> okay, also found some hints that indicate that 33 kHz to 133 kHz is
> a good range. No problem in generating the signal. But now it comes
> to coupling it to the cable.

You couple it single-endedly. The other end needs a ground plane of some
sort. An earth point or a large metal structure will help. Check that it
is not connected to the cable ... None of this will work if the cable runs
in metal conduit. Then only metal detectors will work right. I recommend
the proton precession gradiometer kind. If the metal was in the ground for
a long time then this should work perfectly (gets nicely megnetised by the
earth field). You will also find all the water and gas pipes, sewers
(manholes etc) and rebars in the concrete ...

Peter

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