Patent GB-819658-A (GB)
Title: Improvements in or relating to electric pulse signalling systems
IPC: H04J3/06
Filed: 1956-05-09
Abstract: 819,658. Multiplex pulse code signalling. GENERAL ELECTRIC CO. Ltd., and IMM, R. C. April 25, 1957 [May 9, 1956], No. 14392/56. Class 40 (5). In a multi-channel pulse code communication system a plurality of speech channels are combined in frequency multiplex, the combined signal being transmitted in a binary pulse code an auxiliary pulse signal being transmitted in time multiplex therewith and being modulated, preferably in delta code, by a composite signal including a synchronizing component and a further intelligence component. In the embodiment described, twelve audio channels, combined in frequency division multiplex in the range 60 to 108 kc/s. are sampled at a frequency of 114 kc/s. in the coder 2, Fig. 1, and converted into 9-unit binary code groups, the recurrence frequency of the pulse intervals in a group being 1140 kc/s. Every tenth pulse interval is used to transmit the output of an auxiliary delta coder 5 modulated both by a 0.3 to 3.5 kc/s. audio channel on line 6 and a 4.375 kc/s sine wave synchronizing signal from oscillator 7. The coder outputs are directed to the pulse reshaper 10 and output circuit at appropriate intervals by gating circuits 8, 9, respectively, controlled by the 114 kc/s. pulse generator 4 through the phase-splitting circuit 11. The output of generator 4 is also supplied to the coders 2, 5 and it is controlled by a 1140 kc/s. master oscillator 3 the output of which also is fed to the coder 2. The main coder may be of the type described in Specification 735,251. In the auxiliary delta coder the synchronizing wave fed to valve 16, Fig. 2, and the audio channel signal fed to valve 15 are added in the common anode circuit and fed via transformer 20 to the grid of valve 22 of a trigger pair 22, 23. Also fed to this grid in a series circuit are the 114 kc/s. pulses from generator 4, Fig. 1, through valve 28 and transformer 27 and, in a subtractive sense, the integrated (demodulated) output of the trigger circuit provided by valve 32 and integrating circuit 38. The delta coded pulses thus produced from valve 23 are fed to the gating circuit 9, Fig. 1, through the cathode follower 30. Direct current restoration diodes 41, 42 are provided to ensure that the operating conditions of the trigger circuit 22, 23 remain the same irrespective of the relative incidence of output pulses. At the receiver, the incoming pulse train passes through a slicer 51, Fig. 3, and a sampling circuit 52 for pulse reshaping, as described in Specification 709,214, to the main decoder 57 for the recovery of the twelve frequencymultiplexed channel signals. The pulses are also fed through a differentiating circuit 54 to lock in a 1140 kc/s. oscillator 53. A 114 kc/s. pulse generator 61, which together with the oscillator 53 controls the decoder 57, is controlled by the output of a divide-by-ten circuit 59 fed through a limiter 58 from the oscillator 53. The pulses from the sampling circuit 52 which occur in every tenth pulse interval are passed by the gating circuit 62 under the control of the pulse generator 61 to the auxiliary decoder. If the transmitter and receiver are . operating in synchronism the auxiliary audio channel signals occur on output 64 and the 4.375 kc/s. synchronizing signal on the output leading to a detector 65 responsive thereto and producing a signal which inhibits the gating circuit 67. If synchronism is not present, the gate 67 is open to allow extra pulses to be fed to the input of divider 59 from a multivibrator 66 running at about 100 c/s. and locked to the 114 kc/s. divider output. Each such pulse is arranged to start the divider counting at zero again which alters the phase of its output in steps until synchronism is achieved and the gate 67 is closed. Specification 693,862 also is referred to.