>
> >Then there's the TX-RX method, send 1kHz into one coil, and use
> >another to pick it up, using synchronus boxcar detector integrator if
> >need be, to eliminate noise.  Level shifts tell you that the amount
> >of magnetic coupling has changed.
> >
>
>Developing this idea, how about the other metal detector methods such as
>BFO or pulse induction?  Pulse induction in particular can achive pretty
>good ranges.

BFO is inherently unstable, and rain, temperature, etc would all factor in.

Pulse induction might be workable.

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