Television

The invention:



System that converts moving pictures and sounds

into electronic signals that can be broadcast at great distances.



The people behind the invention:



Vladimir Zworykin (1889-1982), a Soviet electronic engineer and

recipient of the National Medal of Science in 1967

Paul Gottlieb Nipkow (1860-1940), a German engineer and

inventor

Alan A. Campbell Swinton (1863-1930), a Scottish engineer and

Fellow of the Royal Society

Charles F. Jenkins (1867-1934), an American physicist, engineer,

and inventor










The Persistence of Vision



In 1894, an American inventor, Charles F. Jenkins, described a

scheme for electrically transmitting moving pictures. Jenkins’s idea,

however, was only one in an already long tradition of theoretical

television systems. In 1842, for example, the English physicist Alexander

Bain had invented an automatic copying telegraph for sending

still pictures. Bain’s system scanned images line by line. Similarly,

the wide recognition of the persistence of vision—the mind’s

ability to retain a visual image for a short period of time after the image

has been removed—led to experiments with systems in which

the image to be projected was repeatedly scanned line by line. Rapid

scanning of images became the underlying principle of all television

systems, both electromechanical and all-electronic.

In 1884, a German inventor, Paul Gottlieb Nipkow, patented a

complete television system that utilized a mechanical sequential

scanning system and a photoelectric cell sensitized with selenium

for transmission. The selenium photoelectric cell converted the light

values of the image being scanned into electrical impulses to be

transmitted to a receiver where the process would be reversed. The

electrical impulses led to light of varying brightnesses being produced

and projected on to a rotating disk that was scanned to reproduce

the original image. If the system—that is, the transmitter and

the receiver—were in perfect synchronization and if the disk rotated

quickly enough, persistence of vision enabled the viewer to

see a complete image rather than a series of moving points of light.

For a television image to be projected onto a screen of reasonable

size and retain good quality and high resolution, any system employing

only thirty to one hundred lines (as early mechanical systems

did) is inadequate.A few systems were developed that utilized

two hundred or more lines, but the difficulties these presented

made the possibility of an all-electronic system increasingly attractive.

These difficulties were not generally recognized until the early

1930’s, when television began to move out of the laboratory and into

commercial production.

Interest in all-electronic television paralleled interest in mechanical

systems, but solutions to technical problems proved harder to

achieve. In 1908, a Scottish engineer, Alan A. Campbell Swinton,

proposed what was essentially an all-electronic television system.

Swinton theorized that the use of magnetically deflected cathode-ray

tubes for both the transmitter and receiver in a system was possible.

In 1911, Swinton formally presented his idea to the Röntgen

Society in London, but the technology available did not allow for

practical experiments.





Zworykin’s Picture Tube

In 1923, Vladimir Zworykin, a Soviet electronic engineer working

for the Westinghouse Electric Corporation, filed a patent application

for the “iconoscope,” or television transmission tube. On

March 17, 1924, Zworykin applied for a patent for a two-way system.

The first cathode-ray tube receiver had a cathode, a modulating

grid, an anode, and a fluorescent screen.

Zworykin later admitted that the results were very poor and the

system, as shown, was still far removed from a practical television

system. Zworykin’s employers were so unimpressed that they admonished

him to forget television and work on something more

useful. Zworykin’s interest in television was thereafter confined to

his non working hours, as he spent the next year working on photographic

sound recording.

It was not until the late 1920’s that he was able to devote his full

attention to television. Ironically, Westinghouse had by then resumed

research in television, but Zworykin was not part of the

team. After he returned from a trip to France, where in 1928 he had

witnessed an exciting demonstration of an electrostatic tube, Westinghouse

indicated that it was not interested. This lack of corporate

support in Pittsburgh led Zworykin to approach the Radio Corporation

of America (RCA). According to reports, Zworykin demonstrated

his system to the Institute of Radio Engineers at Rochester,

New York, on November 18, 1929, claiming to have developed a

working picture tube, a tube that would revolutionize television development.

Finally, RCA recognized the potential.



Impact





The picture tube, or “kinescope,” developed by Zworykin changed

the history of television. Within a few years, mechanical systems

disappeared and television technology began to utilize systems

similar to Zworykin’s by use of cathode-ray tubes at both ends of

the system. At the transmitter, the image is focused upon a mosaic

screen composed of light-sensitive cells.A stream of electrons sweeps

the image, and each cell sends off an electric current pulse as it is hit

by the electrons, the light and shade of the focused image regulating

the amount of current.

This string of electrical impulses, after amplification and modification

into ultrahigh frequency wavelengths, is broadcast by antenna

to be picked up by any attuned receiver, where it is retransformed

into a moving picture in the cathode-ray tube receiver. The

cathode-ray tubes contain no moving parts, as the electron stream is

guided entirely by electric attraction.

Although both the iconoscope and the kinescope were far from

perfect when Zworykin initially demonstrated them, they set the

stage for all future television development.





Vladimir Zworykin



Born in 1889, Vladimir Kosma Zworykin grew up in Murom,

a small town two hundred miles east of Moscow. His father ran

a riverboat service, and Zworykin sometimes helped him, but

his mind was on electricity, which he studied on his own while

aboard his father’s boats. In 1906, he entered the St. Petersburg

Institute of Technology, and there he became acquainted with

the idea of television through the work of Professor Boris von

Rosing.

Zworykin assisted Rosing in his attempts to transmit pictures

with a cathode-ray tube. He served with the Russian Signal

Corps during World War I, but then fled to the United States

after the Bolshevist Revolution. In 1920 he got a job at Westinghouse’s

research laboratory in Pittsburgh, helping develop radio

tubes and photoelectric cells. He became an American citizen

in 1924 and completed a doctorate at the University of

Pittsburgh in 1926. By then he had already demonstrated his

iconoscope and applied for a patent. Unable to interest Westinghouse

in his invention, he moved to the Radio Corporation

of America (RCA) in 1929, and later became director of its electronics

research laboratory. RCA’s president, David Sarnoff,

also a Russian immigrant, had faith in Zworykin and his ideas.

Before Zworykin retired in 1954, RCA had invested $50 million

in television.

Among the many awards Zworykin received for his culture changing

invention was the National Medal of Science, presented

by President Lyndon Johnson in 1966. Zworykin died on

his birthday in 1982





See also : Color television; Community antenna television; Communications

satellite; Fiber-optics; FM radio; Holography; Internet;

Radio; Talking motion pictures.