GB602969A - Improvements in or relating to multi-channel signalling systems - Google Patents

Abstract

602,969. Thermionic distributers. McDERMOTT, T. J., and COOP, E. Nov. 13, 1945, No.. 30384. [Class 40 (iii)] [Also in Group XL (c)] In a multi-channel signalling system each channel circuit is rendered operative in turn for a predetermined period by an initiating pulse and a common terminating pulse is applied to all the circuits to terminate the operation of that channel circuit which is operative at the time. The invention is described with reference to a system having nine channels eight of which carry pulse modulated signals and the ninth a synchronizing signal which may comprise three equally spaced pulses of equal duration. At the transmitter a control oscillator 1, Fig. 1, produces positive-going pulses at a frequency of 81 Kc /s. These are inverted at 2 and applied to a counter 3 which at every ninth pulse delivers an initiating pulse to the first channel circuit 5, to render it operative to pass the modulated channel pulse from lead 6 to the modulator 7 of the transmitter 9. The next positive pulse from generator 1, applied to circuit 5, renders it inoperative and, in ceasing to operate, the channel circuit generates a negative pulse applied through lead 10 to form the initiating pulse for .the next channel circuit 11. This circuit is then operative until closed down by the next positive pulse from generator 1, and so on. The eighth pulse of each series of nine pulses counted by circuit 3, triggers the synchronizing signal generator 4 to modulate the transmitter 9. A similar chain of channel circuits is used at the co-operating receiver, Fig. 2 (not shown). The time relationship between the received synchronizing signal and the eighth pulse in each group of nine counted by the local counting circuit, controls a correcting voltage applied to the local control oscillator. A form of channel circuit such as 5, 11, Fig. 1, comprises a cathode-coupled relaxation oscillator, Fig. 3, having valves 41, 42 with a common cathode resistor 50. The channel is operative when valve 42 is made conducting and signals from lead 44 on its suppressor grid 43 are passed to its anode circuit. The negative initiating pulse is applied through lead 49 to the suppressor grid 48 of valve 41. Anode current is cut off and a positive impulse fed to the control grid of valve 42 which becomes conducting to maintain 41 in the cut-off condition. The positive terminating pulse, applied through condenser 47 to the control grid of valve 41 restores the circuit to the quiescent state in which 41 is conducting and 42 is non-conducting. The negative-going initiating pulse for the next channel circuit is derived, by differentiation, from the trailing edge of the positive-going square pulse across resistor 50 which occurs while valve 42 is conducting. Specifications 588,416, 588,417, 590,215 and 592,804 are referred to.