Patent GB-590631-A (GB)
Title: Improvements in telegraph systems
IPC: H04L7/00
Filed: 1945-02-19
Abstract: 590,631. Synchronous movements ; type-printing telegraphy. WESTERN ELECTRIC CO., Inc. Feb. 19, 1945, No. 4200. Convention date, Feb. 21; 1944. [Class 40 (iii)] A start-stop printing telegraph receiver includes means for generating locally artificial start and stop impulses which become effective to maintain the transmitter and receiver in synchronism in case a start signal fails to arrive. The locally-generated impulses cause the receiver mechanism to pass through a predeter. mined munber of cycles on the failure or termination of signals and, in a cipher system in which the message signals are combined in the transmitter and receiver with similar random signals, means may also be provided for producing a corresponding number of cycles of the transmitting mechanism to prevent the random-signal generators getting out of step. General operation. Signals generated by tape-transmitter 11, Fig. 1, are repeated by relay 31 over plug 33 to a radio-transmitter 36 and the received signals from radio-receiver 201, Fig. 2, are repeated by relay 206 to selector magnet 301, Fig. 3, of a reperforator unit 302. During an idle marking interval, condensers 238, 239 become charged from battery 243 applying a positive potential to the grid of valve 236 and thereby causing the operation of relay 228 in its anode circuit. Relay 228 operates relay 217. When the armature of relay 206 moves to,spacing position at the beginning of transmission, condensers 238, 239 discharge and relays 228, 217 release. Just before the distributer of reperforator 302 reaches its stop position at the end of a cycle, contacts 312 on the distributer shaft 306 are closed to operate relays 252, 253, which lock to battery -258. Relay 253 opens the circuit of two relays 247, 263, but these relays are temporarily held energized by a charging current through condenser 266, the actual time of release being determined by variable resistances 271, 272 in circuit with biassing windings. Relay 253 also connects ground over lead 268, the armature of relay 247 and leads 218, 212, 214 to magnet 301 to operate this relay to marking condition independently of relay 206, thus producing an artificial stop pulse. Relay 247 releases its armature, thereby placing magnet 301 again under the control of relay 206, just before the true stop pulse should be terminated by the beginning of the start pulse. If the start pulse is not received, the release of relay 263 operates relays 213, 256 to transmit an artificial start pulse at the armature of relay 213. Relay 256 opens the circuit of relay 259 which, however, is held by condenser 274 until about the middle of the true-start-pulse period. When relay 259 falls back, it releases relays 252, 253 to restore the impulse-generating circuit to normal. At the end of message transmission, the apparatus goes through a series of similar cycles during which artificial stop and start impulses are alternately generated and the tape is perforated with an " all-marking " signal combination. The series of cycles continues until condensers 238, 239 have charged sufficiently (the spacing contact of relay 206 being continuously open) to operate relay 228 which in turn operates relay 217 to stop the operations. Resistance 244 in the discharge circuit of condensers 238, 239 prevents the pulse-generating circuits being put in operation in response to a stray pulse during an idle interval. Ciphering arrangements. Plug.68 is inserted in jack 34 and message signals from transmitter 41 are combined in relay 58 with random signals from transmitter 49, a combination of like signals producing a mark and unlike signals a space. The ciphered received signals are retransmitted by mechanism 316 over jack 286 to relay 323, whereby they are repeated over lead 324 and combined with corresponding random signals from transmitter 326 reproducing the original signals for operation of a printer 331. At the transmitting end, relays 101 ... 104 and 106 are provided to maintain the two random transmitters in step. Relays 101, 103, 104, 106 are normally energized, the two last by vacuum tubes 107, 108, the grids of which are rendered positive by the charging of condensers 163, 168 respectively. When a message commences, relay .102 operates over taut-tape contacts 109, releasing relay 103 and energizing start magnet 133 of transmitter 41. Relays 104, 106 also release due to the discharge of condensers 163, 168. When the brushes of distributer 40 move off their " stop " contact, relay 101 releases and the signals are repeated. by relay 46. When transmission stops, relay 102 releases, relay 101 operates over " stop " contact of distributer 40, relay 46 is released and magnet 52 is operated to advance random transmitter 49 through a series of cycles. These continue until relay 1.04 operates due to the charge on condenser 163, re-energizing relays 101, 46. The charging circuit of condenser 163 is so adjusted that the random transmitters at both ends are operated through the same number of cycles. Shortly afterwards, relay 106 operates to restore the circuits to normal condition. Testing. Key 203 provides for testing the impulse-generating circuits locally by means of a test message sent from transmitter 302, and key 232 is used for setting up conditions for the adjustment of resistances 271, 272 for the proper timing of the artificial stop and start pulses. Specification:> 245,149, [Class 40 (iii)], and 365,975 are referred to.