GB902206A - Improvements in or relating to communication systems - Google Patents

Abstract

902,206. Telegraphy. SIEMENS & HALSKE A.G. Nov. 14, 1960 [Nov. 13, 1959], No. 39086/60. Class 40 (3). In a telegraph system in which the transmitted and received characters are arranged in groups, there is added to each group a control signal indicative of a characteristic of that group. At the receiver this control signal is compared with a second control signal derived by the receiver from the received character group. If the two signals are not similar, or do not bear a predetermined relation to each other, the receiver transmits a callback signal to the transmitter, which retransmits the incorrectly received group. Stores are provided at the receiver and transmitter for recording the character signals; preferably at least two groups are stored. It is arranged that interference which simulates the reception at the transmitter of a call-back signal, and therefore produces repetition of at least one group, does not cause the receiver printer to print the group characters twice. Faulty reception of a group, Fig. 1.-The transmitter station A transmits the characters a, b, c, &c., and after each seven characters transmits a control signal γ. If the derived, or second, control signal at the receiver B is not γ but, say, #, group II, the receiver transmitter sends a call-back signal # to the transmitter A. The group being transmitted upon reception of the signal #, group III, is terminated by a repetition characteristic #instead of the control signal γ, and the two groups, II and III, transmitted previously, are repeated. On reception of the signal # at B, the two groups II and III previously received and stored are not passed to the teleprinter. The retransmitted groups II and III, if now received correctly, as in Fig. 1, are passed via the store to the teleprinter. Reception of a spurious signal, Fig. 2.-As in Fig. 1, the letters of the alphabet are transmitted sequentially in groups. Group II is received correctly at B, but during transmission of group III the transmitter A receives an interference signal S which simulates a callback signal #. Group III is therefore terminated by a repetition characteristic e, and the groups II and III are retransmitted. At the receiver B the signal # is recognised, but since the previously received control signal and the derived signal agreed, γ group II, the stored signals now blocked to the teleprinter are group III and the retransmitted group II. The retransmitted group III is passed to the teleprinter. An embodiment of the invention is described with reference to Fig. 3 (not shown). With twowire transmission the repetition signal e is not necessary, the transmitter and receiver being connected serially.