GB392730A - Improvements in or relating to television apparatus and the like - Google Patents

Abstract

392,730. Television. BAIRD, J. L. and BAIRD TELEVISION, Ltd., 133, Long Acre, London. April 29. 1932, No. 12384. Addition to 322,481, (Class 40 (iii), Telegraphs, Electric]. [Class 40 (iii).] The use of scanning apertures, whose width is greater than their depth, as described in the parent Specification, is applied to systems having a stationary scanning aperture as described in Specification 321,961, [Class 40 (iii), Telegraphs, Electric], and the effective width may be continuously varied. Receivers. The aperture 3, Fig. 1, in a fixed mask 2 in a television receiver of the kind described in Specification 360,942, has its width a greater than its depth b, and the scanning spot 70 is correspondingly shaped. Successive scanning paths overlap by an amount ¢a, but other degrees of overlapping may be adopted, as described in Specification 321,389; [Class 40 (iii), Telegraphs, Electric], and uniformity of illumination may be secured as described in Specification 381,882. The ratio b a must be an integer to secure uniform illumination. The source of light may be a flaming arc 1 of the type described in Specification 380,109. The'lens 8 may be omitted and the arc 1 juxtaposed to the mask 3, as described in Specification 380,234, and a Kerr cell, Fig. 5 (not shown), may be similarly arranged. In order that the picture may be scanned more finely in some parts than in others, the width of the slot 3 may be variably determined by a tapered slot 12, Fig. 2, in an opaque covering of paint, metal foil or black paper on a. glass, celluloid or mica disc 9. The strength. of illumination is varied by variation of the depth b of the aperture. The cant of the mirrors is adjusted to prevent overlapping of successive scanning paths in spite of variation in the width of the latter. The disc 9 may be geared up to the scanning disc by a belt drive, Fig. 4 (not shown); in a 3 : 1 ratio, the slot 12 having. in that case three maxima and three minima of width. The scanning-strips may be narrow and contiguous at the centre of the picture and progressively wider towards the edges, and the outermost strips may overlap, Fig. 7 (not shown), as described in Specification 321,389. In this event the aperture 3 may, be tapered, Fig. 5 (not shown), to diminish the effect of overlapping, or instead of being continuously: tapered it may be shaped into rectilinear steps' calculated to yield uniform illimination. Transmitters. The above arrangements, if applied to transmitters, would cause difficulty through the unsuiitable loading of the amplifiers. At the transmitter, therefore, an aperture of uniform size is employed and overlapping or underlapping of successive scanning-paths is permitted, or the disc 9 may be replaced by a glass annulus 14 having a cross-section which varies from rectangular (19) at 16 to concave (18) at 15, the active portion of the annulus behaves like a cylindrical lens, so that the effective shape of the scanning spot varies as the annulus rotates in synchronism with the scanning mirror drum. Specification 391,931 also is referred to.