GB419811A - Improvements in or relating to television, picture telegraphy and the like transmitting systems - Google Patents

Abstract

419,811. Television transmitters. ELECTRIC & MUSICAL INDUSTRIES, Ltd., Blyth Road, Hayes, Middlesex, and BROWNE, C. O., 29, Monk's Drive, West Acton, London. March 7,1933, No. 6864. [Class 40 (iii).] Television transmitting apparatus comprises a line synchronizing photo-cell separate from the photo-cell for producing the picture currents, a line synchronizing light source, a scanning device of which each element takes part in translating an image of a strip of the object to be transmitted over the picture photo-cell and an image of the line source over the line photocell and means for inserting the line synchronizing signals and the picture signals into the transmission channel on opposite sides of a datum line corresponding to black in the object. The invention is described in connection with the transmission of a film 1 which is moved continuously in front of an illuminated slit 2 and the image 11 of a strip of the film is swept by a mirror drum 6 across an aperture 9 in a screen 7, Fig. 3, behind which is located a photo-electric cell 10. For the production of the line and frame synchronizing impulses an additional light source 13 is projected on a slit 12 which is normally obscured except for a portion 15 by the annular portion 19 of a shutter disc 14 which makes one revolution during the passage of two picture frames before the slit 2. At the end of each line an image 17 of the aperture 15 is passed over an aperture 16 in the screen 7 behind which is placed a second cell. One of two notches 24, 25 of the shutter 14 exposes the slit 12 to the light source 13 for the frame synchronizing impulses for a period during which the picture scanning slit 2 is obscured by one of the radial arms 20, 21 of the shutter 14. The synchronizing impulses are reversed in phase, and additional signals produced by a light source co-operating with a slot 27 which is uncovered by a notch 22 or 23 during the generation of the synchronizing impulses are also reversed in phase to ensure that the intensity of the cathode beam is reduced to zero during its return movement across the receiving screen. For preventing damage to the film by the light source 3 if the driving mechanism fails, a safety shutter 31 loosely mounted on the shutter shaft 29 contacts in its normal position with a stop 35 so that arms 32, 33 prevent the light beams from reaching the apertures 2, 27. The shutter 31 is moved to its non-obscuring position by the shutter 14 through a friction coupling 36 when the magnet 38 is energized in parallel with the switching on of the light 13. The length of the arm 32 may be such that the aperture 12 is obscured except for its end portion 15 by which the mirror wheel produces synchronizing impulses. The line and framing signals may be produced by separate apertures and light sources, the line synchronizing impulses being suppressed during the generation of the framing impulses.