Patent GB-821121-A (GB)
Title: Start-stop telegraph signal generator
IPC: H04L25/40
Filed: 1957-08-13
Abstract: 821,121. Printing-telegraph transmitters. TELETYPE CORPORATION. Aug. 13, 1957 [Nov. 27, 1956], No. 25525/57. Class 40 (3). In a start-stop telegraph signal generator comprising a multi-stage electronic distributer having a stop stage and a start stage as well as a plurality of signal impulse stages to which potentials indicative of the different permutation code elements are respectively applied, and through which stages an electron beam is stepped by successive driving pulses to cause the corresponding code signal impulses together with the start and stop impulses to be sent over an output line, the electron beam is driven through the successive stages of the distributer under control of a pair of oscillators of different predetermined frequencies providing the distributer with driving impulses of correspondingly different frequencies by means of a gating circuit under control of the electronic distributer in such a way that the oscillator of higher frequency governs the rate at which the start and signal stages of the distributer are successively energized, whilst the oscillator of lower frequency causes the stop stage of the electronic distributer to be energized for a period which is longer than the time during which the start and signal impulse stages are individually energized. In this way the duration of the stop impulse is greater by a predetermined amount than that of the other impulses to be transmitted. The generator is described in connection with a transmitter in which contacts, such as 10, 11 ... 14 are selectively closed in accordance with the perforations in a message tape. In the stop stage of the magnetron distributer 31, current flows through the winding 17 of the stepping magnet of the tape transmitter, and the reduced potential of the stop-stage target 22 allows the point 42 to become negative so that valves 46, 48 are cutoff and a positive pulse over lead 49 to connection 53 renders valve 54 conductive so that the coil 57 of the distant receiving magnet is energized. Also the positive pulse at 53 holds conductive the right-hand valve of the pair 56 so that the left-hand valve applies a positive potential to the point 53 until a negative pulse appears over the lead 49. When a negative pulse applied to the grid 32 completes the stop stage the discharge is transferred to target 23 and the point 42 rises to ground potential so that valves 46, 48 conduct and a negative pulse at the junction point 53 cuts off the valve 54 so that a spacing pulse is sent to the receiving coil 57. During the succeeding stages corresponding to the code elements, the receiving coil 57 is selectively energized according to the closure of the contacts 10 ... 14. At the sixth stage the negative voltage on the target is transferred immediately to the target 22 to initiate the stop stage. The negative pulses applied to the grids 32 ... 33 for stepping the magnetron 31 are passed over connections 64, 65 from the anode circuits of interconnected valves 123, 124 controlled over conductor 119 from the output of the third member 70 of three similar magnetron dividing circuits 68, 69, 70 of which the first circuit 68 is fed with pulses over oonductors 96, 97 from a flip-flop generator comprising valves 93, 94. The outputs over conductors 100, 110 control associated flip-flop generators comprising valves 103, 104 and 113, 114, and the output at 119 from the third magnetron 70 controls a flip-flop. generator comprising valves 123, 124 to provide the negative pulses over conductors 64, 65 to step the magnetron distributer 31. The pulses to the generator 93, 94 are applied over conductor 87 from the anode circuit of one of two pentodes 76, 77 associated respectively with the lower frequency circuit 67 controlled by crystal 72 and circuit 66 controlled by crystal 71 to produce the element periods of shorter length. When the magnetron 31 reaches the stop stage the negative potential at junction point 42 is also passed over conductor 73 and switch 126 to the grid of valve 74 which cuts off and applies a positive potential to the suppressor grid 78 of the pentode 76 which responds to the oscillations from the lower frequency circuit comprising valves 67, 83 and passes them over conductor 87. At the same time valve 75 is conductive so that the negative voltage at the suppressor grid 79 cuts off the pentode 77, and renders ineffective the output of the oscillator comprising valves 66, 81 and crystal 71. When the stop stage has been completed the rise in potential at the junction 42 makes valve 74 conductive to reverse the conditions of the pentodes 76, 77. The durations of the shorter elements and of the stop element may be independently altered by the change of crystal 71 or 72 associated with the valve 66 or 67, and by opening the switch 126 all the elements including the stop element have equal lengths. The arrangement may be used for 6-unit code by having a code contact member 133 with a switch 62 moved to contact 128, and a 7-unit code together with start and stop elements can be transmitted by the use of a controlled contact member 135 and the movement of the switch 62 to engage contact 134.