High voltages, reference grounds, and probe wires all sound like electric
field sensing techniques.  Another possibility, if you can get at the far
end of the wire, is to run a current through it, to produce a magnetic
field.  Then, you would use a coil of wire as a pickup.  You'd ground the
far end of the cable and ground one side of your driving amp.  My guess is
that attempting to drive a pair of wires with one as the return probably
conspires to cancel out the signal you are seeking.


On Sun, May 19, 2013 at 4:25 PM, Bob Blick <bobblick@ftml.net> wrote:

> I put a warble tone out on a known buried wire today, using a copper
> water pipe outside my house for ground. The water pipe doesn't go
> underground except way on the other end of the house, so it was
> sub-optimal.
>
> It worked great for the wire above ground, easily four feet away my
> detector was clipping.
>
> But as soon as the wire went underground I got nothing, absolutely
> nothing. The test wire is in a plastic conduit less than a foot below
> ground.
>
> My setup used a warble tone on an MP3 player running into a
> reasonably-capable integrated amplifier putting out about 25 VAC. For
> the detector I had a telephone handset amplifier I modified for high
> input impedance and a stiff wire probe about a foot long.
>
> The buried wire was a power cable, I also tried driving one conductor
> signal hot and another signal ground. Not very mych range aboveground,
> nothing below.
>
> I'll try again driving in a local ground stake.
>
> Bob
>
>
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