Patent GB-848291-A (GB)
Title: Improvements in or relating to pulse time modulation systems of communication
Inventor: STARR ARTHUR TISSO
IPC: H04B14/02
Filed: 1958-10-28
Abstract: 848,291. Circuits employing bi-stable magnetic elements. STANDARD TELEPHONES & CABLES Ltd. Oct. 28, 1958, No. 34435/58. Class 40 (9). [Also in Group XL (c)] Relates to a multi-channel pulse time modulation system in which the distributer comprises a plurality of bi-stable magnetic cores which are biased respectively by differing amounts in such manner that a triggering wave having regularly repeated inclined portions causes the cores to be triggered in succession to produce a corresponding sequence of output pulses. The pulse transmitter includes an oscillator 19, Fig. 2, supplying sinusoidal waves to a phase splitter 20 providing four outputs with respective relative phases of 0 degrees, 90 degrees, 180 degrees and 270 degrees, which are connected respectively to group modulators 21 to 24. Each group modulator has connected to it six signal channels and generates time-modulated pulse trains for the six channels, the outputs from the modulators being combined at 25 and applied via a conductor 26 to a carrier-wave transmitter. A group modulator, Fig. 3, comprises six ferrite or like cores 29 to 34 which form the pulse distributer and also produce the timemodulated pulses for the respective channels. Each core is provided with a signal input winding 35 wound "-straight," and a trigger winding 36 wound " straight," all the windings 36 being connected in series to, for example, the zero phase output from the phase splitter 20. A bias winding 39 is also provided on each core and is wound " straight " on cores 29 to 31 and " reverse " on cores 32 to 34. The bias windings are connected in series with a bias source 27 and the number of turns on each winding is so arranged that the triggering level in the absence of any signal input in the winding 35 is different for each core, the triggering range being restricted to a straight portion of the sinusoidal wave. In the absence of any signal currents in the windings 35 the triggering of the cores 29 to 34 will produce channel pulses equally spaced in time. Signal current in a winding 35 will make the corresponding output pulse earlier or later, according to the direction of the current. The output pulses are supplied via output windings 41, wound " reverse " and connected in series, and diode 42, to unblock a transistor 43 and apply an output pulse to the combining circuit 25, Fig. 2, which comprises a transistor 61 which also receives the pulses from the remaining group modulators. The cores are triggered back to their normal position by the negative-going position of the sine wave, the resultant pulses from the output windings being blocked by the diodes 42, 44. A sawtooth triggering wave may be used instead of a sinusoidal wave. One channel may be used to transmit a synchronizing pulse, or alternatively one of the four group modulators may be provided with an extra core to generate an unmodulated synchronizing pulse, this necessitating closer spacing of the biasing for the cores. At the receiver, Fig. 6 (not shown), the synchronizing pulses are selected from the incoming pulse train and supplied via a filter which produces a sinusoidal output, to a phase splitter of the type shown in Fig. 2 the outputs from the phase splitter being applied respectively to group demodulators corresponding to the group modulators of Fig. 2. A group demodulator, Fig. 7, comprises six ferrite cores 72 to 77 each having a trigger winding 78 wound " straight," a bias winding 79 wound " straight " on cores 72, 73, 74 and " reverse " on cores 75, 76, 77, and an output winding 80 wound " reverse." The bias windings 79 are arranged to produce triggering levels corresponding to those of cores 29 to 34 at the transmitter. The output windings 80 are connected to one side of corresponding flip-flops 82 and the output of one side of each flip-flop is connected through a low-pass filter 83 to the corresponding channel output conductor. At the beginning of the channel 1 period the core 72 is triggered by the sine wave applied from the phase splitter 70 to winding 78 and a negative pulse is applied from the output winding 80 to switch over the flip-flop 82. When the negative time-modulated pulse for channel 1 arrives over conductor 63 and returns the flip-flop 82 to normal the low-pass filter 83 is thereby supplied with a rectangular pulse whose duration depends on the timing of the incoming channel pulse and the channel 1 signal is recovered in known manner. The remaining channels operate in turn in like manner. Specifications 583,541 and 640,099 are referred to.