GB587939A - Improvements in or relating to multi-channel electrical pulse communication systems - Google Patents

Abstract

587,939. Multiplex signalling ; pulse modulation. STANDARD TELEPHONES & CABLES Ltd., and LEVY, M. M. May 26, 1944, No. 10305. [Class 40 (v)] A multiplex signalling system employs as a distributer a delay network traversed by a synchronising wave or pulse, and means are provided for eliminating effects due to distortion of the wave or pulse as it traverses the network. As shown in Fig. 2, a pulse originating in the reciprocally-coupled valve pair 42 is fed to the output line 32 through a diode 35, vnd is also fed to the network 1 provided with toppings 5 ... 9 leading to the signal channels 13 . . . 17, which are thus brought successively into use. When the original pulses are rectangular, their vertical sides become more and more inclined as they proceed along the network, but their width at half their full amplitude remains fairly constant. If, therefore, the distorted pulse is applied to an amplifier 10 with a suitable grid bias 11, the valve will begin to pass current at the correct moment. The amplifier should preferably be a pentode valve with a high resistance 12 inserted in its grid lead. A diode may be connected between the grid and earth. The resulting pulse in the anode or cathode circuit is used with or without differentiation to open the transmitting or receiving apparatus 13 . . . 17 in the relevant channel. In the channel 15, the distorted pulse at tapping 7 is applied to the grid of a back-biassed valve 19 reciprocally coupled to a valve 20. The valve 19 is unblocked by the pulse from tapping 7, thus blocking the valve 20 for a time dependent on the bias on its grid 22. If a microphone 24 is inserted in the bias circuit, the duration of negative pulses generated across the cathode resistor 26 is dependent on the momentary speech voltage. These pulses may be differentiated by the circuit 28, 29 and the resulting leading pulse suppressed by the diode 31, the positive trailing pulse 33 being passed through a diode 38 to the common output line 32. The multi-vibrator 42 may be as described in Specification 587,940, and may be synchronized by a pulse from the far end of the network 1 fed back through a shaping amplifier 46. In a modified arrangement, Fig. 3, the valve pair 42 feeds pulses to the network 1 as before, and tappings, 5 ... 8 on the network are connected to the reversal channels 13 ... 17. A further oscillator 48 operates at a frequency equal to that of 42 multiplied by half the number of channels and is synchronized therewith as described in Specification 578,690. Its output is converted to square pulses 50, 51 in phase opposition in the shaping circuit 49, and one set is supplied to the channels of odd number and the other to the channels of even number. The delayed pulses from the network 1 and the pulses 50, 51 from the device 49 are applied to valve circuits in the respective channels 13 ... 17 in such fashion that a channel is rendered operative only when the pulses are superposed. Specification 587,941 also is referred to.