Patent GB-662956-A (GB)
Title: Improvements in or relating to pulse-modulation signalling systems
IPC: H04J3/06
Filed: 1949-03-02
Abstract: 662,956. Multiplex pulse signalling. PHILIPS ELECTRICAL, Ltd. March 2, 1949 [March 5, 1948], No. 5714/49. Class 40 (v). In a pulse multiplex communication system the constant amplitude pulses of a synchronizing pulse train occurring at channel recurrence frequency are time modulated at a frequency which is a subharmonic of the channel recurrence frequency and higher than the highest signal modulation frequency, and at the receiver, a synchronizing voltage derived therefrom, is fed to a circuit tuned to a subharmonic of the channel recurrence frequency, serving to synchronize a generator operating at channel frequency. As described, the transmitter comprises an oscillator 13, Fig. 1, working at four times the channel recurrence frequency and controlling a pulse generator 12 of the same frequency. A frequency-dividing pulse generator 11 is fed from generator 12 and operates at channel recurrence frequency. Generator 11 feeds pulses to the cascade of channel gating pulse generators 6 ... 9, the termination of each gating pulse being determined by pulses from generator 12 over lead 14. The generators 6... 9 control channel pulse phase modulators 15 ... 18 through amplifiers 1 ... 4 respectively. Three channel signals from terminals 5 are fed to amplifiers 2, 3, 4 respectively. and amplifier 1 of the synchronizing signal channel is modulated by a sine wave oscillator 23 stabilized at half the channel frequency by the generator 11. Each intelligence channel may include a low-pass filter cutting off at a frequency lower than that of the synchronizing signal from oscillator 23. The pulses of the synchronizing channel are distinguished from those of the intelligence channels only by their modulation. All the pulses are fed to a radio transmitter 24, 25, 26. At the receiver the pulse train at the output of the radio receiver 27, 28, 29 is fed to the pulse phase demodulators 30 ... 33, which are controlled by gating pulse generators 35 ... 38 excited in succession like those at the transmitter. The demodulated channel signals are fed through amplifiers 44, 45, 46 to output terminals 48, in the case of the communication channels, The synchronizing signal, recovered from demodulator 33, controls a pulse generator 70, 71 controlling the gate pulse generators over lead 39. All the pulse demodulators are similar to that used for extracting the synchronizing signal, which comprises a secondaryemission valve 49. The phase modulated pulses 1, 2, 3, 4, &c., Fig. 3, A, are fed to grid 50 and rectangular gating pulses S, Fig. 3, H, to screen grid 51. The gate pulses are also applied to an integrating circuit 43 which drovides saw-tooth pulses which are fed to the anode 55. When the valve is rendered conducting by the short signal pulse on grid 50, the secondary-emission auxiliary cathode 52 rapidly assumes anode potential which is dependent upon the pulse timing due to the saw-tooth pulse applied thereto. At the conclusion of the signal pulse the valve is cut off and, thereafter, the time constant of the electrode 52 is long, depending on condenserresistance combination 53, 54, so that the electrode potential remains substantially constant until the arrival of the next signal pulse. The resulting output B, Fig. 3, in the case of the synchronizing channel is a rectangular wave of half-cycle frequency. This wave is fed through amplifier 58 to a tuned circuit 60, 61, whereby it is converted to a sine wave C. After appropriate phase-shifting in circuit 62, the wave D passes to a full-wave frequency doubling rectifier 63 ... 69, the output wave E being used to synchronize a multivibrator 70 at the cycle frequency. The multivibrator output wave F is differentiated in circuit 71 and the negative peaks of the resultant wave G form the pulses fed over conductor 39 to control the gate pulse generators 35 ... 38.