GB416848A - Improvements in or relating to television picture telegraph and the like transmitters - Google Patents

Abstract

416,848. Television transmitters. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Electra House, Victoria Embankment, DOWSETT, H. M., 47, Drayton Gardens, Winchmore Hill, both in London, and CADZON, R., Ardentinny, Argyllshire. Feb. 23, 1933, No. 5584. [Class 40 (iii).] In television transmitting system in which a cathode ray tube has a photo-electrically sensitive electrode which emits photo-electrons from individual parts in dependence on the degree of illumination of those parts and which is scanned by a cathode beam, the picture to be transmitted is projected through a light permeable anode positioned on the same side of the light-sensitive electrode as the electron gun so that the photo-electrons emitted variably obstruct the scanning ray to provide the picture signals. The object to be transmitted is focused on a photo-electric cathode 2 with which is associated a translucent fine gauze screen 3 forming the light-permeable anode. The scanning cathode ray controlled by plates 6 of which only one pair is shown, passes over the cathode 2 from the different areas of which photo-electrons are liberated in accordance with the degree of illumination of these areas, and obstruct to a varying degree the electrons of the cathode ray passing to the plate 2. These variations cause corresponding changes in the voltage drop across a resistance 15 connected through a condenser 14 to one of the output terminals 12, 13. Electrons returned to the anode 3 pass to earth via resistance 10 and voltage changes set up across this resistance are smoothed out by a condenser 11. In an alternative arrangement, (Fig. 2 not shown) the electrode 2 is connected to the anode 3 through a resistance replacing the resistance 15 connected in series with a portion of the battery 16, the resistance 10 and condenser 11 of Fig. 1 being omitted. A magnetic field may be applied near the photo-electric cathode to ensure that the photo-electrons follow substantially parallel paths and a supplementary meshelectrode may be provided between the electrodes 2, 3 to accelerate the electrons to the anode 3 and thereby to prevent their return to the cathode 2. Specification 394,597 is referred to.