GB476181A - Scanning disc for television transmitters - Google Patents

Abstract

476,181. Television. RADIOAKT.- GES. D. S. LOEWE. June 9, 1936, Nos. 16091 and 16092. Convention dates, June 11, 1935 and June 25, 1935. [Class 40 (iii)] With the object of obtaining interlaced scanning of a continuously moving kinematograph film and simultaneously to utilize the apertures for the generation of synchronizing signals of framing frequency at isochronous intervals, the apertures are arranged to form two or more spirals giving a total odd number of apertures, while the first aperture of each spiral lies on a line connecting the first and last of all the apertures, such line constituting a diagonal of the image area on the disc. During each scanning of an image the disc rotates as many times as there are spirals so that the apparent radial movement of the apertures is equal to but in opposite direction to the movement of the film. In the arrangement shown in Fig. 2, the apertures 1 .. 120, and 120.. 239 form two spirals, and the disc 23 revolves twice whilst each image is scanned. Thus, allowing for film movement, each spiral is capable of scanning the image area during one revolution, but a second disc 6 rotating at half the speed of the scanning disc 23 is provided with an obturating spiral 50 so that only one scanning spiral is effective. Consequently, during two revolutions of the disc 23 an image is scanned once by each spiral and the two sets of lines are interlaced. Synchronizing signals at line frequency are obtained by the passage of the apertures 1 .. 239 across a bright marginal line 5 of the image area 2, while signals at the framing frequency are derived by passage of an arcuate slot 7 across the line 5 in conjunction with apertures 8, 9 in the disc 6. The optical arrangement is shown in Fig. 5, with the discs 6, 23 rotating in the planes of intermediate images of the film 25 formed by the lens system 24, 25<1>, 10. In a modification, the disc apertures are arranged to form four spirals, and the disc revolves four times whilst each image is scanned. The synchronizing signals are separated at the receiver by amplitude filtering. The line signals may be derived by providing on lines joining the apertures to the centre of the disc a series of slots forming a light siren, but in this case it will be necessary to introduce at the receiver a frequency reducer, Fig. 6 (not shown), of ratio 1/n, where n is the number of spirals on the disc. Specification 465,184 is referred to.