Patent GB-692423-A (GB)
Title: Improvements in or relating to telegraph repeaters
Inventor: RIDLER DESMOND SYDNEY
IPC: H04L25/04
Filed: 1949-09-27
Abstract: 692,423. Telegraph regenerative repeaters. STANDARD TELEPHONES & CABLES, Ltd. Sept. 22, 1950 fSept. 27, 1949], No. 24811/49. Class 40(iii). A regenerator for start-stop signal combinations is arranged to retransmit into a channel on which synchronization is effected by means of a regular series of pulses controlling the timing of the regenerated signal elements. Since with 'this system the incoming signals bear no strict time relation with the synchronous output it is possible for the mark-space transients in the incoming signals to coincide with the synchronizing pulses. If this occurs there is a possibility of misreading and incorrect regeneration of the signal elements. According to the invention automatic means are provided for delaying by a fraction of a signal element any received combination the regenerated transients of which would otherwise coincide with the pulses. The invention is described in conjunction with an electronic regenerator of the type disclosed in Specification 692,411. Fig. 1 shows a block schematic of the complete system, and Fig. 2 is a detailed circuit diagram of the portion of Fig. 1 enclosed within the rectangle shown by broken lines. Incoming fine unit code telegraph signals of the usual 20 millisecond duration appearing on lines 1 are applied to a balanced modulator 2 fed with 5000 P/S negative pulses and are effective to cause positive 5000 P/S pulses to appear either on line 4 or 5 depending whether a mark or space signal element is being received. On receipt of the start space signal the pulses appear on line 5 and the first triggers a cold cathode tube 7 in a trigger pair 7, 8. Tube 7 applies a positive potential to the trigger of tube 10 which then responds to the 5000 P/S pulses applied to its cathode, the tube firing and extinguishing at each pulse. Tube 10 supplies a counting circuit comprising three ten-cathode counting tubes 13, 14, 15 of the type disclosed in Specification 692,415, [Group XIX], and two further tubes 11, 12. Tube 13 counts each pulse from the 5000 P/S source, tube 14 every tenth pulse and tube 15 every hundredth pulse. After 49 pulses and thereafter after every further 100 pulses, positive bias exists simultaneously at the tenth cathode of tube 13 and the fifth cathode of tube 14, these biases being applied on the one hand to rectifiers 24 and 26 shunting line 5 and on the other hand to rectifiers 34 and 36 shunting line 4. By this means a trigger pair 20, 28 is allowed to take up the condition existing on lines 4 and 5 at 50, 100, 150, &c. pulses (i.e. 10, 30, 50, &c. milliseconds) after receipt of the start signal, namely at the middle of rack signal element. In accordance with the invention, trigger pair 20, 28 then controls the regeneration of the signals by a further trigger pair 46, 52 supplied with 50 P/S positive synchronizing pulses over lead 42. The positive biases set up across cathode resistors 40 and 41 remove the shunts provided by rectifiers 57, 59 and allow the pair 46, 52 to be triggered back and forth in accordance with the conditions set up by the incoming signals on pair 20, 28 but with a timing determined by the 50 P/S source. To prevent inconvenient regeneration when the incoming signal transients coincide with the synchronizing pulses a fixed phase relation is established between the synchronizing pulses and the 5000 P/S pulses by directing the former from the latter. At the same time negative 50 P/S pulses are derived spaced from the positive pulses by 10 milliseconds. These pulses have a duration slightly greater than the 5000 P/S pulses and are applied over line 60 to tube 7. If now the first 5000 P/S pulse on line 5 during the spare signal occurs at the same time as a negative pulse on line 60 (indicating that the positive synchronizing pulses 10 milliseconds later will coincide with the transitions 10 milliseconds later in trigger pair 20, 28) the former will be neutralized and tube 7 will not be fixed until the next pulse matures. Accordingly the counting operation and the transitions in trigger pair 20, 28 are delayed by 200 microseconds and no longer coincide with the synchronizing pulses. The circuit is reset and the counting operation stopped after 136 milliseconds as described in Specification 692,411 by the connections extending from the tenth cathode of tube 13, the eighth cathode of tube 14 and seventh cathode of tube 15.