GB932830A - Improvements in or relating to communication systems - Google Patents

Abstract

932,830. Error-detecting telegraph systems. SIEMENS & HALSKE A.G. Sept. 1, 1961 [Sept. 1, 1960], No. 31519/61. Class 40 (3). In a communication system binary coded message signals are transmitted in groups. A first characteristic signal is derived from each group as transmitted and a second from the group as received. The receiver returns the second signal to the transmitter where it is visually compared, e.g. after punching a tape or printing, with the first signal. Lack of identity indicates an error in transmission. The comparison may, in addition, be performed at the receiver. In the embodiment described, a calling signal from the transmitter sets the distant receiver to its receiving state and the local teleprinter ready to print the message transmitted. The group of message signals is transmitted and is printed by the local printer and by the receiver. Evaluating units at the transmitter and receiver derive the first and second characteristic signals, e.g. by counting the number of space signals in the group. At the end of the transmission of the group a switch is operated which causes a termination signal to be transmitted. This causes the signals from the evaluating units to be printed at their local printers and to be transmitted to the other station, where they are printed. Thus at the transmitter printer there appears both the first and the second signals. This permits visual comparison for detection of error. The transmitter is automatically set ready for transmission of the second group of signals after the receipt of the second characteristic signal, or at a predetermined time after the end of transmission of the first group if no second signal is received.