GB579860A - Electric pulse modulation signalling systems - Google Patents

Abstract

579,860. Pulse modulation. STANDARD TELEPHONES & CABLES, Ltd. (International Standard Electric Corporation). Feb. 11, 1944, No. 2541. [Classes 40 (iii) and 40 (v)] In a pulse-modulation signalling system in which signals are represented by short impulses, each short impulse is replaced by two or more closely-adjacent impulses in order to prevent false operation of the receiver by interfering impulses. Thus in Fig. 2, the impulse sequence 3a, 3b represents the beginning and 4a, 4b the end of a signal, whereas 9a and 10a represent interference. As shown in Fig. 5, the pulse transmitter 30 supplies short single impulses representing the beginning and end of durationmodulated rectangular pulses. These impulses are applied directly to the grid of a gas-discharge tube 31 and indirectly through a delay network 35 to a similar tube 32, the two closely-adjacent impulses being taken off across a resistance 33 common to their anode circuits. These impulses 13 are received at 14, Fig. 4, and are applied directly to one grid 15, and through a delay network 18 to a second grid 17 of a valve 16. As this valve only passes current when both grids receive an impulse simultaneously, a single impulse 19 appears in the anode circuit and is passed to a double-stability circuit 21 of known type which serves to rebuild the duration-modulated rectangular pulse 22. The closely-adjacent impulses may be three or more in number and one or more of them may be inverted. The transmitter 30 of Fig. 5 may comprise the telegraph keying circuit shown in Fig. 6, in which a sine-wave generator 40 is connected to the grids of two gas-filled tubes 41, 42 the latter connection including a phaseshifting or delay network 44 ... 47. When the key 48 is down and the condenser 46 in circuit, pairs of signals are sent out from the common anode load 51 with an interval corresponding to a mark ; and in the other position of the key, with an interval corresponding to a space. The output of Fig. 6 is utilized as the pulse source 30 of Fig. 5.