Patent GB-666975-A (GB)
Title: Improvements in telegraph distributors
Inventor: BAKER GEORGE THOMAS
IPC: H04L13/14
Filed: 1948-06-14
Abstract: 666,975. Thermionic distributers. BRITISH TELECOMMUNICATIONS RESEARCH, Ltd. May 19, 1949 [June 14, 1948], No. 16004/48. Class 40 (iii). A telegraphic or like distributer circuit arrangement comprises a plurality of control circuits to which pulses are fed successively over paths which extend through the control circuits to a transmitting device, and biasing means in each path which are controlled by intelligence potentials applied thereto simultaneously so that the pulses either pass through a control circuit to control the transmitting device, or do not pass through, according to the condition of the potential applied to the biasing means. The embodiment described is a five-unit start-stop telegraphic distributer controlled by a perforated tape. In the normal condition valves V4 ... V6, V9 and V12 are conducting and an asymmetric multi-vibrator MV operates continuously, valve V7 conducting for 20 ms. and V8 for 10 Ás. Each time valve V8 conducts it produces a negative pulse on a re-set lead R and a positive pulse on a drive lead D. A stop-switch Z and a scale of six counter C6 are each arranged to be triggered by a negative-going pulse so that the leading edge of the re-set pulse would make a stop-valve V9 non-conducting, but a control switch SW prevents this. The trailing edge of the drive pulse would step on the counter C6 but the grid of counter-valve V1 is held near cathode potential over a rectifier MRB. When automatic tape transmission begins tape contacts SW are closed and the first reset pulse on lead R transposes the stop switch V9, V10, sending on a negative pulse over a start-signal lead SS to reverse a line-switch V11, V12 and operate a transmit relay M to space to send out a start-signal. Ten micro-seconds later a drive pulse on the lead D attempts to trigger the first counting pair V1, V4 but the grid of V1 is still held near cathode potential and this pulse has no effect. The next time multi-vibrator valve V7 conducts the re-set pulse has no effect on the stop-switch Z but is applied directly to the lineswitch L, operating it to its marking condition with V11 non-conducting. A condenser C4 has now charged sufficiently to render the rectifier MRB non-conducting and thus remove the locking bias from VI. The following drive pulse (10 Ás. later) therefore reverses the first counting pair V1, V4 and primes V2. The anode pulse from V1 is applied to a rectifier MRB1, the bias of which is controlled by the first tape-feeler contacts SC1. If these contacts are closed the rectifier MRB1 is biased from a potential divider comprising R13 and R15 and is blocked, the pulse passing to the grid of V12 over a decoupling rectifier MRA1. The valve V12 is thus extinguished again before the transmit relay has had time to respond to the marking condition of the line-switch valves V11, V12 and a space continues to be transmitted. If however the tape contacts SC1 are open the anode pulse from V1 is short-circuited to earth over the rectifier MRB1 and the valve V12 remains conducting to cause the transmit relay M to send a mark. The conventional counting circuit C6 comprises three trigger pairs V1, V4; V2, V5; V3, V6 and is triggered by successive multi-vibrator drive pulses so that the valves conducting together are V1, V5, V6; V1, V2, V6; V1, V2, V3 ... as each valve V1 ... V6 is triggered in turn to its conducting condition and extinguishes the other valve of its pair. As each valve Vl ... V5 conducts a.negative anode pulse is passed to the respective gate circuit comprising a rectifier MRB1 ... MRB5 controlled by tape-contacts SC1 ... SC5. The code elements set up on these contacts are therefore transmitted in turn by the line-switch V11, V12 and the transmit relay M. The next re-set pulse on lead R is then applied to the line-switch L and sends on an invariable mark or stop element, there being no corresponding gating circuit in this case. The corresponding anode pulse from the last counting valve V6 is then applied directly to the grid of valve V10 and the stop-switch Z is reversed. When valve V9 consequently conducts it reduces the potential applied via a potentiometer R10 to the multi-vibrator condenser C3, thus delaying the time at which valve V7 next conducts and so ensuring the transmission of a long stop signal. A tape-feed relay P is arranged to step on the tape each time the stop-switch valve V9 conducts again at the end of a character. Instead of the re-set and drive pulses being spaced apart by 10 Ás. they may be coincident, the drive pulses then being of greater amplitude. The gate circuits may be modified by connecting each counter over a condenser to its rectifier MRA as shown and connecting an earthed condenser and earthed resistor in parallel to the lead between the first condenser and the rectifier MRA. The contacts SC are then inserted between the connections to the resistor and second condenser. When keyboard operation is employed each key besides setting the code contacts SC1 ... SC5 also closes the starting switch SW. The relay P now serves to lock the operated code-bars until transmission is completed.