Saturday, September 13, 2014

9/13/14 Report - Problems With Air Tests. How To Test Your Metal Detector. Buried Objects and Disappearing Signals. Tropical Storm Edouard.

Written by the TreasureGuide for the exclusive use of

Not long ago I said the best way to compare detectors is to take the detectors out in the field and compare them on targets that have not yet been dug and compare the signals.  That gives you a comparison in the specific environment.   I'll explain my ideas on testing detectors today and explain some of the problems with some common approaches.

Everybody knows about air tests.  One of the problems that I have with air tests is that the test targets are often not the best.  People tend to use a clad coin of one denomination or another.  As I've explained before, unless you want to find a clad coin, that is not the most relevant test.   Different detectors react to different types of targets differently, therefore you should use test targets that include the types of things you are most interested in finding.  A single test target won't tell the entire story. 

Some people use a nickel because it has a relatively low conductivity, supposedly something like gold, but however true that might be, few gold items are shaped like nickels.   Most gold targets are not solid disks and few are as thick as a nickel.

One big problem with air tests is that they usually aren't done in the type of environment where you will actually use your detector.  They are often done in a house or yard, where there are power lines, underground cables or other sources of electrical interference.  Some detectors react better than others around sources of electrical interference.  That will affect your air test results.  Most beaches are relatively free of electromagnetic interference.

An air test does give you a little information, but it isn't a very good test for comparing detectors or for figuring out how deeply real targets can be detected in the field.

Another approach is to take the detector out and dig a hole and bury a target and then see how deeply the target can be detected.  Of course, for that test to be most accurate, the target should be buried in the type of ground you intend to hunt.   Some detectors will work better in dry ground, others in wet  salt sand, etc. 

Even if you are in the right type of sand or soil, you will not get an extremely good  measure using a newly dug hole.   A target in a newly dug hole will NOT give the same response as a target that has been buried for a good amount of time.

You've probably heard about the "halo effect."  Supposedly a naturally buried object will have a halo effect and therefore give off a stronger signal than a newly buried target.   I won't get into how the halo effect is supposed to work, or even what it is, but I can say that a newly buried target won't give the same signal as a naturally buried target that has been in the ground a while.

Have you ever dug a hole to get a target in the wet salt sand and you couldn't find the target in your scoop or in the hole?   It seemed to disappear.

Here are some things that could have happened.  The object could have slipped down deeper in the hole, or it could now be sticking to the side of the hole and standing on edge, thus presenting less surface area for the detector to detect.  Those are two ways that a target can seem to disappear in a hole, but there is another.

Go to a beach where there is compact wet salt sand.  Dig a hole.  Now run your detector over the hole.  If you are in all-metals mode, you might well get a signal from the hole where you disturbed the sand. 

If you can find some black sand and run your coil over it, you might get some false signals, but if you dig a hole in the black sand, or even disturb the smooth black sand, you'll probably get a bigger signal from that.

If you don't get a signal from the disturbed sand of a new hole or the black sand, your detector is probably canceling that source of noise out and you'll therefore likely be getting less depth.

The thing is, a newly dug hole will change the ground, either causing false signals or changing your ground balance so that your detector is less sensitive.  That is another way an object can get lost in a hole,  The hole itself disturbs the ground, which can cause false signals or a change how your detector is ground balanced.

Another problem with digging a fresh hole in sand, especially wet sand, is that the entire matrix changes.   Just watch a newly dug wet sand hole.  Water will come in and fill it.  Sand and shells will move about and settle,  And if you threw a coin into that hole, you saw where and how it was before you covered it, if that is what you did, but you won't know how or where it settled after that.

Since a target in a newly dug hole will settle, and since a newly dug hole disturbs the sand and creates false signals or changes the detector's ground balance, I do not find newly buried objects a good way to test a detector on a target.   The sand or soil in a newly dug hole is not settled like the sand or soil surrounding a naturally buried object.  And it may have not had time to create a halo effect. 

To me, setting the object on the ground where you intend to detect, and then raising the coil above the object is just as good, or in my opinion, a better way to go.  That way the detector will be responding to the natural undisturbed ground in that area.   It is true that you won't be detecting "through" that type of ground, but if your settings are right, that won't matter much.   I think you will get as good an estimate of depth by raising the coil over an object on the surface as by digging a hole and disturbing the ground. 

Also,if you experiment a little, you'll see that an object in a very well packed area will generally give off a better signal than the same object buried in course material, such as course shell sand.


As you can see there are three areas of weather to watch.  (See map at top of post.) The weather system that has been bringing us wind and rain has now moved into the Gulf.

Edouard is still out in the Atlantic, and there is one more disturbance following Edouard.

On the Treasure Coast we still have a small surf and fairly good tides.

Happy hunting,