Patent GB-802456-A (GB)
Title: Arrangement for maintaining synchronism for start-stop telegraph apparatus during reception via transmission paths which are susceptible to interference
IPC: H04L7/00
Filed: 1956-08-03
Abstract: 802,456. Printing-telegraph receivers. CREED & CO., Ltd. Aug. 3, 1956, No. 23990/56. Class 40 (3). In a start-stop teleprinter for receiving code groups of signal elements, each group beginning and ending with the normal start and stop elements respectively and comprising means for generating locally auxiliary start and stop elements which have durations shorter than and lying within the time periods of the received start and stop signal elements and which are applied to control the operation of the teleprinter, if the normal start or stop signal element is missing or delayed, means is included for rendering the auxiliary start signals completely ineffective at the commencement of the transmission of the code groups of signals, and means operating after a specified delay renders the auxiliary start signals effective when corresponding normal start signals are missing or delayed. The teleprinter receiving shaft 10 is driven from the rotating shaft 7 by a clutch 15 operated by a member 9 in response to the start element. A member 11 operated at a time corresponding to the end of the second code signal element moves to the right, against a biasing spring 16, a shaft 12 carrying a stop 14 which becomes disengaged from a projection 13 on a clutch 8 so that a drum member 3 is driven from the shaft 7, and is arrested after it has made a revolution. The drum 3 comprises discs with conducting segments 4 located so that they short-circuit the contacts 1 for a period within the normal stop period. Contacts 2, which are normally closed, are opened for a period within that corresponding to the start element of the next signal, the drum being arrested shortly after the end of the start element period, but being released again towards the end of the second signal element of the code group. In the circuit arrangement, Fig. 4, the receiver magnet M is energized in the stop condition over a circuit including the winding 22 of a relay I and the closed contacts r of the receiver relay R. If the relay R has not been operated during the period of the stop element, a circuit is closed for the magnet M through an auxiliary winding 25 and through contacts 1, closed by the drum during this period and contacts 2 or a1. Further rotation of the drum 3 opens contacts 2 so that a local start element is generated provided the contacts a1 are not closed by relay A in its released condition. At the beginning of a transmission, the relay A is not energized, but during the reception of signals the relay I is intermittently operated so that a relay V which is slow to release becomes permanently energized. At contact v a charging circuit is completed for the capacitor C2 allowing the relay A to energize after a period of about 9 secs. and opening contact al to remove the short circuit of the start contacts 2. At the end of signal transmission the period between the locally generated start and stop elements is such that the relay V releases followed by the release of relay A which at the closed contact a1 restores the short circuit of the start contacts 2 so that the teleprinter is brought to rest. The arrangement is intended to operate for continuous regular transmission from a tape, and if such transmission is interrupted for keyboard operation the relay V is intermittently released so that relay A is not energized and the released contacts a1 short circuit the contacts 2 of the auxiliary start element. At operated contact a2, a lamp L1 is lighted indicating that the auxiliary start contacts are operative.