Patent GB-370545-A (GB)
Title: Improvements in or relating to automatic secret telegraph systems
IPC: H04L9/38
Filed: 1931-02-04
Abstract: 370,545. Telegraph transmitters. KILBURN, B. E. D., 31, High Holborn, London.-(Smart, J. H. ; of Great Northern Telegraph Co., Avenue Edward VII, Shanghai, China.) Feb. 4, 1931, No. 3553. [Class 40 (iii).] In an automatic perforated-tape telegraph system, messages are sent in secret form by the operation at the transmitting end, of means which effects the transmission of impulses equivalent to those which would be obtained by physically turning over the tape at predetermined intervals of its length. At the receiving end the impulses of the mutilated message are utilized to perforate a tape which is passed through a translating device whose operation is modified and correspondingly controlled at predetermined intervals to pass on the decoded impulses to a further perforator, of known type, from which is obtained a tape perforated in accordance with the original message. Transmitter. The impulse transmission, equivalent to the effect of turning over the tape, is obtained by reversing the order in which the usual pecker rods G, H rise to engage the perforations in the tape and at the same time by interchanging the polarities of the current normally sent to line by the peckers. The tape is moved by a pin wheel B mounted on a shaft B<1> carrying a ratchet C and pawl C<1> connected to a lever C<2> on which is mounted a roller C<3> which is normally free to engage a recess C<5> in a continuously rotated cam C<4>. The order in which the pecker rods G, H rise to the tape is controlled by cams D<1>, D<2> in combination with a link K, positioned by a plunger M<2> of a controlling electromagnet M, M<1> and associated with a bar J, pivoted at J<1> and with its end freely mounted in a slot in the link K. In the arrangement shown, which is adjusted for the " reversed " tape, the cam D<1> and its associated link K<1> are ineffective, and cam D<2> operates the bar J through the link K4 so that the projections J3, J2 are raised in succession to allow the pecker rods H, G to rise in succession. Simultaneously with the movement of the link K by the electromagnet M, M<1>, a contact tongue M<4> is moved to engage the contact M<5> or M<6> by which the polarities of the current sent to the line by the coils N2, N3 and the associated tongue N4 are reversed when the tape is, in effect, turned over. The reversal of the transmitting arrangements, that is from " straight " tape to " reversed " tape, and vice versa is controlled by the operation of a relay 0 which at contact O<2> or O<3> operates coil M or M<1> to position the plunger M<2> and the associated link M<3> through which the order of operation of the pecker rods is determined by the cams D<1>, D2 and the associated link rods. The operation of the relay 0 may be controlled by an auxiliary tape with perforations at predetermined intervals, or by mechanical or electromechanical control of the armature O<1> from the shaft B<1>. If the reversal should occur in the middle of a signal, e.g. in the middle of a dash, and after perforation 3, Fig. 1, has been engaged by the corresponding pecker rod, the pecker when passing through hole 6 will not send the correct reversed signal current and will give rise to a false signal indication. In order that the perforation(s) produced immediately after a reversal may have their correct significance in the " reversed" portion of the receiving tape, the transmitting tape is stepped back to the centre hole prior to reversal, and the perforations corresponding to two centre holes are retransmitted in reversed form. In this way, the first perforation (s) after reversal is/are correctly related to the portion of a signal transmitted before reversal. At the receiving end, the translator is arranged to ignore the repeated signals, as is described later. To effect the stepping back of the tape the tongue O<1> which on each reversal is operated to one of the contacts 02, 03, energizes a relay F<1> which moves its armature F against a spring (not shown) to position a stop into engagement with the arm C<2> and out of engagement with the arm E<2> so that a roller E3 engages a recess E<5> of a cam E<4> and operates a pawl E<1> to rotate one step in the reverse direction a ratchet E on the shaft B<1>. General considerations and translator arrangement. Fig. 2b shows the form of the received tape when a tape perforated as in Fig. 2 is passed through the transmitter operating in the reversed manner, the perforations which are lost being indicated in Fig. 2a by the crossed dots. It is shown that the missing holes can be deduced by examination of the perforations appearing opposite the next subsequent centre hole on the received tape. The translator, shown diagrammatically in Fig. 5, through which is passed the received tape bearing the mutilated message, is provided with pecker rods P, R, and selector or corrector rods P<1>, R<1> which are simultaneously raised with the pecker rods to engage the perforations (if any) opposite the next centre hole of the tape and are subsequently raised to neutralize, if necessary, spring current initiated by the operation of a cam S<1>, closing the circuit of windings U2, V<2>. The contacts closed by the rods P, R are connected to the coils U<1>, V<1> of relays U, V which are effective respectively in " straight " or " reversed " working, the operative relay being selected by a tongue T<1> operated to one of the contacts T<2>, T3 and controlled by a switch T<4> which is changed over in conformity with the control relay O at the transmitter. The current impulses decoded by the peckers P, R, P<1>, R<1> and the corresponding relay U or V are passed during the closure of contacts Y<1>, Y2 to a relay Y and to a perforator of known type which reproduces on a tape the decoded message. At each reversal of the switch T<4>, a ratchet wheel T<5> under control of a cam and electromagnet T<5> is arranged to step forward the tape (not shown) three holes in order that the repeated impulses may be ignored by the translator. The selector rods P<1>, R<1> are arranged to operate in conjunction with the pecker rods P, R so that they take account of a next subsequent set of perforations, and thereby co-operate with the actual setting of the pecker rods P, R to provide the correct current impulses to the working relay U or V, and also to neutralize the spacing current circuit for the winding U<2> or V<2> and prepared by the cam S<1> when a marking current should be transmitted. In lieu of a transmitter modified as described, a perforator may be arranged to give actual reversals of the signal perforations at predetermined intervals on a tape, which is then passed through an unmodified transmitter, preferably of the Wheatstone type.