Patent GB-538054-A (GB)
Title: Improvements in or relating to electron image dissecting arrangements
IPC: H04N5/228
Filed: 1939-11-13
Abstract: 538,054. Cathode ray tubes; impedance networks television; valve amplifying circuits. JAMES, I. J. P. Nov. 13, 1939, No. 29948. [Classes 39 (i), 40 (iii) and 40 (v)] In a television transmission system a composite electron beam from a photo cathode 12, Fig. 1, is focused in the plane of and scanned across a number of collector electrodes 14 so that each elemental area of the electron image is scanned in turn over all the electrodes ; this gives rise to a number of discrete signals similar in form but out of phase, these signals being fed to a delaying network so that they can be added together to give a single augmented signal. The electrodes 14 are separated by screens 15 ; each may comprise a thin film of metal arranged between two insulating plates of mica coated on the outside with a metal film acting as screen. A plate with a narrow transverse slit may be arranged in front of the electrodes so that only a " line " of electrons can scan the electrodes 14 ; these may be coated with secondary emissive material to obtain electron multiplication, the secondaries being collected by further electrodes. The electrode 12 may be thermo-electrically sensitive and the composite beam may be magnified by (i) reducing the length of the focusing coil 16 or (ii) by electrostatic means consisting of accelerating fields placed behind a slit in a metal plate through which " lines " of the beam pass, the enlarged image being received by collector electrodes. The lost endportion of the signal can be arranged to occur during the synchronising pulse. In a modification instead of arranging the ends of the electrodes 14 in one plane they may be staggered along the tube to give the time delay required prior to adding the discrete signals. In a further modification the composite beam is scanned over an electrode 50, Fig. 4, with a number of perforations 51 a-e in line ; behind the plate 50 is arranged a similar perforated plate 52 followed by two deflector electrodes 55, 56 between which a magnetic field in the direction H is maintained. The plates are charged so as to produce a deflection of electrons passing between them. Deflector plate pairs 57a-d are placed between the electrodes 55, 56 and a reflector electrode 54 is used. A Faraday cylinder output electrode 59 is connected to the amplifier 60. As an elemental area of the beam is scanned across the plate 50 some electrons pass through the perforations 51a, 53a, between the plates 55, 56 and plate pair 57a to be reflected at the negatively biased plate 54, back in time to join the next set of electrons from the same elemental area entering through the perforations 51b; this sequence is repeated at all the perforations, the augmented signal being received by the collector 59. The plates 57 ensure that electrons reflected by the plate 54 do not pass through the perforations 53 a-e; the electrons may be reflected between the plates 52, 54 a number of times to give synchronism between their movement and that of the elemental area. Films may be transmitted in the method described, either by using a whole of a film frame or by single line transmission. The discrete signals from the electrodes 14, Fig. 1, similar in form but out of phase are added together by a delay network ; each electrode 14 is connected to the grid of a valve such as 20, 21, 22 &c., Fig. 2, whose cathode output impedances are the resistances 23, 24, 25. The valves are connected by matching resistances 29, 30, 31 to tappings 32, 33, 34 on the delay network 35 comprising series inductances 36 and shunt capacities 37 with end resistances 38, 39. The time delay may be obtained by using quartz crystals in liquid cells, the time being taken up in the passage of the signal through the liquid ; or the time delay device described in Specification 471,913 may be used. The number of sections in the delay network may be reduced by using reflected signals. To obtain these one end of the network is mismatched say by open- or short-circuiting that end.