Patent GB-724752-A (GB)
Title: Improvements in or relating to the transmission of electric signals
IPC: H04J3/00
Filed: 1950-03-07
Abstract: 724,752. Multiplex pulse code signalling; pulse discriminating circuits. SOC D'ELECTRONIQUE ET D'AUTOMATISME. March 7, 1950 [March 7, 1949; Feb. 15, 1950], No. 5804/50. Classes 40 (5) and 40 (6). [Also in Groups XIX and XL (b)] In order to distribute to their utilization circuits the individual message signals, in the combined pulse train of a pulse or pulse code multiplex signalling system, each message signal is associated with a signal of distinctive amplitude level which appears at the distribution point before or with its message signal and selects the appropriate utilization circuit, after which it is caused to cease. In all the systems described, each channel signal comprises a message signal preceded by a pilot signal, which may be present in the combined pulse train or added before distribution takes place. The distinctive amplitude level may be present in the combined pulse train, and associated with the pilot or the message signal, or may be generated at the point where the combined pulse train is received. Receivers.-In one embodiment, the incoming pulse train from conductor 1, Fig. 1, is applied in parallel over conductor 11 to all the channelselecting circuits 9. The pilot pulses which are coded to indicate the channel amplitude level are selected by circuit 2, or locally generated and supplied from conductor 5, and are passed to the decoder 14. The latter supplies the amplitude levels over the common conductor 7 to the channel selectors 9. In Fig. 3, the coded message signals are additionally coded by the amplitude level and after decoding in circuit 15 open up the appropriate channel selector 9. The pilot signals from selector 2 or conductor 5 control the operation of the decoder 15. In another embodiment using the same kind of message signals, the uncoded pilot signals control a pulse producer 18, Fig. 6, which operates the coders 17 to produce coded amplitude levels characteristic of the respective channels. These coders may be of the type described in Specification 679,390. The circuits 16 are fed in parallel with the doubly coded message signals and individually with the coded amplitude levels from coders 17 and are arranged to perform a subtraction as described in Specification 716,172, [Group XIX]. The resulting coded message signals are applied through individual decoders 15 to the channel selectors 9. Some of the individual circuits for the embodiment shown in Fig. 3 are shown in Fig. 11. The incoming pilot signals consist of characteristically spaced pulse pairs and the coded message signals are additionally coded with the individual channel amplitudes. For separating the pilot signals a threshold device 64 responds to a double amplitude pulse due to the superposition of the two pilot pulses at the output of a delay line 61 and a parallel non- delay path 62. The output pulses from circuit 64 are used to cancel out the pilot pulses arriving with the'message signals at the decoder 15, and to gate open the valve 67 through a delay line 69 to allow the decoded message signals to pass to the output point 70. The latter is connected in parallel to the channel selector circuits of which one is shown. In these, the input pulses, which are amplitude modulated by the message signal and also carry the channelselecting amplitude level, have superposed thereon a high-frequency voltage from source 90 and pass to two parallel paths which start conducting at different amplitude levels. These comprise differently biased rectifiers 94, 95 and feed the transformer 102 in push-pull so that pulses of below the appropriate amplitude cannot pass either rectifier, while those of above this amplitude cancel out in the transformer. Those of the required amplitude pass rectifier 94 only and their high-frequency modulation is detected by the triode 104 and passed to the utilization channel. In another circuit, Fig. 12 (not shown), the doubly amplitude-modulated message pulses are converted into pairs of pulses, the spacing of which is modulated, the different channel signals being selected by coincidence circuits similar to 61, 62, Fig. 11. Transmitters.-A circuit for producing coded message signals, and pilot signals coded with characteristic amplitude levels comprises the gate valves 26, 27, 28, Fig. 7, to the control grids of which are applied the message-modulating signals. The valves are gated on in succession by interlaced pulse trains from inputs 31, 30, 29 applied to their suppressor grids. The amplitude-modulated output pulses are fed in parallel to the coder 33 through a delay line 32 which correctly times them relative to the pilot signals derived from the gating pulses by fixed coders 34, 35, 36. The pilot and message signals are-applied in parallel to the output 37. In another circuit which produces pilot signals in the form of pulse pairs and doubly coded message signals, the gating pulses for valves 26, 27, 28, Fig. 8, are produced by a generator 47 and binary counter chain I, II, III, 48, and these pulses are also fed in parallel to a circuit 50 to produce the pilot pulse pairs which are fed to the output 37. The amplitude-modulated message pulses from valves 26, 27, 28 are supplied to coders 34, 35, 36 respectively to produce the channel amplitude level codes which are fed in parallel to a circuit 43. The message pulses are also fed in parallel through isolating rectifiers 44, 45, 46 to circuit 43 which codes them and adds the channel amplitude level codes thereto, the resultant code groups feeding the output 37 through delay line 32. In another embodiment, the gate pulse generator I, II, III, 47, Fig. 10, feeds in succession only those gate valves to the control grid of which is applied a modulating signal. For this purpose, signal detectors 55, 56, 57 energize relays 58, 59, 60 respectively to direct the normal gating pulse to the associated valve if a signal is present. In the absence of a signal the pulse is directed to the preceding valve by the other relay contact. The combined amplitude-modulated message pulse outputs are fed to coder 51, the code of which corresponds to the smallest channel-selecting amplitude level provided for the first message channel. The other coder 62 is fed through individual delay lines 53, 54, from the valves 27, 28 respectively, the delays being multiples of the time interval between successive pulses of the same coded message signal train. The coder 52 produces an output corresponding to the smallest channel selecting amplitude level and circuit 43 combines, adds and codes the amplitude-modulated message pulses from valves 26, 27, 28 and the outputs of coders 51, 52.