Patent GB-840501-A (GB)
Title: System for the transmission of signals
Inventor: DUUREN HENDRIK CORNELIS ANTHON
IPC: H04L1/00
Filed: 1956-07-25
Abstract: 840,501. Printing-telegraph systems. STAAT DER NEDERLANDEN TEN DEZE VERTEGENWOORDIGD DOOR DE DIRECTEUR-GENERAAL DER POSTERIJEN, TELEGRAFIE EN TELEFONIE, DE. July 25, 1956 [July 26, 1955], No. 22978/56. Class 40 (3). The second and each subsequent signal element of each code combination is different in frequency from the preceding element, the correctness of reception of a code combination being detected by counting the number of frequency changes therein. In a two-way communication system the detection means at one station permits or prevents transmission to the other station depending upon whether the number of signal elements counted thereby is equal to or less than the predetermined number in a code combination. In the system described, five-element signals of marks M and spaces S are converted into 6-unit signals of M's and S's by adding an element between the 3rd and 4th elements of the 5-unit signal. By allotting four frequencies to represent the two-element combinations MM, MS, SM, SS, the 6-unit signal can be transmitted as the sequential transmission of three frequencies, provided successive frequencies are different, or, in terms of M's and S's the middle twoelement combination is different from that which precedes and that which follows it. For twenty-four of the thirty-two 5-unit signals, the added element is the reverse of the second element of the 5-unit signal, e.g. the 6-unit signal corresponding to MSSSS is MSSMSS. For four of the eight " exception " signals, the fourth element is made identical with the second element of the 5-unit signal, e.g. MMSSS becomes MMSMSS, as MMSSSS would be inadmissible. For the remaining four exception signals, viz. line-feed, K, T and X, the third and fourth elements in the 6-unit signal are changed. For example the signal for the character K, represented in the 5-unit code by MMMMS, is converted to MMSMMS since the signal MMMSMS would be inadmissible, and the signal MMSSMS would be identical with the 6-unit signal for the letter J. Transmitter arrangement, Fig. 3. The 5- unit code signals derived from a tape transmitter ST stepped by pulses from a generator P3 are simultaneously applied by a pulse from a generator P1 to trigger circuits A, B, C, E, F and a pulse opposite to its input pulse is applied from the trigger B to the trigger D for the fourth element of the 6-unit code. The outputs of the six triggers A . . . F are applied to a code converter CC comprising a number of rectifier networks which are arranged to detect the eight " exception " signals, and under control of a generator P2 allow pulses to pass back to reverse the trigger D for four of the signals or the triggers C and D for the remaining " exception " signals. Under the control of a distributer V, the mark-space combinations on trigger pairs AB, CD and EF are applied sequentially over connections 1, 1 ; 2, 2 and 3, 3 to a circuit combination G, H which in accordance with the input MM, MS, SM or SS   is able to control the circuit I to produce the respective frequency. Receiver arrangement, Fig. 4a. The signal received at O is fed to circuits FI . . . FIV selectively responsive to the four frequencies, and controlling associated triggers A . . . D whose outputs are applied by conductor R to the inputs of six triggers E . . . J. When one of the triggers A . . . D is operated in response to a received frequency representing the first pair of the six elements, a pulse is applied to a generator P1 which operates the first stage K of a three-position counter K, L, M and the triggers E, F are operated in accordance with the elements of the first pair. If a second frequency is received and detected within a predetermined period, the second stage L is operated and the output of the operated trigger A, B, C or D applied to triggers G, H to set up the second pair of code elements. Similarly the reception of the third frequency within the predetermined period operates the stage M, and the elements of the third pair are set up on the triggers I, J. If the elements are not received within the predetermined time limits, the counting chain KLM restores to its normal position. The elements from the triggers F, H together with pulses from output terminals of the triggers A, B, C, D are fed to a code converter CC comprising a number of rectifier networks arranged to detect from outputs of the trigger circuits A, B, C or D together with selected outputs of the triggers F, H, the four signals which require inversion of the third element, and an output from the converter CC in combination with a pulse from the stage M of the converter 1 reverses the trigger G. As the fourth element of the 6-unit code is discarded in the reconstituted 5-unit code, the output of the trigger H is applied solely to the converter, whilst the outputs of the triggers E, F, I, J and that of G, reversed, if necessary, are passed to a trigger N under control of a distributer P2 which passes the elements of the 5-unit signal in conjunction with start and stop elements derived from circuits ST, SP to a printer PR, which is normally blocked, but which is released for operation by a pulse from a circuit PB triggered by a pulse from the final stage M of the counter KLM. The three. elements may each have a duration of 10 m/secs. for a normal teleprinter signal of 150 m/secs. so that the transmission line may be a fiveelement multiplex. Alternatively each frequency element may have a duration of 5 m/secs. with an interval of 5 m/secs. between the elements.