Television Picture Tube: An ordinary TV picture tube, however, is a bulky vacuum tube and requires relatively high power for its operation. Researchers are attempting to replace the TV tube with a thin, flat display panel requiring no vacuum. This panel, the "solid-state picture tube," operates on a principle known as electroluminescence, a phenomenon in which certain materials, such as zinc sulfide and semiconductor p-n junctions, emit light when an appropriate voltage is applied across the material.
Indicator.-The indicator displays all the information gathered by the radar and usually provides a mounting for most of the operating controls. In addition, it contains the precision time-measuring circuits that determine the ranges of the targets detected by the radar. The basic device used for displaying the information is ordinarily a cathode ray tube, similar to the picture tube of a television picture tube receiver, though generally much smaller.
Every electronic instrument, however, whether a TV receiver or a complex computer, must have an input and an output device that "connects" with the outside world. In the TV receiver, for example, the input is the antenna and the output is the picture tube. For the computer, the input device may be a typewriter or a magnetic tape, while the output may be sheets of paper printed by a typewriter, or a TV-like picture on a cathode ray tube.
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