Patent GB-635224-A (GB)
Title: Improvements in or relating to start-stop telegraph systems or the like
IPC: H04L25/45
Filed: 1946-09-24
Abstract: 635,224. Thermionic distributers; telegraph systems. INTERNATIONAL BUSINESS MACHINES CORPORATION. Sept. 24,1946, No. 28518. Convention date, Nov. 27, 1945. [Class 40 (iii)] A start-stop telegraph or like transmitting system comprises signal output means and a plurality of parallel circuits connected thereto, each circuit including a trigger tube and a coupling tube in series, further means being provided for subjecting the output means to the control of each trigger tube in succession by rendering the coupling tubes conductive in succession. In the embodiment described a start-stop code having six intelligence code-elements is employed. The output of an oscillator V20 is amplified by a push-pull pair V21-V22 and further amplified via a gain-control 65 by valve V24 and applied to a signal output transformer TS. An amplified output is also applied to a monitoring transformer TM by a valve V23 in parallel with V24. In the normal or standby condition valves V0, V10, V17 and thyratron G9 are conducting. Current flows from a point 17 on the potential divider 1 ... 6 of the power supply over lead 23, transmitting resistor 59, lead 60, resistance 70, standby thyratron G9 and through both halves of a resistor 45 to the lower end of the potential divider 1 ... 6 and a condenser 13 respectively. The resistance drop in the transmitting resistor 59 biasses valves V21, V22 to cut-off and no oscillations are transmitted, which is the mark or idle condition. The mid-point 451 of resistor 45 is raised in potential and raises the control-grid potential of storage trigger tubes G1 ... G6 which, however, are precluded from firing by their suppressor grid bias. If now a combination of tape or key contacts C1 ... C6 are closed the respective thyratrons G1 ... G6 will fire since their suppressor grids are now connected to their cathodes. In addition a start contact CS will be closed, firing a start thyratron G8 which provides a path from point 18 on the divider 1 ... 6, through resistor 26, valve V10, tube G8 to the lower end of the divider 1 ... 6. The potential drop in resistor 26 biasses distributer valve V0 to cut-off, and after a suitable delay valve V1 conducts. The distributer valves VO ... V8 thereupon conduct in turn, as described in Specification 532,633, and as each conducts it raises the grid of an associated coupling valve V11 ... V16 to the conducting potential. The potential drop in resistor 26 also sends a negative pulse via a condenser 82 to extinguish the standby tube G9, thus stopping the current flow through the transmitting resistor 59, causing oscillations to be transmitted for the start or space element and biassing the storage tubes G1 ... G6 to cut-off again. As each coupling valve V11 ... V16 in turn conducts it will find its associated storage tube G1 ... G6 conducting or not according to the code set up on the key or tape contacts C1 ... C6. When the contact is closed, current flows through the transmitting resistor 59, lead 60, resistor 61, the conducting coupling valve and its associated storage tube, and no oscillations are transmitted, representing a mark condition. When distributer valve V8 conducts it extinguishes a stop-valve V17 which disconnects the anodes of the storage tubes G1 ... G6 from their potential source at the top of the potential divider 1 ... 6 and those tubes which had fired are extinguished. Valve V10 is also biassed to cut-off when distributer valve V8 ceases to conduct, extinguishing the start tube G8, and making the standby tube G9 conductive to send out the stop or idle marking condition. When the distributer valve V8 is extinguished valves V10 and V17 conduct again and the standby condition is completely restored. Circuit parameters may be so arranged that each signal element occupies 10 ms. If, when a key is depressed, the code contacts C1 ... C6 are arranged to remain closed for 45 ms. of the 80 ms. occupied by each character and a second key is depressed 40 ms. after the first, it will keep the contacts closed for 5 ms. after the first character has been transmitted and so set up the required character on the storage tubes G1 ... G6. The depression of the second key does not have any immediate effect since the standby tube G9 is extinguished at the time and the control grids of the storage tubes are thus negatively biassed. Thus two successive keys may be depressed 40 ms. apart, although a third key must not be depressed for a further 80 ms. When power is first applied to the circuit it is necessary in order to produce the standby condition to close contacts CS and so fire the standby tube G9.