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# Coil freq. help

- To: femm@yahoogroups.com
- Subject: Coil freq. help
- From: " Alexandru Marian" <sestert@yahoo.com>
- Date: Sun, 18 Nov 2001 09:32:44 -0000
- User-agent: eGroups-EW/0.82

    Hello List,
    I am building a metal detector.
    It is based on 2 coils, with equal frequency. When the search coil
    will pass over metal, this will change its fixed freq. and the system
    will scream.
    The search coil will have 15 turns of 0.4mm, 6inch diameter, should
    be 70kHz. The second coil...it just says "take a small former, wind
    some 150 turns, you might need thiner wire"
    I will probably not be able to find an osciloscope to emasure the
    second coil, so that looks like a big problem.
    It means ill need the math, freq. function of coil diameter, turns,
    wire thickness and core. Ill need some screw for the core, moving it
    should allow me 70kHz +- 250Hz.
    I supose that when the 2 frequencies are very close, the sistem will
    not make too much sounds...

    Thanks in advance for any ideeas,
    Alex

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