GB590468A - Television transmitting system - Google Patents

Abstract

590,468. Television transmitters. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. May 3, 1944, No. 8399. Convention date, Aug. 29, 1942. [Classes 39 (i) and 40 (iii)] In a television transmitter in which signals are produced by a low velocity cathode-ray beam scanning a target electrode, negative impulses are applied to the target to reflect the beam entirely during certain periods, for example, during the return strokes following the line and frame scans. This avoids the necessity of suppressing the beam during the return strokes and enables signals to be derived by collecting electrons reflected from the target without having undue modulation of the beam by suppressor signals. The invention is shown as applied to an Orthicon tube in which a low velocity cathode-ray is projected from a cathode 3 towards a target 2 and reflected from the target to an amplifying system including multiplying electrodes 32, 33, 34 and collector anode 35, electrons being subtracted from the reflected beam at the target in accordance with the distribution of charge thereover. The Orthicon tube includes the usual deflecting plates 20, 21 and coils 22, 23 and lift plates 24 serving to effect a separation of the incident and reflected beam as described in Specification 560,904. Negative impulses for preventing subtraction from the beam during the return strokes thereof are applied to'the electrode 6 on the back of the target 2. These impulses are derived from the horizontal or line deflection generator 78 and the vertical or frame deflection generator 82 through amplifiers 90 and 92 which are connected so that the output of 90 is applied to the cathode of 92, the output of 92 being fed to a further amplifier 104 for application to plate 6. The invention may also be applied to Orthicon tubes of the kind described in Specification 543,890.