Patent GB-648257-A (GB)
Title: Improvements in or relating to the conversion of electrical signals into luminous images and vice versa
IPC: H04N9/22
Filed: 1946-11-16
Abstract: 648,257. Television. OKALICSANYI, F. Nov. 16, 1946, Nos. 34036/46, 6031/47, 6633/47 and 6634/47. [Class 40 (iii)] [Also in Group XL (a)] In a colour television system employing a cathode-ray tube means are provided for imposing a line structure on the electron distribution over the scanned surface and for periodically deflecting this line structure into at least two alternate positions in fixed relationship to which colour selective means are arranged. Fig. 1 shows the general arrangement applied to a transmitter-receiver system employing a picture signal generating tube 1 and a picture reproducing tube 1a in each of which the means for imposing the required line structure comprises a grid 9 (9a) of closelyspaced fine wires, arranged, inside the tubes, at right angles to the line scanning direction, and between the electron guns and the scanned screens 2 (13). Deflecting rods 10 (10a) positioned adjacent the grids and supplied with square wave pulses at line (or frame) frequency deflect the electron line structure alternately to two positions (corresponding to the two halves of the square wave) at which different colours are scanned (or reproduced) by means of colour screens 12 (12a) consisting of alternate strips of different colours parallel to and registering with the wires of grid 9 (9a), the (transmitter) colour screen 12 being positioned outside tube 1 and focussed on to grid 9 and signal plate 2 by means of the optical system 3 whilst the (receiver) colour screen 12a is positioned inside tube 1a between the fluorescent screen 13 and a groundglass diffusing screen 14. Fig. 3 shows a picture reproducing cathode-ray tube 15 fitted with a metallic (e.g. nickel) grid 17 consisting of a plurality of wires 18, the electron shadows of which may be deflected, by means of the deflecting coil 19, to either of two positions 20, 21 on the fluorescent screen on which are strips 22, 23, running parallel to wires 18, of different fluorescent salts emitting light of the desired colours. In an alternative arrangement, Figs. 4, 4a, 4b (not shown), the colour screen comprises a plurality of coloured glass fibre rods (or strips) of 0.005 inch diameter (or width) and the grid electrode is formed from a metal sheet having the same plurality of stamped-out slots 0.005 inch inside separated by gaps also 0.005 inch wide, the colour screen and grid electrode being separated by a thin mica slot, the side of which is adjacent the grid electrode being coated with a layer of fluorescent powder. In a further alternative receiving tube arrangement the fluorescent layer 44, Fig. 6a, which is carried by the colour strips 46, is rendered conducting by means of a transparent metal layer between which and the grid electrode 17 a potential difference is established which gives rise to a plurality of electrostatic cylindrical lenses so that the electron beam is focused into a plurality of thin lines instead of, as in the previous arrangements, being only stopped out to form a shadow line structure. To overcome the loss of light the transparent metal layer may be replaced by a second grid electrode, Fig. 6c and 6d (not shown). The second grid electrode may be combined with the colour filter by forming a fabric having coloured glass threads running in one direction interwoven with' the grid wires (running at right angles), Fig. 7 (not shown). Fig. 8 shows a receiver arrangement in which the image on the screen of the cathoderay tube 101 is projected, by means of the optical system 107, 107a, on to a viewing screen 105 in front of which is placed a colour filter 104 and a grid arrangement 108, the filter comprising alternate red and green strips running at right angles to the line scanning direction 106 and the grid consisting of parallel metal wires having highly-reflecting surfaces, each wire lying opposite the junction of each pair of colour strip. In operation flashes of light from each wire in turn operate via a photo-electric cell 109 and pulse generator 110 and timing circuit 111 to blank the tube beam for periods determined by the circuit 111 so that the position of the projected images is varied periodically relative to the colour filter 104. In a modification of this arrangement the reflecting wire grid and the photo-electric cell are dispensed with and the pulses for blanking the tube beam are derived directly from a wire grid in the screen end of the tube, fluorescent powders of different colour emissions being deposited between the elements of the grid (Figs. 9, 9a and 9b, not shown).