Detectors 087
Detectors 087 : Particle Detectors: (4.3) Cat's-Whisker Detector: (3) Types: (How a crystal detector works in a radio receiver. (A) The amplitude modulated radio signal from the receiver's tuning section. The rapid oscillations are the radio frequency carrier wave. The audio signal (the sound) is contained in the slow variations (modulation) of the size of the waves. This signal cannot be converted to sound by the earphone, because the audio excursions are the same on both sides of the axis, averaging out to zero, resulting in no net motion of the earphone's diaphragm. (B) The crystal conducts current in only one direction, stripping off the oscillations on one side of the signal, leaving a pulsing direct current whose amplitude does not average zero but varies with the audio signal. (C) A bypass capacitor across the earphone smooths the waveform, removing the radio frequency carrier pulses, leaving the audio signal. Historically, many other minerals and compounds besides galena were used for the crystal, the most important being iron pyrite ("fool's gold"), iron disulfide),silicon, molybdenite (MoS2), and silicon carbide (carborundum, SiC). Some were used with gold or graphite cat's whiskers. Another type had a crystal-to-crystal junction instead of a cat's whisker, with two crystals mounted facing each other. One crystal was moved forward on an adjustable mount until the crystal faces touched. The most common of these was a zincite-bornite (ZnO-Cu5FeS4) junction trade-named Perikon, but zincite-chalcopyrite, silicon-arsenic and silicon-antimony junctions were also used.
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