14" mono depth problem

I run a GPX4000, I recently bought 2 coils, a round 8" mono Commander and a round 14" mono Nugget Finder.
It appears through air testing with nuggets that the 8" is not far behind the 14" in depth, which appears strange.

Would someone with a round 14" mono coil please help by air testing with a dollar coin and post the results with your settings, normal, sens extra and sens smooth if possible.

Thanks in advance.

You probably need a bigger target, what sized nuggets have you been testing?

A flatish 10 grammer about one half the surface area of a dollar coin on the flat, a flatish 1.3 grammer and a flatish 0.3 grammer.
Thanks.

llanbric wrote:A flatish 10 grammer about one half the surface area of a dollar coin on the flat, a flatish 1.3 grammer and a flatish 0.3 grammer.
Thanks.

Well, as we all know, air tests aren't accurate, especially with coins. However, you'd need to be looking for in situ targets to test on. I have air tested a 7 gram nugget with others there using different detectors/coils and the diffs were only incramental, my SD 2000 with standard 18" did the best (just about says it all), so, in situ that wouldn't have been the case.

I say don't worry about it, a 10 grammer only incramentaly better with that coil sounds about right.

Btw, are you looking for small nuggets or 10 grammer type nuggets? What do you think a small nugget is? I'm guessing you're new to this given your question? If not, excuse me If so, I would suggest use a smaller coil like your 8" or an 14" elip.

I'm guessing you probably know this already, but just in case you didn't: You can't test a GPX indoors. Especially when comparing coils. The two Monoloops that you were testing have a similar depth with the 8" being more sensitive to smaller nuggets and specimens whereas the 14" can detect larger pieces at depth. Without drawing out an argument from anyone who may choose to disagree, I'm of the opinion that the newer Commander coils output stronger fields compared to other coils of a similar size... which would possibly put the 8" Mono Commander on par with the 14" Mono NF coil.

The electromagnetic field emanating from every wire and appliance in your home will make it seem that your PI detector is barely working. It won't affect the VLF detectors to the same extent. What's happening though, is that the detector is being overwhelmed by the magnetic fields in the house and this is sort of similar to the way a large signal from an iron target will mask a nugget below or around it. Again. you need to be at least 50 yards from any electrical wires or signals in order to see how the coil performs.

Gday

I think the results you got doing air tests are probably about right, given outside interference and perhaps the detectors electronics trying to tune out metallic objects in the vicinity, these factors will all help to de- sensitise the coil, making it less sensitve to the targets, the bigger the coil the greater the effect, so your 8" coil will seem more effective the the 14" coil.

Tests are better done away from any electrical or metallic objects and done with targets buried in the ground, you will get much better results doing it that way, if the results you get are still poor then you need to look at your detectors settings, failing that then you may want to send the 14" coil to have it checked, a 14" coil should be capable of detecting a flattish 10 gram nugget at 12" or more, given that the ground mineralisation is not too extreme.

Hope I am not trying to teach you how to suck eggs on this, but this also could be helpful to other readers as well.

cheers

stayyerAU

Thanks all for your input.

The testing was done in the field, at least 10 kms from any residence or power lines.

I've been detecting about 8hrs weekly on average since March 2008, got JP's dvds, I'm at the stage where I now feel I know what I'm doing, found 32gms gold from 0.3gm to 10gm, I also have a large collection of lead from .22 to 0.7" musket balls etc.

The 8" coil is for finer gold and tight spots, overgrown areas etc.

The 14" I bought to get more depth.

Air test in normal timing, gb fixed, gain 8, audio normal, using a flatish nugget half size of a dollar coin:
8" round mono depth 8.5"
14" round mono depth 11.5"

I would have thought the 14" coil would pick up the test nugget at about 14" going on the performance of the
8" coil.

Stayerau, Your idea of burying targets is probably what I should do next. Shame there aren't definitive test procedures available, the coil manufacturers wouldn't like it.

If you bury a target
you still won't get a proper result,
you need to test on targets insitu then dig and
measure,but this will only give you an idea in that
spot as the ground changes {sometimes only metres away}
you will get differant results,
i.e= in most cases the hotter the ground=less depth.
This is just my opinion
Cheers Fencejumper

The coil manufacturers must have some way of testing their coils.

Yes they do, pro's testing on test beds usualy holes drilled in from
the side of a creek bed so the soil above target is not disturbed
the tests on computers in workshops don't mean anything,
the true test comes when they are in the hot ground that
covers most of goldfields
cheers

Gday

Even burying targets in mineralised soils in test beds still wont give a definative result, because long buried targets are usually surrounded by whats known as a "halo", this halo effect is also picked up by the detector and makes the target more noticeable, without the halo its possible that the target wont be heard.

There are too many variables to make any definate conclusions about what a coil should or shouldnt do, so if a manufacturer made this claim and that, they would probably be shot down over it, its only time in the field using these things that you learn what its capabilities are.

cheers

stayyerAU

I spoke with David Watters of Trackline at Bendigo, he suggests that the 14" coil has a larger yet disapated field compared to the smaller more intense field from the 8" coil, hence the 14" not as good on smaller targets but better on larger deeper targets.

Thanks to all.

Can't help much on this subject, but I can add, instead of an 8" or 14" round mono I would try a either a NF 12x24" mono, GoldStalker 12x18.5", or a Commander 12x15" mono instead for the best all round performance balance between sensitivity on small gold, depth on larger gold, and also scanning ground coverage.