Patent GB-693859-A (GB)
Title: Improvements in or relating to electric pulse signalling systems
IPC: H04J3/06
Filed: 1951-02-20
Abstract: 693,859. Multiplex pulse signalling; pulse frequency dividing circuits. GENERAL ELECTRIC CO., Ltd., and STENNING, L. C. Feb. 13, 1952 [Feb. 20, 1951], No. 4161/51. Classes 40 (v) and 40 (vi). In a pulse signalling system, in order to identify a particular instant or series of instants, for example for providing a synchronizing pulse in a pulse code modulation system, at least two trains of pulses are simultaneously transmitted, their recurrence frequencies being F/a, F/b, &c., where a, b, &c. are different integers having no common factor. The several trains thus point in time, for example by pulse coincidence in all trains, to a particular instant or series of instants. In the multichannel pulse code signalling system described, the channel distributer 53, Fig. 1, and coder 54 are controlled by a pulse generator 1 giving positive-going pulses of the codeelement recurrence frequency 480 Kc/s. These pulses are also fed to frequency dividers 2, 3, 4, 5 which divide by five, seven, eight and nine respectively to produce trains of wider pulses. The instants when in all four trains pulses occur simultaneously, therefore occur 480,000 divided by 5 X 7 X 8 X 9, i.e. 191 times per second. A pulse is produced at each of these instants at the output of gate circuit 32, which passes a pulse when pulses occur simultaneously at the outputs of gate circuits 21, 31. The latter pass pulses when dividers 2, 3 and 4, 5, which are connected respectively thereto, produce pulses simultaneously. The pulse from gate circuit 32 opens valve 34 to pass one pulse from generator 1 to lock the phase of the generators which control the distributer 53 and coder 54, which may be oscillators or staircase counters. In order to transmit a synchronizing signal to the receiver, the outputs of dividers 2, 3, 4, 5 are added together and transmitted in place of the normal pulse code signal, after time slicing. They are fed through diodes 41, 42, 43, 44, respectively, to a common point 46, to gate open the circuit containing diodes 48, 49 to transmit corresponding pulses from generator 1 to the switch or relay 55. The latter is operated, when synchronization is to be effected, to disconnect the channel signals from the output terminal 56 and connect the synchronizing trains thereto. At the receiver, incoming pulses are fed from terminal 61, Fig. 5, to the decoder 62, an oscillator 66 and a delay line 63. Means are provided for separating each of the pulse trains transmitted for synchronization. For example, that for separating the train due to the divider 2, Fig. 1, the recurrence frequency of which is one-fifth of the code element recurrence frequency, comprises gate circuits 64, 65. Circuit 64 detects coincidence between incoming pulses from terminal 61 and pulses from delay line 63 delayed by five code element periods. Circuit 65 detects coincidence between pulses from circuit 64 and incoming pulses delayed by ten code element periods in delay line 63. The second gate circuit is provided to prevent false operation due to fortuitous coincidences. The train of pulses thus separated is applied to a time slicer 68 which passes standard duration pulses derived from a pulse generator 67 operating at code element recurrence frequency and controlled by the oscillator 66 which is frequency controlled by the incoming pulse code signals. The four trains thus separated are used to phase lock the oscillators 69, 72, 73, 74, respectively, and these oscillators control pulse generators 71, 75, 76, 77 respectively which reproduce the four pulse trains from which the synchronizing pulse is derived. The gate circuits 78, 79, 80 derive the synchronizing pulses and correspond to circuits 21, 31, 32 at the transmitter, while gate circuit 82 corresponds to valve 34 and supplies pulses to lock the phase of the distributer and decoder oscillators in circuits 83, 62. A delay netowrk may be provided to ensure the application of the synchronizing pulses at the correct instant. When a very low recurrence frequency is used for the synchronizing pulses and it is desired to identify one particular instant a signal may be sent to indicate that the next occurring pulse is the required one. When the system is synchronized and operating normally pulses in a particular time position in the multiplex may be given a characteristic modulation to be used as a check of synchronism as described in Specification 693,862. If the received signal and the decoder slip out of register an alarm signal may be sent back to the transmitter to operate relay 55 so that the synchronizing arrangements are brought into operation. The identified instants may be time modulated to convey intelligence.