Patent GB-489531-A (GB)
Title: Improvements in or relating to station selection in a telegraphic communication system
IPC: H04L25/04
Filed: 1937-10-08
Abstract: 489,531. Interconnection of telegraph stations. CREED & CO., Ltd. Oct. 8, 1937, No. 27379. Convention date, Dec. 24, 1936. [Class 40 (iii)] In a party - line system, each station on receipt of its call signal, such as the letter A, C, or E, sends its reply signal, such as B, D, or F, and is prepared by its call signal so that when a lock-out signal, such as Y, is sent by the calling station, the called and calling stations alone are left in circuit. If the operator at A wishes to call station C and exclude all other stations, he first starts the motors at all stations by breaking the line by means of his key 19 whereupon, at every station, line relay 34 acts to release slow-release relay 36, thus energizing the self-locking relay 37 to start the motors 41 and light the white lamp 42. The operator at A then sends his own call letter A, which is recorded at all stations and, in addition, selects a code lever, Fig. 3 (not shown), as described in Specification 365,975, at the home station to close contact 21, whereupon the call-responsive relay 38 pulls up and locks and the answerback relay 6 acts through bail 1 to operate the answer-back key 3, which is the key for the answer-back letter B of the station and is distinguished from the other keys of the keyboard by being fitted with a striker 4 for engaging the bail 1, Fig. 1, and Fig. 2 (not shown). Letter B is thereupon recorded at all stations, and the operator at A now sends the letter C to call station C, where similarly contact 21 is closed, relay 38 pulls up and locks, white lamp 42 is lighted, and the answer-back key, in this case the key for letter D, is operated, so that ABCD has now been recorded at all stations. Station A next sends the lock-out signal Y, which prints Y at every station and also selects a code lever to shift contact 24, whereupon at every station relay 39 pulls up and locks, lighting the red lamp 43 which remains lighted throughout the message to indicate that the line is busy. At the called and calling stations, A and C, where relay 38 has been energized, relay 37 holds on and the motor 41 and white lamp 42 consequently remain in circuit; but at every other station relay 37 releases on operation of the contact 24 by the lock-out signal; and the motor 41 and white lamp 42 go out of action, while the keyboard 32 and keys 18, 19 are short-circuited through the armatures of the de-energized relay 38 and energized relay 39 to provide a through path for the line 31. Clearing. During the message the slowrelease relay 36 at every station and the callresponsive relay 38 at every working station remain energized. The clearing key 19 is timed by a dashpot to give an interruption long enough to drop all relays 36, whereupon relays 38 are unlocked at the working stations and relays 39 are unlocked at all stations, extinguishing the lamps 43, while relays 37 at all stations pull up and lock and light the lamps 41. The stop signal Z is now sent by station A and recorded at every station, where in addition it selects a code lever to open contact 23, thereby releasing the relay 37, motor 41 and white lamp 42. Thus the letters ABCDYZ have been recorded at all stations with the message interposed at stations A and C, where the motors were running during its transmission. Break signal. The break signal can be given during a message by the key 18, which is timed by a dashpot to open the line for an interval which is not long enough to drop the slow-release relays 36, so that the connection is not broken. Intervention by monitoring station. A monitoring station is provided with a key 48 whereby it can enter the circuit after being locked out. Depression of key 48 starts the local motor 41 and removes the short-circuit from the keyboard and break keys 18, 19. The operator can then receive the message by means of his receiver magnet 35, and if necessary he can interrupt and set up a new connection by depressing key 19.