The Evolution of Mechanical television since 1843

Overview

The concept of television was created by many individuals in the late 19th and early 20th centuries, and its roots date back to the 18th century. The first practical transmissions of moving images via a radio system used mechanically rotating perforated plates to scan the scene into a time-varying signal that could be reconstructed at the receiver to approximate the original image. The development of television was interrupted by World War II. With the end of the war, fully electronic methods of scanning and displaying images became standard. Several different standards for adding color to transmitted images were developed in different regions using technically incompatible signal standards. Television broadcasts expanded rapidly after World War II and became an important mass media for advertising, propaganda, and entertainment.

Television broadcasts can be distributed over the air with VHF and UHF radio signals from terrestrial broadcasting stations, microwave signals from orbiting satellites, or wired to individual consumers via cable TV. Many countries have moved away from the original analog radio transmission methods and now use digital television standards that provide additional functionality and save radio frequency bandwidth for more profitable use. Television programs can also be distributed via the Internet.

Television broadcasts can be financed by advertising revenue, from private or public organizations willing to bear the costs, or in some countries by television license fees paid by the owners of the receivers. Some services, especially cable or satellite, are paid for by subscription.

Television broadcasting is supported by continuous technological developments, such as long-distance microwave networks, which allow programs to be distributed over a wide geographical area. Video recording methods allow programming to be edited and played back for later use. Three-dimensional television has been used commercially but has not received widespread consumer acceptance due to limitations in display methods.

Mechanical television

Fax transmission systems were pioneering methods for mechanically scanning graphics in the early 19th century. The Scottish inventor Alexander Bain introduced the fax machine between 1843 and 1846. English physicist Frederick Bakewell introduced a working laboratory version in 1851. The first practical fax system to operate on telegraph lines was developed and commissioned by the Italian priest Giovanni Caselli. from 1856 onwards.

The light electrical conductivity of selenium was discovered by English electrical engineer Willoughby Smith in 1873. This led, among other techniques, to telephoto, a way of sending still images over telephone lines as early as 1895, to all kinds of electronic imaging devices, both stationary and mobile, and eventually to TV cameras.

Nipkow’s record. This diagram shows the circular paths traced by the holes, which can also be square to increase accuracy. The black area of ​​the disc shows the scanned area.

The First Patent

As a 23-year-old German university student, Paul Julius Gottlieb Nipkow proposed and patented the Nipkow disc in 1884. This was a rotating disc with holes in a spiral, so each hole scanned a row of images. Although he never built a working system model,

The “image rasterizer” variations of Nipkow’s rotating disk became extremely common. Constantin Perskyi had coined the word television in a paper read to the International Electric Congress at the International World’s Fair in Paris on August 24, 1900. Persky’s article looked at existing electromechanical technologies and mentioned the work of Nipkow and others. However, it was not until 1907 that advances in reinforcing tube technology, including Lee de Forest and Arthur Korn, made the design practical.

Georges Rignoux and A. Fournier first introduced the direct transmission of images in Paris in 1909. The 64 selenium cell matrix, which was separately connected to a mechanical commutator, functioned as an electronic retina. At the receiver, a kind of Kerr cell modulates the light, and a series of mirrors at different angles attached to the edge of the rotating plate scanned the modulated beam onto the display screen. Separate circuit-controlled synchronization. The 8 × 8 pixel resolution on this concept screen was enough to convey clearly individual letters of the alphabet. An updated image was sent “multiple times” every second.

CRT Technology

In 1911, Boris Rosing and his student Vladimir Zworykin created a system that used a mechanical mirror drum scanner to transfer “very rough images” in Zworykin’s words along wires to a “Braun tube” (cathode ray tube or “CRT”). in the receiver. The transfer of moving images was not possible because the scanner “did not have sufficient sensitivity and the selenium cell was very delayed”.

In May 1914, Archibald Low presented his first television system at the Institute of Automobile Engineers in London. He called his system “Televista.” The events were widely covered worldwide and were usually covered by Seeing By Wireless. The demonstrations had impressed Harry Gordon Selfridge so much that he included Televista in his 1914 scientific and electronic exhibition in his shop. It was also of interest to Deputy Consul General Carl Raymond Loop, who completed the U.S. Consulate Report on London, which contained significant details of Low’s regime. Low’s invention used a matrix detector (the camera) and a mosaic display (receiver/viewer) with an electromechanical scanning mechanism that moved the rotating roller over the cell contacts, providing a multiplex signal to the camera /viewer data link. The receiver used a similar roller. The two rollers were synchronized. For this reason, it was different from any of the mid-20th century TV systems, and in many ways, Low had a digital TV system 80 years before the advent of today’s digital television. World War I began shortly after these demonstrations in London and Low participated in sensitive military work, so he did not apply for a patent until 1917. His “Televista” patent No. 191,405 entitled “Improved Device for Electronic Transmission of Optical Images” was finally published in 1923 – possibly The patent states that the scanning roller had a row of conductive contacts corresponding to the cells in each row in the array and arranged to take samples of each cell alternately as the roller rotated. says that … “The roller is driven at 3,000 rpm by a motor, and the resulting variations in light are transmitted along a normal conductive wire.”

The cell matrix disclosed in the patent is 22 × 22 (almost affecting 500 cells/pixels) and each “camera” cell had a corresponding “viewer” cell. Loop said it was “a screen divided into a large number of small squares of selenium,” and the patent states “every … space I place in a selenium cell.” Low covered the cells with liquid insulation and a roller connected each cell alternately through this medium as it rotates and passes over the table. The receiver used bimetallic elements that acted as shutters that “emitted more or less light according to the current flowing through them …”, as stated in the patent. Low said the biggest drawback of the system was the selenium cells used to convert light waves into electrical impulses, which reacted too slowly and spoiled the effect. Loop reports that “The system has been tested with a resistance equivalent to four miles, but Dr. Low believes there is no reason why it should not be as effective over much longer distances. The patent states that this connection could be either wired or wireless. the price is considerable because the conductive parts of the roll are made of platinum … “

In 1914, the demonstrations certainly received a lot of media interest, and The Times reported on May 30:

The inventor, Dr. A. M. Low, has found a way to transfer visual images with wire. If all goes well with this invention, we may soon show that we can see people from a distance.

The Daily Chronicle reported on May 29:

For the first time, Dr. Low gave a public presentation on a new device he has invented for the electric vision that allows people using the phone to see each other at the same time.

In 1927, Ronald Frank Tiltman asked Low to write an introduction to his book, in which he acknowledged Low’s work, referring to Low’s various related patents, and regretted that they were “too technical in nature to be incorporated.” Later, in his 1938 patent, Low envisioned a much higher cell density of the “camera” achieved by the deposition process of a cesium alloy on an insulating substrate, which was later cut to divide it into cells, which is the core of the state of the art. Low’s system failed for a number of reasons, mainly because it was unable to reproduce the image with reflected light and simultaneously capture shades of light and shadow. It can be added to the list of systems, such as Boris Rosing’s system, which mainly reproduced shadows. With subsequent technological advances, many such ideas could be implemented decades later, but they were impractical at the time.

In 1923, Scottish inventor John Logie Baird designed a complete television system using the Nipkow record. Nipkow’s was an obscure, forgotten patent and not at all obvious at the time. He created his first prototype in Hastings, where he was recovering from a serious illness. In late 1924 Baird returned to London to continue his experiments there. On March 25, 1925, Baird gave his first public presentation of televised silhouettes in motion at the Selfridge department store in London. Because the contrast of the human face was not enough to show up in his system at the moment, he televised the canopies, and by mid-1925 he named the head of the belly dummy “Stooky Bill,” whose face was painted to emphasize its contrast. “Stooky Bill” also didn’t complain about the long hours of staying in front of the blinding light level used in these experiments. On October 2, 1925, suddenly the doll’s head appeared on the screen incredibly clearly. On January 26, 1926, he presented images of real human faces sent to 40 respected scientists at the Royal Institute. This is widely regarded as the world’s first public television demonstration. Baird’s system used Nipkow disks to both scans and display the image. A brightly lit subject was placed in front of a series of rotating Nipkow plates with lenses that would scan images through a static photocell. It is currently believed that it was a thallium sulfide (Thalofide) cell developed by Theodore Case of the United States that detected light reflected from the subject. This was transmitted by radio to a receiver unit where the video signal was fed to a neon lamp behind a similar Nipkow disk synchronized with the first one. The brightness of the neon lamp was varied with respect to the brightness of each dot in the image. As each lens on the disc passed, one scan line was reproduced from the image. With this early device, Baird discs had 16 lenses, but along with the other discs used, a moving image with 32 scan lines was produced, enough to identify a human face. He started at a frame rate of five per second, which was soon raised to 121⁄2 frames per second and 30 scan lines.

First Broadcast

In 1927, Baird sent a signal over 438 miles (705 km) of telephone lines between London and Glasgow. In 1928, the Baird Television Development Company / Cinema Television broadcast the first transatlantic television signal between London and New York, as well as the first broadcast from the country to the ship. In 1929, he participated in the first experimental mechanical television service in Germany. In November of the same year, Baird and Bernard Natan Pathesta founded the first French television company, Télévision-Baird-Natan. In 1931, he made the first outdoor broadcast of Derby. In 1932, he introduced ultra-shortwave television. Baird Television Limited’s mechanical systems peaked at 240 lines of resolution at the company’s Crystal Palace studios and later on BBC television broadcasts in 1936, although in action images (unlike the seated presenter) the mechanical system did not scan the television scene. directly. Instead, a 17.5 mm film was imaged, developed rapidly, and then scanned while the film was still wet.

The success of the Scophony Company with its mechanical systems in the 1930s allowed them to export to the United States when World War II limited their business in Britain.

American inventor Charles Francis Jenkins was also a pioneer in television. He published an article on “Motion Pictures by Wireless” in 1913, but it was not until December 1923 that he transmitted moving silhouettes to witnesses. On June 13, 1925, Jenkins publicly introduced a synchronized transmission of silhouette images. In 1925, Jenkins used a Nipkow plate and transmitted a silhouette image of a moving toy windmill five miles away (from a naval radio station in his laboratory in Washington DC, Washington) using a plate scanner equipped with a lens. 48 line resolution. He was granted U.S. Patent 1,544,156 (Transmitting Pictures over Wireless) on June 30, 1925 (filed March 13, 1922).

The Termination

On December 25, 1926, Kenjiro Takayanagi introduced a television system with a 40-line resolution that used a Nipkow disk scanner and CRT monitor at Hamamatsu Industrial High School in Japan. This prototype is still on display at the Takayanagi Memorial Museum at Shamatsu University on the Hamamatsu campus. By 1927, Takayanagi improved the resolution to 100 lines, which was not exceeded until 1931. By 1928, he was the first to convey the human face in halftone. His work influenced the subsequent work of Vladimir K. Zworykin. In Japan, he is considered the man who made the first fully electronic television. His research to create a production model was halted by the US after Japan’s defeat in World War II

In 1927, a group of Bell Telephone Laboratories introduced a television broadcast from Washington to New York using a prototype using a flat-panel plasma display to make images visible to the public. The monochrome display measured two feet x three feet and had 2,500 pixels.

Herbert E. Ives and Frank Gray of Bell Telephone Laboratories dramatically introduced mechanical television on April 7, 1927. The reflected light television system included both small and large viewing screens. The small receiver had a screen two inches wide and 2.5 inches high. The large receiver had a screen 24 inches wide and 30 inches high. Both sets were

is capable of reproducing reasonably accurate, monochrome moving images. In addition to the images, the series also received synchronized sound. The system transmitted images along two routes: first a copper wire connection from Washington to New York City, then a radio link from Whippany to New Jersey. By comparing the two transmission methods, the viewers did not notice any difference in quality. The topics of the broadcast included Trade Minister Herbert Hoover. The beam of the flying dot scanner would illuminate these objects. The beam-producing scanner had a 50-slot plate. The disk rotates at 18 frames per second and captured one image at approximately 56-millisecond intervals. (Current systems typically send 30 or 60 frames per second, or one frame every 33.3 or 16.7 milliseconds.) Television historian Albert Abramson stressed the importance of the Bell Labs presentation: “It was, in fact, the best presentation of a mechanical television system ever. than any other system could even begin to compare it in image quality. “

In 1928, WRGB (then W2XB) was launched as the world’s first television station. It was shipped from General Electric’s plant in Schenectady, New York. It was commonly known as “WGY Television”.

Mirror-drum-based television

Meanwhile, in the Soviet Union, Léon Theremin had developed a mirror-drum-based television that began with 16-line resolution in 1925, then 32-line and finally 64-line interleaving in 1926. As part of his thesis on May 7, 1926, Theremin electronically transmitted and projected almost simultaneous moving images. foot square screen. By 1927, he had achieved a 100-line image, the resolution of which was not exceeded until 1931 by the RCA at 120 lines.

Because only a limited number of holes could be made in the discs and discs exceeding a certain diameter became impractical, the picture resolution of mechanical television transmissions was relatively low, ranging from about 30 lines to about 120. Nevertheless, the picture quality of 30-Line broadcasts was constantly improving with technological advances, and by 1933, broadcasts using the British Baird system were remarkably clear. A few systems spanning 200 lines in the area were also broadcast. Two of these were the 180-line system installed by the Compagnie des Compteurs (CDC) in Paris in 1935, and the 180-line system started by Peck Television Corp. in 1935 at the VE9AK station in Montreal.

Anton Codelli (March 22, 1875 – April 28, 1954), a Slovenian nobleman, was a passionate inventor. Among other things, he had designed a miniature refrigerator for cars and a new rotating engine. Interested in television, he decided to apply his technical skills to new media. At the time, the biggest challenge for television technology was to transmit images with sufficient resolution to reproduce recognizable characters. As media historian Melita Zajc said, most inventors had decided to increase the number of lines used by their systems – some approached the magical number of 100 lines at the time. But Baron Codell had a different view. In 1929, he developed a television set that had a single line – but that formed a continuous spiral on the screen. Codelli was based on understanding his ingenious design from the human eye. He knew that subjects in peripheral vision did not have to be as sharp as subjects in the middle. The Baron’s mechanical television system, with the sharpest image in the middle, worked well, and he was soon able to transmit images of his wife Ilona von Drasche-Lazar in the air. However, despite the support of the German electronics giant Telefunken, Codell’s television system never became a commercial reality. Electronic television eventually became the dominant system, and Codelli moved on to other projects. His invention was largely forgotten.

Conclusion

The development of fully electronic television (including picture dissectors and other camera tubes and cathode-ray tubes) marked the beginning of the end for mechanical systems as the dominant form of television. Mechanical TV usually produced only small images. It was the main type of television until the 1930s. The last mechanical television broadcasts ended in 1939 on a handful of stations maintained by U.S. public universities.

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