Experiment with suprizing results

Winter is getting old.  I'm ready for Spring and some nice weather.  But, since I'm still stuck inside, I wanted to try an experiment that may prove valuable when it is time to get outside and begin Treasure Hunting again.

Time and again we have been told that the shape of the detector's search field beneath the coil would look like a 'snow cone' if we could see it. Pointing down into the ground like a "V".  I do recall reading one article that described it more as half of a basketball, which always seemed  more accurate to me. But I still didn't know for sure.  So, how much should I overlap my swings in order not to miss anything? The following experiment gave me the answer and forever changed the way I will use my detector.

I used a cardboard box with two shallow slots cut in it to support the detector (see MDsetup.jpg) and a second box, about half as tall, to support a large piece of paper at the center of the search coil.

The detector I used for this test is a Bounty Hunter LandStar from 2001.  The LandStar is a 3 tone detector and has both a Discriminate mode and a No Motion All Metal Mode along with a Ground Balance control.  As on most detectors, the amount of discrimination can be adjusted.  Headphones were used. (I like the Koss or Sony earbuds. Cheap and comfortable)

Settings for the test were: Sensitivity at half scale or about 5 on a scale of 10. Discrimination control at 0 (fully counterclockwise) so all types of metal would be detected and indicated by one of the 3 tones. All the tests were conducted using a U.S. 5cent piece (Nickel). 

When in All metal Mode, Ground Balance was at the Preset or fully clockwise position.

 When in All Metal Threshold, the Ground Balance control was turned counterclockwise till a tone was heard in the headphones, then back clockwise until the tone was barely audible (the Threshold).

The test was done with 5" (5inchcoil.jpg), 8" (8inchcoil.jpg)and 10" coils. (10inchcoil.jpg)

With the detector on and set as noted above and paper in place, the 5cent piece was waved in front of the search coil and when a tone was heard, the position of the coin was marked on the paper.  After 10 or a dozen points were plotted, it was easy to see the general shape of the search field. 

Performance in Discriminate Mode was very disappointing! Of course, doing this same test with a more conductive target would give better performance, and iron seems to almost 'pull' the search field out from the coil.  But the low conductivity of the nickel coin gives me a fairly good idea of how the detector would respond to gold, which is also lower in conductivity than silver or copper.

Detection depth went up dramatically when the detector was used in All Metal and another increase in depth is seen when the Threshold technique is used.  Some will argue that an air test is not a real test of the abilities of a detector, and I agree.  The proof is in the ground.  But I do contend that depth in ground will never exceed the depth of an air test.  Even the mildest ground will have some mineral content that will diminish the capabilities of a detector.

I hope all of you reading of this experiment will try it with your detector and post the results here. Hopefully this will get some of you off the couch and learning more about your detector and making more and better 'finds' when Spring does get here.

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Interesting experiment, Occupant.    Just looking at your graphic results, it looks like the 1/2 coil width overlap per sweep rule of thumb still works out to a good standard.   

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Hi CANI. Great, I look forward to seeing the results.  

I was surprised that with the 10" coil and the detector set to Discriminate, the nickel wasn't seen till it was all the way under the small center 'receive' coil. In effect the 10" coil was only seeing 5" wide. So, if each swing was moved forward the width of the coil, which seems to be the usual recommendation, only 25% of the ground under the swing was searched! The area under the 5" center being only one fourth of the area under the full 10 diameter. (3.14 times the  radius squared) Area under the 5" dia. center receive coil = 19.6 sq. in.  Area under the whole 10" outer coil= 78.5 sq. in. Then there was the meager 3.25 inch depth too.  I'll be doing the same experiment with another detector soon. Stay tuned.
Hi Aggie,
True. Half coil diameter overlap looks just about right.  I read in a post somewhere to "place two basketballs side by side so they touch and look at the open space between them where they touch the floor.  That is what you get when advancing a full coil width between sweeps."

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Good point John.  The coils I tested are all concentric coils. The 8" comes standard on the detector. Don't have a DD, but that would be an interesting comparison. Hopefully, someone on the forum will do this test with a DD coil and post the results here.

What part of VA. are you in?  I'm near the coast with a couple of great detecting sites near Smithfield & Surry and another near Charlottesville.

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		Quote:			Posted by occupant
	Good point John.  The coils I tested are all concentric coils. The 8" comes standard on the detector. Don't have a DD, but that would be an interesting comparison. Hopefully, someone on the forum will do this test with a DD coil and post the results here. What part of VA. are you in?  I'm near the coast with a couple of great detecting sites near Smithfield & Surry and another near Charlottesville.

		Quote:			Posted by occupant
	Good point John.  The coils I tested are all concentric coils. The 8" comes standard on the detector. Don't have a DD, but that would be an interesting comparison. Hopefully, someone on the forum will do this test with a DD coil and post the results here. What part of VA. are you in?  I'm near the coast with a couple of great detecting sites near Smithfield & Surry and another near Charlottesville.

Occupant......I'm in the Northern Neck of Va.."Warsaw Area". There's some good hunting in Va..
Enjoy the hobby, have a good day..John in Va

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Johnlaw