New Zealand Gold Prospecting & Metal Detecting Forums Archive

The forum has moved to community.paydirt.co.nz, see you there!

This forum is now an archive to preserve the knowledge and finds posted here.

Advice on different metal detectors - I'm having problems with a Garrett AT Pro not detecting deep enough

Ronnie		Posted : Friday, 1 May 2015 10:33:22 AM(UTC)
Rank: Gold Flake Groups: Registered Joined: 30/03/2015(UTC) Posts: 15 Location: Christchurch Thanks: 8 times		Hi there I am after a few pointers. I am planning on running an experiment where I put some nuts (ie nuts and bolts) with numbers stamped into them in the soil on a hillslope, to trace how much the soil moves. The placement of the nuts will be very precise (measured with a total station)and I will return after winter to find them with a metal detector and determine their new location and therefore movement. The questions I have are, what is the typical ranging depth for a 'Garrett AT Pro'? And, are more expensive/higher end metal detectors likely to find things at a greater depth? I did a 'dry run' with some nuts yesterday (they were not buried in the soil), and the Garrett AT Pro that I was using was not beeping if the coil was more than about 10-15 cm above the targets, but it was beeping if it was less than 10cm above the target. For my experiment, I am looking to find targets which may be up to about 30cm+ beneath the soil surface. I was trialing the device in both standard and pro modes, under the custom setting. The iron discrimination setting was turned off, and I trialed it with other 'pixels'/notch discriminations on and off, and and varying levels of sensitivity. Is there anyone else on the forum who has used a Garrett AT Pro? And if so, what sort of depths were they able to detect things in the soil? Any advice on the capabilities of this and other machines would be greatly appreciated! Regards, Veronica

c4bb0ose		Posted : Friday, 1 May 2015 2:22:18 PM(UTC)
Rank: Gold Nugget Groups: Registered Joined: 7/09/2014(UTC) Posts: 97 Thanks: 1 times Was thanked: 32 time(s) in 29 post(s)		You could try turning the sensitivity up, this will get you greater depth, but will also possibly give you false positives. I actually cannot rember for the record if the at pro has a sensitivity level but I imagine it does.

Metal Kiwi		Posted : Friday, 1 May 2015 2:41:08 PM(UTC)
Rank: Gold Ingot Groups: Registered Joined: 19/06/2011(UTC) Posts: 1,210 Location: Auckland Thanks: 498 times Was thanked: 484 time(s) in 322 post(s)		Hi Ronnie, Interesting project. You could increase your depth detected by increasing the size of the nuts and using brass or copper instead of steel. FYI my Minelab E Trac detector will pick up copper / brass / iron down to about 18" . Some of the things that affect depth are the metal, the size, the shape and orientation in the soil, the soil itself and the equipment used to detect it. Anyone out there with say a GPX5000 will usually see much deeper than 18" . HH MK
		WWW BLOG

Mudwiggle		Posted : Friday, 1 May 2015 2:45:43 PM(UTC)
Rank: Gold Ingot Groups: Registered, Moderators Joined: 22/10/2013(UTC) Posts: 742 Thanks: 182 times Was thanked: 683 time(s) in 317 post(s)		30cm would be a hard hit (if, say a 5mm mild steel nut). This is where using 'easy' metals like copper would help. If you use ferrous, then after a year the nut should start to build a rust halo which might help increase sensitivity. I would: Do a full reset (hold power button about 10s until the double beep) Run Pro mode, zero disc turn sensitivity right down, then manually ground balance (rather than auto) ** make sure ground is clear of any metal then wind the sens back up. Make sure iron audio is on This should give you max depth for your targets. Sweep Low and Slow. I use 1s/m when intensively hunting and aim to knock the daisy heads off. 50% coil overlap for each sweep. Keep in mind that every cm the coil is above the soil is 1cm lost depth. What nuts are you using? I'll try my machine on the same. Edited by user Friday, 1 May 2015 2:47:12 PM(UTC) \| Reason: Not specified

Ronnie		Posted : Friday, 1 May 2015 3:09:14 PM(UTC)
Rank: Gold Flake Groups: Registered Joined: 30/03/2015(UTC) Posts: 15 Location: Christchurch Thanks: 8 times		Thanks for all your inputs. @c4bb0ose: I tried varying the sensitivity, but even at the highest level of sensitivity, it was still only detecting to about 15cm above the targets. @Metal Kiwi: we had gone for steel over copper due to cost and availability. Brass could be worth looking at though. Thanks for the info on the different machines. We have borrowed this one, so if we can't get it to pick up nuts to the depth that we want, and the ones you mentioned will, then we will look at investing in our own one. I know the one that we are using has been modified, by moving the monitor lower down and cutting off 2/3 of the stem (so it can fit in a tramping pack), but I don't see why that should affect how well it works... @ Mudwiggle: we were looking at using nuts with 10mm or 12mm thread diameters, which are 17mm and 24mm across, respectively. I'll try resetting it and go out and have another go. Your technique sounds similar to what I was doing, as I read the whole manual before I even started! Fingers crossed the reset helps! I was trying to see if different types of nuts came up any better or worse when they were deeper, but didn't get that far yet! I've got stainless steel, galvanized steel and zinc (coated?) nuts to compare. Thanks!

Mudwiggle		Posted : Friday, 1 May 2015 3:55:20 PM(UTC)
Rank: Gold Ingot Groups: Registered, Moderators Joined: 22/10/2013(UTC) Posts: 742 Thanks: 182 times Was thanked: 683 time(s) in 317 post(s)		Just tried an M10 galv nut with the AT Pro (Stock 8x11" coil), and was losing it around 40cm (reasonably iron rich ground and not buried) You won't get a nice BEEP at this range, just a twitch of a tone followed by the iron 'grunt' Settings as per previous post performed best. Full sensitivity was stable. Also tried a 10mm galv washer, but there was no improvement in signal. Plus, if they turned in the soil you'd have an edge target... You mention using steel over copper due to cost. Haven't seen the price on a GPX yet then? grin Good luck, interested in seeing what machine/depths/materials you end up with. MW

Ronnie		Posted : Friday, 1 May 2015 7:30:52 PM(UTC)
Rank: Gold Flake Groups: Registered Joined: 30/03/2015(UTC) Posts: 15 Location: Christchurch Thanks: 8 times		No luck! Even if it wasn't 'beeping' at that range, would it still register on the target ID? Cos I wasn't getting that either. The targets that I use will be single use, where as if we bought a metal detector, it would be able to be used over a longer period.. There is potential for this project to continue into a PhD project, if I can get a set of methods sussed! As far as I can tell, this type of soil movement hasn't been studied in an agricultural setting before, so I've got nothing to go off except my own ideas (and advice from people such as yourselves! ;) ). If I need it, and I talk to people nicely, the department may buy one, and people can use it for other projects as well... How much of a better reading would copper give over steel? If its going to make a huge difference I can probably talk my supervisors around on the issue...

Mudwiggle		Posted : Friday, 1 May 2015 8:28:46 PM(UTC)
Rank: Gold Ingot Groups: Registered, Moderators Joined: 22/10/2013(UTC) Posts: 742 Thanks: 182 times Was thanked: 683 time(s) in 317 post(s)		You're still going to be limited by the capability of most machines. They aren't designed to go really deep (no-one wants to dig a 3' deep hole for a tear tab...) The numbers are the first to disappear though. Then the sounds get fainter, then scratchy. Unfortunately, there is a little of the black art to it too and a lot of it comes down to putting the hours in and learning the machine behaviour. Reading the manual gets you started (and I congratulate you for that!). What you are trying to do should be well within the capability of the AT Pro though. I'd be very surprised if your targets migrate deeper than 30-40cm over the course of the trial. I've detected several paddocks that have been grazed/planted/cropped etc, and most targets, dating back to early 1900's have been in the top foot of soil. I have pulled rare ones out from deeper although they are the exception. I think you might be focusing too much on the worst-case scenario of your targets going deep. The other alternative is to find a local wand waver who can apply their skillset to pick up the targets for you? Maybe one of the 'hotter' gold machines, or a PI (they go deep enough to be a pain sometimes!) might be better

Ronnie		Posted : Friday, 1 May 2015 9:08:05 PM(UTC)
Rank: Gold Flake Groups: Registered Joined: 30/03/2015(UTC) Posts: 15 Location: Christchurch Thanks: 8 times		The depth the nuts will go depends on the depth of the soil though, and the soil conditions. The ground will be wet or saturated the entire winter in Southland, meaning that the soil will be soft and the nuts might get pushed a bit deeper. Particularly toward the bottom of the slope! To pick up targets at 40 cm+ you have a point, but to be limited to 15 cm would be a bit of a worry! I'll do a bit more playing around over the weekend and hopefully I can get a bit more of a hold on the technique and the different tones etc, and it is just my understanding of the machine that is the problem! I'll have another chat to my supervisor next week Re: getting someone in to do it if I don't iron things out over the weekend....