Patent GB-722401-A (GB)
Title: Improvements in or relating to telegraph signal responsive systems
IPC: H04L25/24
Filed: 1950-02-17
Abstract: 722,401. Telegraph regenerative repeaters. WESTERN ELECTRIC CO., Inc. Feb. 17, 1950 [Feb. 18, 1949], No. 4134/50. Class 40 (3). Relates to an electronic telegraph regenerative repeater for mark-space signal code combinations in which the signals are regenerated under the control of an oscillator producing impulses timed so as to. occur at the centre of correctly timed received signal elements. The oscillator is started up upon receipt of space element but is restored to dormancy unless the space element persists throughout a period corresponding to half a signal element at which time the first impulse from the oscillator matures and triggers a counting chain which applies back a holding potential to maintain the oscillator operating. The arrangement prevents the regenerator from going through a complete cycle of operations in response to a short spurious space signal, such as an interfering signal. The counting chain is arranged to have a count of either seven or eight depending upon whether a five or six unit code is employed, and at the completion of its count removes the holding potential and allows the oscillator to stop. The regenerator is reset with marking potential on the outgoing line irrespective of the nature of the final received signal element. In one embodiment, Fig. 1, the incoming signals, curve A, Fig. 3, on line 21, are applied through noise filter 22, 23, 25 to the grid of the right-hand triode of tube 11, the negative space signals cutting-off the triode. The oppositelyphased signals occurring at the grid and anode and then applied to the grids of the right- and left-hand triodes respectively of tube 13 and are effective to bring up to just below cut-off the bias of the left-hand triode during the receipt of a space signal and that of the right-hand triode during the receipt of a mark signal. Tube 13 controls a flip-flop circuit, tube 12, and is supplied on both grids with timing impulses, curve F, Fig. 3, generated by an oscillator, tube 15, and timed to occur at the theoretically correct times for the centres of the received signal elements. Dependent on which half of tube 13 is brought up to cut-off level, the positive-going excursions of the timing impulses produce an output pulse at the corresponding anode, curves Hand J, Fig. 3, and so trigger the flip-flop circuit to one or other of its stable states. In this way the flip-flop circuit is caused to generate an undistorted replica of the incoming wave, the potential at the right-hand anode, curve K, Fig. 3, being applied through the left-hand triode of tube 11 to the outgoing line 113. Oscillator 15, generating the timing impulses, is set into operation upon receipt of the start element and is stopped at the end of seven cycles (corresponding in time to a start, five-code and a stop element) by means of a binary counting chain comprising tubes 17, 18 and 19. The positive pulse which occurs at the anode of the right-hand triode of tube 11 during the start element is applied through conductors 29 and 291 to render conducting the right-hand triode of tube 16, this in turn cutting off the left-hand triode of tube 15 and starting up the oscillator. In tube 15 the right-hand triode is the oscillator and the left-hand triode acts as a control stage for switching the oscillator on and off. The oscillator cathode output, curve E, Fig. 3, is applied to the right-hand triode of tube 14 to generate the timing impulses, the impulses being applied through condensers 83 and 84 to both grids of tube 13 as described above, and to the input of the counting chain through condensers 136 and 138. Each of the tubes in the counting chain is connected in a flip-flop circuit and the circuits are connected in cascade so as to trigger each other in succession. The circuits are initially set in the idle state with the right-hand sections conducting. Upon receipt of a signal the circuits are all reversed by the first impulse occurring at the left-hand anode of tube 13, see curve H, Fig. 3, this impulse being applied through condenser 91 and conductor 93 to cut-off the left-hand triode of tube 16, and the anode potential of this tube being in turn applied through conductors 117 and 118 to the left-hand grid of tube 17. The resulting fall in potential on the right-hand grids of tubes 17, 18 and 19 is applied through resistors 161, 162, 163 to conductors 164 and 93 and thence to the lefthand grid of tube 16 to maintain the tube cut-off. A potential sufficient to maintain tube 16 cut-off remains on its grid until the counting chain reverts to its original condition with all of the right-hand triodes conducting. The connection between the left-hand anode of tube 16 and the right-hand grid via resistor 116 maintains the right-hand triode conducting and thereby, the oscillator operating. The counting chain responds to each negative transition of the timing impulses applied through condensers 136 and 138 and at the end of the seventh impulse reverts to its original state with the right-hand triodes conducting. (See curves N, P and R, Fig. 3, showing the anode current of the right-hand triodes of tubes 17, 18 and 19, respectively.) The potentials on all of resistors 161, 162 and 163 now rise, allowing the left-hand triode of tube 16 to conduct. The right-hand triode is accordingly cut-off, the oscillator stopped and the circuit re-set in readiness to receive the subsequent signal code combination. Should the start element last for less than half a signal element and therefore cease before the first impulse appears at the left-hand anode of tube 13 to trigger the counting chain, the righthand triode of tube 16 will cut off and stop the oscillator. The complete cycle of operations in the regenerator is not initiated therefore unless a start signal persists for at least half a signal element. To ensure that the repeater always rests with a marking potential on the outgoing line, the left-hand triode of tube 14 is connected to the left-hand triode of tube 15 (oscillator control tube) and has an anode load common with the left-hand triode of the flipflop circuit, tube 12. When the oscillator is stopped by rendering the left-hand triode of tube 15 conducting, the left-hand triode of tube 14 also conducts and sets the flip-flop circuit with the left-hand tube conducting which is the correct condition for marking potential on line 113. To accommodate six unit code combinations, the counting chain is modified by the addition of further double-triode tube, Fig. 1 (not shown). This tube is connected so as to render tube 17 insensitive to the first timing impulse applied through condensers 136 and 138 thereby increasing from seven to eight the number of impulses required before the circuit reverts to its original condition. In a modified circuit, Fig. 2 (not shown), the timing impulses are applied to the left- and right-hand sides of the flip-flop circuit through unidirectional conducting devices, such as diodes, the incoming signal train being applied to render the left- or right-hand diode conducting in accordance with nature of the signal elements. The circuit applying signals to the outgoing line is also modified by the use of a double-triode arranged to charge and discharge the line capacitance through the low impedance of a valve thereby maintaining the sharp transition between mark and space potential and preventing distortion. Specifications 604,936, [Group XL (c)], 630,373 and 670,874 are referred to.