video signal[′vid·ē·ō ‚sig·nəl]
an electrical signal designed to produce an image. A video signal is formed by photoelectric converters (a superorthicon or vidicon in television or a photoelectric cell or photomultiplier in picture transmission) or by the detection of electromagnetic waves received by a radar set.
In television the instantaneous values of the video signal at the output of the television camera tube are proportional to the brightness of individual parts of the optical image on its light-sensitive surface. The possible peak-to-peak values of a video signal in black-and-white and color television are limited by the levels of the black, which is the reference level (when the video signal is zero), and the white (the maximum value of the video signal). For television braodcasting systems the lowest frequency of the television signal spectrum is equal to the frame frequency (50-60 Hz), and the highest is the greatest frequency of the change in brightness of the transmitted image along a line (6-6.5 MHz). In picture trans-mission a light spot passes sequentially over a fixed image. The rays reflected from the latter impinge on a photoelectric converter, thus creating video signals. The highest frequency in the video-signal spectrum is a function of the rate at which the image is scanned and varies over a wide range (80 Hz to 6 kHz). The video signal in radar is in the form of pulses. The lowest video-signal frequency of the spectrum is equal to the repetition rate of the radiated pulses (50-400 Hz) and the highest is practically inversely proportional to the duration of the radiated pulse (1-10 MHz).
N. G. DERIUGIN