TEST CARD
All TV stations transmit a tuning signal for some time before the start of the program proper, to facilitate the tuning in of receivers. The signal takes the form of a Test Card which, besides other geometrical figures, such as checker board pattern, always includes one or more circles and both horizontal and vertical patterns of lines. The circles and other geometrical figures aid in the correction, where necessary, of frame linearity and of aspect ratio. The vertical pattern of lines serves for the fine tuning of channel selector, and the horizontal one for the accurate adjustment of the spacing. Fig. 30.12 shows a test card offering a particularly wide range of possibilities.
You can receive the correct aspect ratio by adjusting ...
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