Consumer Electronics

THE HIGHEST VIDEO FREQUENCY

For the picture to be reproduced with sufficient sharpness and wealth of detail, its area must be split up into about 400,000 elements. At the rate of 25 pictures a second, a total of 10,000,000 of these elements will have to be scanned per second. Let us assume an extreme case in which all the elements are alternately bright and dark. The picture signal—the voltage derived from the camera tube—would then be a toothed wave, with five million positive teeth and five million negative gaps, part of which is shown in Fig. 30.16.

Let us further replace this toothed wave with a sine wave (dotted line). This sinusoidal oscillation represents a frequency of 5 MHz. An alternating voltage, with this frequency, is the most rapidly ...