Patent GB-837238-A (GB)
Title: Error suppressing telegraph system
IPC: H04L1/00
Filed: 1957-07-26
Abstract: 837,238. Code telegraphy. MACKAY RADIO & TELEGRAPH CO. July 26, 1957 [July 27, 1956], No. 23741/57. Class 40 (3). In an error-detecting telegraph system, providing in some cases the correction of faulty signals, signal combinations constituted by a plurality of elements of one or the other of two kinds are converted by the addition of an element of one or the other kind so that in the converted signals, the number of elements of one kind has the same predetermined numerical characteristic, e.g. the total number of mark elements must be odd, each converted signal is transmitted over two multiplexed transmission channels as a first transmission and a second transmission respectively, and at the receiver, the first transmission is examined and is used for recording if the signal exhibits the predetermined numerical characteristic, whilst if the signal is faulty this transmission is ignored and the second transmission of the signal is examined for the predetermined characteristic with the result that if an error is not detected, the second transmission of the signal is utilized to control the recording of the character. If the first and second transmissions are faulty an alarm is operated. Transmitter arrangement.-The code elements from a tape transmitter SP, Fig. 1B, selectively operate relays K1 ... K5 of which the first four, K1 ... K4, each have three pairs of contacts (1, 2), (3, 4) and (5, 6), whilst the fifth relay has two contact pairs (1, 2) and (3, 4). The contacts (1, 2) selectively connect marking or spacing potential to five segments of a distributer having two sets of six segments respectively allocated to the transmission of the 6-unit signal on two channels. The tongue of the contacts 3, 4 of the relay K5 is connected to the sixth segment of the first channel, and, with the contact arrangement shown, is effective to apply a mark or a space element so that the total number of mark elements in the 6-unit signal is an odd number. A transfer relay TR operated over connection p1 from the distributer during the transmission of the sixth code element transfers the settings of relays Kl ... K5 to relays SK1 ... SK5 which on operation lock up over the released contact of relay RR and which over their contacts repeat the 5-unit signal and the added (sixth) element to the second set of six segments of the distributer. During the first code element of the second channel a pulse from the distributer over the line p2 operates the transmitter SP to step the tape for the sensing of the next character, and during the transmission of the first code element of the subsequent character the release relay RR is operated over line p3 to open the locking circuits of those relays SK1 ...SK5 which had been energized. Receiver arrangement.-The first five element of a signal from a receiving distributer selectively operate relays R1 ... R5, Fig. 2, each having three pairs of contacts (1, 2), (3, 4) and (5, 6), and the relays operated being locked up over a conductor 9. The 5-unit signal is applied by contacts (1, 2) to the conductors o1 ... o5 and the operation of the banks of contacts (3, 4) and (5, 6) is such that if the received signal includes an odd number of marking elements a negative voltage is applied to a conductor 8, to which a positive voltage is applied if the signal is erroneous. In the two channel receiving arrangement, Fig. 3b, if the incoming 6-unit signal is correct, the negative voltage on conductor 8 operates relay A1 over contact 10 of a relay S1 operated by a pulse over connection p1 from the receiving distributer, and the winding of a relay F from which a short-circuit connection is received by the operation of a push button PB for a short time at the beginning of reception. The operated contacts of relay A1 pass the 5-unit signal on conductors ol ... o5 to relays RC1 ... RC5 which are selectively operated, locked up over connection 13 from a positive voltage V1, and apply the signal combination to an extensor circuit which passes the signal with the addition of start and stop elements to the receiving teleprinter or perforator. If the signal on the first channel is correct, the repetition of the signal on the second channel is ignored. The operation of contact 11 of relay S1 completes a charging circuit for capacitor 12 and the release of contact 11 operates relay H1 which breaks the locking circuit over conductor 9 for the relays R1 ... R5. If the signal on the first channel is incorrect, and the repetition on the second channel is correctly received, relay A2 is operated when relay S2 is energized by a pulse on conductor p2 from the distributer, and the winding of relay F is again energized. The operation of relay A2 allows the 5-unit signal from the second storage bank RS2 to pass over conductors o<1>1 ... o<1>5 and via back contacts of relay A1, not operated and relays RC1 ... RC5 to the extensor and the teleprinter. The release of relay S2 operates relay H2 which opens the locking circuit over conductor 9<1> to the relays R1 ... R5 of the storage bank RS2. If the signal received over the second channel is found to be incorrect, relay A2 is not operated and a signal from its back contacts, wired for word space in the arrangements shown, is passed to the relays RC1 ...RC5 for application to the extensor and the signal recording apparatus. Also, if an error is recorded for successive channel receptions, the relay F which is slow to release, is arranged to be de-energized by the occurrence of successive positive pulses, indicative of errors, over the conductors 8, 81 and at contact 16 closes the operating circuit of a lamp L and bell B. At contact 14<1> the relay F locks itself released until conditioned for reoperation by actuation of the push button PB. A pulse passed over conductor p3 from the distributer soon after the commencement of the two-channel cycle operates relay S3 to open the locking circuit of the relays RC1 ... RC5.