Monday, June 8, 2009

History Of Television Broadcasting

Television (TV) is a widely used telecommunication medium for transmitting and receiving moving images, either monochromatic ("black and white") or color, usually accompanied by sound. "Television" may also refer specifically to a television set, television programming or television transmission. The word is derived from mixed Latin and Greek roots, meaning "far sight": Greek tele (τῆλε), far, and Latin visio, sight (from video, vis- to see, or to view in the first person).
Commercially available since the late 1930s, the television set has become a common communications receiver in homes, businesses and institutions, particularly as a source of entertainment and news. Since the 1970s the availability of video cassettes, laserdiscs, DVDs and now Blu-ray discs, have resulted in the television set frequently being used for viewing recorded as well as broadcast material.
Although other forms such as closed-circuit television are in use, the most common usage of the medium is for broadcast television, which was modeled on the existing radio broadcasting systems developed in the 1920s, and uses high-powered radio-frequency transmitters to broadcast the television signal to individual TV receivers.
Broadcast TV is typically disseminated via radio transmissions in the 7-1000 megahertz-range of the FM frequency band[1]. Signals are now often transmitted with stereo and/or surround sound in many countries. Until the 2000s broadcast TV programs were generally recorded and transmitted as an analog signal, but in recent years public and commercial broadcasters have been progressively introducing digital television broadcasting technology.
A standard television set comprises multiple internal electronic circuits, including those for receiving and decoding broadcast signals. A visual display device which lacks a tuner is properly called a monitor, rather than a television. A television system may use different technical standards such as digital television (DTV) and high-definition television (HDTV). Television systems are also used for surveillance, industrial process control, and guiding of weapons, in places where direct observation is difficult or dangerous.
Amateur television (HAM TV or ATV) is also used for experimentation, pleasure and public service events by amateur radio operators. HAM TV stations were on the air in many cities before commercial TV stations came on the air .

In its early stages of development, television employed a combination of optical, mechanical and electronic technologies to capture, transmit and display a visual image. By the late 1920s, however, those employing only optical and electronic technologies were being explored. All modern television systems rely on the latter, although the knowledge gained from the work on mechanical-dependent systems was crucial in the development of fully electronic television.

The first time images were transmitted electrically were via early mechanical fax machines, including the pantelegraph, developed in the late 1800s. The concept of electrically-powered transmission of television images in motion, was first sketched in 1878 as the telephonoscope, shortly after the invention of the telephone. At the time, it was imagined by early science fiction authors, that someday that light could be transmitted over wires, as sounds were.[citation needed]
The idea of using scanning to transmit images was put to actual practical use in 1881 in the pantelegraph, through the use of a pendulum-based scanning mechanism. From this period forward, scanning in one form or another, has been used in nearly every image transmission technology to date, including television. This is the concept of "rasterization", the process of converting a visual image into a stream of electrical pulses.[citation needed]

In 1884 Paul Gottlieb Nipkow, a 20-year old university student in Germany, patented the first electromechanical television system which employed a scanning disk, a spinning disk with a series of holes spiraling toward the center, for rasterization. The holes were spaced at equal angular intervals such that in a single rotation the disk would allow light to pass through each hole and onto a light-sensitive selenium sensor which produced the electrical pulses. As an image was focused on the rotating disk, each hole captured a horizontal "slice" of the whole image, in a scanning fashion.[citation needed]

Nipkow's design would not be practical until advances in amplifier tube technology became available in 1907. Even then the device was only useful for transmitting still "halftone" images - represented by equally spaced dots of varying size - over telegraph or telephone lines. Later designs would use a rotating mirror-drum scanner to capture the image and a cathode ray tube (CRT) as a display device, but moving images were still not possible, due to the poor sensitivity of the selenium sensors.[citation needed]

Scottish inventor John Logie Baird demonstrated the transmission of moving silhouette images in London in 1925, and of moving, monochromatic images in 1926. Baird's scanning disk produced an image of 30 lines resolution, just enough to discern a human face, from a double spiral of lenses.[citation needed]. Remarkably, in 1927 Baird also invented the world's first video recording system, "Phonovision" -- by modulating the output signal of his TV camera down to the audio range he was able to capture the signal on a 10-inch wax audio disc using conventional audio recording technology. A handful of Baird's 'Phonovision' recordings survive and these were finally decoded and rendered into viewable images in the 1990s using modern digital signal-processing technology[3].
In 1926, Hungarian engineer Kálmán Tihanyi invented the entirely electronic camera tube and entirely electronic display and the transmitting and receiving system.[4][5][6][7]

By 1927, Russian inventor Léon Theremin developed a mirror drum-based television system which used interlacing to achieve an image resolution of 100 lines.[citation needed]

Also in 1927, Herbert E. Ives of Bell Labs transmitted moving images from a 50-aperture disk producing 16 frames per minute over a cable from Washington, DC to New York City, and via radio from Whippany, New Jersey. Ives used viewing screens as large as 24 by 30 inches (60 by 75 centimeters). His subjects included Secretary of Commerce Herbert Hoover.[citation needed]

In 1928, Philo Farnsworth made the world's first working television system with electronic scanning of both the pickup and display devices, which he first demonstrated to news media on 1 September 1928, televising a motion picture film.[citation needed]

The first practical use of television was in Germany. Regular television broadcasts began in Germany in 1929 and in 1936 the Olympic games in Berlin were broadcast to television stations in Berlin and Leipzig where the public could view the games live

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