Patent GB-349074-A (GB)
Title: Telegraph receiving or repeating circuits
IPC: H04L25/14
Filed: 1930-02-17
Abstract: 349,074. Code and type-printing telegraphy. WESTERN UNION TELEGRAPH CO., 195, Broadway, New York, U.S.A. Feb. 17, 1930, No. 5286. Convention date, March 5, 1929. [Classes 40 (iii) and 40 (v).] A synchronous electric telegraph system incorporates thermionic valves of the " thyratron " type in which the application of a positive potential to the grid serves as a trigger to start the plate current which continues to flow irrespective of changes in the grid potential until the plate voltage is removed. In a repeating system means is provided for normally transmitting over the line current of one polarity when the valve is inoperative, the operation of the valve causing current of the opposite polarity to be transmitted. In Fig. 1 incoming signals are applied through a ring 4, brush BR, and segments 5, 6 alternately to the grids of two " thyratron " valves 1, 2 whose platefilament circuits are alternately closed through a ring 7, brush BR2, and segments 8, 9. When a negative signal is received, neither of the valves is operated, and negative current is transmitted by a battery B2 connected across the terminals of a transmitting line L1. A positive impulse operates one of the valves 1, 2, and the constants of the circuits are adjusted so that the positive plate current sent to the line L1 exceeds the negative current flowing from the battery B2. The grids of the valves are normally maintained negative by small batteries Cl, C2 connected through resistances r1, r2 to the filaments. In the system shown in Fig. 2 signals received over a line L are retransmitted alternately over two lines L1, L2. The signals are applied through a ring 10 and segments 1, 2, 3 .. to the grids of four " thyratron " valves 1a .. 4a in succession. When no positive signal is received negative current is sent by batteries B3, B4 connected across the terminals of the transmitting lines L1, L2. If a positive signal is received when, for example, the brush BR1 engages segment 1, the grid of the valve 1a will be made positive, and as the brush BR3 passes over segment 2, current will flow in the plate circuit and a positive impulse will be transmitted to the line L1, the constants of the circuits being adjusted so that the current flowing in the lines L1, L2 from the plate circuits of the valves is greater than the negative current from the batteries B3, B4. As the brush BR3 passes off segment 2, a brush BR2 contacts with segment 4 of its ring set, and a battery B2 is introduced to counterbalance the positive potential applied to the plate of the valve 1a by batteries B1, B3. The valve 1a will now respond correctly to the impulse received as the brush BR1 engages segment 5. Restoring or modifying imperfect signals. Fig. 3 shows an arrangement for restoring, in a repeater system, impulses which have been lost or greatly attenuated during their transmission. The received impulses are applied alternately through a brush BR1, and a segmented ring to the grids of two " thyratron " valves 1, 2. Positive and negative impulses which are received are retransmitted as described with reference to Fig. 1. When no signal is received, a small battery C applies a positive potential to the grid of one of the valves as the brush BR1 engages a segment, and a positive current will be sent to the line L1 as one of the brushes. BRa, BRb completes the plate circuit of the valve operated. If no signal is received, as the brush BR1 engages the next segment, the battery C will tend to operate the other valve, but on account of the overlapping arrangement of the segments Al .. , B1, .. current will still be flowing and the potential of the grids will be reduced so that the valve is not operated. Negative current will be transmitted to the line L1. If no effective signal is received as the brush BR1 engages the next segment, the battery C will operate one of the valves since no plate current flowed during the transmission of the previous (negative) impulse. In Fig. 4 is shown an arrangement for operating alternate sets of printing magnets by positive and negative impulses from the receiving line. The line wires l1, l2 connected, to the grids of "thyratron " valves 1, 2 are bridged by a potentiometer resistance P. Positive and negative impulses operate the valves 1, 2 respectively. The plates are connected to sets A, B of printer magnets, and as the brush BR2 passes over its ring 21, the magnets of the set A are operated by positive signals, whilst the magnets of the set B are energized by signals of negative polarity. A small battery C1 applies a normal negative potential to the grids of the valves 1, 2 and an additional battery C2 approximately equal to C1, is included to prevent a shortcircuit through the latter when its circuit is closed by the brush BR1.