Patent GB-546175-A (GB)
Title: Improvements in or relating to telegraph systems
IPC: H04L1/14
Filed: 1940-11-29
Abstract: 546,175. Type-printing telegraphy. CREED & CO., Ltd., and MASON, F. P. Nov. 29, 1940, No. 17052. Addition to 514,853. [Class 40 (iii)] In a type-printing system in which the transmission of a signal combination is repeated if the signal has not been correctly received, printing of the incorrect signal is prevented by the transmission of a characteristic signal combination, e.g. - + -. Fig. 2 shows a single station, the distributers TR, TL and RS, RR, RL being associated with the transmitter and receiver respectively. Signal combinations set up by the tape transmitter TT1 ... TT5 are sent by distributer TR and radio-transmitter RT from station X and received at station Y by radio receiver RRR, relay RRA and distributer RR, thus energizing combinations of relays CA ... CE. The energized relays CA &c. lock-up over contracts ca1 &c. and ga1, prepare circuits at ca2 &c. for relays EA &c., and replace marking potential by spacing potential on the corresponding contacts 6 ... 10 of distributer TR at station Y, so that the same signal combination should be sent back to station X, where is is received by distributer RR and applied over its contacts 6 .. 10 to the contacts TT1 ... TT5 of the tape transmitter. If the received signal combination is different from that transmitted, one or other of the relays BA, BB is energized and opens the holding-circuit of a relay F, which was energized over contact 1 of distributer RL. Relay F over contact f3 connects spacing potential to contacts 15, 17, 20, 22 of distributer TR, other contacts of which are permanently connected to marking potential as indicated. As the brush of distributer TR passes over contacts 15 to 22, the combination SMSMMSMS is transmitted, the first three pulses SMS being a non-printing signal, the two pulses MM being without effect, and the final three pulses SMS being a repetition of the non-printing signal. At the receiving station Y, the three pulses SMS are received by distributer RR as its brush passes over contacts 15 to 17 (and again as it passes contacts 20 to 22) and energize relays DA, DC but not DB, so as to open the circuit of the printer magnets PM1 ... PM5. If, however, the signal combination repeated back to station X is the same as that set up on the tape transmitter, neither of the relays BA, BB energizes, relay F remains energized, the circuit of the tape feed magnet TT is closed by relay H in due course, and the distributer TR sends a printing signal consisting of nine marking pulses, so that the selected character is printed. The circuits of the selector magnets PM1 ... PM5 are prepared by relays EA ... EE and closed over the second contact of the distributer RL. The receiving relay RRA is controlled by valve circuits VCC, VRC, which, as described in Specification 540,839, cause the relay RRA to be affected in the same way by interference or by fading. The circuits are modified by the provision of a relay RB, which is energized when the distributer brush RS is passing over its first five segments, i.e. during the reception of the signal combination, so as to reduce the sensitivity of the valve circuit during the reception of code signals as compared with its sensitivity during the reception of the non- printing signal. Specification 540,839 is referred to.