GB1230041A - - Google Patents

Abstract

1,230,041. Tuning indicators; pulse modulation circuits. MITSUBISHI DENKI K.K. 23 Jan., 1969 [23 Jan., 1968; 24 Jan., 1968; 26 Jan., 1968], No. 3764/69. Headings H3Q and H4L. A timing indicator device for a television receiver comprises means for establishing a magnetic field having a strength varying in accordance with the correctness of tuning, and pulse-generating means disposed in the magnetic field and including a saturable magnetic core, having a first winding connected to a source of saw-tooth current provided by an output of a horizontal deflection circuit, and a second winding to produce one pulse signal in each horizontal scan interval, the pulse signal having a duration controlled by the strength of the magnetic field. Toroidal saturable core 10 carries an input winding 14 which is fed with a saw-tooth current (20, Fig. 2, not shown), i.e. the line scan, being connected in series with the line deflection coils 52. Due to saturation in the core, a corresponding train of rectangular pulses is obtained in output winding 16, the width of which is dependent upon the direct current in winding 18 on a U-shaped magnet 12. between the limbs of which the core 10 is positioned. The current in winding 18 is derived from a D.C. amplifier 66 coupled to a detector 64, which is fed from a narrow-band video I.F. amplifier 62 branched off at the video detector 34 of the receiver. Simultaneous closure of switches 70, 72 which respectively apply power from power source 68 to narrow band amplifier 62 and the output from winding 16 to the picture tube 40, via video amplifier 36, produces on the picture tube a vertical line (74, Figs. 5 (a), 5 (b), not shown) derived from the positive-going of the pulses in winding 16, the position on the tube being constant but the width of which varies in accordance with the accuracy of tuning.