power line problems

[golfnut]

I spoke to club guy with a 3030 and he has no drama getting finds from beneath pylon distribution systems.

My IGSL got zero finds, I suspect my IDX will suffer too.


I looked at the e and h field from a UK 400kV plant

Beneath at 1m above ground its E= 1.9V/m and B= 5uT
50m away its E= 0.13V/m and B =0.4uT

Anyone know ideas for reducing all of the noise signal?

Im guessing this is a few orders of mag above a small roman bronze, so how dou you get 30 - 50dB of rejection with no loss of sens to the wanted?

S

[dfbowers]

Concentric pancake coil? But there are trade offs with sens. Either that or come up with a differential front end with a centertapped coil.

[Carl-NC]

Was the IGSL unstable, or overloaded? If not, then likely the powerlines weren't a problem.

[Davor]

IGSL has a somewhat frugal front end regarding powerline filtration. Mine is a bit edgy too.

[golfnut]

Just curious what is the best option, I agree Don balanced is better to common mode stuff out.



I cant think of a topology for a 50/60Hz notch which would sit before the preamp that wont add loss/generate noise. Maybe its ok and I could try it.


A twin T type notch following the preamp is practical - but with large amplitude out of band signals its good to get rid of them as early as possible in the chain.

Anyone turned a machine around from deaf under big power lines to usable.


My IGSL is broken up currently- it wont be re-assembled.

Steve

[Funfinder]

I'm sometimes hunting directly below such 380kV lines (those are ca. 50m above) and many detectors are completly useless there
as example Garrett (the Pro Pointer and the small sniper Coil is no problem but everything larger than that is).

Better look for non-motion detectors (often or even always those are immune there) if ya don't wanna lose 50-70% of sensitivity on such sites.

This info was worth over 20 dollars so enjoy it! :-D