Hot wire barretter
From Wikipedia, the free encyclopedia
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 developed to permit the reception of amplitude modulated signals, something that the coherer (the standard detector of the time) could not do.
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[edit] Description and construction
An extremely fine platinum wire, about .003 inch in diameter, is embedded in the middle of a silver wire having a diameter of about one-tenth inch. This compound wire was then drawn until the silver wire had a diameter of about .002 inch; as the platinum wire within it was reduced in the same ratio, it would be drawn down to a final diameter of .00006 inch (1.5 μm). The result was called Wollaston wire. A short piece of the extremely fine composite wire is supported on two heavier silver wires, in a loop inside of a glass bulb. The leads are taken out through the glass envelope and the whole device was sealed up and put under vacuum.
[edit] Operation
The hot wire Barretter depends upon the variation (usually an increase) of a metal's resistivity as a function of increasing temperature. The device is biased by a D.C current adjusted to heat the wire to its most sensitive temperature. When an oscillating current from the antenna flows through the extremely fine platinum wire loop, it rapidly increases and decreases its electrical resistance. Headphones were connected in series with the D.C. circuit and the variations in the flow of current was rendered as sound.
[edit] External links
[edit] Patents
- U.S. Patent 706744 , "Current Actuated Wave Responsive Device" – August, 1902 ("barretter" detector)
- U.S. Patent 727331 , "Receiver for Electromagnetic Waves" – May, 1903 (improved "barretter")
