Patent GB-635477-A (GB)
Title: Improvements in multi-channel time-modulated pulse communication systems
IPC: H04J3/04
Filed: 1945-05-14
Abstract: 635,477. Multiplex pulse signalling. STANDARD TELEPHONES & CABLES, Ltd., and LEVY, M. M. May 14, 1945, No. 12118. [Class 40 (v)] [Also in Group XL (b)] In a multichannel time-modulated pulse communication system, means are provided for producing a train of " safeguard " pulses for defining the limits of the cyclical durations of the respective channels, and for applying these pulses to cause the operation of the modulator at the maximum time limit if the signal wave fails to do so before this limit. One embodiment, Figs. 1, 2 (not shown), is fully described in Specification 587,941. In a second embodiment, in which ten channel trains are used, each having a pulse recurrence frequency of 10 kc/s., a master sine-wave oscillator 43, Fig. 3, working at 100 kc/s. feeds a pulse forming circuit 45 producing pulses 46. A multivibrator frequency-divider 47 fed from unit 45 passes 10 kc/s. pulses to a selective amplifier 48 tuned to the eleventh harmonic of the input pulses and giving a sine wave output at 110 kc/s. which is fed to a pulse-forming circuit 50 producing pulses 51. The selector pulse trains applied to the channel modulators such as 57<8> are derived from individual gating valves 55<1>... 55<10>, which are fed with the 100 kc/s. pulses from unit 50 after a time delay produced by a selected number of equal sections of the delay network 52. When the pulses coincide in the gating valves, which happens once per channel cycle at a fixed time therein, a pulse is passed to the associated channel modulator. The delay time of each section of network 52 is one microsecond in a system with the constants already mentioned, the ten sections giving a total delay time of <1>/10,000 second. Also applied to the channel modulator, such as 57<8>, is the modulating signal wave from source 56 and safeguard pulses at channel recurrence frequency from unit 45, through a network 61, having a delay period equal to the maximum permissible time modulation of the output pulses. The modulator comprises a multivibrator circuit, the curve ABCD, Fig. 4, representing the grid voltage of one of the valves. In the absence of a signal wave input AB is the sudden drop in grid voltage when the negative selector pulse is applied and the circuit triggers over to its unstable condition. At B the grid condenser starts to discharge until the grid voltage reaches the triggering value represented by line OO<1>. The circuit then triggers back to its stable condition, CD, to await the next selector pulse. The modulating signal modifies the triggering voltage value and hence produces a train of variable duration pulses at the grid such as 58, Fig. 3, which may be differentiated in unit 59 to produce time-phase modulated sharp pulses 60. The " safeguard " pulses ensure that, if the modulating signal voltage would move point C, Fig. 4, beyond the limit of the channel duration, the multivibrator is triggered back at the end of the channel period by a safeguard pulse, as shown at A<1>B<1>C<1>D<1>. The delay network 52 may, alternatively, form part of the stabilizing circuit of a 110 kc/s. multivibrator replacing unit 50 and fed from amplifiers 48, as indicated by the dotted line feeding back from the output impedance 53 of the line to the unit 50. Specification 635,476 also is referred to.