Air tests with mercury dime - five detectors

[Charlie P. (NY)]

I don't put much stock in air tests. I hunt coins in the dirt, not in the air like skeet. How do you "ground balance" the detector before hand for the air test? Soil and the minerals and moisture in it make it a much better conductor than air and so the relative difference between the coin and its surroundings are less easy to detect.

Bury that dime 9" in your front yard, and then another with a pulltab 1" beside it at 4" down and a third with a nail 1" beside it and 4" down and test again. That's when the higher priced units begin to show their stuff. Can they still see the coin through junk and the null of an iron mask circuit?

If you get a repeatable hit on a quarter 12" down in your test garden you'll probably do all right in the wild. But if you didn't know that quarter was there would you dig on the signal it returns? There is a big difference between "It hits a 12" deep quarter!" and "I get a solid, repeatable signal with a 12" deep quarter and the display value stays constant or only jumps one unit from all directions."

I have 13 "plantings" in my test garden:

'79 Lincoln cent at 8"
'70 Lincoln cent edge-up at 8"
0.715" lead musket ball at 12"
1963D Quarter at 12"
'83 Quarter edge-up at 12"
'06 cent flat at 1/2"
Pull tab at 2" over '81 cent at 6" & offset 1"
Nail at 2" over '78 cent at 6" & offset 1"
'91 Nickel at 6"
'88 dime at 6"
Shotshell base at 5"
Three different style pulltabs side-by-side at 5"
Aluminum screw cap at 4"

Each of these is marked with a plastic golf "T" in a yellow/red/white repeating sequence so I know what I'm over by my map (I keep copy inside the garage and one at my desk so I can grab a detector and test it & myself regularly).

The trash at the tail end is handy as it will tell you how any notch setting is effecting the other targets.

I also keep a find log of what the TID read-out was & indicated depth and then what I dug and actual depth.

 

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[khouse]

Charlie,
The xterra 70 has 0 to 90 gb increments. So I just manually set it in the middle at #45. I don't expect it to find coins at 12 inches in the ground with it. The original post was not about what the detectors do in the real world. But was simply an air test on a mercury dime with a repeatable tone.

I do have a test garden with all us coins and pull tabs buried 6 inches deep on all targets. The Xterra and even the Ace 250 has no problem finding all of them with proper ID. Even raising the coil 3 or 4 inches still makes my machines beep.

 

[QUICKSILVER (appletree)]

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[Digger]

Here is a video I did of my DFX's air test on a gold ring. It got roughly 10". My Minelab SE does a little better on air tests.

http://www.detectorplace.com/detecting/dfxdepth.mpg

I think the difference between the low and high end detectors is their ability to get more of that air test depth in the ground as well.

 

[Functional]

bavarianminister:

I agree with Charlie P. on this, even if his tests only provide indications of how the MD's perform in the specific soil conditions present in his test garden. Air tests are ok for finding a maximum range in air and not much else. With most of the detectors mentioned in this thread, having different coil sizes and frequency of operation, theres no real way of determining which actually performs best for any one person in the locations and soil conditions they encounter.

Established knowledge says that coil size increases depth. Likewise frequency of the detector also affects depth. As does the type of soil, its moisture content, temperature and general humidity. Frequency itself changes slightly based on soil content and conditions, so a target that usually registers as one thing on a TID, can register as something else under different conditions. (Theoretically it might be possible to get a slightly longer depth of detection in soil, as compared to air, simply because the soil might alter the frequency in some beneficial manner that allows for greater distance, but I haven't seen any evidence of this.)

If I had access to several makes and models of MD I'd make my own test garden with separate area's of landscape soil and local highly mineralized soil. And I'd include gold and platinum in the mix of potential targets, along with hot rocks to make it interesting.

F.

 

[oldbill]

MB, due to the salts in the ground, in some cases the detector CAN go deeper in the ground than the air because the salt gives the metal a halo making it appear as larger than it is! Bill

 

[oldbill]

Easy Money, sorry but I know a bit about EMF and believe me it can happen due to the electronic field. Bill

 

[TomNWMI]

Easy Money, sorry but I know a bit about EMF and believe me it can happen due to the electronic field. Bill

Agreed Bill,

Certain soil conditions will give better depth than in air. Any long time water or beach hunter has experienced this many times. Case in point, ML X70 with stock coil on a Lake Michigan beach, 3 copper pennies found one after another within 10 mins at a measured 15" with STRONG signals. I was sure on the first that I had somehow mistakenly let the coin slip down so I used great care digging out the other two to determine there depth. I have seen the same results in these type conditions with other machines as well. Let the "experts" believe what they want, some of us know better.

HH Tom

 

[Digger]

While I understand what these "experts" are saying, I don't believe their theories are correct.

First off, I've found plenty of copper coins far less than "hundreds" of years old that show signs of leaching. Here is one example just over 100 years old that you can see has been leached away.

Second, a coin in the ground, especially wet ground, will appear larger to the detector than in the air. For this reason the coin in the ground would be detected deeper, because it seems larger, than a coin in the air.

The problem we have here is that too many people, including myself, have experienced the phenomenon to discount it as "myth."

 

[Digger]

When you find something deeper in the ground than in the air with a vlf, for example, you are not finding "it" you are finding "it's" halo, or "it's" bunch of deteriorated metal that has broken off and moved about near the original target, nothing more, nothing less.

I do understand, to some degree, what you're saying. Why it happens or how it happens I don't claim to know. All I know is that it DOES happen.

I look at it sorta like Big Foot. While I can be told all kinds of scientific reasons why Big Foot is a myth, It will never lead me to believe the people that claim to have seen one are not experiencing something. To call Big Foot a myth is to call those who claim to have seen one either imagining things or a lier.

I'm a common sense type guy and to me it doesn't seem like rocket science to believe the Indian Head above should have a larger profile, because of it's added thickness, than it normally would. If this is true then it would also explain why one could also expect a detector to see it as a bit larger and hence detect it a bit deeper.

I guess all I'm trying to say is I know the phenomenon is real and, like Big Foot to those that have experienced the phenomenon, no amount of scientific reasoning will make me believe it's only my imagination.

I offer up for exhibit A your own test garden. Test your targets when the soil is dry and then give it a good wet down. I think you'll find when the test garden is wet you will detect your targets deeper.

 

[EDDE]

If your goal is to find deeper, quality targets, the Shadow X5 is a true all terrain detector, packing plenty of muscle to handle just about any hunting situation. It's simple to use, feather-light, and loaded with fingertip user options to maximize performance and minimize programming hassles. Once you've experienced the superior depth and discrimination capabilities of the X5, you'll find those "hunted out" sites aren't so hunted out after all! Finally...a single metal detector that really can do it all from coinshooting to relic hunting to competition hunting to beach hunting to cache hunting to gold nugget prospecting! And at $1099.00

they dont make it anymore so good luck finding one NEW
i bought mine 3 years ago for 850 from a dealer

 

[EDDE]

by the way EASY killer postings as always

 

[oldbill]

Easymoney now we are saying the same thing but without the salt in the ground there would be no halo! Bill

 

[TomNWMI]

Those mysterious halos.. a contrarian view

How do detectors work? They pickup the weak emf induced in a target by the transmitted field. I know thats a VERY basic answer but thats about it really. Ring shaped objects are the ideal target as the surface currents encounter little resistance. coins slightly less so as the current can encounter some resistance due to the varying dimensions of the coins surface. Now lets look at halos, where's that nice even current flow, its not there just lots of resistance.. far from a first order target like a ring.

In my humble non-scientific opinion halos if they exist, may actually impede the detectability of non-ferrous targets. Ever detect a green "fuzzy" copper penny? you are lucky to get a hit on them from one direction of approach at 6" in damp ground!

Thats my story and I'm sticking to it. That is untill someone actually scientifically proves me wrong!

Tom

 

[TomNWMI]

Appreciate the reply EM

Very intersting stuff but just a tad over my head. anyway, its all about current flow and the resultant induced emf in the target. So what you are saying is that part of the field is in a manner of speaking out of phase with the other and reduces or maybe even eliminates the the possibility of surface eddy currents??

Most talk on the forums is about salt and salt water and its effects. what about the most common condition ocurring on earth?

CALCIUM CARBONATE!!!

Limestone... chalk... marble.. Granite...

What we all commonly refer to as HARD WATER..

I have never hunted a salt beach but have tons of hours on fresh water beaches and literally thousands of hours fresh water wading here in Michigan.

Yep I would like to read an "essay" on hard water and ITS effects on conductivity as it relates to VLF metal detectors. DIFFERENT THAN SALT BUT SO SIMILAR IN MANY WAYS AS WELL.

All I can say at this point from my experience is that hard water is is mostly our friend when it comes to detecting. 8) 8)

HH Tom

 

[U.K. Brian]

I won't go into "halo" as you need to do a series of test over ten or fifteen years but European coins make U.S. coins look like wagon wheels and have had up to three thousand years to sink in the soil so if it existed to the coinhunters benefit it would be really important here.
Silver coins do get destroyed Easymoney if in acid ground or salt conditions. Many hammered silver have become totally perforated even if supposedly "pure" silver. I agree though that there's just as many that form a nice patina or do some copper coins and become at one with the soil and immune from any halo threat (because thats what a halo is).

The machine that put current through the soil was the U.S. Depth Doubler by Compass. It worked well in the respect that extra depth could be gained but unfortunately our best/oldest sites are loaded with thousands of years of iron and the halo and detectability of the iron and its masking effect would also increase.

Re detecting deeper in damp soil. This is correct but only in the certain circumstances. Again if its a heavily iron contaminated site the effect is more on the iron so in fact it can be possible to make more good finds if the soil is dry. You need a machine that can handle dry conditions well, most can't.

 

[erikk]

I will pay more attention to air test, the first time I go metal detecting and find coins in the air and not buried in the ground ? Argh!

Ed D. My 2.

 

[Larsmed]

hey TT

is that maxine talkin?? heheh!

 

[Foilman]

Easy,
I respectfully disagree.
You say silver and gold stay shiny -not always!

It corrodes less but it corrodes, tarnishes, etc.

also gold and silver are almost always alloyed with something as you know.

If it is tarnishing or corroding or leaching or breaking down or breaking into bits, OR OXIDIZING, the image is getting bigger.

You even say yourself it could take decades. duh, if you find something from 1980 it has already been in the ground for decades.

It seems that you are arguing words and jargon just to argue a point which is wrong in my experience!

 

[TomNWMI]

This debate about halos and their effects on detectability is analogous to

the debate on use of high end speaker connect cables. Of course it has been scientifically proven (so they say) that insulated strands of oxygen free copper transmit a purer signal with little to no loss of a broader range of frequencies. Whether or not the listener can perceive the difference depends on their ear and of course whether or not they are using high end amps and speakers ect.

I still claim that halos (if they exist around non-ferrous targets) along with the oxidation of the surface of those targets are a negative factor in their detectability. Not a 50/50 deal, more like 99%.

On most subjects I am an optomist and like to think the best until proven otherwise but not on this one.

HH Tom