GB812635A - Improvements in or relating to electron discharge tube circuit arrangements - Google Patents

Abstract

812,635. Television pick up tubes. MARCONI'S WIRELESS TELEGRAPH CO. Ltd. Feb. 14, 1957 [May 2, 1956], No. 13541/56. Class 39(1). In a cathode ray storage tube circuit a low velocity electron beam from a single gun, is split into two equal parts by an anode 7, Fig. 1, having two apertures 8, 9 and the parts are then aligned by respective pairs of plates 10, 12 ; 11, 12, plate 10 being common, plates 11, 12 carrying independently adjustable potentials from potentiometers, after which the beam parts are separately deflected by respective pairs of deflective plates which are energized by sawtooth waveforms of 500 cps (writing beam 3a) and 50 cps (reading beam 3b) and the writing and reading beams 3a, 3b are then passed through respective grids 21, 22 carrying independent DC potentials to impinge on a charge storage target comprising discrete conductive strips 20, Fig. 3, formed on an insulating carrier 19 on the other side of which are two signal plate ribbons, the grids and signal plate ribbons extending transversely to the target strips 19 and having a width less than half the height of the signal strips, the signal input being applied to signal plate 24, a carrier frequency being applied to grid 22 traversed by the reading beam and the output amplitude modulated signal (carrier amplitude modulated by the signal) being taken from signal plate 25. The signal plates are gold coatings on the " Pyrex " (Registered Trade Mark) carrier 19 and the target elements 19 are rectangular gold strips. The writing beam stores charges on the strip elements 20 the amount of stored charge varying with the signal potential applied to backplate 24. Grid 21 has a steady bias of -40 volts to prevent undesired secondary emission. The output from signal plate 25 is fed through circuits tuned to the carrier frequency to a display unit. The grid 22 may have an adjustable negative bias, e.g. of 10 volts if the peak carrier voltage applied thereto is 20 volts. An earthed screening plate 17, prevents crosstalk between the two screening fields. The gun has indirectly heated cathode 1, 2, beam forming grid 4, and anodes 5, 6 and 7. The signal/ noise ratio is reduced because ten writing scans (at 500 cps) take place for every reading scan (at 50 cps) the writing scan frequency being correlated with the radar pip repetition frequency so that each incoming radar pip is stored at the same point in the target, the noise and other irregularly occurring signals occurring irregularly in time and thus being of much smaller amplitude, i.e. not being additive in successive scans. The signal/noise ratio may be further improved by connecting two tube units in cascade in the same or separate envelopes.