Quote:
Originally Posted by Dave J.
Simple twin-T notch filter tuned for 60 Hz will knock out most aluminum and copper interference in the Americas. Oddly enough these materials seem to know where they're located and in most of the rest of the world their frequency is 50 Hz. For use worldwide, just cascade a 60 Hz notch with a 50 Hz notch and ya got it covered.
The original Fisher Gold Bug (approx. 1986) had a 60 Hz notch filter for knocking out those pesky aluminum and copper signals. The system was set up to nonetheless be able to detect a full can of beer, since ya wouldn't want to pass that up. Unfortunately we weren't able to keep it from detecting empty beer cans as well, even just a few drops of dried beer residue was enough to fool it. But that was the all-analog olden days. Nowadays we're working on a software app to solve the problem.
--Dave J.
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My Filter is for Reject of 50Hz, and sensibility of other all frequency.
http://www.geotech1.com/forums/showthread.php?t=14475