Patent GB-692411-A (GB)
Title: Improvements in and relating to telegraph repeaters
Inventor: TERRY VICTOR JOHN
IPC: H04L25/12
Filed: 1948-04-01
Abstract: 692,411. Code telegraphy. STANDARD TELEPHONES & CABLES, Ltd. March 25, 1949 [April 1, 1948], No. 9220/48. Class 40 (iii). A regenerative repeater for start-stop printing telegraph signals comprises a chain of coldcathode gas discharge gaps, means for rendering said gaps conducting sequentially to time the intervals occupied by the elements of a signal combination, means under the joint control of said chain and the received signals operative at the middle of each signal element period to condition a transmitter circuit to transmit a signal element of the same kind as that received and means to cause said transmitter circuit to remain in that condition until again reconditioned. As described, a pulse generator 1 supplies negative pulses at 0.2 ms. intervals to a counting lead 2 and also to a balanced modulator 4 controlled by telegraph signals received on terminals 10, 11. Each signal element is of the usual 20 ms. duration and so biases the rectifiers that a mark or space produces positive pulses in the mark lead 16 or the space lead 17, respectively. The transit from mark to space due to a received start element produces therefore positive pulses on the space lead 17, the first of which fires a start tube CT23 which in turn extinguishes a normally conducting stop tube CT28. The resulting positive cathode pulse primes the control electrode of a counting gate tube CT35 and since a negative pulse is applied to its cathode from the generator 1 this tube fires to start a counting arrangement MCT38 ... 40, of which tube MCT38 counts each pulse, MCT39 counts every tenth pulse, and MCT40 counts every hundredth pulse. Each multi-cathode tube MCT38 ... 40 is of the type described in Specification 692,415, [Group XL (a)], and the anode-cathode gaps, e.g. K41 ... K50 are arranged in a circle. Successive generator pulses transfer the discharge normally existing across the gap K41 to the gaps K42 ... K50 in turn and then back to K41 again, and so on, only one anode-cathode gap conducting at a time. Throughout the duration of the start element, when the control electrode of CT35 is primed, each pulse from the generator 1 fires that tube and passes a positive pulse to the transfer electrodes 74 of tube MCT38, discharging the gaps K42 ... K50 in turn. The ninth pulse causes the gap K50 to conduct and so primes a further gate tube CT36 which fires on the next pulse, so that on the tenth pulse both the gaps K41 and K52 are conducting. Similarly the twentieth pulse causes gaps K41 and K53 to conduct and after the forty-ninth pulse gaps K50 and K55 are conducting and a pulse is then applied to block both rectifiers of a pair MR87, MR88, which form a gate circuit as described in Specification 636,700, [Group XL (c)], and a positive generator pulse is therefore applied to the control electrode of a space tube CT95. A mark tube CT98 is similarly primed over a further gate arrangement MR103, MR104, but since only 10 ms. have elapsed since the start element was initially received positive pulses are present on the space lead 17 and are applied only to the control electrode of the space tube CT95 which therefore fires on the next generator pulse, sending on a space via relay TR97. and extinguishing the mark tube CT98. The gaps K50 and K55 conduct simultaneously again after each further 100 pulses, i.e. at 20 ms. intervals. and test the polarity of each code element at its nominal centre, either the mark or space tube being fired in dependence upon the presence of pulses on the mark lead 16 or space lead 17 respectively. When a hundred pulses have been counted the gap K60 conducts for the next ten pulses until the gap K51 conducts again and it is therefore necessary to prevent these ten generator pulses from reaching tube MCT40 if the latter is to respond only to each hundredth pulse. The cathode pulses from gap K60 are therefore normally short-circuited to earth over a rectifier MR113 and the cathode resistor of gap K50, but when the latter is conducting at the 100th pulse the rectifier MR113 is biased to its non-conducting condition and the hundredth pulse thus triggers a third gate tube CT37 and transfers the discharge in counting tube MCT40 from gap K61 to K62. The successive gaps in tube MCT40 are similarly rendered conducting at 20 ms. intervals. Minimum stop element. It is arranged that each stop element shall have a minimum length of 0.6 of an element. The minimum character length is thus 6.6 elements or 136 ms. and at the end of this time gaps K50, K58 and K67 are all conducting and apply pulses to block the rectifiers MR114, MR119 and MR121 and the next generator pulse on the stop lead 16 is therefore applied over rectifier MR115 to the stop tube CT28 instead of to earth over one or more of these rectifiers, which fires, extinguishing the start tube CT23 and so cutting off the priming pulses from the counting gate tube CT35 and preventing further counting. The negative pulse induced in the secondary of a cathode transformer T124 causes the counting gaps K41, K51 and K61 to conduct and the whole circuit is then restored to normal. False-start suppression. If the counting is started by a false start condition of less than 10 ms., e.g. by a momentary fading or disconnection, then when at 10 ms. the counting gaps K50, K55 and K61 become conducting and block rectifiers MR131 ... MR133 a mark condition will have returned on the incoming channel. The next pulse on the mark lead 16 therefore fires the stop tube CT28 over rectifier MR134 instead of going to earth over one or more of the rectifiers MR131 ... MR133 and so returns the circuit to normal as described above. Regeneration of supervisory signals. If a supervisory signal comprising a long spacing condition is received then after 130 ms. pulses are still present on the space lead 17. Counting gaps K50, K55 and K67 are then conducting and block rectifiers MR136, MR138 and MR140 so that the next pulse on the space lead 17, instead of going to earth over one or more of these rectifiers, fires a tube CT143, extinguishing a normally conducting tube CT144. The cathode pulse of CT143 fires the stop tube CT28 and the counting circuits return to normal. Since tube CT144 is non-conducting the pulses on the space lead 17 are short-circuited to earth over resistor R19 and the unblocked rectifier MR149. Rectifier MR151 is blocked by the cathode potential of the tube CT143 which is conducting and the first pulse produced on the mark lead 16, when the supervisory signal has ended, is therefore applied over rectifier MR154 to the start tube CT23 which fires. The counting chain therefore starts again but after 10 ms. gaps K50 and K55 both conduct and block rectifiers MR156, MR158. The next pulse on the mark lead 16 therefore fires the tube CT144 whose cathode pulse operates the stop tube CT28 to restore all circuits to normal as previously described. This increase of 10 ms. at the end of the supervisory signal replaces the 10 ms. lost at the beginning. Automatic insertion of stop element. A further embodiment shown in Fig. 1 together with Fig. 3 (not shown), provides the facility of automatically transmitting a stop element whether or not one is received, but will not, therefore, deal with a long spacing supervisory signal. After 120 ms. the counting gap K67 conducts and prohibits spacing pulses from reaching the space tube CT95. After 130 ms. gaps K50 and K55 are also conducting and allow a rectifier (MR106 in Fig. 2B) to pass positive pulses which are derived from the generator 1 and so trigger the mark tube CT98. At 132 ms. the gaps K50, K56 and K67 are all conducting and together allow the stop tube CT28 to be fired by a generator pulse derived from an additional coil on the primary winding of transformer T3, returning all circuits to normal as before. Instead of the multi-cathode tubes MCT38 ... 40 a chain of separate discharge tubes might be used or the multi-cathode tubes and circuits described in Specification 691,901. Again, instead of a scale of ten counting arrangement a binary chain might be used, employing successive pairs of discharge tubes as described in Specification 621,817, [Group XXXIX], and a generator frequency of 6,400 c.p.s. Specifications 639,827, 692,436, [Group XIX], 692,456, 692,457 and 692,458 also are referred to.