The central idea: scanning
Any television system has to solve one problem: how to send a two-dimensional picture over a channel that carries only one signal at a time. The answer, in every system, is scanning. The picture is divided into a pattern of points or lines. The camera measures the brightness of each in order, the signal travels, and the receiver reproduces the same sequence in step. If the sequence repeats fast enough, the viewer’s eye merges it into a moving image. The debate in the early decades was whether scanning should be done with moving parts or with electron beams.
The mechanical path
Paul Nipkow, a German student, patented a scanning disc in 1884. A spiral of holes around the edge of a rotating disc scanned a scene one line at a time, with a light-sensitive cell behind it. At the receiver, a matching disc and a varying lamp rebuilt the picture. Nipkow apparently never built a working system, and the technology to amplify the weak signals did not yet exist.
In the 1920s, John Logie Baird in Britain produced working demonstrations. He showed moving silhouettes and then more detailed images in 1925 and 1926, and he transmitted pictures across the Atlantic in 1928. Charles Francis Jenkins in the United States and others pursued similar systems. Mechanical television had real appeal: it was simple and could be built with modest resources. Baird’s 30-line pictures were small and crude, but they were recognizable faces, and some experimental programs were broadcast to hobbyists in Britain beginning in 1929 and in the early 1930s.
The approach had a ceiling. To improve the picture, a disc needs more holes and a faster spin, and it quickly becomes large, noisy and delicate. A scanned picture also needs a very bright subject, since each hole passes little light.
The electronic path
Electronic scanning removes the moving parts. A beam of electrons can be aimed and swept by electric or magnetic fields far faster than any disc could rotate. The concept had been described in 1908 by Alan Archibald Campbell-Swinton, a Scottish engineer, who proposed using cathode ray tubes at both ends of a system. He did not build it.
The cathode ray tube itself dated from the work of Karl Ferdinand Braun in 1897. As a display, it was the natural receiver for electronic television. The camera was the harder problem.
- Boris Rosing in Russia experimented with a cathode ray tube receiver in 1907, combined with a mechanical camera, and his student Vladimir Zworykin later moved to the United States.
- Philo Farnsworth, a young inventor in the American West, designed an electronic system in the mid-1920s and transmitted a simple image in 1927 with his image dissector camera tube. He later worked with backers in San Francisco and Philadelphia.
- Zworykin, working at Westinghouse and later RCA, patented an early electronic camera design in the 1920s and developed the iconoscope, a more sensitive storage camera tube, by the early 1930s. RCA, led by David Sarnoff, supported the effort strongly.
- In Britain, a team at EMI led by Isaac Shoenberg, including engineers such as Alan Blumlein and James McGee, developed the Emitron camera on storage principles.
Hungarian engineer Kálmán Tihanyi also filed patents on camera and display ideas in the 1920s and 1930s, and his work is sometimes cited as influential on later systems.
Patents and priority
Farnsworth’s patent on his image dissector and system was challenged by RCA, which argued that Zworykin’s earlier application had priority. In a patent interference proceeding in the 1930s, the patent office ruled in Farnsworth’s favor on the key point, and RCA later agreed to pay license fees, according to most accounts. This is why some histories portray Farnsworth as the inventor of electronic television. Others emphasize that Zworykin’s iconoscope, with its storage principle, was the more practical camera, and that the final broadcast systems used many contributions beyond any individual.
It is fair to say that the two men worked independently, that both made essential contributions, and that company resources greatly influenced how their ideas were developed. Farnsworth’s later life, as told in popular retellings, includes sharper claims of neglect than the documentary record may support, so it is best to treat the dramatic versions cautiously.
The 1936 BBC trial
Britain provided a direct comparison. When the BBC began its public high-definition service in November 1936, it alternated between two systems week by week: Baird’s 240-line system, which still used mechanical elements in parts of its camera and a film-based intermediate process, and the electronic 405-line Marconi-EMI system. The EMI system produced a better picture and was more flexible for live outdoor work. In February 1937, the BBC chose Marconi-EMI. A fire at the Crystal Palace, where Baird’s company had its laboratories, in late 1936 did not help his cause, though the technical decision rested on performance.
Legacy
The picture tube remained the standard television display until the flat panels of the 2000s, and cathode ray tubes were also widely used in radar displays, oscilloscopes and computer monitors, as well as in displays for radar detection. The fundamental principle of scanning remains in display technology, even though modern screens address pixels electronically. The invention of television was less the work of a single genius than a collective achievement, with people on several continents solving parts of the puzzle. The result, after years of work by competing companies, was a medium that could scale to a mass audience, which the mechanical systems could not.