Patent GB-853708-A (GB)
Title: Improvements in or relating to radio receivers employing visual display systems
Inventor: HARRIES JOHN HENRY OWEN
IPC: H04N9/31
Filed: 1956-06-29
Abstract: 853,708. Television. HARRIES TELEVISION RESEARCH Ltd. June 13, 1957 [June 29, 1956], No. 20257/56. Class 40(3). In a "compatible" colour television receiver utilizing both colour and monochrome display means the latter are rendered operative and inoperative respectively .in response to the presence of a predetermined characteristic of the colour signals and inoperative and operative, respectively when such characteristic is not present (i.e. when monochrome signals are being received). The predetermined characteristic may be the colour signals themselves or the synchronizing "burst" signal in the case of the N.T.S.C. system. Fig. 1, shows one embodiment of a receiver utilizing the latter system in which by means of a quadricorrelator circuit or by means of rectification and integration of the "burst" signal (block 23) a D.C. control voltage is derived the amplitude of which is higher when colour signals are received than when monochrome signals are received. This voltage is then employed to control the cathode-coupled triodes 28, 29 so that when colour signals are present the potential of anode 39 is low and that of anode 40 high whilst when colour signals are not present, anode 39 is at high potential and anode 40 at low potential. In the former condition (colour signals present) the potential of anode 39 is lower than that of the cathode 9 of the monochrome display tube 6M and the tube is, consequently, biased-off. The potential of anode 40, however, is higher than that of the cathodes 14, 15, 16 of the colour display tubes 6B, 6R, 6G and the latter therefore are operative. When colour signals are not received the colour tubes are biased-off due to the low potential of anode 40 whilst the monochrome tube is operative due to the high potential of anode 39. In a second embodiment (Figs. 2 and 3), only three display tubes are employed the screens of each of which are provided with a single line of phosphor b, r and g producing the appropriate component colours whilst the screen of one tube, 6R is provided, in addition, with a single phosphor line m producing a black/white response. The scanning of each tube is effected in line direction only and the frame scanning component supplied by a mirror 47 electromagnetically operated by a coil 67 from a source 66. In operation the output of 23 (similar to 23 Fig. 1) causes a greater current to flow in auxiliary deflecting coils 48, 49, 50 when colour signals are received than when monochrome signals are received so that in the former condition the colour phosphor strips are scanned whilst in the latter condition the beams of tubes are deflected away from the colour producing phosphors and the beams of tube 6R, which then impinges on the black/white phosphor stripe m, is effective to produce the monochrome image. To ensure that both the colour and monochrome images occupy the same area on the viewing screen 8 the mean position of the frame scanning mirror 47 is altered by an amount proportional to the deflection produced by the auxiliary coils 48, 49, 50. This may be achieved by a further coil 64 having an armature linked to the mirror as described in connection with Fig. 5 (not shown), the current in which is determined by the output of 23 or, such current may be introduced in series with the scanning control coil 67 (Fig. 4, not shown). Instead of employing separate cathode-ray tubes a single tube of the "shadow-mask" type each elementary area of the screen of which is provided with three colourphosphor dots and a single substantially whitelight producing phosphor dot and having three electron guns for colour reproduction and an additional gun for black/white reproduction, may be employed. The signals displayed may be radar signals . Specification 853,707 is referred to.