GB540281A - Improvements in television - Google Patents

Abstract

540,281. Television. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Aug. 31, 1940, No. 13695. Convention date, Aug. 31, 1939. [Class 40 (iii)] In a television transmitter utilizing a cathode-ray tube having a mosaic screen of electron-emissive capacity elements scanned by a beam having nearly zero velocity at the screen, blanking impulses are periodically applied to the control grid to produce " pedestals " on which synchronizing pulses are subsequently added. As shown in Fig. 1, the cathode-ray tube comprises in known manner an indirectly heated cathode 2, a control grid 3, accelerating electrodes 4, 6, a focusing coil 9, a screen 11, a slotted shield 17, a collecting electrode 19, and scanning coils 16 and plates 14. The screen 11 is of the type common in iconoscopes, but is translucent to receive the image of an object 12 projected thereon by an optical system 13. Blanking pulses from a generator 26 are applied to the control electrode 3 through an amplifier 32 and a condenser 5. The picture signal with the blanked out level shown in Fig. 2 is transmitted by coupling 22 to amplifier 20 feeding a transmitter 23 through another amplifier 21 in which synchronizing pulses from the generator 26 are added. The blanked out level or "pedestal" may be raised above the blacklevel by illuminating the screen 11 from a constant light source 41 or by the introduction of pulses through a switch 46 into the amplifier 21. The complete signal is then as shown in Fig. 5