Inductive output tube

The inductive output tube (IOT) or klystrode is a variety of high frequency transmitting linear-beam vacuum tube, similar to a klystron, which evolved in the 1980s to meet increasing efficiency requirements for high-power RF amplifiers. The primary commercial use of IOTs is in UHF television transmitters, where they have mostly replaced klystrons because of their higher efficiencies (35% to 40%) and smaller size. IOTs are also used in particle accelerators. They are capable of producing power output up to about 30 kW continuous and 7 MW pulsed and gains of 20–23 dB at frequencies up to about a gigahertz.

The inductive output tube (IOT) was invented in 1938 by Andrew V. Haeff. A patent was later issued for the IOT to Andrew V. Haeff and assigned to the Radio Corporation of America (RCA). During the 1939 New York World's Fair the IOT was used in the transmission of the first television images from the Empire State Building to the fair grounds. RCA sold a small IOT commercially for a short time, under the type number 825. It was soon made obsolete by newer developments, and the technology lay more or less dormant for years.

The inductive output tube has re-emerged within the last twenty years after having been discovered to possess particularly suitable characteristics (broadband linearity) for the transmission of digital television and high-definition digital television.

The power output of the modern 21st century IOTs is orders of magnitude higher than the first IOTs produced by the RCA in 1940–1941 but the fundamental principle of operation basically remains the same. IOTs since the 1970s have been designed with electromagnetic modeling computer software that has greatly improved their electrodynamic performance.

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