| 摘要 |
1299756 Photo-electric apparatus VYZKUMNY USTAV ROZHLASU A TELEVISE 5 Jan 1970 [7 Jan 1969] 489/70 Heading G1A [Also in Divisions H1, H3 and H4] In a colour television apparatus having three (primary) colour signal channels and voltage responsive means for varying the gain in each channel, a single mobile control element is variably coupled to each of three fixed electric elements depending on its position, the coupling occurring without mechanical contact, and means responsive to such variable coupling provide each voltage responsive means with a correspondingly variable voltage in such a manner that the relative level of the colour signals is altered while maintaining constant the luminance level corresponding thereto. In one embodiment the fixed elements are three 120 degrees segments of a parallel disc capacitor (as described, only one disc is actually segmented) and the control element is a dielectric disc movable by a lever between the discs to vary the relative capacitances of the three sections, Fig.3 (not shown). Each capacitor forms part of a respective RC potential divider connected across a common 10 MHz oscillator, the tapped voltage being rectified to provide variable D.C. voltage, the sum of which is constant, and which are used to control variable gain amplifiers in the three channels Fig.4 (not shown). In a second embodiment, Fig.2 (not shown), a light source at the end of a lever is movable within an equilateral triangle having photo-transistors or photo-diodes at its apices to provide the variable voltages. For flying spot scanners the variable voltages can be used to control the voltages on the photomultipliers. |
