Construct Test Garden For Mastering Your Metal Detector
Learn Metal Detector's Responses to Various Targets & Optimize Program Settings in Controlled Environment
Halo Effect is A Key Factor
One of the first things many beginners do is burying a few coins to see how deep they can be detected. The usual result is disappointment because people do not know that newly buried coins are quite difficult to detect. The reason for that is absence of so called "Halo Effect" which has been developed as the time passes: coins become electrically more associated with surrounding earth materials and the molecules of metal begin to "leak" into the surrounding soil.
That is why the "halo effect" is responsible for one type of "elusive" signals. Such form of signal disappearance usually takes place during the recovery of an iron target, or any target that your detector is adjusted to reject. For example, after having been buried in the ground for years, an iron object that is larger than a square nail tends to develop a strong halo around it - an aura of both nonconductive and conductive properties that make the motion discriminate mode create the positive response.
When the search coil passes over this iron object, you hear a "good" signal even if the Discrimination is set up on "reject iron." Sometimes the signal does not repeat with each sweep of the search coil. You decide to dig it anyway. During the recovery, you disturb the ground around the object, thus removing the halo which has been created around the iron target by oxidation. Once this happens, the motion discriminate mode does not create the positive target response anymore as it rejects the iron target thoroughly - you get no signal. You may want to read more about this phenomenon in my article on Halo Effect.
How To Construct Your Own Test Garden
You should construct your Test Garden (Test Plot) to help you learn the capabilities of your detector and educate yourself about what you intend to find. A test garden cannot completely prepare you for what you may encounter in real metal detecting situations. However, it can help you better understand the effects of ground minerals, moisture content, target angle, oxidation/rust, trash proximity, target defects, surface textures (more details on these effects are given in my articles: "Metal Detector's Depth Penetration" and "Less Discrimination Lets You Find More". Your test garden can also provide lots of practice in target pinpointing if you take a creative approach to designing your testing ground.
A "Test Garden" Full of Collectible Iron Junk
You should create your test plot as soon as you purchase your detector or even before that, provided you are familiar what desirable targets are available in areas that you intend to search. The sooner you set it up, the quicker the "seeded" targets become ready for testing - they will develop some halo effects around them. After a while, your test garden will be qualified for experimentation, and your detector will be able to pick up signals from the coins buried by you at different depths.
When you purchase your metal detector, it is best to conduct an Air Test (Bench Test) with target samples and record the test results in "Target VDI Charts". Being armed with this invaluable information, you will have more ideas on how to improve your Test Garden's design.
To construct your Test Garden, you should:
1) Select an area on your property or, if you do not own a land, somewhere at the remote location where it could not be disturbed by plowing or construction. Your selected spot should not have hard and rocky soil and tree roots, and the ground should not be saturated with water. Your patch does not have to be large.
2) Scan the plot with a large search coil (if it is available) and without Discrimination so that you can remove all metal from the ground down to 15 inches. You do not need to bury your test targets any deeper because your detector would not "see" artificially buried targets deeper than that anyway.
3) Select targets that represent all major groups of metals on a Discrimination/Conductivity scale (Discrimination/FE-CO scale on Minelab FBS metal detectors) such as nails (square, wrought and modern), foil and a piece of thin brass sheet metal, coins (nickel, copper and silver), a bottle cap, a screw cup, a few different pull tabs, and any other desirable and undesirable targets. You can also select a pint jar filled with scrap copper and a gallon tincan.
4)Bury all selected objects in rows about three feet apart and draw a map showing where and at what depth each item is buried. It is best to arrange the objects in the order of increasing conductivity according to the "Conductive Order of Metals". Also bury coins at varying depths, from two to 10 inches deep. Bury a coin at about two inches but stand it on edge, another coin at about three inches with a nail nearby, and so forth. The more position varieties, the better. Be creative! Bury the jar at twelve inches to the top of its lid. Bury the tincan with the lid two feet below the surface. All target locations should be marked with colored nonmetallic objects such as, for instance, golf teeth.
The purpose of the buried coins and other objects is to familiarize yourself with the detector's characteristic response to each target. The jar and gallon tincan will help you learn how to recognize "dull" sounds of large, deeply buried objects.
When your Test Garden "matures", experiment with different sizes of search coils as well as different program settings. Just make sure you draw an accurate map and keep it up to date when you make additions to your test garden.
Your test garden is important because it will help you master your current metal detector, determine program for any task you intend to accomplish, and provide excellent testing ground for your next detector should you decide to upgrade. However, keep in mind that at hunt sites where mineral content is drastically different from the mineral intensity at your Test Garden, the audio and video responses to the same targets may also differ grandly. In fact, every detecting site is different in regards to its mineral content, and the metal detector's responses to rejected and accepted targets vay accordingly. That is why learning the responses to good targets before you excavate them at new hunt sites is often required for best results.
And finally, someday a hungred years later, a future metaldetectorist will be extremely ecstatic to explore your test garden and dig up your coins - Roosevelt dimes ("Holly cow!") and State quarters ("Wow! Holly Molly!")! :)
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