Air testing metal detectors, Does it work?

[jeff of pa]

Ah yes, and Bigfoot exists because others have told me so.

As I said I understand the hallo effect concept because it can be scientifically explained to a point. The concept that a detector would get better depth in the ground, having to deal with mineralization, trash, etc, just seems to be lacking in a scientific explanation. In this case it would make it more theory than fact. Again, I understand the hallo effect concept that applies to coins that have been in the ground a long time, but this phenomenon is limited to certain conditions, and since it is limited to ONLY certain conditions, it sure doesn't seem honest to make a blanket claim that detectors go deeper in the ground than the air, so air tests are worthless for depth testing.

Generally I find these claims made by people who get crappy air tests on their favorite detector.

But hey, I know Bigfoot is out there somewhere just waiting to be found.

ya Know people who Argue the same point over & Over
Do so because deep down they Feel they are wrong.
but don't want to loose the argument.

Please Re-read this if expecting
Fruther comment from me

 

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[Digger]

air test quarter 6"
fresh buried Quarter 5"

Long lost Quarter 9"

ever dig a taget & Loose it ?
you broke the ground & added air.
repack the ground
walk away and come back later.

And does this happen EVERY TIME? If not, then it's reliant on certain conditions. I.E. not something you can claim WILL happen, but CAN happen. So claiming air tests don't give you an idea of the potential depth is misleading. And then there is that pesky lack of scientific explanation thing.

So the accurate statement would be with the exception of certain conditions, a detector will get no deeper than it gets in a air test and in fact will more often get less. This also means an air test does indeed have value in determining potential depth. Oh wait, but I already said that didn't I?

Sometimes facts take repeating before some people are able to comprehend.

 

[Old Town]

I have no electronic background but once had a detector's radio signal described to me by a Navy man who was trained on sonar and radar and all things related. He said a detector's signal would always work at its best potential in the air where the minimal interference existed. A vacuum chamber is the only environment that would be better for it to work in. Needless to say we don't live in a vacuum.

He went on to say any water or dirt you will encounter can only absorb or block your detector's signal. As we all know, some earth conditions are better for detecting than others. It was his trained feeling that the more porous the earth, the better to allow the radio wave to pass. Metal or iron content in any soil would absorb and thus ruin a signal too. Exactly like a load in microwave tubing absorbs microwaves at the terminal end of waveguide used in radar, etc. This same man said the reason you get better depth in wet soil over dry soil had nothing to due with conductivity. Conductivity is a bad thing. To conduct the signal is to trap or contain it as with a load in the waveguide. You always lose strength when you make your signal work through or along some other material. The reason you get better depth in wet conditions is because the water molecules make "less dense" pathways throughout the soil matrix. In essence you've "loosened" the soil density. Water does occupy space but it is less dense than the soil it is displacing. The end result is soil more easily penetrated by your radio wave. You always get better penetration in fluffy earth over packed or dense earth. (minerals not withstanding)

His theory matches my field experience exactly. I always get better air test distance or depth than what I get in any ground. I can't speak to those who own Minelabs and get such poor air test results. My own Soverign and E-Trac air test out to 12 inches on a clad quarter. My Cibola does 13 inches on this same quarter. I notice no big difference between brands or between multi or single frequency machines. If my E-Trac only air tested 6 inches on a quarter I'd toss it over the side in very deep water. But mine checks out fine. I can't explain your lesser Minelab result.

In conclusion, my air tests are always deeper than my field and test garden results. Always. Have never seen an exception. I think air tests are meaningful. Which is to say if my machine tested at only 6 inches through the air, I move on to something else.

Old Town

 

[Digger]

Again Old Town I agree completely. The idea of an air test being a best case scenario is also supported scientifically.

All my detectors have always tested better in the air than in the ground consistently. I have pulled a few deeper than air test coins, but that is the exception to the rule.

Tested:
White's Eagle Spectrum
White's XLT
White's DFX(4 different ones)
White's V3 and V3i
Minelab Sovereign GT
Minelab X-Terra 70
Minelab E-Trac(2 different ones)
Garrett Master Hunter CX
Garrett Master Hunter CX Plus
Teknetics Omega 8000

 

[bigscoop]

Digger,

I just got off the phone with an engineer at Fisher Research Labs and this is what he told me:

"Only in very rare conditions will a detector read deeper then it reads in an air test. We have units that air test at 14" but in actual hunting conditions they will only go to about 9 inches."

He went on to explain that in rare conditions the signal can be absorbed into the ground, or in the case of large targets or targets with high conductivity it can be slightly extended, but that this was not the norm.

So it appears, according to this engineer from Fisher Research Labs, the correct answer to the original question is, "Yes, generally speaking, for the most part the air test is a reliable means of checking detector depth."

 

[Old Town]

Digger, I believe when we get "extra depth" we might be detecting halo effect minute particles from the target that fall within our actual ground penetration. Say your machine can do 7 inches in a particular soil. You come upon a small iron object that is very rusty at 9 inches. The iron object's particle field (halo) extends several inches in all directions. This now places it within range of the detector. You really didn't get extended depth even though you made a deeper recovery. You were sounding on real metal particles that fell within your range.

What is tough about this whole issue is getting a precise record of our target depths and types. First you have to compare like targets. No way you can compare a coin recovery to a cannon ball. Bigger targets air and ground test deeper than little ones. So assume like targets always.

I believe most people exaggerate their deep target recoveries. Myself included. So anecdotal accounts are not very scientific in my mind. Now I've never found a coin deeper than 11 inches in the wild. My test bed 12" quarter is also a good test. It's been there for over 5 years and gives a good indication of extreme depth in my soil type in Florida. My Cibola, Vaquero, Tejon, and E-Trac are the only detectors that have ever beeped on this coin. All of these machines air test at, or slightly beyond, 12 inches. My soil is very fluffy and without minerals. I'm convinced of air test validity.

OT

 

[bigscoop]

I hung my metal detector horizontal from the ceiling and while air testing it the darn thing kept going off everytime I walked by it, an hour later I was completley nude and it was still going off everytime I walked by it. Then it dawned on me...."airhead!"

 

[macnab]

Can you REALLY find Bigfoot with a metal detector?? WOW!!

 

[CincinnatiKid]

No, but bigfoot1 can find you with a metal detector in 2015.
Also, what Sandman stated in 2010 x2.
Love resurrected threads!
Peace ✌

 

[Professor of Engineering]

Hello Everyone,

I use air tests to determine a baseline for VDI’s and target tones. In the field, both of these can possibly change with soil conditions, contamination from other targets, depth, and orientation of the located target …etc. I do not in my experience believe they are very reliable for true depth.

Regards,

 

[Treasure_Hunter]

Let me know the next time you see coins floating in air...;-)



Posted From My $50 Tablet....




“A well-regulated militia, being necessary to the security of a free state, the right of the people to keep and bear arms shall not be infringed.”
― James Madison
The Constitution of the United States of America

 

[luvsdux]

I've posted my opinion when this has come up before and here it is again. I agree for the most part that air testing doesn't equal actual, in ground results. However, I feel air testing is a very useful function when comparing different machines and/or coil size results. Also, if you know your detector has detected a target at say, 8 inches and it no longer does under the same conditions, settings etc. you have an earlier figure to compare to. To me, that alone is a worth making up a chart using several targets and settings for future use. And air tests can also be useful to see if different setting make much of a change or not. My two bits.
luvsdux

 

[Charlie P. (NY)]

Wow! Old thread.

But yes, air testing will tell you how you will do at finding flying coins and for detectors so insensitive they will work indoors.

Put the coin out of doors on the ground at least. You need to know how they work near soil. There will be more than air between you and a good coin.

It's like test driving a car in the dealer's showroom.

 

[SouthFLdigger]

My observations are these:

Air testing will show a machine's depth potential. So if one machine air tests at 8", and one tests at 11", the 11" machine will always test deeper in the same soil. I've tested this a million times and it was true every time.

Your machine will not detect coin-size objects in the ground beyond its air-test depth. You might get improved depth due to halo effect on iron but in such cases you are actually detecting minute metal particles inside the original air-test depth. Not extra depth.

All machines lose depth in the ground compared to air tests. How much depth lost is dependent on soil makeup and density.

Last of all - nobody will agree with all above statements. This is a highly debated issue in metal detecting.

OT

.

Agreed 100% and this has been my observation as well, confirmed by experts from Minelab.

 

[Treasure_Hunter]

My personal observations I have done on my derectors don't agree. I get far more depth in ground than I get in the air on my excals and Sov GT.... In air on stock 10" on excal I was getting maybe 5" air test but in real world I dug hundreds and hundreds of targets at 10-12 inches.



Posted From My $50 Tablet....




“A well-regulated militia, being necessary to the security of a free state, the right of the people to keep and bear arms shall not be infringed.”
― James Madison
The Constitution of the United States of America

 

[hikerdude]

I air tested my old Bounty hunter Lone Star against the BH Land Star I just got and the Lone had 1in. more depth. Does anyone know if the results of an air test are dependable?

When I hit a coin at 6 inches, and I dig 5 inches, and run my md over the hole, the signal disappears, then I dig a little bit further, and I get a hit with my pin pointer and find the coin? That tells me, my md detects deeper in the dirt than in the air.

 

[SouthFLdigger]

My personal observations I have done on my derectors don't agree. I get far more depth in ground than I get in the air on my excals and Sov GT.... In air on stock 10" on excal I was getting maybe 5" air test but in real world I dug hundreds and hundreds of targets at 10-12 inches.



Posted From My $50 Tablet....




“A well-regulated militia, being necessary to the security of a free state, the right of the people to keep and bear arms shall not be infringed.”
― James Madison
The Constitution of the United States of America

I don't own an excal, however physics is physics. If a specific transmitter with long wave propagation characteristics (2.3-70 Khz) with a set RF power output such as a metal detector has a specific transmitting range and detection, it will be ideal and optimal in air. Ground loss tangent, eddy currents, magnetic inhomogeneities associated with minerals and other factors will mean there will always be a net loss in ground unless volume density reduction is involved or water saturation enhances propagation. Assuming a metal detector has the right processing hardware, software and properly coded algorithms in the spatial frequency domain, detection range will always be best in air assuming the above did not take place. The air test is great for determining free air loss characteristics and ultimate potential of a metal detector in non-mineralized loamy or sandy soil. A metal detector with the right hardware and software that air tests very well will usually (not always) perform better than one that does not air test as well.

Example, two Etracs one with a specific software version (v3) that codes a mineral gradient different than say Etrac number 2 with a different firmware and hardware surface mounted components and PCB. Version 3 air tests at 13" on a quarter version 2 air tests at 10" on a quarter. Version 3 will have better in ground performance than V2. This is why you see F75 and F75 LTD, SMALL CHANGES IN HARDWARE AND SOFTWARE. The LTD version will air test significantly better in air and ground!

 

[Charlie P. (NY)]

Sounds very nice. But you lost credibility when you identified a VHF transmitter as "long wave".

 

[Treasure_Hunter]

I'm speaking from 6 years experience with Minelab excals and Sov GTs. I get more than twice the depth in ground than I get on air tests. I have yet to see any coins or gold jewelry floating in the air, but I have found lots buried deep at the beaches ..



Posted From My $50 Tablet....




“A well-regulated militia, being necessary to the security of a free state, the right of the people to keep and bear arms shall not be infringed.”
― James Madison
The Constitution of the United States of America

 

[SouthFLdigger]

Sounds very nice. But you lost credibility when you identified a VHF transmitter as "long wave".

Really, a metal detector does not operate in the VHF range at all, they effectively operate between 2 to 100 Khz. Which happens to be long wave by its non technical nomenclature. I never mentioned VHF or any such thing.

Longwave - Wikipedia, the free encyclopedia

Thanks for the helpful "credibility" comment. My experience with metal detectors confirm what other tester and fellow detectorist posted before regarding air tests.