Patent GB-254779-A (GB)
Title: Electric telegraph systems
IPC: H04L5/16
Filed: 1925-04-01
Abstract: 254,779. Western Electric Co., Ltd., (Western Electric Co., Inc.). April 1, 1925. Transmitting and receiving systems for code telegraphy.- The transmitter is shunted bv a device offering high impedance to normal signal impulses but operable by an abnormal impulse from the receiving station for the purpose of (a) giving a break signal indication at the transmitting station, or (b) effecting disconnection of the transmitter from the line, or (c) reversing the direction of transmission over the line. Fig. 1 shows a cable system provided at each station with a device for purpose (a). Switches 9, 14 in the position shown connect the transmitter T at station A to the receiver R at station B, and a lead 1 in parallel with the transmitter T is connected through a biasing battery 2 to the grid of a thermionic valve 10 of which the plate-filament circuit includes a slow-acting relay 11. The energization of this relay closes the circuit of a dash-pot relay 12 which in turn closes the circuit of a bell or other indicator 13. During normal operation the current in the output circuit of the valve 10 is insufficient to operate the relays 11 and 12. When, however, the receiving operator, wishing to break signal, moves the switch 14 on to contact 15. a strong impulse from battery 3<1> charges the grid of the valve 10 to a positive potential sufficient to close the circuit of the indicator 13. Fig. 2 shows in addition devices for effecting purposes (b) and (c). In this case the relay 12 closes a circuit which includes, in addition to a signal lamp 29, a relay 28 provided with two armatures. When the relay 28 is energized one armature closes a locking circuit for the relay through a manually-operable key 27, and the other connects the local receiver R to line in place of the local transmitter T. The abnormal impulse for effecting these operations is sent from a battery 26 at the other station upon actuation of a switch 20 spring-opexated in the direction of the arrow. The switch first closes a contact 21 to energize a relay 22 provided with two armatures, of which one closes a locking, circuit for the relay through a manuallyoperable key 23, and the other connects batterv 26 to, and disconnects the local receiver R from, the line. The switch 20 subsequently closes a contact 24 to energize a relay 25, provided with two armatures, of which one closes a locking circuit for the relay through the key 23 and simultaneously breaks the circuit of the relay 22, and the other connects the local transmitter T to the line. Restoring or modifying imperfect signals; eliminating effects of disturbing currents.-Figs. 3 and 4 show the arrangements at one terminal station and at a mid-line re-shaping and repeating station respectively for a system in which an abnormal signal impulse from the terminal station which is at the moment receiving effects a reversal of the direction of repeating at the mid-line station in addition to a reversal of the line connections with the transmitter and the receiver at each terminal station. The receiving arrangement at each terminal station includes a shaping network N as described in Specification 248,823, and an amplifier A as described in Speci- 248.822. The transmitter T or the receiver R is connected to line according to the position of the tongue of a relay 50 of which the windings are connected as shown to a biased relay 51 adapted, as described in Specification 239,745, to short-circuit a portion of the amplifier to protect the receiver from earth or other excessive currents when the station is converted from transmitting to receiving. Assuming that the station represented in Fig. 3 is transmitting, the signal impulses are repeated at the mid-line station, Fig. 4, from cable 30 to cable 66 by way of the back contact 180 of a relay 80, contacts 75 and 76 of a relay 77 shaping network C, amplifier D, contact 78 of relay 77, and the back contact 94 of a relay 91. When the operator at the terminal receiving station wishes to reverse the direction of signalling, he depresses the kev at that station corresponding to the key 55, Fig. 3. This effects successively (1) closure of a contact 59 to earth the local valve 60 to prevent its operation, (2) closure of a contact 56 for sending an abnormal impulse from battery 56a over the cable 66, (3) closure of a contact 57 to operate the local relays 50 and 51, thus reversing the line connections of transmitter and receiver at that station. At the repeating station, Fig. 4. the abnormal impulse operates the relay 83' through the relay 82<1>, valve 81<1>, and a back contact of the relay 91. The movement of the switch arm 83a of the relay 83<1> effects successively the following operations. (1) A contact 84' is closed in the circuit of the lefthand winding of a relay 92 to hold the tongue of this relay in the circuit-opening position shown. (2) A contact 85<1> is opened to de-energize this winding. (3) A segment 86<1> is engaged by a brush 89<1> to energize the relay 80 and the righthand winding of the relay 92. One armature of the relay 80 is thus moved to earth the valve 81 to prevent its operation, the other armature is moved to open the contact 180 and to connect the battery 80<a> to the cable 30 for transmission of an abnormal impulse to the terminal station, Fig. 3, and a protective short-circuit of a portion of the amplifier D is made by the relay 92. (4) The segment 86<1> is disengaged from the brush 89<1> to de-energize the relay 80. (5) A segment 87<1> is engaged by a brush 88<1> to earth the cable 30. (6) A contact 90<1> is closed to energize the lower winding of a relay 77 which operates to make the connections of the signalling circuit through the contacts 98, 99, and 100 instead of the contacts 76, 75, and 78 respectively to reverse the direction of repeating. The abnormal impulse received at the terminal station, Fig. 3, operates the relay 62 through the relay 61 and the valve 60 to close a contact 62<a>. The relays 50 and 51 are thus operated, the former reversing the line ronnections of the local transmitter and receiver, and the latter closing a short-circuit to protect the receiver.