GB585827A - Improvements in or relating to the demodulation of time-modulated electrical pulses - Google Patents

Abstract

585,827. Pulse modulation. STANDARD TELEPHONES & CABLES, Ltd., and LEVY, M. M. June 1, 1943, No. 8798. [Class 40'(v)] In a signalling system employing short phase-modulated pulses, reception is effected by combining the received train of constantwidth pulses a, Fig. 4, with a train b which is delayed by a constant time To slightly longer or shorter than the pulse repetition period. The pulses c derived from the overlap of the trains a; bare duration-modulated and the signal may be obtained by utilizing the pulses c to charge a condenser. The transmitted pulses may be received on a radio receiver RR . and detector D, Fig. 3, the detected pulses a being applied directly to a grid G1 of a doublegrid valve V. Pulses b delayed by a network DN are applied to the other grid G2. The grids are biassed so that current passes only when both grids receive a pulse, the anode current being thus of the form c. A resistance R shunted by a condenser C is provided in the anode circuit and the voltage across the combination varies in accordance with the original signal voltage. Both sets of pulses may be applied to a single grid, the valve passing current only when both are present. The network DN may be terminated by a resistance R1 of such value that reflection of the pulses is prevented ; or the termination may be left open and reflected pulses utilized as the delayed pulses, the tapping on the network, being then omitted. The received pulses, which are all of the same duration, may if necessary be lengthened by any suitable means, e.g. by the means described in Specification 585,826, or by interposing between the detector D and the network DN the circuit shown in Fig. 5. The pulses are applied to a delay network DN1, terminated by anon-reflecting resistance R5 and having a series of tappings connected to the grids of a series of valves VI, V2, ... the anodes of which are connected together and by a resistancecapacity coupling to the grid of a valve CV. The valves are biassed to cut-off, and the delayed pulses open each valve in turn before the preceding valve cuts off. When current is passing through any of the valves V1, V2, &c. the valve CV is cut off, and pulses of lengthened duration may be taken off from the terminals O. The number of valves may be reduced if the resistance R5 is removed, so that pulses are reflected at the open end.