Patent GB-592796-A (GB)
Title: Improvements in or relating to communication systems and apparatus
IPC: H04L19/00
Filed: 1944-05-19
Abstract: 592,796. Type printing telegraphy ; thermionic distributers ; valve circuits. NATIONAL CASH REGISTER CO. May 19, 1944, No. 9747. Convention date, Sept. 16, 1942. [Classes 40 (iii) and 40 (v)] In a telegraph system in which bursts of signals representing symbols are sent from an electronic signal generator at the sender to a receiver over a single channel, each burst comprising a number of signals according to the symbol to be transmitted, the spacing between the end of a burst and the commencement of the next is arranged to be constant, electronic means at the receiver controlled by the number of signals in the bursts setting up direct representations of the symbols. In the a.rrangement shown, symbols representing the letters of the alphabet are transmitted to a receiving apparatus, five symbols being transmitted in succession. The sending apparatus consists of'five banks of tubes, one of which is shown, Fig. 1, each tube representing one letter and being connected to a key which is set manually. When the desired key, shown as A, is set a positive voltage is applied to the grid of tube A priming it so that when a starting impulse from the start tube, Fig. 6 (not shown) is impressed on conductor 90 tube A fires. Its anode voltage drops impressing a negative impulse on conductor 105, which extinguishes any previously conducting tube whose anode is connected to conductor 105, and its cathode potential rises, so that the " space " tube fires since its grid potential rises also. The " mark " tube fires followed by the " shift " tube after a delay due to condenser 135, impressing negative impulses at terminals 124, and 144, and a positive impulse at 130. The " mark " and " shift " tubes are provided with common anode supplies respectively so that each is not extinguished until the " mark " and " shift " tubes of the succeeding bank fire. A second letter' is set up on the second bank of tubes, the positive impulse at terminal 130 being used as a starting impulse, so that the tubes fire in succession. The other three banks are operated in sequence until the " shift " tube of the fifth bank becomes conducting when the potential rise of its cathode is used to fire a stop tube, Fig. 6 (not shown) which terminates the transmission. The " mark " and " shift " tubes of the fifth bank are extinguished when the corresponding tubes in the first bank fire in the next transmitting. operation. Due to the common anode supply for all the symbol and " space " tubes, the " space " tube of the fifth bank is extinguished when the first symbol tube in the first bank is fired in the next operation. The negative impulses on conductor 105 and similar conductors for the other banks of tubes control a small amplitude signal generating tube, Fig. 6 (not shown) and at terminal 124 and similar terminals control a large amplitude signal generating tube so that for each letter indicated an appropriate number of small amplitude impulses followed by a large amplitude control or marking impulse are transmitted over a single channel to the receiving station. By arranging for the delays in firing the various "shift" tubes to be equal the spacing between bursts of signals is made equal. The receiving apparatus consists of discriminating means, Fig. 14, which distinguishes between large and small amplitude impulses, the large impulses only being applied to routing means, Figs. 12 and 13, which routes the bursts of signals to the correct bank of tubes, Figs. 7 and 8 to 11 (not shown), where the symbol represented by the number of impulses in the burst is indicated, i.e. the impulse from the first bank of tubes in the transmitter are routed to the first bank in the receiver and so on. Impulses of large and small amplitude are applied at terminal 330 of the discriminating circuit, Fig. 14, the part containing tubes 300, 301 being responsive to all impulses and the part containing tubes 366, 367 being responsive to large amplitude impulses only. Tube 300 is normally non-conducting and tube 301 conducting. When a positive impulse is applied from terminal 330 to the grid of tube 300, the tube conducts causing a drop in anode voltage which is impressed on the grid of tube 301 to cut it off, positive impulse being impressed on terminal 358. Tubes 366, 367 operate in a similar manner and by adjusting resistances 308, 333, tube 300 can be made responsive to all impulses while, by adjusting resistances 374, 381 tube 366 is made responsive to large amplitude impulses only. The routing means comprises a group of five control tubes, Fig. 13, operative in succession upon receipt of large amplitude impulses applied from terminal 396 (Fig. 14) over conductor 502 to the. grid of the tubes, and five pairs of relay tubes, Fig. 12, such that when one of the control tubes, say tube I, fires it primes the next tube and by impressing the rise of its cathode potential on the grid of relay tube 525 (Fig. 12) through terminals 492, 493 also primes that tube, so that tube 525 alone conducts when impulses are applied from terminal 358, Fig. 14, over common conductor 360 to the grids of all the relay tubes. Relay tube 526 was previously conducting but is cut-off due to the drop of anode potential of tube 525, so that its anode potential rises, impressing a positive impulse through terminal 425 to the first bank of symbol representing tubes, Fig. 7. When the next large impulse is received control tube II will conduct, cutting-off tube I, priming tube III, and also priming the II relay tube instead of the I relay tube 525 so that the second burst of impulses on conductor 360 will be applied from terminal 463 to the second bank of symbol representing tubes, Fig. 8 (not shown). The control tube I, Fig. 13, has to be fired before the first burst of impulses are received, in order to prime the relay means for the first bank of symbol restoring tubes so that it responds to the first burst. Since a large impulse is not available to fire the tube, a positive potential is applied to its grid by closing switch 509. Each of the five banks of symbol restoring tubes are similar to that shown in Fig. 7. The first tube in each bank is fired before receipt of the impulses by closing the presetting switch 442, so that the " mark " tube is primed. Impulses are applied to the grids over conductor 423 from terminal 425, Fig. 12. As one tube fires the previous tube is extinguished so that at the end of the first burst of impulses marked by a large amplitude impulse, only the tube corresponding to the first letter set up at the transmitter is conducting. The large impulse routes the second burst of impulse to the second bank of tubes and the second letter is indicated and so on. Speeification 592,797 is referred to.