The history of television technology is both complex and far-reaching, involving the work of many inventors and engineers in several countries over many decades. Initially, work proceeded along two different but overlapping lines of development: those designs employing both mechanical and electronic principles, and those employing only electronic principles. Electromechanical television would eventually be abandoned in favor of fully electronic designs.

Electromechanical Television

The origins of what would become today’s television system can be traced back to the discovery of the photoconductivity of the element selenium by Willoughby Smith in 1873, the invention of a scanning disk by Paul Gottlieb Nipkow in 1884, John Logie Baird’s demonstration of televised moving images in 1926 and Philo Farnsworth’s Image dissector in 1927.

The 20-year old German university student Nipkow proposed and patented the first electromechanical television system in 1884,[1] although he never built a working model of the system. Nipkow’s spinning disk design is credited with being the first television image rasterizer. 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. The photoconductivity of selenium and Nipkow’s scanning disk were first joined for practical use in the electronic transmission of still pictures and photographs, and by the first decade of the 20th century halftone photographs, composed of equally spaced dots of varying size, were being transmitted by facsimile over telegraph and telephone lines as a newspaper service.

However, it wasn’t until 1907 that developments in amplification tube technology made the design practical. The first demonstration of the instantaneous transmission of still silhouette images was by Georges Rignoux and A. Fournier in Paris in 1909, using a rotating mirror-drum as the scanner, and a matrix of 64 selenium cells as the receiver.

In 1911, Boris Rosing and his student Vladimir Kosma Zworykin created a television system that used a mechanical mirror-drum scanner to transmit, in Zworykin’s words, “very crude images” over wires to the electronic 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”.

On March 25, 1925, Scottish inventor John Logie Baird gave a demonstration of televised silhouette images in motion at Selfridge’s Department Store in London. AT&T’s Bell Telephone Laboratories transmitted halftone still images of transparencies in May 1925. Charles Francis Jenkins was able to demonstrate on June 13, 1925, the transmission of the silhouette image of a toy windmill in motion from a naval radio station to his laboratory in Washington, using a lensed disk scanner with 48 lines per picture, 16 pictures per second. But if television is defined as the live transmission of moving images with continuous tonal variation, Baird first achieved this privately on October 2, 1925. But strictly speaking, Baird had not yet achieved moving images on October 2. His scanner worked at only five images per second, below the threshold required to give the illusion of motion, usually defined as at least 12 images per second. By January, he had improved the scan rate to 12.5 images per second. Then he gave the world’s first public demonstration of a working television system to members of the Royal Institution and a newspaper reporter on January 26, 1926 at his laboratory in London. Unlike later electronic systems with several hundred lines of resolution, Baird’s vertically scanned image, using a scanning disk embedded with a double spiral of lenses, had only 30 lines, just enough to reproduce a recognizable 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. He also demonstrated an electromechanical color, infrared (dubbed “Noctovision”), and stereoscopic television, using additional lenses, disks and filters. In parallel, Baird developed a video disk recording system dubbed “Phonovision”; a number of the Phonovision recordings, dating back to 1927, still exist.[5] In 1929, he became involved in the first experimental electromechanical television service in Germany. In November 1929, Baird and Bernard Natan of Pathe established France’s first television company, Télévision-Baird-Natan. In 1931, he made the first live transmission, of the Epsom Derby. In 1932, he demonstrated ultra-short wave television. Baird’s electromechanical system reached a peak of 240 lines of resolution on BBC television broadcasts in 1936, before being discontinued in favor of a 405-line all-electronic system developed by Marconi-EMI.

Meanwhile in Soviet Russia, 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 June 7, 1926 he electrically transmitted and then projected near-simultaneous moving images on a five foot square screen.[4] By 1927 he achieved an image of 100 lines, a resolution that was not surpassed until 1931 by RCA, with 120 lines.

However, Herbert E. Ives of Bell Labs gave the most dramatic demonstration of television yet on April 7, 1927, when he field tested reflected-light television systems using small-scale (2 by 2.5 inches) and large-scale (24 by 30 inches) viewing screens over a wire link from Washington to New York City, and over-the-air broadcast from Whippany, New Jersey. The subjects, who included Secretary of Commerce Herbert Hoover, were illuminated by a flying-spot scanner beam that was scanned by a 50-aperture disk at 16 pictures per minute.

Electronic Television

In 1911, engineer Alan Archibald Campbell-Swinton gave a speech in London, reported in The Times (UK), describing in great detail how distant electric vision could be achieved by using cathode ray tubes at both the transmitting and receiving ends. The speech, which expanded on a letter he wrote to the journal Nature in 1908, was the first iteration of the electronic television method that is still used today. Others had already experimented with using a cathode ray tube as a receiver, but the concept of using one as a transmitter was novel. By the late 1920s, when electromechanical television was still being introduced, inventors Philo Farnsworth, Vladimir Zworykin and Hungarian Kálmán Tihanyi were already working separately on versions of all-electronic transmitting tubes.

The decisive solution was first described in 1926 by Tihanyi, and appeared in patent applications for his “Radioskop” he filed in Hungary that same year. In 1928 Tihanyi was awarded patents for his inventions in both France and Great Britain. He applied for patents in the United States in June of the following year, but the U.S. patent for his display tube would not be granted until October 1938, and the patent for his camera tube the following May.

On September 7, 1927, Philo Farnsworth’s Image Dissector camera tube transmitted its first image, a simple straight line, at his laboratory at 202 Green Street in San Francisco.  By 1928, Farnsworth had developed the system sufficiently to hold a demonstration for the press, televising a motion picture film. In 1929, the system was further improved by elimination of a motor generator, so that his television system now had no mechanical parts. That year, Farnsworth transmitted the first live human images with his system, including a three and a half-inch image of his wife Elma (”Pem”) with her eyes closed (possibly due to the bright lighting required).

Farnsworth gave the world’s first public demonstration of a complete all-electronic television system on August 25, 1934 at the Franklin Institute in Philadelphia. Other inventors had previously demonstrated components of such a system, or had shown an electronic system using still images or motion picture film. Manfred von Ardenne demonstrated an all-electronic television system using cathode ray tubes at the Berlin Radio Show in August 1931, but as he never built a camera tube, his system was limited to using the CRT as a flying spot scanner to transmit motion picture films and slides. Farnsworth became the first to use all-electronic cameras and receivers to transmit and receive live, moving images. Unfortunately, his cameras needed too much light, so his work came to a stop.

Vladimir Zworykin was also experimenting with the cathode ray tube to create and show images. While at Westinghouse in 1923, he developed an electronic camera tube. But in a 1925 demonstration, the image was dim, had low contrast and poor definition, and was stationary. The tube never got beyond the laboratory stage, but RCA (which had acquired the Westinghouse patent) believed the patent on Farnsworth’s 1927 image dissector was written so broadly that it would exclude any other electronic formation of an image. And so RCA, armed with Zworykin’s 1923 patent application, filed a patent interference suit against Farnsworth. The U.S. Patent Office examiner disagreed in a 1935 decision, finding priority of invention for Farnsworth against Zworykin. Farnsworth claimed that Zworykin’s 1923 system would be unable to produce an electrical image of the type to challenge to Farnsworth’s patent. Zworykin was unable or unwilling to introduce in evidence a working model of his tube that was based on his 1923 patent description. In October 1939, after losing an appeal in the courts and wishing to go forward with the commercial manufacturing of television equipment, RCA agreed to pay Farnsworth US$1 million (the equivalent of $13.8 million in 2006) over a ten-year period, in addition to license payments, to use Farnsworth’s patents.

However, while working at RCA in 1931, Zworykin had designed an improved camera tube based on the technology developed by Tihanyi. Zworykin called the new tube the iconoscope, and it would be the primary type of camera tube used in the U.S. until replaced by the image orthicon tube in 1946. Tihanyi’s patents for both his camera and display tubes would eventually be acquired by RCA.

In Britain Isaac Shoenberg used Zworykin’s idea to develop Marconi-EMI’s own Emitron tube, which formed the heart of the cameras they designed for the BBC. Using this, on November 2, 1936 a 405 line service was started from studios at Alexandra Palace, and transmitted from a specially-built mast atop one of the Victorian building’s towers; it alternated for a short time with Baird’s mechanical system in adjoining studios, but was more reliable and visibly superior. So began the world’s first high-definition regular service. The mast is still in use today.

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