February 9th, 2008
Television (from Greek ???? – “far” and Latin “video” – “I see”) is a communication system for transmitting and receiving moving image and sound at a distance. Television is based on sequential transfer of frame elements by means of deflection. The image frequency is chosen predominantly on the basis of the motion translation smoothness criterion. To narrow the transmitting frequency band, the two-field interlace is applied, enabling to double the frame frequency (thus increasing the smoothness of translation of moving objects).
In a general arrangement, the television path (from light to light) includes the following devices:
Video camera. Its lens is projecting image onto some light-sensitive surface. A frame scanning circuit reads the brightness of image elements line after line. First, the odd-numbered lines are transmitted (1st field), then go even-numbered ones (2nd field). Color information is transmitted by means of subcarrier frequency. Thus, the frame of color total television signal frame (CTSF) is formed. Specialized document cameras are applied for filming and transmitting documents.
Video-tape recorder (not necessary). Records and reproduces interlace of lines and fields when needed.
Transmitter. Radio-frequency signal is modulated by television signal and transmitted to the air (translation via cable is possible). Sound is usually transmitted using different frequency by means of frequency modulation.
Receiver – TV set. With the help of sync pulses contained in CTSF, a television frame is being unfolded on the TV screen (kinescope, LCD panel, plasma panel).
Television technologies where not invented by a single person and at once. Television is based upon the discovery of photoelectric effect in selenium by Willoughby Smith in 1873. The invention of scanning disk by Paul Nipkov in 1884 gave impetus to development of mechanical television, which had been popular up to 1930-s. The Nipkov disc based systems were practically realized only in 1925 by J. Beard in Great Britain, Ch. Jankins in the USA, I.A. Adamyan and, independently by L. S. Termen in the USSR.
The first patent for the electronic television we use now was granted to Boris Rosing, Professor of the Saint Petersburg Technology Institute, who filed a patent application “The way of electric transfer of image” on July 25, 1907. However, he only succeeded in transfer of stationary image at a distance – in his trial on May 9, 1911. For the first time in history, moving image was transmitted at a distance on July 26, 1928 in Tashkent by inventors Boris Grabovsky and I. F. Belyansky. Though the statement of the Tashkent tram trust, based hereupon the trials were conducted, gives evidence of roughness and vagueness of the images received, the Tashkent trial should be considered the moment of birth of modern television.