Patent GB-765227-A (GB)
Title: Improvements in telegraph distributors
Inventor: GAITE HAROLD DODIMEAD
IPC: H04L13/14
Filed: 1954-04-27
Abstract: 765,227. Telegraphy; thermionic distributers. BRITISH TELECOMMUNICATIONS RESEARCH, Ltd. April 15, 1955 [April 27, 1954], No. 12204/54. Class 40 (3). In a distributing arrangement for a telegraph transmitter employing the start-stop telegraph code, operating pulses for effecting control of a transmitting relay at successive intervals are obtained from successive members of a counting ring of valves arranged to be operated by pulses from the cathodes of two valves comprising a multivibrator which is locked to a constant frequency source, the pulses being supplied to the transmitting relay by way of a plurality of gate circuits respectively controlled by the elements of the desired signal. In Figs. 2-5 the basic timing of operations is effected by a 100 c/s resistorcapacitor phase-shift oscillator V1a, V1b, the output from which is squared in stage V2b and applied to lock a 25 c/s multivibrator V3a, V3b, at each other pulse. The counting ring comprises valves V6a, V6b, V7a ... V8b, alternate ones of which are connected at their cathodes to form two groups which receive the 20 ms. multivibrator pulses appearing alternately on leads 15 and 16. The valves are thereby rendered conducting in sequence each for 20 ms., the resulting negative-going anode pulses being applied via rectifier gates MR5- MR10 to a common lead 12 in dependence upon the setting of transmitter contacts in a tape reader connected to a socket SKB. The operated contacts apply earth potential via leads 1-5 and the presence of an earth on a rectifier prevents the transmission of a pulse. Lead 12 controls the transmitting relay RLA via a trigger circuit V9a, V9b. The circuit is biased over R78 so as normally to rest with the relay at mark and a negative pulse from lead 12 reverses the trigger. Valve V6a controls the start signal valves V6b-V8b the five signalling intervals, and valves V5a and V5b the stop interval. No control is applied to rectifier MR5 associated with the start valve V6a since a pulse is always required. The apparatus is arranged to operate with a stop signal of 30 ms. duration, and in order to modify the circuit timing which normally proceeds in steps of 20 ms., the seventh operation of the counter at V5a, corresponding to the beginning of the stop interval, is arranged to cut-off a normally conducting valve V4b. This then raises the grid potentials of the multivibrator over the anode connection 18 and causes the next change-over to take place after one pulse, i.e. after 10 ms., instead of after two. The seventh and eighth operations of the counter thereby occupy 10+20=30 ms. The operation of stage V5b results in a 20 ms. negative pulse on lead 13 which cuts-off V2a and thereby renders V10 conducting to apply a negative pulse to pin 10 of socket SKB to operate the tape drive magnet. Tape sensing and tighttape contacts are arranged during correct operation to apply an earth to pin 7. This extends over lead 6 to a neon tube 12 and maintains the tube extinguished. If, however, the contacts open, the neon is controlled by the potential at the junction of R57, R83, and when V4b cuts off at the seventh counter operation as described above, the neon fires and thereupon applies positive bias to the grid of V5a. This valve then remains conducting and the counter operation stops. At the same time V4a is rendered conducting and stops the operation of the multivibrator. The apparatus may be remote from the tape reader and an additional socket SKA is provided for a local reader. To prevent operation in the event of readers being plugged into both sockets, the wiring of the pins in the plugs and sockets is arranged whereby a positive potential appears on pin 8 of SKA and holds V2a conducting via rectifier MR3. This prevents the tape drive pulse from being applied to the remote reader. The positive potential is also applied via rectifier MR14 and lead 12 to hold the transmitting relay at mark. Switch TS is closed when the local reader is used and connects earth over lead 6 in place of that from the tape sensing tighttape contacts at pin 7 of SKB. The transmitting relay may be placed in the mark or space condition independently of the tape contacts by a potential applied via pin 11 to lead 11. Start-stop operation of the counting ring in the event of a manual keyboard being used in place of a tape reader is effected by a contact which is closed whenever a key is depressed and applies a negative potential to pin 7 and thence over lead 6 to neon tube V12. The neon tube is thus cut off at each key operation to allow the circuit to complete one cycle of operation.