Fleming: pioneer of radio’s early days

By Mike Smyth, specialist technical writer
Friday, 08 March, 2013



Sir John Ambrose Fleming is regarded as the man who established the practical fundamentals of the thermionic valve era of radio and electronics.

The late nineteenth and early twentieth centuries were dominated by inventors and engineers who between them made major contributions to radio and electronics. And while some of them made fortunes from their inventions, many lost their money in long drawn-out patent arguments in long drawn-out legal battles.

One such inventor was John (later Sir John) Ambrose Fleming, a physicist and electrical engineer who invented a two-element thermionic valve diode which became known by various names, including the ‘Kenotron’.

Often called the father of electronics, Fleming has also been described as the ‘common thread’ that linked the work of Edison, Marconi, de Forrest and Tesla.

Born in England in 1849, over his long life (he was 95 when he died in 1945) Fleming had a variety of interests including mountaineering, watercolour painting and photography. He was also a devout Christian and at one time delivered a sermon at St Martins in the Fields church in London on evidence for the resurrection.

At the age of 11 he built engines and model boats, and his own camera, which sparked his life-long interest in photography. Although he wanted to become an engineer, his family’s straitened circumstances meant that Fleming had to work a little, to earn a little, to learn a little, in order to reach his goal.

Educated initially at University College in London and later at Cambridge University (where he gained his BA), he became a BSc student at University College in 1870 and studied chemistry at the Royal College of Science (now Imperial College). It was here that he came across Volta’s battery; his studies of the battery led to publication of his first scientific paper, which was the first to be read at the Physical Society of London (now the Institute of Physics).

Still short of money he took up a science teaching post at Cheltenham College while continuing his own research, communicating with James Clerk Maxwell at Cambridge.

Ever keen to advance his knowledge, at the age of 27 and with the help of a grant and savings, he went back to Cambridge as a student before graduating with a First Class Honours degree in chemistry and physics. He then gained a DSc in London and became the first professor of Physics and Mathematics at Nottingham University.

For 26 years he was a consultant to the Marconi Wireless Telegraph Co, initially to help design a power plant and transmitter for Marconi’s successful transatlantic radio transmission in 1901.

Early signals were hard to detect using a galvanometer, so Fleming reasoned that if he could get the received signal to flow in only one direction, it would be detected more easily. In other words, the signal would be rectified. So in 1904 he invented the two-electrode thermionic vacuum rectifier, also called an oscillation valve or ‘Fleming tube’ (which remained dominant until superseded in the 1950s by the development of the transistor). He found that it worked well at rectifying high-frequency signals and made them more clearly seen on a galvanometer. In that same year, he applied for and was granted a patent in the US for the device, and it was quickly and widely adopted for detecting Morse code.

In 1906, US engineer Lee de Forrest added a modulation grid to Fleming’s valve, enabling it to act as an amplifier, oscillator and detector. This Audion, or triode, made possible long-distance communications in telephone and radio and, later, radar. However, arguments broke out over the similarities and differences between Fleming’s and de Forrest’s devices, resulting in marathon and expensive legal battles that were not finally resolved until 1943 at which time the US Supreme Court ruled Fleming’s patent invalid because of an improper disclaimer. It also said that the technology was ‘known art’ when filed. (Incidentally, this same court also decided in 1943 that Nikola Tesla was the true inventor of radio.)

Fleming was also a pioneer in electric lighting and heating and, of course, responsible for the ‘right hand’ and ‘left hand’ rules of electric motors. As an electrical engineer with the Edison Co he superintended the introduction of incandescent lighting in England in the early 1880s.

Like so many inventors of those times, his work overlapped with others following the same paths of research. But Fleming has to be regarded as the man who established the practical fundamentals of the thermionic valve era of radio and electronics.

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