Patent GB-313456-A (GB)
Title: Improvements in television apparatus
IPC: H01J29/00
Filed: 1929-06-11
Abstract: 313,456. Tihanyi, K. June 11, 1928, [Convention date]. Void [Published under Sect. 91 of the Acts]. Vacuum tubes.-A transmitting and receiving tube for television has a pencil of cathode or like rays, scanning one or more photoelectric layers, on which the view is projected. In the transmitter, Fig. 1, cathode rays are emitted from the cathode k and strike the diaphragm g or other device which only allows a thin pencil of rays k1 to pass through. This pencil of rays k1 is deflected in two directions by electric fields, c, C, rhythmically controlled by the modulator M, so that the pencil k1 scans the image carrier Tr on which a lens F throws an image of the object. The image carrier Tr, under the action of light incident thereon, varies the potential transmitted by rays k1 to anode A, which variations affect carrier waves of frequency W1. The receiver, Fig. 2, operates in a similar manner. Carrier waves of frequency W2, varied by the modulator M in the transmitter, control the fields c, C to obtain synchronization with the transmitter; and carrier waves of frequency W1 control, through diaphragms Gm, the intensity of the rays emitted from cathode k, and restricted to a thin pencil by diaphragm g. This pencil k2 strikes a fluorescent screen L and reproduces the image scanned in the transmitter. The image carrier. The image carrier, Fig. 4, consists of a network of insulating filaments 5 provided with photo - electric elements f. Another form is shown in Fig. 5 in which earthed wires 6 carry insulators 7 on which are mounted photo-electric elements f. The wires 6 may be replaced by strips (Fig. 14, not shown). The earthed grids increase the capacity of the photo-electric elements and the form shown in Fig. 4 may be provided with an earthed network. The elements f may be mounted on an insulating diaphragm whose other surface has an earthed metal plate (Fig. 8, not shown). Fig. 3 illustrates the action of the image carriers. Conductors 2 carrying photo-electric elements fare insulated from each other by insulators 3. The light incident on the elements f causes emission of electrons and consequent positive charging of these elements f proportional to the intensity of the incident light. This charging affects the current impulses transmitted by the cathode rays k1 in passing through the image carrier. The pencil of rays k1 thus reduces the positive charges on the photo-electric elements f and even charges them to a small negative potential, so that the image carrier is preferably swept by homogeneous light removing these negative potentials between each complete scanning. Modification using reflecting image carrier. The transmitting tube, Fig. 9, has a reflecting image carrier consisting of a glass plate 38 with square plates of alkali metal 39 and has an earthed metallic coating 40 on the reverse side. The grid 41 receives the electrons emitted from the carrier while the Faraday cylinder 42, or Perrin electron receiver 42, 43 receives the reflected electrons. Treatment of cathode ray pencil. The deflection of the beam k2 in the receiver is dependent on the electron velocity. This is maintained constant by the device shown in Fig. 10 in which the beam k2 passes through a number of grids 10, 12 charged alternately to positive and negative potentials. An homogeneous pencil of rays k1 in the transmitter is obtained by passing the cathode beam through a magnetic or electrical field provided by plates 14, 15, Fig. 12, and subsequently through a diaphragm 16. To thin the cathode pencil k1, it is passed through an electrical longitudinal field 91, Fig. 13, opposite to the direction of motion of the cathode pencil and provided by two plates 90, 92. This deflects the electrons towards the axis of the tube as shown by the arrow in the beam k1. The fluorescent screen. The fluorescent screen has an electric field in front of it accelerating the electrons and increasing the fluorescence. (Fig. 11, not shown). A mixture of fluorescent material such as calcium sulphide with copper, uranium or manganese is recommended. To increase the intensity of fluorescence, the pencil of cathode rays may be concentrated with either glowing or cold cathodes in a known manner. The cathode rays may act indirectly on the screen as shown in Fig. 15 in which the pencil k2 charges the separate grid elements f to negative potentials corresponding to its strength, and these grid elements influence the electrons emitted from the cathode filaments H which impinge on the screen L. Fig. 16 shows a construction in which the photo-electric grid elements f are placed between the fluorescent screen L and the electrode 65. Fig. 17 shows another construction in which the elements f are mounted on an insulated plate 87, carrying metallic plates 88 on the reverse side, which is also coated with fluorescent material L. Cathode rays k impinge on the elements f, and electrodes K1 emit electrons. The screen L may be swept with homogeneous light after each complete scanning to remove any residual charges. The screen L may have fluorescent marks at its corners &c. to facilitate adjustment of the cathode pencil. The screen may be used with an enlarging camera.