GB1188193A - Improvements in or relating to Synchronous Telegraph Systems - Google Patents

Abstract

1,188,193. Telegraphy. SIEMENS A.G. 28 Sept., 1967 [29 Sept., 1966], No. 44153/67. Heading H4P. Mutilation of idle time and RQ telegraph signals is detected by transmitting these signals three times in succession, the receiver indicating a fault if less than three (or a multiple of three) successive such signals are detected. At the transmitter, when a continuous mark or continuous space (calling or clearing signal) is received from a subscriber a counting circuit causes the subscriber to be inhibited for the duration of three characters and causes three idle # or idle α signals to be transmitted. At the receiver, the received signals pass to a three character store which feeds a printer. A 3- character cyclic counter counts any received idle α or idle # signals. If three successive idle signals are counted no error has occurred. If two are counted it is assumed that an idle signal has been mutilated to form a text character and so the character following the two idle signals is inhibited and a continuous mark sent to the receiver output. If only one idle signal is counted it is assumed that this is a mutilated text character and an error symbol is printed in its place. Received signals are also checked for errors, e.g. by parity check, and errors result in an RQ signal being transmitted thrice.