GB555213A - Television transmitting system - Google Patents

Abstract

555,213. Cathode-ray tubes. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Feb. 11, 1942, No. 1827. Convention date, Feb. 11, 1941. [Classes 39 (i) and 40 (iii)] In colour television transmission tubes the mosaic is flooded after each scan with low velocity electrons from a source independent of the electron gun used for scanning, the flooding taking place during a portion only of the fly back period of the beam. Signals are not generated during the fly back period. Pictures are projected on the mosaic 20 through colour screens 48, which may consist (i) of a disc divided into sections R, G, B, Fig. 2a, or (ii) of segments R, G, B, Fig. 2b, separated by opaque parts 54 ; with the second form the mosaic is scanned in darkness. To flood the mosaic one or a number of separate cathodes 56 are used, each with a control electrode 60, whose potential is sufficiently negative to prevent electron flow from the associated cathode. The impulse generator 36 controls the vertical deflection of the scanning ray and has means associated therewith for giving during a portion only of the fly back period a positive impulse to the control electrodes 60 whereby electron flow is allowed ; also associated with this generator and with the generator 32 for the horizontal deflection are means to apply negative impulses to the control electrode 14 of the gun to prevent electron flow during the whole of the fly back periods from the main cathode 12. In a modification the control electrodes 60 are dispensed with, the cathodes being held normally at a potential positive to the accelerator electrode 18 ; for the flooding period a short negative potential period of the cathode is obtained. The flooding means may be used with arrangements using different lenses for each colour or with moving picture films, where successive frame images are of different colour. Specification 434,942 is referred to. The Specification as open to inspection under Sect. 91 also states that the flooding means may be used in other forms of television transmitting tubes and also where a residual charge on the mosaic is eliminated only after two or more scanning cycles. This subject-matter does not appear in the Specification as accepted.