Patent GB-653867-A (GB)
Title: Improved electronic regenerative repeater
Inventor: WHEELER LEONARD KEITH
IPC: H04L25/24
Filed: 1948-07-23
Abstract: 653,867. Telegraph repeaters. POSTMASTER GENERAL. July 23, 1948, No. 19774. [Class 40 (iii)] An electronic regenerative repeater for start-stop codes comprises an electronic switching circuit to which the incoming signals are applied and which in turn controls an output relay, a multivibrator circuit which times the said switching circuit by applying priming pulses thereto and is started and stopped by a charactertiming circuit, and means for automatically applying a stop signal to the outgoing line to provide an idle period between successive characters whether or not a stop signal is received. This artificial stop signal is not sent on during the reception of a long spacing (e.g. supervisory), signal, and arrangements are described for preventing the character timing circuit from operating to a false start signal of short duration. In the embodiment described the supply voltages are Œ 150 v. and the signal voltages Œ 80 v. In the normal marking or negative condition of the receiving line X valves V<SP>2</SP>, V', V<SP>6</SP> and V<SP>10</SP> are conducting. When a positive start element is received it is applied over lead K to the suppressor grid of valve V<SP>5</SP> of a character timing circuit CTC. Since the multivibrator MVB is at rest and valve V3 is not conducting positive potential is also applied, over resistor 29 and lead I, to the control of V5, and this valve therefore conducts, reversing the flip-flop valve pair V6, V7. The potential of a lead G then becomes earth and this is applied to the multivibrator MVB which starts, V' conducting again after 10 ms. (and after each further 20 ms.), and producing a negative pulse on each of leads B, C and J. The first negative pulses on leads B and C are applied to the suppressor grids of valves V<SP>1</SP>, V2, respectively, in an output trigger circuit OTC. If a mark is being received on the line X, and hence on lead A the potential applied by it to the suppressor grid is just above earth. The pulse on lead B is arranged to be longer than that on lead C and when the latter has finished, the pulse on B plus the marking potential on A is sufficient to make the output trigger valve V<SP>1</SP> non-conducting, and to cause the valve V<SP>2</SP> to conduct and transmit a mark over relay POR. But since the starting space is at present being received on the line X, the potential applied over lead A raises the suppressor grid of V<SP>1</SP> to a high potential and the negative pulse on lead B is ineffective, while the pulse on lead C makes V<SP>2</SP> non-conducting and V<SP>1</SP> conducting to transmit a space. Subsequent multi-vibrator pulses test the incoming elements in a similar way at their nominal centres until the sixth element has been retransmitted, i.e. after 130 ms. The natural relaxation period of the character - timing flip - flop circuit CTC is rather more than 130 ms. but when at 130 ms. the multivibrator valve V<SP>3</SP> ceases to conduct it applies a positive pulse over lead H which is sufficient to trip the flip-flop V<SP>6</SP>, V<SP>7</SP> back again with V<SP>6</SP> conducting. The rise in anode potential of V<SP>7</SP> is applied over lead D to make output trigger valve V<SP>2</SP> conduct and send an artificial stop-element, which persists until a further start signal is received. With V<SP>6</SP> conducting the lead G applies negative potential to the suppressor grid of V<SP>3</SP> and the multivibrator stops, with V<SP>4</SP> again conducting. Supervisory signalling. For exchange working it is necessary that the repeater should handle a long spacing signal without inserting a stop element at the end of a character period. Incoming signals are therefore applied over lead P to the control grid of a valve V<SP>11</SP> and to the suppressor grid of a second valve V<SP>12</SP>. If a mark is received neither valve can conduct but a positive spacing signal causes V<SP>11</SP> to conduct, which in turn prevents V<SP>12</SP> from conducting. When a spacing signal has lasted for 120 ms. however, the time-constant of the intervalve coupling allows V<SP>12</SP> to conduct, and over lead M it holds V<SP>6</SP> non-conducting. If the signal received is merely the all-spacing character signal then before 130 milliseconds a mark will be received, but if it is a longer spacing supervisory signal V<SP>6</SP> will still be held non- conducting after 130 ms., when the stop pulse over lead H tends to reverse the trigger V<SP>6</SP>, V<SP>7</SP>. The lead D is therefore held negative and the output trigger OTC remains free to respond to the received signals. As soon as the supervisory signal ceases, the masking potential biasses off V<SP>12</SP> and V<SP>6</SP> conducts, operating the output trigger to mark over lead D and stopping the multivibrator over lead G. False start suppression. When a start condition is received and reverses the timing trigger V<SP>6</SP>, V<SP>7</SP> a negative pulse is applied over lead O and suppresses the valve V<SP>19</SP> of an Eccles-Jordan pair. The screen of V<SP>0</SP> therefore conducts by the anode is prevented from conducting by negative bias on the suppressor grid. If the condition changes to marking before 10 ms., i.e. it is not due to a proper start element, valve V<SP>5</SP> ceases to conduct and a positive potential is applied over lead N to make V<SP>9</SP> conducting. A pulse is therefore applied over lead L to restore the timing-trigger V<SP>6</SP>, V<SP>7</SP> to normal, ready to receive a correct start-element. If, however, the start condition persists, the anode circuit of V<SP>9</SP> remains non- conducting and after 10 ms. it receives a negative pulse over lead J from the multivibrator. The trigger V<SP>2</SP>, V<SP>10</SP> therefore reverts to normal and reception proceeds normally.