Patent GB-784751-A (GB)
Title: Check circuit for electronic ciphering arrangement for teleprinter signals
IPC: G09C1/10
Filed: 1955-01-18
Abstract: 784,751. Code telegraphy. STANDARD TELEPHONES & CABLES, Ltd. Jan. 18, 1955 [Jan. 18, 1954], No. 1558/55. Addition to 784,530. Class 40 (3). The electronic ciphering and deciphering arrangement of the parent Specification in which the start element of the teleprinter signal brings into operation a timing circuit producing a number of pulses which are applied to a counting circuit producing through a rectifier network a number of sequential reading pulses which under control of contacts operated by a perforated tape bearing a succession of key, or ciphering, characters are electrically combined with the pulses of the input teleprinter character signals to produce the ciphered or deciphered signals, includes a testing arrangement controlled by the input or output character signals, and by pulses produced in the circuit arrangement for indicating the absence of pulses whose presence is necessary for, or fundamental to, the correct operation of the arrangement. The ciphering and deciphering circuit arrangements employed are identical with those described in the parent Specification, the testing arrangement which is shown in Fig. 10 is connected at terminals A ... E to corresponding terminals of Fig. 7 to which pulses are applied from the key tape apparatus shown in that Figure, and from portions of the apparatus responsible for the generation of the reading pulses or of the signal pulses derived from the combining operation. As in the parent Specification the start and stop elements are positive and negative respectively. Conductor 15a leading to terminal A and connection 38 applies a positive reading pulse corresponding to the start element. To conductors 18 and 48, with the switch S in the position shown, are applied by the switches K1 . . . K5 from their upper or lower contacts, all the positive reading pulses which are applied over conductors 15b . . . 15f. A pulse M applied over 15g to a valve V7 operates the magnet SM for stepping the cipher or key tape, and if this operation is correctly effected the closure of contacts 41 permits a pulse on conductor 15h to pass through a circuit 40 to conductor 28 via terminal B. If, during the ciphering or deciphering operation all these positive potentials are present on the relevant conductors 18, 28, 38, 48, a positive potential is applied by the rectifier network SR5 to the grid of the valve V6 which conducts and holds an alarm relay in operated condition. During spacing element periods of the ciphered or deciphered signal, there is no pulse on the conductor 71b, and if at that time a pulse is missing on one of the conductors 18 ... 48, the anode current of the valve V6 is considerably reduced, and the alarm relay releases to operate a warning device. The loss of the M pulse for stopping the key tape cannot be detected when the circuit is not modified for signal regeneration as this pulse coincides with the stop element (mark) or the output signal, giving rise to a positive pulse on the conductor 71b which holds the valve V6 conducting and the alarm relay operated. In the case of signal regeneration the output character signal is delayed by 10 ms. relative to the reading pulses and the absence of the M impulse is detected when the fifth code element is a space and positive potential is absent from the conductor 71b. The operation of the switch S to its lower position 2 connects conductor 48 to a conductor 72 connected to the output of the valve V2B of the combining circuit, Fig. 5, whose operation is described in the parent Specification, which should, after the application of the pulses over conductor 16 to the valve V2A, produce pulses corresponding to the pulses which would be applied directly from the lower contacts K1 . . . K5 and over switch S in its position 1, this operation effecting a test of the operating condition of the valves V2A, V2B.