lets discuss air tests

[moonshine]

ill tell you what i think, and then you tell me why it is wrong. im curious to learn more about this subject.

the detector creates/projects an electromagnetic field, then picks up a field generated by a metal (conductive) object.

i do not understand how "air" can interfere with an electromagnetic field.

if anything i would think an air test would be the maximum depth you could acheive, PLUS the conductivity created by the coin "charging up" the surrounding soil over time MINUS the interference from the ground minerals.

(with the two detectors i have used in my life the air test has been a good indicator of the detectors performance in the field.)

really curious to learn more about the subject.

 

[Jason in TN]

I think that if you expect to get deeper readings on coin in the ground than a air test you are in for a suprise. Cause it ain't going to happen.

 

[larrybass]

O.K. there Moonshine, thanx for the neat post. Here's a little of what I believe... 8) First off, it's just called a test and that's all it is, it's not proof. Although, like you said, it does show the deepest that your machine can ever possibly read anything, anywhere, period! 8) It's Not always about how deep a machine can pick up say, a coin in various areas. Nope, ya have to leave that to your (fun part) field tests. Air test's are convenient and very educational when you are stuck indoors and want to learn some neat stuff about your particular machine. Trust me, there is ALOT to learn and I mean, quite a bit more, than you think you already know about your unit. As a matter of fact, I'm going to take a little step out on this limb here and say that, I'll bet anyone, right here, and right now, that done with sincere interest & lots of learning as the reason or motive, air testing will teach even you, much about your detector that you did not already know. Any takers?

For the sharper ones in here, this so -called air-testing, can and may, turn into a very interesting way to while away some of those long winter hours. At the same time you are getting as close as you possibly can to actual "real" detecting. Many long cold winter nights up here in Kanuksville, have been put to good use getting to know just what my detector is telling me. For hours at a time, I've sat with many different targets around me in a metal free area of my studio, and then ran a series of tests to observe what the machine sees and just how it describes that data to me. There are many surprises to be experienced while doing this kind of testing, especially if you get serious and pull out a real pile of "different" metal objects around the house to test. I could keep writing on the various ways, objects, covers, multi's etc etc that I use in some of my testing but this would take up a lot of space here and that's not why I'm posting, Mr.Moonshine.

All that my post here to-day is really saying, is this: Try some (open minded) air testing this week in a nice warm cozy spot in your house, away from any big hunks of metal, of course. Grab a good handful of coins, pins, badges, buttons, rings, tabs,keys etc etc and spread them out around you, to start. Get your machine tuned properly, the way you think it's supposed to be set-up and then see what kind of stuff you come up with when these objects are passed over the coil, at those settings...You very well may be surprised at some of what you see and hear.

There are many, many versions of this testing procedure and I will throw in a few of some that I do, in future posts here, but for right now, why not start a little air testing of Your machine to-day, while it's still fresh in your mind, from Moonshines post? What have you got to lose? Maybe some of your preconceived notions of your own personal equipement, perhaps. Plus you WILL learn some New stuff. Knowledge IS good. 8)

So folks, go ahead and air-test, have fun with it and try to prove me wrong while you're at it, if you want... 8)


Lb

 

[bazinga]

I think that if you expect to get deeper readings on coin in the ground than a air test you are in for a suprise. Cause it ain't going to happen.

A 'halo' effect will form on objects in undisturbed ground for a long time. Thus creating a larger object to detect and gaining depth.


A minelab won't airtest worth a poop, but take it out in the field and it will detect the same coin deeper if it is in the ground vs. an air test.

 

[jeff of pa]

bscofield Answered your Question Perfectly.

Halo Effect &

Detectors that Analyze the Ground in order to Decide the Object Need the Ground not air.

 

[U.K. Brian]

Everyone who considers 'halo' effect is going to transform their depth of detection should rush straight out and bury a few test items then leave them for twenty plus years and see whats happened.
This is unless you are after iron/ferrous who's depth and target signature will increase as it breaks down rapidly especially in damp or aggressive soil.
Gold can't break down over a short a period as 2000/3000 years. Pure silver develops a patina that in effect insulates it so it becomes as one with the surrounding soil. Pure copper does the same. Bi metals and metals that are contaminated or adulterated will have an accelerated decay rate in acid soil. But they are the very coins that are in such bad condition as to be not collectable.
To get a true halo the item has to remain stationary for many, many years. So no wave action, no flooding,no ploughing, no earthquakes, no worm action and no heavier item nearby which will cause lighter items around it to rise in the soil.
A mistake often made is to use a detector that has an auto mode like the Sovereign which in air will drop the sensitivity to a mid point when it can't locate a ground effect. If switched out of auto a much better air test will result.

 

[Jason in TN]

UK I agree with you the Halo effect is a myth. In real life this does not happen. In ground that has not been disturbed your detector will get deeper than ground that has been. This has nothing to do with the halo it is because of the detector being able to penetrate the undisturbed ground better.

 

[larrybass]

Hi again folks, some pretty good comments in here so far. To re-direct a little though, my earlier post went on about actually testing your own machine out, and hardly mentioned anything to do with depth of the machine at all. There is a natural tendancy for fixation on depth I know, there always has been, but I'm talking about simply "seeing" how your machine reacts to different metals under nice controlled conditions. With all those different programs and knobs and switches and auto this and auto that, which all these new machines have now, it will be very interesting for you to see what your machine is thinking when you pass metal objects by the coil, right there in front of your own eyes. Is anyone catching on to what I'm talkin' about here?

Lb

 

[Knipper]

I've been detecting since 1976, mostly in MN, IA and WI. I've owned and used at least 20 different detectors, all top of the line for their day. My observation on air tests vs. deep targets in the ground is this:

In some cases, an air test will detect a coin at a greater distance. I've observed this is usually the case when compared to detecting a target in very mineralized ground which effectively sets up more 'resistance' to the transmitted signal.

Most of the time, my detectors have located deep coins in undisturbed soil DEEPER than the detector will sound off for the same target in the air. I've never found a gold coin, so I can't address that one, but I've observed it to be true for any other coin I've found.

You don't have to make a test garden and wait 20 years to observe this, either. I've dug conical shaped deep plugs (where practical and permitted) for targets I believe will be beyond 4-6 inches deep. When the soil is moist, the plug comes out intact (moisture of the soil is another factor in all this...) At this point, I've observed that after immediately checking the hole with no further digging (to determine if the target is in the plug or still in the hole), if the target is still in the hole, it will sound LOUDER (presumably because I've taken away some of the barrier to the detector's signal)

Now, after the target is recovered (digging down another 2-4 inches beyond the plug depth) if I air test the target, it has almost always been fainter in the air test than the signal I heard while the target was in the ground!

To further demonstrate what I'm saying, take the target you just dug, place it back in the hole (flat), put the loose dirt on it followed by the plug...tromp it flat and then run your detector over the target again. MOST of the time, you will find you will NOT be able to hear the target at all, or sometimes, it will be so much fainter that you probably would have missed it to begin with.

How could this happen unless several points were true...

1st, that the soil barrier does in many cases does decrease the effective depth of your machine (in either discriminate mode or all metal)

2nd, that the reason you even heard the the target to begin with is that somehow, lying undisturbed in the soil for a period of time, the target's 'field' has been enhanced by some process. This 'enhancement' is what is commonly referred to as the "The Halo Effect".
I don't know if there is really a "halo" involved or not, or if in fact oxides from the target are leaching into the surrounding soil...it doesn't matter. I just know that I've observed the above results many times with many different machines over the years, and I'm convinced it exists, no matter what one may choose to call it.

Of course I'm also assuming that these targets are deep to begin with...at the very outer fringe of the depth your detector can reach.

I've hunted twice in England...mostly plowed fields (20 days total of solid detecting, morning till evening, every day). First of all, I find their soil (at least where I've hunted) to be the most neutral I've ever seen. It's actually difficult to manually ground balance in some places as you don't get a very big difference in threshold (if any) between the coil 4ft off the ground and dead flat resting on the ground. Also, after a recent plowing, the field may be 'frothy' with just as much air as soil above the target (assuming no rain has fallen to compact the matrix of soil). So, detecting depth tends to be limited to what a machine can typically detect in air tests. Neutral soil, not tightly packed, disturbed every year by plowing and, if deep plowing is done every five years or so ( sometimes to a depth of 3 to 4 feet) even more disturbed soil. I don't put this kind of hunting in the same ballpark as what I explained above.

So, whatever you want to call it, Halo or leaching oxides, I think SOMETHING is going on, and being aware of it may help you find deeper targets.....


Knipper

 

[Night Stalker]

Ditto with Brian! Great Answer....

 

[Charlie P. (NY)]

Well there's something going on. Whether the "halo" effect is caused by leaching from the coin or some catalytic reaction, or just minerals and salts in the surrounding soil reacting with the moisture to create additional electromagnetic fields or what-have-you. Has the soil been changed or just "energized" at the moment you happen to be passing over? I can't say. I know dissimilar metals experience galvinometric corrosion, and the gold and silver, being more "noble", cause the lesser minerals in the soil to corrode (not the other way around). I am sure the detector detects this and I am convinced there is a halo effect occuring.

I now the nitrates in the grass fertilizer hit the copper pennies pretty hard at one park I detect at.

The air test is just one test and really only proves how well a detector works with exposed objects. I would not drop $$$ on any detector based on that one test alone. I don't shoot flying coins.

 

[WV Hillbilly]

This is a much debated + confusing subject . My question is if a coin is laying pratically on top of the ground , basically an air test , why does that coin give off a much louder signal than a coin that is buried deeper ? Seems to me the detector is having to deal with ground conditions both ways . I think we all can agree the deeper the coin the fainter the signal . Now if one believes a halo effect causes a coin to produce a larger target than it does in air or newly lost , 1/2 - 1 inch down why isn't it louder deeper rather than the other way around ?

 

[Charlie P. (NY)]

Because the field strength of the coil is stronger nearer the coil and them little dotted lines they put in the catalog drawings are closer together? The better comparison would be: does a coin buried 2" read better than a coin held 2" away".

Remember, our detectors are tuned to percieve an object that conducts better than the surrounding dirt. Air is a poor conductor, so it's a gimmie for the detector to contrast the coin to the surrounding air.

 

[WV Hillbilly]

Another question , do the target id numbers read the same in an air test as they would in the ground ?

 

[swingman]

my 2 cents

I have 2 Minelabs - the older Sovereign and the new SE. Neither air tests very well; i.e., I have found coins deeper in the ground. Why? The only reason I can think of is the 'halo effect'. Yes, I think gold has little or none. Silver a bit more, and the rest could be a lot.
One poster suggested you'll learn a lot air testing, and I agree. Try several silver and gold rings - turn them at various angles to the coil. You might be surprised at what you read.

 

[moonshine]

thanks for responding everyone, i appreciate the feedback.

 

[WV Hillbilly]

I really hope that a detector will detect deeper in the ground than it will in air because I was bored yesterday + tried some air tests . I was really impressed with the distance my detector will pick up in air tests . If it will do just as well in ground I'll be a very happy camper or should I say MD'er .