation.-The channel separator and demodulator for one channel, for example, the fourth, are shown in Fig. 3b. The step-wave is applied to the grid of valve 21 which is so biassed that it conducts at the fourth riser of the wave, and the differentiating coil 30 in its anode circuit produces a corresponding sharp negative pulse Q, Fig. 2b. The flip-flop multivibrator pair 23, 24 is triggered by this pulse and is restored before its normal time by the next time-modulated channel signal pulse R over lead 101, through the valve 22. The duration-modulated pulses S thus produced are passed through low-pass filter 34 to the audio amplifier 27 for the demodulated signals. The gate valve 22 only responds to a signal pulse if, at the same time, a positive pulse R from the common cathode point of valves 23, 24 is present on its grid. Calling.-The pulses at the anode of valve 23 are applied to valve 25 through a low-pass filter comprising resistance 35 and the input grid capacity, and also to the anode of rectifier 26. The full line T, Fig. 2b, indicates unmodulated pulses thus applied. The bias on valve 25 is derived from the rectifier 26 and it conducts on the peak of such pulses to produce a cathode potential which, applied through lowpass filter 37 ... 39, to the grid of amplifier 27, enables the latter to function. Calling is accomplished by advancing the channel pulses to their extreme position. The narrow pulses produced at the anode of valve 23 after passing the filter to valve 25 are of such low amplitude that they cannot cause valve 25 to conduct, so that valve 27 is cut off and a ringing relay in its anode circuit opens to connect a ringing generator to the outgoing line.