GB457135A - Improvements in or relating to television apparatus - Google Patents

Abstract

457,135. Television. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Electra House, Victoria Embankment, London.-(Assignees of Vance, A. W. ; 109, North 5th Street, Camden, New Jersey, U.S.A.) May 23, 1935, No. 15068. Convention date, May 23, 1934. [Class 40 (iii)] Relates to means for producing scanning and/or deflecting impulses from a source of alternating current of predetermined frequency by frequency multiplication, particularly for interlaced scanning systems to avoid " pairing" of adjacent lines. In the embodiment described the picture frequency is 60 cycles per second, and the line frequency 7290, giving a ratio of 121¢ which is suitable for the interlaced scanning system described in Specification 420,391. The line frequency is derived by frequency multiplication from the 60-cycle mains 3, being applied to, and saturating, an iron-cored inductance 1, from which a 180 cycle component is selected by a filter 9, 11 and fed to an amplifier 7. From thence the output passes to further frequency triplers 15, 23, 25, 27, comprising saturated valves, and amplifiers 17, 19, 21, 29 arranged between the frequency multipliers. The 14,580 cycle output from the unit 29 is fed to a valve 31 which permits the passage of only the positive peaks of the input and automatically controls their amplitude. This is accomplished by including in its cathode circuit the self biassing resistance 41 and also an opposing source 45 in the grid circuit tending to render the grid positive. In the equilibrium condition the valve is biassed almost to cut-off and permits only peaks of constant amplitude to pass, the bias changing with changes of signal strength. The output from valve 31 is halved in frequency by a dynatron frequency divider 46 fed to a limiter 47, amplified at 59 and appears in the output resistance 61. The picture frequency of 60 cycles, is derived from a valve 63 biassed close to cut-off which passes the 60-cycle positive peaks of a composite wave containing 60, 540, 1620 and 4860 cycle components derived from the frequency multiplying stages and fed to the grid of the valve 63, the output from which is amplified by a valve 103 and appears in the common output resistance 61.