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Larger coil lower sensitivity or visa versa?
Posted by: tiftaaft
Date: September 05, 2017 12:48AM
I am curious what other Explorer members have found.... do you get better results using a larger coil, but having to lower sensitivity to quiet the falsing, or using a smaller coil with the ability to raise the sensitivity higher? Understanding that every hunter's ground varies and what works for one may not work for another, but just curious.

I have several coils ranging from 5" to 15"... and have found it difficult to get any depth out of the 5"... but my ground is also very harsh and mineralized.

Re: Larger coil lower sensitivity or visa versa?
Posted by: IDXMonster
Date: September 05, 2017 06:55AM
Great question Tim, I wonder the same thing every time I go out.

Re: Larger coil lower sensitivity or visa versa?
Posted by: tiftaaft
Date: September 05, 2017 01:53PM
Quote
IDXMonster
Great question Tim, I wonder the same thing every time I go out.

I have been bouncing back and forth between the stock coil and either the Ultimate or now the WOT. I really need to get out and do some controlled testing in the wild... different settings/different coils. Best intentions.. until I hear a nice high tone... all bets are off. ;)

Re: Larger coil lower sensitivity or visa versa?
Posted by: Charles (Upstate NY)
Date: September 05, 2017 06:04PM
Large coil for depth in light trash, small coil for target separation in heavy trash, medium coil for the middle ground between those two site conditions.

Larger coils simply gulp a larger bucket of ground mineralization below the coil. If your soil is mineral free and there's no EMI then it doesn't matter noise/sensitivity wise, all coils will be about equal in stability. But in mild to heavy mineralization the larger the coil the larger the gulp of mineralization they bite off and the noisier they will be, and may require backing off the sensitivity.

Right now its bone dry here, when the rains return and soak that iron and mineralization its going to be worse, a lot worse for the WOT. You lose some depth in bone dry soil but the iron and mineralization also quiets down significantly.

Next consider the physical size of the magnetic field vs the density of the magnetic field a given coil produces. Large coils produce large (but less dense) magnetic fields that extend further into the soil than small coils, but the field lines are not as packed together. So they go deeper, but suffer some performance fall off on smaller targets as there are less field lines to strike the target. On the flip side a small coil produces a higher density magnetic field with many more field lines to strike a target, but a smaller size field that doesn't extend into the soil as far. Good for getting hits on small to tiny targets, but not really any deeper than the small coil goes. When you wind a coil for an Explorer you can't just add more magnet wire winds to a larger coil, the length of wire to remain within coil specs is about the same, so larger coil fewer loops of wire, small coil more loops of wire.

The actual size of the magnetic field a WOT produces is huge, you can detect your car door from about 4 foot away. The issue is there are not that many magnetic field lines to strike a target 4 foot from the coil. If the target is big enough like a car door then yes but a coin never going to happen. The further away from the coil the fewer number of field lines there are.

With the WOT you have to consider the actual shape of the magnetic field it produces. The curvature of the WOT coils field is such that its particularly good at curving at around the 8-10 inches depth to strike a coin that's tilted about a 45 degree angle in the ground. Versus the stock coil. They can be difficult to pinpoint because the angle of the coin tends to shoot out its signal half sideways. Ideally you want the field lines to strike the target at 90 degrees to the largest surface of the target, for example field lines traveling straight down striking a coin laying flat produces the strongest signal. For whatever reason the WOT tends to curve just right to strike the flat of a coin that's oriented at a 45 degree angle at that particular depth. I dug many with a WOT, typically knew what I was dealing with by the signal shooting out sideways so I'd break the clod apart and check for that. With the stock coil I pretty much never dug those, with the coin angled like that in the ground at that depth not enough field lines were striking the target.

Trivia: I once mounted the 15 inch WOT coil on 4 wheels and pushed it around a field, true story lol.



Edited 2 time(s). Last edit at 09/05/2017 06:13PM by Charles (Upstate NY).

Re: Larger coil lower sensitivity or visa versa?
Posted by: IDXMonster
Date: September 05, 2017 06:27PM
Somebody's gonna have to mount ME on four wheels and push ME around the field here pretty soon...it's hell being 49...:lol:
Great explanation and that's the way I've always understood how the field is less dense the larger the coil gets. I love the huge coils for wide open low trash/ low mineral places but I'm heavily leaning on the 11" stock coil on the CTX lately. It's the perfect balance or everything,including balance!

Re: Larger coil lower sensitivity or visa versa?
Posted by: tiftaaft
Date: September 05, 2017 08:18PM
Great info as always Charles. I didn't realize the magnetic field density is different depending on the coil size, but that makes perfect sense. Also a good comment on the dry hard ground... that one I had.figured out... which is why I have been swinging the 13 and 15" coiks late this summer. I have the stock and smaller coils ready for action once the rainy season hits... if it ever does.

Re: Very good explanation - Thank you for that one! Let me know if you are going to write a book, I'll buy a few copies!N/T
Posted by: BigTony
Date: September 05, 2017 09:31PM

(This message does not contain any text.)



BigTony

Re: Very good explanation - Thank you for that one! Let me know if you are going to write a book, I'll buy a few copies!
Posted by: IDXMonster
Date: September 05, 2017 09:46PM
Quote
BigTony
n/t

No kidding. I know you've been to the archives Tony,there's the makings of a book in there somewhere! Information is king. Excuse me...CORRECT information is king. This is why we love the Minelabs. Did I mention the 1906 V nickel and 2 no date Shield nickels I dug yesterday? Because I was able to discern nickels from pull tabs, in an old village commons right next to a country tavern! I have it on video...glad I took the camera!

Re: Larger coil lower sensitivity or visa versa?
Posted by: tiftaaft
Date: September 05, 2017 10:27PM
Quote
Charles (Upstate NY)

Trivia: I once mounted the 15 inch WOT coil on 4 wheels and pushed it around a field, true story lol.

And Charles, based on your recent featherlight mod on the explorer... I can only imagine the hot rod that WOT 4 wheeler must have been!!! :)

Re: Very good explanation - Thank you for that one! Let me know if you are going to write a book, I'll buy a few copies!
Posted by: BigTony
Date: September 11, 2017 10:33PM
IDX - I don't know why I missed your post about those cool finds. Congratulations! Shield nickels and a V nickel, crazy man - go back and go slow.
just plain terrific



BigTony

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