90th Anniversary of the first mechanical TV demonstration

Mechanical television: 90th anniversary of first mechanical television demonstration

Update: This Doodle was canceled by Google. The reason could be the crash of a German plane in the French Alps.


 

Mechanical television or mechanical scan television is a television system that relies on a mechanical scanning device, such as a rotating disk with holes in it or a rotating mirror, to scan the scene and generate the video signal, and a similar mechanical device at the receiver to display the picture. This contrasts with modern television technology, which uses electronic scanning methods, for example electron beams in cathode ray tube (CRT) televisions, and LCD displays, to create and display the picture.

90th Anniversary of the first mechanical TV demonstration

90th Anniversary of the first mechanical TV demonstration: Google Doodle

Mechanical-scanning methods were used in the earliest television systems in 1920s and 1930s. By late 1920s many radio stations were broadcasting experimental television programs using mechanical systems. However the technology never produced high enough quality images to become popular with the public. Mechanical-scan systems were largely superseded by electronic-scan technology in the late 1930s, which was used in the first commercially successful television breadcasts which began in the late 1940s.

A mechanical television receiver is also called a televisor in some countries.

 History of the Mechanical television

Early research

Invention of the television was work of many people in the 19th century and early 20th century.

Facsimile transmission systems for still photographs pioneered methods of mechanical scanning of images in early 19th century. Alexander Bain introduced the facsimile machine in 1843 to 1846. Frederick Bakewell demonstrated a working laboratory version in 1851.

Willoughby Smith discovered the photoconductivity of the element selenium in 1873, laying the groundwork for the selenium cell phototube which was used as a pickup in most mechanical scan systems.

As a 23-year-old German university student, Paul Julius Gottlieb Nipkow proposed and patented the Nipkow disk in 1884. This was a spinning disk with a spiral pattern of holes in it, so each hole scanned a line of the image. Although he never built a working model of the system, Nipkow’s spinning-disk “image rasterizer” was the key mechanism used in most mechanical scan systems, in both the transmitter and receiver.  Constantin Perskyi had coined the word television in a paper read to the International Electricity Congress at the International World Fair in Paris on August 25, 1900. Perskyi’s paper reviewed the existing electromechanical technologies, mentioning the work of Nipkow and others. However, it was not until 1907 that developments in amplification tube technology, by Lee de Forest and Arthur Korn among others, made the design practical.

The first demonstration of the instantaneous transmission of images was by Georges Rignoux and A. Fournier in Paris in 1909. A matrix of 64 selenium cells, individually wired to a mechanical commutator, served as an electronic retina. In the receiver, a type of Kerr cell modulated the light and a series of variously angled mirrors attached to the edge of a rotating disc scanned the modulated beam onto the display screen. A separate circuit regulated synchronization. The 8×8 pixel resolution in this proof-of-concept demonstration was just sufficient to clearly transmit individual letters of the alphabet. An updated image was transmitted “several times” each second.

In 1911, Boris Rosing and his student Vladimir Zworykin created a system that used a mechanical mirror-drum scanner to transmit, in Zworykin’s words, “very crude images” over wires to the “Braun tube” (cathode ray tube or “CRT”) in the receiver. Moving images were not possible because, in the scanner, “the sensitivity was not enough and the selenium cell was very laggy”.

Mechanical Television

Mechanical Television Diagram: Google Doodle

Television demonstrations

By the 1920s when amplification made television practical, Baird employed the Nipkow disk in his prototype video systems. On March 25, 1925, Scottish inventor John Logie Baird gave the first public demonstration of televised silhouette images in motion, at Selfridge’s Department Store in London.  Since human faces had inadequate contrast to show up on his primitive system, he televised a ventriloquist’s dummy named “Stooky Bill” talking and moving, whose painted face had higher contrast. By January 26, 1926 he demonstrated the transmission of image of a face in motion by radio. This is widely regarded as first television demonstration. Baird’s system used the Nipkow disk for both scanning the image and displaying it. A bright light shining through a spinning Nipkow disk set with lenses projected a bright spot of light which swept across the subject. Selenium photoelectric tube detected the light reflected from the subject and converted it into a proportional electrical signal. This was transmitted by AM radio waves to a receiver unit, where the video signal was applied to a neon light behind a second Nipkow disk rotating synchronized with the first. The brightness of the neon lamp was varied in proportion to the brightness of each spot on the image. As each hole in the disk passed by, one scan line of the image was reproduced. Baird’s disk had 30 holes, producing an image with only 30 scan lines, just enough to recognize a human face. In 1927, Baird transmitted a signal over 438 miles (705 km) of telephone line between London and Glasgow. In 1928, Baird’s company (Baird Television Development Company/Cinema Television) broadcast the first transatlantic television signal, between London and New York, and the first shore-to-ship transmission. In 1929, he became involved in the first experimental mechanical television service in Germany. In November of the same year, Baird and Bernard Natan of Pathé established France’s first television company, Télévision-Baird-Natan. In 1931, he made the first outdoor remote broadcast, of the Epsom Derby. In 1932, he demonstrated ultra-short wave television. Baird’s mechanical system reached a peak of 240-lines of resolution on BBC television broadcasts in 1936 though the mechanical system did not scan the televised scene directly. Instead a 17.5mm film was shot, rapidly developed and then scanned while the film was still wet.

An American inventor, Charles Francis Jenkins also pioneered the television. He published an article on “Motion Pictures by Wireless” in 1913, but it was not until 1923 that he transmitted moving silhouette images for witnesses, and it was on June 13th, 1925 that he publicly demonstrated synchronized transmission of silhouette pictures. In 1925 Jenkins used Nipkow disk and transmitted the silhouette image of a toy windmill in motion, over a distance of five miles from a naval radio station in Maryland to his laboratory in Washington, D.C., using a lensed disk scanner with a 48-line resolution. He was granted the U.S. patent No. 1,544,156 (Transmitting Pictures over Wireless) on June 30, 1925 (filed March 13, 1922).

Herbert E. Ives and Frank Gray of Bell Telephone Laboratories gave a dramatic demonstration of mechanical television on April 7, 1927. The reflected-light television system included both small and large viewing screens. The small receiver had a two-inch-wide by 2.5-inch-high screen. The large receiver had a screen 24 inches wide by 30 inches high. Both sets were capable of reproducing reasonably accurate, monochromatic moving images. Along with the pictures, the sets also received synchronized sound. The system transmitted images over two paths: first, a copper wire link from Washington to New York City, then a radio link from Whippany, New Jersey. Comparing the two transmission methods, viewers noted no difference in quality. Subjects of the telecast included Secretary of Commerce Herbert Hoover. A flying-spot scanner beam illuminated these subjects. The scanner that produced the beam had a 50-aperture disk. The disc revolved at a rate of 18 frames per second, capturing one frame about every 56 milliseconds. (Today’s systems typically transmit 30 or 60 frames per second, or one frame every 33.3 or 16.7 milliseconds respectively.) Television historian Albert Abramson underscored the significance of the Bell Labs demonstration: “It was in fact the best demonstration of a mechanical television system ever made to this time. It would be several years before any other system could even begin to compare with it in picture quality.”

In 1928, WRGB then W2XB was started as world’s first television station. It broadcast from the General Electric facility in Schenectady, NY. It was popularly known as “WGY Television”.

Meanwhile in the Soviet Union, Léon Theremin had been developing a mirror drum-based television, starting with 16 lines resolution in 1925, then 32 lines and eventually 64 using interlacing in 1926, and as part of his thesis on May 7, 1926 he electrically transmitted and then projected near-simultaneous moving images on a five foot square screen. By 1927 he achieved an image of 100 lines, a resolution that was not surpassed until 1931 by RCA, with 120 lines.

On December 25, 1925, Kenjiro Takayanagi demonstrated a television system with a 40-line resolution that employed a Nipkow disk scanner and CRT display at Hamamatsu Industrial High School in Japan. This prototype is still on display at the Takayanagi Memorial Museum in Shizuoka University, Hamamatsu Campus. His research in creating a production model was halted by the US after Japan lost World War II.

Because only a limited number of holes could be made in the disks, and disks beyond a certain diameter became impractical, image resolution on mechanical television broadcasts was relatively low, ranging from about 30 lines up to 120 or so. Nevertheless, the image quality of 30-line transmissions steadily improved with technical advances, and by 1933 the UK broadcasts using the Baird system were remarkably clear. A few systems ranging into the 200-line region also went on the air. Two of these were the 180-line system that Compagnie des Compteurs (CDC) installed in Paris in 1935, and the 180-line system that Peck Television Corp. started in 1935 at station VE9AK in Montreal.

 

Country list of the Mechanical television Google Doodle

Argentina, Armenia, Austria, Benin, Brazil, Bulgaria, Burkina Faso, Burundi, Cameroon, Canada, Central African Republic, Chad, Chile, Colombia, Congo (DRC), Congo (Republic), Côte d’Ivoire, Finland, France, Gabon, Georgia, Ghana, Hong Kong, Iceland, Indonesia, Ireland, Israel, Italy, Japan, Kenya, Latvia, Madagascar, Malaysia, Mali, Mauritius, Mexico, Niger, Nigeria, Norway, Peru, Portugal, Senegal, Serbia, South Africa, South Korea, Spain, Sweden, Switzerland, Taiwan, Togo, United Kingdom and Uruguay

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