GB678034A - Improvements in or relating to television receivers - Google Patents

Abstract

678,034. Television. MASTERADIO, Ltd. March 19, 1951 [March 17, 1950], No. 6716/50. Class 40 (iii). [Also in Group XL (c)] In a television receiver, the central portion of the image is magnified by modifying the line saw-tooth current wave-form so that the central range has an increased velocity, and to limit the image distortion thereby introduced the frame wave-form is modified similarly or subjected to an amplitude increase. In the Figures, the deflection coil 1 is driven with a saw-tooth current 7 to which is added suitably phased half sine-wave current 9 derived from resonant circuit 5, 6 via diode 3, the resulting wave-form 11 having an increased rate of scan over the central range 10. The diode 3 also functions as the conventional energy restoring diode, the impulses passing through the diode when the field in the deflector coil collapses, shock exciting the tuned circuit. A switch 13 or 14 is provided to cut out inductor 5 or add extra capacity and so remove the modifying wave-form to allow the scan circuit to operate normally. An additional switch (not shown) controls the height of the frame scan by adding a small amount of negative feedback or by other means. In another embodiment, Fig. 1 (part not shown), the resonant circuit is energized by coupling from the scanning generator or an oscillator tuned to the same frequency.