GB472923A - Improvements in or relating to television and like receivers - Google Patents

Abstract

472,923. Television. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., KEMP, R. J., and FEWINGS, D. J. April 29, 1936, No. 12215. [Class 40 (iii)] Line and frame synchronizing signals are separated by application to a device having a characteristic with substantially different slope at different points. For example, with a screen-grid valve with a characteristic as shown in Fig. 2, the line signals L produce a sweep over the portion AC whilst the frame signals F of greater amplitude produce a sweep from A to B giving rise to a pulse of opposite sign. In the arrangement shown in Fig. 1, the synchronizing signals consisting of " blacker than black " modulations of different duration are applied over a condenser 1 and converted by a time-constant circuit 2, 3 to signals of different amplitude. The output pulses of opposite sign are taken off through a condenser 14 and separated by rectifiers or one set may be taken from the screen grid through a condenser 15. Preferably, the characteristic is such that the downward-sloping portion lies equally above and below the abscissa line. In the arrangement shown in Fig. 4, the pulses from the time-constant circuit TC are applied to the screen grid 9, the tube having a characteristic as shown in Fig. 5 which is worked over the parts GK, GJ. In the arrangement shown in Fig. 6, the synchronizing signals of different duration are applied to the grid of a triode 19 which is shunted by a condenser 21 and is connected in series with a screen-grid valve 41. Each signal reduces the resistance of triode 19 causing condenser 21 to discharge through the triode by an amount depending upon the duration of the signal. Corresponding opposite voltage-changes are produced across the valve 41 which sweeps over the substantially-flatbottomed part NQ of the characteristic, Fig. 8, for line signals and over the rising portion QP for frame signals. The screen-grid valve 41 may be replaced by a diode or a neon or other discharge lamp, and the triode 19 by a high resistance.