Detectors 155
Detectors 155 : Particle Detectors: (4.15) Hot Wire Barretter: (2) 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 direct current adjusted to heat the wire to its most sensitive temperature. When there is an oscillating current from the antenna through the extremely fine platinum wire loop, the wire is further heated as the current increases and cools as the current decreases again. As the wire heats and cools, it varies its resistance in response to the signals passing through it. Because of the low thermal mass of the wire, it is capable of responding quickly enough to vary its resistance in response to audio signals. However, it cannot vary its resistance fast enough to respond to much higher radio frequencies. The radio frequencies are essentially removed, and the sound is demodulated because the current through the circuit varies with the changing wire resistance. Headphones are connected in series with the D. C. circuit and the variations in the current are rendered as sound
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