Patent GB-784530-A (GB)
Title: Electronic arrangement for ciphering and deciphering teleprinter signals
IPC: H04L9/22
Filed: 1955-01-18
Abstract: 784,530. Code telegraphy. STANDARD TELEPHONES & CABLES, Ltd. Jan. 18, 1955 [Jan. 18, 1954], No. 1557/55. Class 40 (3). An electronic arrangement in which teleprinter character signals are ciphered or deciphered by electrical combination with key character signals comprises a normally inoperative source of timing pulses brought into operation by the start element of a character signal and generating a train of timing pulses controlling an electronic distributer circuit to generate the code elements of the key signal which are combined with the elements of the character signal to produce the ciphered or deciphered signal, the pulse-generating source being rendered inoperative during the stop element period of the output signal. In the diagrammatic arrangement, Fig. 1, the incoming character signals on conductor 11 are fed to the combining gate circuit 6 and to a start-stop circuit 1 controlling a source 2 of timing pulses which are passed over conductor 13 to a scale-oftwo counting circuit 3 which applies pulses to a rectifier matrix 4 passing pulses over a group of conductors indicated at 15 to a tape transmitter 5 so that in accordance with the setting of the tape-controlled contacts by a perforated tape 25, pulses are passed over conductor 16 to the gate circuit 6 in which they are combined with the code elements of the character signals to produce the ciphered or deciphered signals on the output conductor 61. In a modification, Fig. 2 (not shown), connections are made from the transmitter 5 to the matric 4 from which the key signals are passed to the combining circuit 6. In a further modification, Fig. 3 (not shown), generally similar to Fig. 1, the output ciphered or deciphered signals are derived from a twocondition multivibrator controlled by the gate circuit 6 which is controlled by timing pulses from the source 2 in conjunction with the input signal pulses over the line 11. Detailed arrangements. The start element of a character is applied to a valve producing a positive pulse which changes over a start-stop circuit, Fig. 4 (not shown), allowing an oscillating circuit to produce eight impulses spaced at 20 ms. and then to return to normal. In the arrangement described, the start and stop elements are positive and negative respectively. These eight pulses are applied over an input 13 to a scale-of-two counter circuit comprising three double triodes V11, V12, V13 of which the left-hand sections are normally non-conducting, i.e. before the arrival of the first pulse. The anodes of the six triode sections of the valves V11, V12, V13 are connected via conductors 14a . . . 14f selectively to the three lower rectifiers of groups SR7 ... SR14. In the normal condition of the valves V11, V12, V13 a positive pulse is applied from group SR14 to the terminal 30, and in response to the timing pulses, positive a pulses are applied in succession from the groups SR7 ... SR13 to a conductor 15a, conductors 15b ... 15f, and to conductors 15g, 15h. The pulse over 15g triggers a valve V7, Fig. 7, to operate a magnet SM stepping the tape perforated according to the sequence of cipher key characters and which selectively closes contacts K1 . . . K5 so that the pulses on 15b . . .15f can pass selectively and sequentially to the conductor 16 leading to the combining circuit, Fig. 5, in which the input signals on conductor 11 are fed directly to a lower pair of rectifiers and, after inversion by valve V1B, to the upper rectifier pair of the group SR1. The keying signals are fed over conductor 16 to the grid of a valve V2A of which the output is connected to the lower rectifier pair of group SR2 and also to the grid of valve V2B of which the anode output is applied to the upper rectifier pair of the group SR2. If, for example, the input signal and the key signal both have a mark element, substantially zero potential is applied over conductors 11, 16 and positive potential will be applied to the two upper rectifiers of group SR1 and to the two lower rectifiers of group SR2. These four rectifiers will be blocked and of the conductors 33, 34, 35, 36 solely, the conductor 34 will be connected to two blocked rectifiers and thus a positive potential will be applied via the uppermost rectifier of group SR3 to conductor 31 so that a mark is transmitted from the anode output of valve V3A. In the case of the arrangement including signal regeneration the positive pulses denoting mark and space are applied to conductors 31, 32 respectively and in the stop condition there will be positive on the member 31 so that the left-hand side of the valve V4 will be cut off and the right-hand side conducting so that a mark will be transmitted over output conductor 71a. If a positive pulse is present on conductor 32 valve V3B conducts, the right-hand triode of the valve V4 is cut off and a positive (spacing) pulse passes to the conductor 71a. In a modification of the operation of the timing circuit, the potential from terminal 30, Fig. 6, is applied through a reversing valve to a control valve to the grid of which the input signals are applied and which normally is non-conducting. This valve normally holds conducting a further valve which inhibits the operation of the oscillator. The start impulse renders the control valve conducting, starts the oscillator, and the removal of the positive voltage from terminal 30 removes the negative voltage from the control valve which remains conductive until the eighth pulse which makes terminal 30 positive again, thereby cutting off the control valve and stopping the oscillator until the next start element is received.