a) Very rare photography of an early 1929 telecast from General Electric's WGY studios in Schenectady. Radio News

The high-frequency oscillation radiated by the transmitter could be modulated in accordance with the variations in beam current of the television camera, and thus it was possible the wireless transmission of audio and video signals. However, since the image was scanned in very high speed, in order to avoid the flickering effect, the zigzag pattern on the screen must be repeated 25 times per second. In the same time to ensure sufficient image sharpness, it was necessary that 500.000 dots on the screen should be scanned and reproduced, meaning that an information datum should pass about 25 x 500000 = 12.500000 times per second. As aforeseen the movement of the electron beam in the kinescope was rapid enough, however, to ensure a satisfactory reproduction of the video signals transmission was only possible if the transmission frequency were a multiple of the modulation frequency. In this way through many theorical and practical researches the engineers soon found that for the proper video signals transmission it was necessary a minimum frequency of 50 MHz, or a maximum wavelenght of 6 meter. The development of the new field of ultra shortwave radio, giving birth of the so-called high frequency valves, which largely contributed to

(b) The all-electronic television system developed by Farnsworth circa 1937.

handle the transmitting and receiving of the video signals in such frequency range. As aforementioned, since 1929 television transmissions had taken place in Europe, initially by using mechanical system with rotating mirrors. However, Philo Farnsworth in the USA developed the first all-electronic television system. (b) The beginning of the WWII put an end to the so many researches in the television field. In 1946, just after the war, the first transmissions systems using 405, 525, 819 and 625 lines per second were standardized and adopted respectively by England, USA, France and other European countries. Around 1950 the black and white televison was already an important mass communication mean. However, another fanstastic technological step was under preparation in many researches laboratories all over the world through the development of the wireless transmission of the colored images.