Patent GB-706047-A (GB)
Title: Improvements in or relating to multichannel electric pulse signalling systems
Inventor: LITTLE JOHN GILBERT
IPC: H04J3/00
Filed: 1951-09-13
Abstract: 706,047. Multiplex pulse signalling. GENERAL ELECTRIC CO., Ltd. Sept. 4, 1952 [Sept. 15, 1951], No. 21560/51. Addition to 663,785. Class 40 (5) The multichannel pulse communication system of the parent Specification is modified in respect of the duration of certain pulses and the circuits for pulse amplitude modulation, time modulation and distribution. In the 26-channel system described, the waveform generator WG, Fig. 1, produces a train of negative pulses, at channel recurrence frequency and of duration slightly greater than a channel interval, which is fed to the delay line distributer D. Tapping DO on the line D controls a synchronizing signal generator SG which produces a double pulse which is fed to the output amplifier PA in the twenty-fifth channel interval. The other tappings D1 ... D24 feed individual circuits AM1 ... AM24 in which the pulse amplitude is modulated by individual signal sources SIG1 ... SIG24. The outputs of circuits AM1 ... AM24 are combined in four groups 1, 3, 5, 7, 9, 11 ; 2, 4, 6, 8, 10 12; 13, 15, 17, 19, 21, 23 and 14, 16, 18, 20, 22, 24, for application respectively to the pulse time modulators PTMI ... PTMIV, the outputs of which are combined and fed to the amplifier PA. The modulators are supplied with sawtooth waves from generators STGI ... STGIV respectively those for the odd channels being controlled by a square wave of thirteen times the channel recurrence frequency derived from output A of the wave generator WG while those for the even channels receive the same wave, but with a phase-shift of 180 degrees, from an output B. The circuit of a pulse amplitude modulator such as AM1 comprises a valve 102, Fig. 2, to the control grid of which is applied the modulating signal from source SIGI. Its cathode resistance 110 is common also to valve 111 to which is applied the negative-going pulse from D1, the tapping on delay line D, Fig. 1. Valve 111 is normally conducting, to bias the cathode of valve 102 to cut-off. The pulse from D1 reverses this condition and a corresponding negative amplitude-modulated pulse appears at the anode of valve 102, the anode load 113 being common to a group of modulators. The input signal excursions are limited by diodes 108, 109 suitably biased by the voltage-dividing network 103 ... 106. The circuit of a pulse time modulator such as PTM1, Fig. 1, comprises a pair of triodes 121, Fig. 3, to the left and right hand control grids of which are applied respectively, at terminals 120, 122, the negative going sawtooth wave from generator STGI, Fig. 1, and the amplitude-modulated positive-going pulses. The triodes have a common cathode resistor 124 and normally the left hand one is conducting and the right hand one non- conducting. This condition is reversed at a point on the sawtooth wave depending on the amplitude of the amplitude-modulated pulse and is restored at the sawtooth flyback, so that negative duration-modulated pulses appear at the right hand anode. These are squared and inverted by pentode 128 and applied to a critically-damped ringing circuit 129 to produce a pair of positive and negative differential pulses corresponding to the time-modulated and fixed leading and trailing edges of the duration-modulated pulses. The leading-edge pulses are selected by the biasedback valve 132 which provides the time-modulated pulses at terminal 133.