An autocoherer is a self-restoring coherer - a detector of radio
waves - such as a microphonic detector.
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No, this is not possible. Firstly, MP3 radio's do not exist and an MP3 player is a Music Player, not a metal detector.
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A cobra detector is a radar detector. Radar detectors work the
same way a radio receiver does. The radar detector looks for
frequencies that a radar gun uses.
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You can build a metal detector using an AM radio and Calculator.But it is not sure that it will work or not.My brother had made metal detector using an AM radio and calculator two months ago,first it doesn't work at all but than he made some changes than it began working.