The Fleming valve, also called the Fleming oscillation valve, was a thermionic valve diode (called a "vacuum tube" in the USA) invented by John Ambrose Fleming and used in the earliest days of radio communication. As the first vacuum tube, the IEEE has described it as "one of the most important developments in the history of electronics", and it is on the List of IEEE Milestones for electrical engineering.
The Fleming valve was the first practical application thermionic emission, discovered in 1873 by Frederick Guthrie. As a result of his work on the incandescent light bulb, Thomas Edison made his own discovery of the phenomenon in 1880, which led to it being called the Edison effect. Edison was granted a patent for this device as part of an electrical indicator in 1884, but did not hit upon any practical use. Professor Fleming of University College London consulted for the Edison Electric Light Company from 1881-1891, and subsequently for the Marconi Wireless Telegraph Company.
In 1901 Fleming designed a transmitter for Guglielmo Marconi to attempt transmission of radio waves across the Atlantic from Poldhu, England, to Nova Scotia, Canada. The distance between the two points was about 3,500 kilometres (2,200 mi). Although widely heralded as a great scientific advance, there was also some skepticism about this claim, in part because the signals had only been heard faintly and sporadically. In addition, there was no independent confirmation of the reported reception, and the transmission, which merely consisted of the three dots of the Morse code letter S sent repeatedly, came from a transmitter whose signals were difficult to differentiate from the noise made by atmospheric static discharges. (A detailed technical review of the early transatlantic work appears in John S. Belrose's work of 1995.)
The receiver for the transatlantic demonstration employed a coherer of the imperfect junction type which had poor sensitivity and degraded the tuning of the receiver. This led Fleming to look for a detector which was more sensitive and reliable while at the same time being better suited for use with tuned circuits. In 1904 Fleming tried an Edison effect bulb for this purpose, and found that it worked well to rectify high frequency oscillations and thus allow detection of the rectified signals by a galvanometer. On November 16, 1904, he applied for a US patent for what he termed an oscillation valve. This patent was subsequently issued as number 803,684 and found immediate utility in the detection of messages sent by Morse code.
 Oscillation valves
The Fleming valve proved to be the start of a technological revolution. After reading Fleming's 1905 paper on his oscillation valve, American engineer Lee DeForest in 1906 created a three-element vacuum tube (the Audion) by adding a modulation grid. It could act as an amplifier and oscillator as well as detector. De Forest quickly refined his device into the triode, which was then central to the creation of long-distance telephone and radio communications, radars, and early digital computers. Similarities and differences between the Fleming valve and DeForest's triode caused decades of expensive and disruptive litigation, which were not settled until 1943 when the United States Supreme Court ruled Fleming's patent invalid.
 References and notes
- "Milestones:Fleming Valve, 1904". IEEE Global History Network. IEEE. Retrieved 29 July 2011.
- Fessenden and Marconi: Their Differing Technologies and Transatlantic Experiments During the First Decade of this Century
- Radio Communications: A Brief Synopsis
- John Ambrose Fleming (1849-1945) By W A Atherton, Published in Wireless World August 1990
- Do note that Nikola Tesla had already discovered that oscillations, damped or undamped, could be detected after being made to flow one direction or being developed as alternating in direction. For more, see "Nikola Tesla on His Work With Alternating Currents and Their Application to Wireless Telegraphy, Telephony and Transmission of Power : An Extended Interview". ISBN 1-893817-01-6
- The Supreme Court invalidated the patent because of an improper disclaimer and later maintained the technology in the patent was known art when filed. For more see, Misreading the Supreme Court: A Puzzling Chapter in the History of Radio. Mercurians.org.
- U.S. Patent 803,684 - Instrument for converting alternating electric currents into continuous currents (Fleming valve patent)
- Cited by
- U.S. Patent 1,290,438, Jan 7, 1910 : Fleming valve improvement by R. A. Weagant
- U.S. Patent 954,619, Apr 12, 1910 : John Ambrose Fleming patent
- U.S. Patent 1,379,706, Mar 10, 1917 : Fleming valve improvement by R. A. Weagant
- U.S. Patent 1,252,520, Jan 8, 1918 : Fleming valve improvement by R. A. Weagant
- U.S. Patent 1,278,535, Sep 10, 1918 : Fleming valve improvement by R. A. Weagant
- U.S. Patent 1,289,981, Dec 31, 1918 : Fleming valve improvement by R. A. Weagant
- U.S. Patent 1,306,208, Jun 10, 1919 : Fleming valve circuit improvement by R. A. Weagant
- U.S. Patent 1,338,889, May 4, 1920 : Fleming valve improvement by R. A. Weagant
- U.S. Patent 1,347,894, Jul 27, 1920 : Inverter converter by L. W. Chubb
- U.S. Patent 1,380,206, May 31, 1921 : Fleming valve improvement by R. A. Weagant
- U.S. Patent RE16,363, Jun 15, 1926 : Inverter converter by L. W. Chubb
- U.S. Patent 1,668,060, May 1, 1928 : Fleming valve circuit improvement by P. E. Edelman
- U.S. Patent 2,472,760, Jun 7, 1949 : Electrode improvement by H. L. Ratchford
- IEEE History Center
- November 1904: Fleming discovers the thermionic (or oscillation) valve, or 'diode'
- Spark Museum
- Reverse Time Page