Device for simultaneously producing a plurality of television information signals

773,380. Television. PHILIPS ELECTRICAL INDUSTRIES, Ltd. Nov. 11, 1954 [Nov. 14, 1953], No. 32711/54. Class 40 (3). In a colour or stereoscopic television system at least one aspect of the object is imaged on the picture signal generating tube through a grid structure so that the tube output signals contain a carrier frequency wave (determined by the " pitch " of the grid and the line scanning frequency) modulated by signals representative of this aspect. Fig. 1 shows one embodiment producing signals representative of the R (red) and G (green) aspects of an object in which the grid structure 7 comprises a colour filter constructed, as shown in Fig. 2, of an interdigitated series of colour filter strips a and b, the strips a passing both red and green light and the strips b passing red light only. When this grid is interposed in the object light path of the tube 1 a mathematical analysis of the signal developed across the load impedance 5 shows that it comprises, as shown in Fig. 3, (1) signals representative of the R and G aspects occupying a frequency range extending from zero to an upper limit f0 determined by the " pitch " of the grid strips and the (optical) definition of the image focused thereon, and (2) signals representative of the G aspect modulated on a carrier frequency f determined by the " pitch " of the grid strips and the line-scanning frequency. The optical definition of the image (which is adjusted by means of lens 6) focused on the grid and the " pitch " of the latter are selected (for a given line scanning velocity) that signals (1) and (2) do not overlap, so allowing these signals to be separated by means of suitable filters. As shown in Fig. 1, the signals (2) are selected by means of a band-pass filter F1, the green signals being recovered by detection in D1 and the signals (1) after selection by a low-pass filter F2 are combined in A1 with the green signals to provide, by subtraction, the red signals. The grid structure may consist of alternate opaque and transparent strips and be positioned in one of two different optical paths between the object and the tube to provide stereoscopic signals (Fig. 4, not shown) or, for two-colour television, each path may include an appropriate colour filter. To produce three-colour television signals the object light path is split up, by means of the optical system H1, into three separate paths LI, L2, L3 in two of which (L2, L3) colour filters 14, 15 transmitting red and blue light respectively and