GB443952A - Improvements in and relating to electrical circuits for the deflection of cathode ray beams - Google Patents

Abstract

443,952. Television. MANIFOLD, M. BOWMAN-, Heathcot, near Worpledon Station, Woking, Surrey. July 4, 1934, No. 19742. [Classes 40 (iii) and 40 (v)] A cathode-ray beam scans a screen 5, Fig. 2, inclined at an acute angle to the general direction o of the beam, the frame frequency deflecting oscillation being of the form shown in Fig. 5, to maintain the scanning lines equally spaced and the line frequency oscillation being of the form shown in curve 9, Fig. 6 to maintain the lines of equal length. The image frequency oscillation is produced by a relaxation oscillator 15, 16, 17, Fig. 8 in which the product of the resistance and capacity is smaller than that required to produce a straight line wave form. This oscillator is controlled by a source of frame synchronizing impulses 14 and feeds an amplifier 18 from whose output terminals 19 the oscillations are applied to deflect the beam. A similar source of line synchronizing impulses 20 controls a straight-line wave-form oscillator 21, 22, 24; the image frequency oscillation is introduced, over a potentiometer 34 and amplifier 35, to the point E to cause the amplitudes of the line frequency oscillations to vary as in curve 12, Fig. 6. These oscillations are amplified at 25 and mixed with image frequency oscillations derived from potentiometer 32 and fed to a pentode 29 from whose output terminals line oscillations of the form shown in curve 9, Fig. 6, are taken to deflect the scanning beam. The curvature of the wave form of Fig. 5 may be varied without variation of amplitude by varying the point at which condenser 36 is connected to resistance 17, while the amplitudes of both deflecting oscillations may be varied by variation of the potentials applied to resistances 17, 23. Distortion arising from loss of low-frequency components in the coupling between valves 21, 25 may be compensated by providing a coupling comprising a condenser 37, Fig. 9 and resistance 38, whose time constant is equal to that of the condenser 40 and resistance 42 in the input of a valve 41 feeding the image frequency oscillation into the output circuit of valve 25. Where the deflecting means are coils, an adjustable direct current may be superposed on the deflecting oscillations to enable the scanned area to be moved over the screen. In the case of the framing oscillations which have a resistance capacity output coupling, the terminals 19, Fig. 8, are connected to the input of an amplifier 54, Fig. 11, whose output circuit includes deflecting coils 46 and a tapping 55 on a potentiometer 56. Variation of the tapping 55 varies the direct current through the coils. In the case of the line frequency oscillations which have a transformer output coupling, the valve 29 Fig. 8, feeds a transformer 43, Fig. 10, having two secondaries 44 connected by the deflecting coils 46 of a mosaic screen transmitter and also by two further coils 53, of a local monitoring tube, which have tappings on a potentiometer 47 to control the direct current flowing in them. Specification 403,283 is referred to.