Radio communication and television

In television the picture is turned into an electrical signal by a video camera: the frame is divided into very many small points and their brightness is read out one after another as a signal. This video signal is amplified and added through a modulator to the high-frequency oscillations of a generator; the sound signal is modulated separately, and both are fed to the antenna. In the television set the antenna picks up the signal, the input circuit is tuned to resonance with the wanted channel, an amplifier and detector separate the picture and sound signals; the picture goes to the screen and the sound to the loudspeaker. If 25–30 frames are shown per second the eye sees continuous motion. The fast-oscillating waves carried by television channels (tens to hundreds of MHz and higher) travel only as far as the line of sight because of the curvature of the Earth: for an antenna height h and Earth radius R the range is about √(2Rh), which is why transmitters are placed on tall towers or the signal is relayed by satellite. On 26 July 1928 in Tashkent B. P. Grabovsky and I. F. Belyansky transmitted the moving image of a person with their «Telefot» apparatus; television was developed through the efforts of many inventors in many countries.