Hot-wire barretter
early form of radio demodulator
The hot-wire barretter was a demodulating detector, invented in 1902 by Reginald Fessenden, that found limited use in early radio receivers. In effect, it was a highly sensitive thermoresistor, which could demodulate amplitude-modulated signals, something that the coherer (the standard detector of the time) could not do.
The first device used to demodulate amplitude modulated signals, it was later superseded by the electrolytic detector, also generally attributed to Fessenden. The barretter principle is still used as a detector for microwave radiation, similar to a bolometer.
Description and construction
Fessenden's 1902 patent describes the construction of the device. A fine platinum wire, about 0.003 inches (0.08 mm) in diameter, is embedded in the middle of a silver tube having a diameter of about 0.1 inches (2.5 mm). This compound wire is then drawn until the silver wire has a diameter of about 0.002 inches (0.05 mm); as the platinum wire within it is reduced in the same ratio, it is drawn down to a final diameter of 0.00006 inches (1.5 μm). The result is called Wollaston wire.
The silver cladding is etched off a short piece of the composite wire, leaving an extremely fine platinum wire; this is supported, on two heavier silver wires, in a loop inside a glass bulb. The leads are taken out through the glass envelope, and the whole device is put under vacuum and then sealed.
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This entry incorporates text from “Hot-wire barretter” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.