Patent GB-672629-A (GB)
Title: Improvements in or relating to a method of transmission by means of electrical impulses subjected to two simultaneous modulations
IPC: H04J9/00
Filed: 1950-12-08
Abstract: 672,629. Multiplex pulse signalling; pulselengthening circuits. POTIER, G. X. N. Dec. 8, 1950 [Dec. 31, 1949], No. 30143/50. Classes 40 (v) and 40 (vi). In a multiplex time division pulse communication system each pulse of the group is first time modulated by the signals of one channel and then modulated in amplitude or duration by stored amplitude samples of another channel taken at regularly recurring instants. At the receiver, the second channel modulation is stored and modulates pulses recurring at regular instants which are demodulated to recover the channel signal. In the embodiment described, the second pulse modulation is in amplitude and there are six channels. At the transmitter, a pulse generator 107, Fig. 1, operating at group recurrence frequency multiplied by the number of pulses per group, feeds a frequency divider 108 producing pulses at group recurrence frequency. The delay line distributer 109, fed from circuit 108, feeds synchronizing pulses direct to the mixer 118. Further tappings feed time modulators 111, 113, 115 to which the first, third and fifth channel modulating signals are applied from terminals 101, 103, 105, respectively, the modulated output pulses being fed to the mixer 118. From the same tappings are fed the pulse amplitude modulators 112, 114, 116, respectively, to which the second, fourth and sixth channel modulating signals are applied from terminals 102, 104, 106. All the amplitude modulated pulses are applied to a pulse lengthening circuit 117, where under the control of pulses from generator 107 their duration is made of the same order as a channel period. The time modulated pulses, from mixer 118, are amplitude modulated in circuit 119 by the lengthened amplitude modulated pulses from circuit 117, which occur at the same time. At the receiver the incoming pulses on line 120 are distributed by gating circuits opened in succession by pulses from the delay line 124 derived from the synchronizing pulse selector 121. The pulse time demodulators 126, 128, 130 provide the first, third and fifth channel signals at terminals 141, 143, 145 respectively. The pulses are also fed to lengtheners 129, 131, 133 where their duration is increased to nearly the pulse recurrence period under the control of the synchronizing pulses suitably delayed in circuit 122. These lengthened pulses amplitude modulate the regularly recurring synchronizing pulses applied to modulators 134, 136, 138, the outputs of which are demodulated in circuits 135, 137, 139 to provide the second, fourth and sixth channel signals at terminals 142, 144, 146 respectively. The pulse lengthening circuit at the transmitter comprises a pentode valve 307, Fig. 3, to the control grid of which are applied the pulses to be lengthened. The valve is rendered conducting by the pulse to charge the anode condenser 308 to a potential dependent upon the pulse amplitude. The condenser is subsequently discharged through diode 311 and the anode resistance 313 of triode 312 when the latter is rendered non-conducting by a pulse applied to its grid. The lengthened pulses appearing across condenser 308 are derived from terminals 318, 319. The pulse amplitude modulators are of known type, Fig. 2 (not shown).