GB395499A - Improvements in or relating to television systems and to electrical wave systems - Google Patents

Abstract

395,499. Phase changing. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Marconi House, Strand, London.-(Assignees of Vance, A. W.; 109, North 5th Street, Camden, New Jersey, U.S.A.) June 8, 1932, No. 16236. Convention date, June 17, 1931. [Class 38 (ii).] In a television system employing for the reproduction of the image at the receiver a cathode ray tube having electromagnetic means such as horizontal deflecting coils and vertical deflecting coils for deflecting the ray in scanning, an arrangement is provided for developing a saw-tooth current wave, as denoted diagrammatically at 67, Fig. 8, within the deflecting means 49, such arrangement comprising means for developing a saw-tooth voltage wave 66 to be applied to the grid of a thermionic valve 61, in the plate circuit of which is connected a circuit 62 having a frequency-impedance characteristic matched to that of the coils 49, the back E.M.F. across the circuit 62 (voltage wave 69) being amplified by a second valve 65 and the resultant voltage wave 70 being applied to the coils 49 for passing therethrough a current wave of the desired sawtooth form. In the arrangement illustrated in Fig. 8 the saw-tooth voltage wave 66 is obtained by alternately building up a charge on a condenser 56 through a high resistance 57, and discharging through a glow tube 55, the natural frequency of discharge being somewhat lower than the line scanning frequency. Under the influence of synchronizing signals received at 52, the glow tube is brought to the discharge point and discharged at the frequency of these signals. Alternative forms of circuit. Instead of the system comprising the glow lamp 55 according to Fig. 8, a screen grid valve 55a, Fig. 9, may be substituted and arranged to discharge a condenser 56 when, for a brief interval, the strongly negatively biased grid is swung to the positive by the periodic discharge at the synchronizing frequency of a glow lamp 73 in series with an inductance 74. Or, in a further arrangement, Fig. 12 (not shown), the glow lamp 73 may be replaced by a grid glow tube. In another modification, Fig. 15 (not shown), the lamp 73 is replaced by a dynatron oscillator, and a D.C. amplifier connection may be employed between the valves 55a and 61, while in a still further development, Fig. 22 (not shown) a dynatron oscillator is employed, but the valve 61 and the compensating inductance 63 of Fig. 9 are omitted, a condenser and resistance being inserted in the plate circuit of the valve 55a. A suitable circuit for supplying the current to the vertical deflecting coils 50 is shown in Fig. 23, the condenser 96 being discharged at the required frequency by a grid glow tube 98, and the voltages developed applied to an amplifying valve 99, the plate circuit of which includes the coils 50.