Patent GB-628249-A (GB)
Title: Improvements in or relating to deflection signal generator for polar scanning of cathode ray tubes
IPC: H03K4/12
Filed: 1945-10-24
Abstract: 628,249. Radiolocation; sawtooth generating circuits. PHILCO RADIO & TELEVISION CORPORATION. Oct. 24, 1945, No. 28120. Convention date, April 25, 1944. [Classes 40 (vi) and 40 (vii)] A rotating radial scan for a cathode-ray beam, particularly for a radar plan-position-indicator, is produced by generating an alternating voltage-wave Ko, Fig. 2, having a rising wavefront and a steep wave-back in each half-cycle, obtaining from it two pairs of saw-tooth voltages of opposite polarity, cyclically varying said pairs of voltages and applying them to the pairs of deflecting plates. In the system shown, Fig. 1, oppositelyphased square waves from the multivibrator 11, 12 are fed to cut-off valves 13, 22 so that rising sawtooth voltage waves are developed across condensers 17 and 25 during alternate half-cycles of the square wave. The two sawtooth waves, after reversal of that developed across condenser 25 in valve 27, are combined in the common load-resistance 20 of the two cathode followers 19, 28 to produce the wave Ko. This wave, after amplification at 29, is fed to a phase-splitting valve 30, the oppositely-phased waves across resistors 31 and 32 being fed through condensers 45 and 46 to the grid of a phase-splitting stage 39, and also through condensers 47 and 48 to the grid of another phase-splitting stage 42. Condensers 46-48 are variable, with their rotors ganged and driven by a motor M. The rotors of each pair 45, 46 and 47, 48 are so arranged that they vary in opposite directions; maximum capacity of 45 corresponding to minimum capacity of 46 &c. Also the rotors of 45 and 46 are arranged to be in quadrature with the rotors of 47, 48. The effect of the condenser rotation is that the resultant sawtooth wave fed to stage 39 varies from a maximum amplitude through zero to a maximum amplitude in the opposite direction at the speed of rotation of the condensers, which is very much less than the sawtooth recurrence frequency. The oppositely-phased outputs from stage 39 are fed to a push-pull deflectionvoltage amplifier 37, 38 feeding one pair of deflector plates 33, 34 of the cathode-ray tube. The outputs from stage 42 similarly. feed the push-pull amplifier 40, 41 supplying the other deflector plates 35, 36. Due to the quadrature relationship of the two pairs of condenser rotors a diametral trace is thus produced on the cathode-ray tube screen which rotates in step with the condenser rotors. If a radial trace only is required, the trace due to one half of the combined wave fed to the amplifier 29 may be blacked out by a square wave voltage fed to the cathode-ray tube from the multivibrator via tube 57. The linearity of the traces may be adjusted by potential dividers 18, 26, an exponential trace with greater speed near the centre of the screen being produced if desired by reduction of the charging voltages supplied to the sawtooth generating circuits. The Specification states that resistance potential-dividers may be used in place of the ganged variable condensers 45-48, and that the circuit may be modified for electromagnetic deflection systems.