GB594795A - Telegraph transmission system - Google Patents

Abstract

594,795. Telegraphic transmission systems. STANDARD TELEPHONES & CABLES. Ltd. (International Standard Electric Corporation). March 29, 1945, No. 7963. [Class 40 (iii)] In a telegraph transmission system in which a character is determined by the time interval between a signal impulse and a start impulse, the spaced impulses are obtained by applying the start impulse directly to a transmission line and to a portion of an artificial line selected in accordance with the desired character, the spaced impulse being derived from the end of the selected portion of the artificial line or reflected back to the beginning of the artificial line before passing to the transmission line. The start and signal impulses may be of opposite polarity, and if the start impulses are continuously produced the artificial line is terminated by its characteristic impedance to prevent reflection of impulses from the end of the line. In the arrangement shown in Fig. 4 the impulse generator comprises a battery 21, a variable resistance 22, a switch 24 and an inductance 23 connected to the transmission line 3 through a condenser 25 of small capacity and a rectifier 26. The artificial line 2 comprises sections, including switches 11, 12, 13 ... controlled by a keyboard operating so that when the artificial line is opened at any selected point the switch 24 is also opened and an impulse is produced at the terminals of the inductance 23. Condenser 25 permits the passage of the steep front of the impulse and the rectifier 26 prevents the reflected impulse from passing to the generating circuit. In a modification, Fig. 5 (not shown), a condenser, normally charged, is discharged by the closure of a switch operated from the keyboard. In a' further arrangement, Fig. 6, the start impulse from a generator 1 is fed to the line 3 by a valve 30 which is made conducting by the impulse which is simultaneously fed through a rectifier 40 to the artificial line 2. The impulse taken from the selected length of artificial line 2 is determined by the closed switch a, b, c, d ... and passes to the grid of a valve 31 which transmits the delayed impulse to the line. Condensers 32, 33 prevent the passage of surges due to the closures of the key contacts. In a modification of Fig. 6and not employing valves, Fig. 7 (not shown), the impulses from the generator and artificial line are applied to the transmission line through load impedances with suitably disposed rectifiers to prevent the passage of reflected impulses to the impulse generator. In one arrangement, Fig. 3 (not shown), in which the artificial line consists of T sections and comprise a series of inductances, the selectively operated switches are arranged to short circuit the line at the mid points of the inductances so that the reflected and start impulses are of opposite polarity. The keyboard of the transmitter may incorporate an arrangement operating so that the impulse generator is operative solely when a key is actuated.