GB402134A - Improvements relating to electrical circuits for producing oscillations of non-sinusoidal wave form for use, for example, with cathode ray devices - Google Patents

Abstract

402,134. Television. ELECTRIC & MUSICAL INDUSTRIES, Ltd., Hayes, Middlesex, and MANIFOLD, M. BOWMAN-, Heathcot, Worplesdon Station, Surrey. May 26, 1932, No. 15011. [Classes 40 (iii) and 40 (v).] Brief recurrent impulses are produced and transmitted for synchronizing a cathode - ray television receiver which employs voltage of saw-toothed waveform for scanning. Generating synchronizing impulses. At a transmitter, pulses Vg1 Fig. 2, are supplied to terminals 1, 2, Fig. 1, from a photo-electric cell controlled by a rotating disc with apertures. At a receiver, these impulses are derived from the received synchronizing signals. In both cases they sustain in the tuned anode circuit 3, 4, sinusoidal impulses Vg2. Valve V2 is negatively biased from terminal 9 so that only the peaks x, x, of the grid voltage are effective. The anode current and voltage of valve V2 are therefore as shown at Ia2, Va2. The impulses pass to the grid of valve V3 through a resistance-capacity combination C, R, having a small time constant, and the resulting wave-form of the grid voltage is as at Vg3. The grid is biased so that only the peaks y, y, are effective. The output from terminals 6, 10 is applied to a transmitter or to a generator of saw-toothed waves. In modifications, (1) an inductance 11 may be shunted on the anode resistance so that the combination may have a small time-constant, and the timeconstant of the condenser coupling need not then be small; (2) a resistance-and-transformer coupling with small time-constant may replace the capacity coupling (Fig. 3, not shown) ; (3) in order that the peaks Vg3 may be brought into phase with the impulses Vg1, a lag of 90‹ may be added by tapping the grid-voltage for valve V2 off a resistance in series with inductance 4, as at 21, Fig. 4. Producing saw-toothed waves for scanning. At the receiver synchronizing impulses denoting line-frequency and frame-frequency are received on a sub-carrier which is separated from the picture currents after demodulation and is applied to terminals 13, 14. The sub-carrier is demodulated by valve V5 and the frame impulses are applied to valve V1, the impedances 15, 19, 20, being designed to separate the line impulses from the frame impulses. Valve V6 is normally non-conducting and permits condenser 16 to become charged through resistance 17 ; on receipt of the synchronizing impulse the condenser discharges through the valve. The saw-toothed wave is passed through valve V7 to the deflecting-coils 18 of the cathode-ray oscillograph, these coils being of such low inductance that the current wave is shaped like the voltage wave. The line impulses applied to valve VI are dealt with by valves V1, V2, in the manner described with reference to Fig. 1, so that the input to valve V3 comprises short impulses y, y, and the saw-toothed wave is produced by the charging and discharging of condensers 26, 27. The inductance of the deflecting-coils 22 distorts the signals and this distortion is neutralized bv means of the resistance-capacity combination 26, 27, 28. Specification 401,634 is referred to.