Patent GB-549358-A (GB)
Title: Improvements in or relating to telegraph apparatus
IPC: H04L13/10
Filed: 1941-04-01
Abstract: 549,358. Type-printing telegraphy ; electrondischarge apparatus. HADBKEL, R. April 1, 1941, No. 4384. [Classes 39 (i), 40 (iii) and 40 (v)] In a telegraph system in -which impulses are 'transmitted to line by an electronic beam which scans code-anodes, and are distributed over signal-indicating anodes by an electronic beam moving synchronously with the signal beam, the electronic beams of both the transmitter and receiver are both started from a fixed initial position by an initial impulse and are returned to it after their scanning movement'to await the next initial impulse. In the apparatus shown, depression of one of a series of keys 24 corresponding to the symbol to be transmitted connects one or more of five anodes 16 - 20 in a cathode-ray tube 11 to the positive lead 228, in accordance with the code representation -of -that symbol. It also closes the contacts 33, 35, common to all the keys whereby a starting signal anode 21 on which the cathode-ray at this time impinges is rendered positive, causing an increase in the current through the tube which, by way of an amplifier 38, delivers a starting signal to the transmission line 39. The closure of the contacts 33, 35 also reverses the polarity of the grid 42 of a triode valve 40, which then passes current to a condenser 50, the rising potential of which is applied to one deflector plate 22 of the cathode-ray tube. The ray is thus caused to scan the anodes 20 - 16 in turn, a signal being transmitted to the line 39 when it reaches any anode connected to postive by the particular key 24 depressed, whereby a set of code impulses in accordance with the contacts made'by the'key will be forwarded. When the key is released the contacts 33, 35 are broken and contacts 33, 34 are made, causing the grid 55 of a thyratron valve to become positive so that the valve discharges the condenser 50 in readiness for the next signal. The transmitted signals are delivered to an amplifier 60 and applied to one deflector plate 78 of a cathode-ray tube 61. The first or starting signal, derived from the anode 21 of the transmitting cathode-ray tube 11, on reaching the grid 83 of a thyratron valve 84 causes it to strike and to complete a circuit through a triode 88, the grid of which is maintained positive, thereby providing a connection from the negative lead 87 through the valves 88, 83 to a condenser 91. This condenser then charges, the rising potential being applied to a deflector plate 65 in the tube 61 to cause the ray to scan a series of anodes 67-76, in synchronism with the scanning of the anodes 20 - 16 in the tube 11. The anodes 67-76, although shown for clearness as concentrically arranged, are in fact in two series side-by-side, so that the code signals applied to the deflector plate 78 cause the cathode-ray to move from one series to the other, current passing to one of the odd-numbered anodes in the absence of a signal and to the corresponding even-numbered anode when a signal is received. Each resulting impulse is applied through a transformer connection to the grid of a corresponding thyratron valve 117-126, which is 'thereby rendered conductive, so that of a series of conductors 137 - 146 connected to the cathodes .of these valves, a combination corresponding to the symbol is rendered positive. These conductors are connected to the five grids of a series of heptode valves 150 each of which corresponds to one of the keys 24, the connections to all the valves being different and such that for each set of code-impulses only the one valve corresponding to them has all five grids rendered positive, being thereby rendered conductive to cause the appropriate symbol to be printed, perforated or indicated. This operation occurs on the completion of a circuit 101 common to the cathode of all the valves, which is made through a thyratron valve 100 rendered conductive by an impulse received from a'terminating anode 77 in the tube 61. 'Immediately after the cathode ray has reached this anode the voltage across the condenser 91 rises to a point at which it fires a thyratron valve 152, which discharges the condenser and imparts through a transformer 154 a momentary negative cut-off voltage to the grid of the valve 88, thereby interrupting, the current through the thyratron valve 84 and rendering it non-conductive. This disconnects the negative lead 85 to the condenser 91 and the cathodes of the valves 117 -.126, . in readiness for the next signal. In an alternative coding arrangement a valve is employed which comprises a number of grids, one 'for each key 24, arranged in a circle around a central cathode, and surrounded by five cylindrical anodes arranged end to end. Each key closes a single contact which renders the corresponding, grid positive, resulting in an electron beam the radial direction.of which is determined by the key in use. Parts of the anodes are covered with insulating material cut away, or otherwise rendered inactive in such a way that the current passes to a different code combination of anodes for each radial direction of the beam corresponding to the particular grid rendered positive. The anode circuits are connected to corresponding pairs of five. pairs of deflector plates in a cathode-ray tube, a scanning ray passing in succession-between the plates being deflected on to a target electrode when between a pair of plates to which a code signal is applied. The resulting impulses derived from the cathode-ray tube are transmitted to the line. The series of heptode valves 150 may be replaced by a single valve, Fig. 3, comprising a cathode 200, five concentric grid structures 201- 205, and a concentric series of anodes 206. The grids are subdivided into two, four, eight, sixteen, and thirty-two parts respectively, there being in the last case one grid to each anode. Alternate grid sections in each grid structure are connected together and to one of the lines 137-146, Fig. 1, respectively, so that -each set of code signals results in all five grids opposite only :the one corresponding anode being rendered positive. In another form of apparatus a coding and a decoding cathode-ray tube are used, provided with similar series of anodes, one for each symbol, scanned in synchronism by the beams, the circuits for initiating and terminating a single scanning operation for each symbol being similar to those previously described. Operation of a 'transmitting key connects the corresponding anode to positive, causing a signal to line when the scanning beam reaches it which produces a deflection of the beam in the de-coding tube (which normally just misses the anodes) on to the corresponding anode. The resulting impulse fires a corresponding thyratron valve which - causes the operation of the printing &c. mechanism for the symbol.