Patent GB-604936-A (GB)
Title: Improvements in electrical signalling systems
IPC: H04L27/24
Filed: 1945-08-17
Abstract: 604,936. Valve-pulse generating and counting circuits. WESTERN ELECTRIC CO., Inc. Aug. 17, 1945, No. 21017. Convention date, Aug. 17, 1944. [Class 40 (vi)] [Also in Group XXXVIII] In a signalling system, the transmitter comprises a sine-wave generator, an electronic counting chain for counting a predetermined number of successive positive and negative half-cycles and means for stopping the generator'after the predetermined number of halfcycles has been transmitted. The receiver includes an electronic counting chain for counting the number of half-cycles received, a marking chain comprising a number of electronic devices being primed in response to the half-cycles, the last device primed only being operated when the last half-cycle has been received. A clamping circuit is arranged to short-circuit the transmission path but is arranged to be inoperative during the period of transmission. The sine-wave generator is arranged to produce true sine waves immediately upon being rendered operable as described in U.S.A.. Specification 2,370,685. Transmitter, Fig. 1. Upon depressing key K, sufficient potential is applied to cold-cathode valve G1 for it to fire, the rise in cathode potential, applied to the grid of the upper triode of valve B causing it to conduct and biasoff valve C to pass insufficient current for any of the valves CT1 ... 0 to conduct. The rise in cathode potential is also applied to the lower triode of valve B allowing anode current to flow through coil OC and, further, applied to clamping valves D, which are arranged across the resistance network connecting the tapping on coil OC and the cathode follower output valve L, feeding line LN one or other of the triodes conducting to prevent any signal from passing to the valve L. With switch S2 operated to produce a single signal, the anode potential of valve G2 falls due to the resistance R35. Upon depressing a key, say KS5, the cathode of valve CT5 in the counting chain is connected to conductor 1 and condenser C2 charges over resistance R30, condenser C1, also charging over potentiometer R32. The rise in the potential of the control anode of valve G2 causes it to fire after a delay due to the charging of condenser C2, extinguishing valve G91 over the coupling condenser C3. The resulting fall in cathode potential biasses off the clamping valves D and the valves B, the upper one reducing the bias in valve C and raising the potential applied to the anodes of the valves CT1 ... 0, the lower triode causing the oscillating circuit OC, OCN to ring, the oscillations being maintained by the lower triode of valve A. The oscillator feeds the upper triode A, operating as a squarer, the valve being cut-off at the end of the first positive half-cycle to produce a positive pulse at terminal 2 of transformer IT connected over coupling condensers to the control anodes of the odd valve CT1 ... 9, firing CT1 as the control anode is primed by connection to earth. The rise in cathode potential primes valve CT2 which is fired at the end of the first negative half-cycle as the anode current in upper triode A restores, giving a positive firing pulse from terminal 1 of transformer 1T. The process continues until valve CT5 fires, raising the potential of line 1 which restores the clamping action of valves D, and allows lower triode B to conduct thus stopping the oscillator at the commencement of the next positive half-cycle. The rise in control anode potential fires valve G1 extinguishing valve G2 and causing upper triode B to conduct and valve C to be less conducting, the valves CT1 ... 5 thus being extinguished. The circuit is now in its original state except that condensers C1, C2 are charged and so do not fire valve G2. A new train of oscillations may be emitted by releasing key KS5 and depressing a key in the bank KS. If a continuous transmission of the same digit is required, key S2 is not operated, valve G2 refiring after a delay while the control anode rises to striking potential, the control and main anodes being connected over key S2. Receiver, Fig. 2. The two triodes of valve RL amplify the train of half cycles received over line LN, the upper triode being biassed near cut off and the lower triode passing current, in the normal condition, the resistances coupling the lower triode of valve RL to the upper triodes of valve DET1 and DET2 being chosen to maintain them cut off and conducting respectively. Since upper triode DET1 is cut off, upper triode INV is maintained conducting, the potential applied to the lower triode RE, connected as a diode being insufficient to cause it to conduct as that condenser A charges negatively over resistance R48, the potential maintaining upper triode RE cut off. The high anode potential of upper triode RE allows current to flow in lower triode INV, the low anode potential holding valve EXT near cut off. The first positive half cycle causes the anode potential of lower triode RL to rise, which in turn allows current to flow in upper triode DET1, the fall in anode potential cutting off upper triode INV, the resulting rise in anode potential allowing the lower diode connected part of valve RE to conduct and charge condenser A positively, the change in grid potential on the upper triode RE rendering it conducting to cut off the lower triode INV. The rise in anode potential allows the valve EXT to conduct and supply increased potential to the anodes of the counting chain of valves CTR1 ... 0. At the termination of the first half cycle, the upper triode DET1 cuts off causing upper triode INV to conduct, the fall in anode potential being supplied over condenser B to reduce the anode current flowing in the lower triode DET1 thus producing a positive pulse which is applied over coupling condensers to the control anodes of odd valve CTR1 ... 9. As the control anode of valve CTR is primed, this valve fires, priming the control anodes of CTR2 and S1 due to the rise in cathode potential. During the second half cycle, the upper triode DET2 cuts off completely the high anode potential maintaining the condenser A charged positively. At the termination of the half cycle, the upper triode DET2 conducts, cutting off the lower triode which, feeds a pulse to the control anodes of even valves CTR2 ... 0 firing primed valve CTR2. The firing of valve CTR2 primes CTR3 and S2 and due to the fall in anode potential neutralises the priming on valve S1. Marking. If a " 3 " digit is stored in the marking chain S1 ... 0, valve S3 will be fired. After the fifth half cycle condenser A dis-' charges cutting off upper triode RE, the anode potential rising to cause lower triode INV to conduct and cut off valve SEL and EXT. The rise in anode potential of valve SEL fires primed valve S5 and increase in current through the common anode resistance R87 reducing the anode potential of valve S3 to extinguish it since the cathode potential is held positive by condenser CC3. The fall in current through valve EXT extinguishes the conducting valves in the chain CTR1 ... 0.