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Published on Jun 27, 2012
The basic BFO employs two radio frequency (RF) oscillators which are tuned to very nearly the same frequency. The frequency of each oscillator is usually determined by an L-C resonant circuit, that is, an inductor and a capacitor. One is called the search oscillator and uses the search coil as its inductor; the other is called the reference oscillator and uses an internal inductor. The outputs of the two oscillators are fed into a mixer which produces a signal that contains the sum and difference frequency components (plus otherintermodulation components) of the two input signals. As we will see shortly, the difference frequency is what we are interested in, and a low-pass filter at the output of the mixer will remove the other components. Note: No responsibility accepted due to injury or damage that may be caused in building or using this Metal Detector.