Finding out how deep my detector goes

[lupillopreciado]

Would anybody in the audience tell me if the best,and easyest way to test if your detector really goes that deep is like ,diging holes in the sand and hiding metal objets.And do you think that, doing it at the beach,will not affect in any way my detector.

 

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[Sandman]

You can try this at a beach and it will give you an idea of the depth at that beach in that part of the state, but the results would be different somewhere else. Also the longer the coin stays in the ground the deeper your detector may detect it due to the "Halo effect." Using your detector at the beach in the dry sand won't hurt it. Don't get it wet from the salt spray or drop it in the water. If you get the coil wet, you can by the way, don't let water in the shaft travel up the shaft when you raise the coil higher than the controls or water will fry the thing.

Read all you can on the hobby and Good Luck,
Sandman

 

[Michigan Badger]

Like the sandman wrote, fresh buried coin tests at the beach can give you an idea of the depth at that beach. Beach sand is a totally different thing from hunting black dirt in the average yard. At the beach there's often not much time for a "halo" (or more likely a certain ground structure) to develop. So, fresh buried there is more accurate.

One good way to test coin depth is to glue coins to wooden dowels and push these down into the sand. Make 5,6,7, etc., inch dowels with a coin glued on the end to be pushed down into the ground the length of the dowel. This way you're not guessing about depth.

Badger

 

[BamaBill]

I'm beginning to believe that halo only exists for iron objects. What we're calling halo is actually a compacting of the soil to exclude voids. I haven't found concrete evidence to back it up, but several things lead me to believe that the air introduced into the soil when freshly turned causes the signal to bounce around and scatter, rather than return in an orderly fashion, the way it would in compacted earth. In fact, if there is any kind of halo that forms around brass, lead, or other non-ferrous targets its extremely small and would be hard to pick up with most detectors. This is conjecture on my part, based on observations. Now, does someone have any concrete evidence to provide about halos or opinions on why freshly buried targets cannot be detected as deep as long buried stuff?

 

[Michigan Badger]

In fact, if there is any kind of halo that forms around brass, lead, or other nonferrous targets its extremely small and would be hard to pick up with most detectors.

100% correct!

The surface size of an object doesn't always determine its detectable depth. Size does matter sometimes of course but metal alloy and frequency are also very important.

Remember the old BFO's? That frequency got you what? maybe 5 inches on a bowling ball

I've tested detectors that got the same depth in the coin garden on a silver dime and silver quarter. I wouldn't argue it but my mind is make up about the "halo" thing. For iron..yes, but not nonferrous.

 

[Skifisher]

I feel the biggest variable in depth is mineralzation of the soil. The aforementioned beach test should be somewhat accurate, the only way to really find out how deep, is to get out there and find stuff. For some reason disturbed ground reads different than undisturbed.

 

[kermit]

I guess it could also depend on how the coin falls in the dirt. If it's flat you will pick it up deeper if it's on edge the signal will be harder to detect.


Kermit

 

[Murph]

Like was said there are lots of variables.

From reading the various forms though the biggest variable seems to be brand loyalty. Everyone has the deepest seeking detector that can be bought, ya cant go wrong

 

[Michigan Badger]

Like was said there are lots of variables.

From reading the various forms though the biggest variable seems to be brand loyalty. Everyone has the deepest seeking detector that can be bought, ya cant go wrong

We're all equal...BUT, the Sovereign GT is a bit more equal.

 

[johnnycat]

I packed the ground in my test garden after I buried the test coins. I cut a 2x4 in half and stuck it in the ground in the coin area and pounded the stick with a large hammer to compact the soil. Now, 5 months later my readings are almost right on. BamaBill I feel the same way you do about the halo.

 

[EasyMoney]

Here we go again...

George Payne, Eric Foster, and Jack Gifford all say that there is ABSOLUTELY ZERO boiling off (halo) effect with anything but iron and steel.

Iron is a highly unstable metal and rusts and deteriorates quickly and easily, but the others do not, and gold, copper, brass, lead, zinc, platinum (especially platinum) do not release their electrons easily at all, and if they do, the effect is not sufficient to cause a "halo effect". A steel penny will have a halo effect though, but not a copper one. In other words, a hole not yet dug has a different matrix effect signal than one that has been dug, or is open.

If a detector finds an old coin deeper in the ground than it does an identical old one freshly buried, it is because of the ground matrix effect change. The matrix has been disturbed when digging a new hole to test it in, and nothing more. There is no halo effect causing the old one to detect deeper than a new one, it does this because the new hole is "different" in it's composition mat than the undisturbed one.

Go to the three gentlemen's metal detector engineering sites and you will find their reading very interesting. Jack Gifford's works are a little easier to read though. George's are better written for at least a low-voltage electrician, but are still a bit complex.

Incidentally, a PI will go deeper in the ground than in the air and it's because of the eddy currents that wrap around the target and continue onward creating a "ghost effect" past the target.

The above is not my opinion, it is a chemical/electronics/physics fact.

And, according to all three detector engineers the air test is the biggest determining factor to show a metal detector's depth abilities. This is why the Garretts 2000, Nexus, Nautilus, some Compasses, Red Heats, and Eric Foster's component VLF's get the best air test AND the best ground test depths, beating the the rest of them like they are a bunch of redheaded stepchildren.

Good luck and HH

EasyMoney

 

[BamaBill]

Ok, I gotta ask the question. Where do you guys get the idea that its the "matrix" being disturbed that has to do with the depth of detection on recently buried vs. in the ground a while? As an ex-Archie that dug my share of features, I can tell you that disturbed ground never has the same stratigraphy that undisturbed ground does. I'm firmly conviced it has to do with the voids (airpockets) that are introduced when the hole is first dug. The electromagnetic waves travel differently through air than through ground. Air tests are just an idea of what the detector is capable of and the electromagnetic waves will travel faster and easier through air than through any kind of ground "matrix". So, if there is a mix of air and solid ground the waves will not travel uniformly through the ground and I'm pretty sure this will cause scattering that will direct energy out of the ground in a such a way as to make more difficult for the machine to pick it up. This idea of a halo around buried items is a sacred cow that needs to be tipped.

 

[EasyMoney]

Bama, what you have stated, further fortifies the situation regarding "matrix". Thank you for your input. A matrix is not only a strata or a conglomerate, it can consist of gasses, liquids, solids, metals, minerals, etc. A matrix is simply the existing conditions, color, or chemical conglomeration found in a specific and exclusive area of substance. When a "matrix" is disturbed it no long has the same moleculer allignment as the surrounding soil and it's other inclusive molecules. In color matrixes, the color is of a different molecular configuration too, before adding to the already existing color scheme, and that is exactly why there are different colors, because they have a different composition than do other colors. They reflect light of different heat frequencies than each other.

If a soil is moved around or away from an area it no longer has the exact same arrangement of all it's minerals any more. In fact, the electromagnetic field is no longer as strong or as weak, it is simply, "disturbed". A piece of steel that has been magnetized has it's molecules arranged magnetically too, just as the soil has it's arranged. When changing them electrically or otherwise, all the electrons and molecules no longer are ligned up in rows with the poles being back-to-back positive (+) and negative (-) like sardines in a can, any more. Some are pointing here, and some are pointing there.

This causes change or alteration AKA "interference", a term used to describe it's lack of ability to use and process any other electrical influence of any other kind very well. Remember that electricity, chemistry, "hole theory", and quantum mechanics are, or can be, all one and the same. It's pretty basic electrical theory though, well-known by any good electronics tech or electrician. The chemical composition would be still intact in the soil, but no longer in the same order, or magnetically charged the same as it's neighboring soil, regardless of whether it has been caused by changes in the amount of air in the soil or metal in the soil, a magnet, an electrical signal, or otherwise.

All this above causes electrical RESISTENCE, and electrical resistence causes a lack of voltage, or "power", be it rf voltage, RMS, sawtooth, sine, negative, positive, pulse, static, DC or AC. It therefore causes less signal to be returned to the detector to read, and this causes the detector to not read as deep as it did before.

In many cases you can actually see and hear this change in action; In the cases of many detectors when one digs a hole and takes the dirt out he or she can get a very loud reading over an empty hole, although the chemical composition is still the same, save for the air in the hole. When putting the soil back in the hole a manual GB detector will need to be retuned in order for the detector to act the same over the dug or (or filled) hole as it did before any hole was ever dug. A refilled hole has a different electrical (magnetic) arrangement (matrix) than one that has never been dug. A very fast auto-retune will often compensate for the change, and many detectors have this built into the detector but some do not.

Additionally, when soil is returned to the hole the top level of the soil's plug is no longer exactly in the same place as it was before, and yes, air has also likely been added to the soil too, but not always. Sometimes there is less air and sometimes there is the same amount.

Again, the halo effect does NOT substantially involve metals other than iron or steel. It can't. If gold fell apart or decomposed easily, it would create a halo effect, but it does not and it will not. Neither will silver or any other precious or semi-precious metal, save for copper, to a miniscule degree. And the info I just gave you is not my opinion, it is the material that they gave us in college when I first studied electronics, and later engineerng at OSU and EWU.

The Fisher Home site discusses this halo effect in much simpler and easier terms than do the three engineer's sites I mentioned earlier. In fact it says that copper has a bare minimum (at best) of leaching out it's chemicals but not enough to create a useable "halo effect" and that gold, silver, etc. do not create a halo effect at all.

Hope this helped.

EasyMoney

 

[doozis]

It just ain't fair
Halo's are supposed to be for good things like Angels, Gold and Silver but
rusty nails are PURE EVIL and yet they get the halo
metal detectors are evil mongers !!!!!!

doozis

 

[99thpercentile]

One of the biggest issues with disturbed soils is the magnetic properties. Assuming that there are some magnetic materials in the soil such as magnetite, when you put soil back in the ground the grain orientations will be different even if the only soil that you use was what you just took out. This will show up best to a magnetometer, which is why filled in fence post holes almost always show up well in magnetometer surveys.

Addressing the original question of how to determine the in-ground depth of detection of your sensor, for unexploded ordnance (UXO) surveys a geophysical prove out (GPO) is always conducted on each site. This involves burying targets that are expected to be found on sites a various orientations and depths. Then the survey technique which will be used on site is done over the GPO to see how many of the targets were identified correctly (XYZ location, inclination and declination). You can download a PDF of the standard for GPO design from the Interstate Technology & Regulatory Council website. Look for the document titled UXO-3, it is a good read.

http://www.itrcweb.org/gd_UXO.asp

 

[hsjrev]

Does lead make a "halo?" It doesn't bench test all that well, but both my Tejon and Compass find lead shot at annoying depths.

 

[EasyMoney]

No halo on lead, but my Compass Relic & Coin finds #8 shot 2" deeper than my Tejon, even if the Tejon is supertuned.

 

[MD Dog]

If all this was about electricity or magnetics then wouldn't the Earths own magnetic freild also play a role and what about lightning, would say a coin that was in the soil in the vicinity of an electrical discharge of such magnitude as a lightning strike have differing magnetic or electrial properties, or maybe there a reaction between the coin and the soil when theses events take place. After all science tells us that all life was started by a freak electrical strike, so maybe thats what is taking place here and that would explain why some of us find more or less of the older coins. It all has to do with the weather and lightning strikes etc...






Or maybe it's just my tector is luckier n yours.

 

[EasyMoney]

No MD..

It's all dependent on the phases of the moon, the luck of the Irish, the amount of salt in your body, the health of all witches in Canada, the position of Saturn in it's early morning phase related to the weight of Pluto, the volume of a dog howling or vomiting, and the time of day that you comb your hair..

 

[MD Dog]

So your tryin ta tell me the color of your socks got nuttin ta do wit it ?