Optimum coil size for certain coins

[sube]

This well be my 46 year of laying the coil to the ground a lot has changed since then mostly the last 10 years . It's seem most of the quarters and half's are gone now (I hunt mainly pubic places) .I generally find penny's dimes and nickels . Since this is the size coin I'm going to find there' got to be a coil that's more sensitive to these size coins. I know the 6 11 and 17 will hit these coins but how big can a coil go before it looses the dime.
The 2 box detectors will not see these coins only large items .
Lower conductors like nickels and gold like a higher frequency and high conductors like lower frequency .
What about coil size is there a magic size coil that really likes this size . Coil size as it gets larger looses sensitivity to smaller size targets so what is the optimum size for these
coins , what coil is optimum for depth on these size coins .
What do you guy's think . sube
.

 

[Jason in Enid]

What about coil size is there a magic size coil that really likes this size . Coil size as it gets larger looses sensitivity to smaller size targets so what is the optimum size for these
coins , what coil is optimum for depth on these size coins .
What do you guy's think . sube
.

This isn't true for American coin sized objects. The CTX 17" coil will detect a dime deeper than the stock coil. According to my use, 2 - 3 inches deeper.

 

[AngelicStorm]

I would say the smaller coil such as the 6 inch since a dime would proportionally seem like a tin can lid compared to what the 17 inch coil would be seeing. You do know how deep the 17 inch coil can read those can lids right?
I may be just a little off but it makes sense to me that the reason the smaller coils pick up smaller targets is because those targets seem larger than "normal" to the coil. Also not to mention the 6 inch coil is better about getting less interference because of it slipping in between the metal obstacles thus letting the frequency eddies to be uninterrupted.

I can't seem to find a proper diagram or picture to explain this. That would be of help.

 

[sube]

AngelicStorm I agree with you I mainly use the 6 because it does see less ground than the stock coil less minerals less targets and I'm able to push the 6 to 28 in manual but the stock coil I can only push it to 24 before it gets to sparky . Thus the 6 goes just as deep as the stock coil . sube

 

[Overvoltage]

I believe SUBE said, "I know the 6 11 and 17 will hit these coins but how big can a coil go before it looses the dime". He is wondering how much bigger the coil could get before the resolution for a dime sized target diminishes. EXcelerator makes S.E.F Butterfly 18x15" and 21x17" coils which are very large. I would suspect they still pick up small coins. Hopefully someone who has used one of these largecoils could chime in. I love the 17" coil and would go bigger (such as 21x17) if one ever comes available for the CTX.

 

[sube]

I would love to swing a 17 where I hunt but swinging a garbage can lid would really tax a old fart like me . That said what does it sound like when I have 12 to 15 hit's on a sweep just using the 6 the average coin depth here is 4 to 6 inches unless I get in a yard with lot's of top soil then 10 plus comes in the picture. Depth real is not the issue for me it unmasking is what counts there are far more coins at 4 to 6 inch than at 10 plus . I have found many coins at 8 inches with the 6 and some at 10 inches few. I think the 10 inch coin is very rare where I hunt that's why I would like the best possible coil for the job on small coins .sube

 

[Overvoltage]

I mostly hunt parks and playgrounds also with most coins 6" or less. I can hear the high tones of good coins through the trash even when there are multiple targets under the coil. I have to use the Pro-Swing or my arm will fall off after about 30 min.

 

[Overvoltage]

Angelic, what coil are you using most?

 

[sube]

Quote I mostly hunt parks and playgrounds also with most coins 6" or less. I can hear the high tones of good coins through the trash even when there are multiple targets under the coil. I have to use the Pro-Swing or my arm will fall off after about 30 min.
How dose your brain keep up I know if I would use the 17 I would probably get to the point where I would just mentally block out all the excess noise . I do that with the 6 now but when I put the stock coil back on my brain goes numb for the first 20 minutes till I get in the groove and my discriminator between my ears catches up . sube

 

[AngelicStorm]

Angelic, what coil are you using most?

I am using the 11" coil the most in yards away from the houses because of the number of metallic debris that is usually near the houses. I will grab my 6" coil for areas such as those or areas littered with metal or even tight spots. In farm fields I will swing the 17" coil with no problems. It does get heavy, but I can deal with it for the ground coverage trade off. Now I have noticed more depth with the 17 inch coil on smaller nickel+ sized objects in these farm fields. Probably because of way less interference.

 

[PryorCreekJoe]

What about coil size is there a magic size coil that really likes this size . Coil size as it gets larger looses sensitivity to smaller size targets so what is the optimum size for these
coins , what coil is optimum for depth on these size coins .
What do you guy's think . sube
.

This isn't true for American coin sized objects. The CTX 17" coil will detect a dime deeper than the stock coil. According to my use, 2 - 3 inches deeper.

I agree with Jason. I see the same, 2-3 inches deeper than the 11" coil on a dime.

 

[CT Todd]

I don't think that the size of the coil other than it being small is the direction to go here. You are talking about hunting in public places and the big easy targets being gone. Aside from the occasional 10 inch dime which would be better to have a larger coil in your hands.I would be more concerned with the silver dimes that are right next to bottle caps and nails then the 10" dime.So whats left are the masked targets that didn't ring pretty or give the perfect TID so the other guys walked on by. Most of the time hunting with a large coil on these type of sites will be counter productive. I think that the key to finding these coins and positive small targets that you mention in these public places is the separation of targets. That leaves you with the smaller sized coils which will give you better separation of ferrous and non ferrous targets that lay right next to each other. There are years of hunters with good units ahead of you on public ground.The easy targets are gone. I agree. On public ground.

Hunting on public ground is easy you just go do it. Doing some door knocking is another way to put yourself back in the big silver game with a big coil.

 

[Johnnyanglo]

Concerning coil size in relation to target sensitivity I've read that if the coil size is doubled (perhaps to increase depth), the sensitivity to smaller targets falls to 1/8, same as if the target size were halved.

So, it would be something like:

Sensitivity = [target diameter]^3

For instance, if the target size is cut in half the sensitivity is reduced by 1/8, that is (1/2)^3

If it is plotted, the target sensitivity grows rapidly compared to the increase in target diameter.



There is another formula (don't know where it came from) that states the best coil size for a particular target is proportional to two-thirds power of the target size.

The formula would be, K * (Target-size)^2/3 = Coil Size K is a variable correction factor for target shape, composition, orientation, and coil characteristics.

This is how this formula would plot out for constant value for K (same target)



Basically the best coil radius is about half the target size, or coil diameter is loosely correlated to target size.


In relation to depth and coil size, there is a formula that states Max Signal = Radius^3/(radius^2 + depth^2)^3
Don't know where I got the formula, but if you plot it for constant target depth, you get this...



The formula says that the max signal will increase as coil radius increases up to a point, and then the target will become small in relation to coil size and sensitivity will decrease. You can see from the plot that the maximum sensitivity to a small target is given when the coil radius = target depth (where the curve turns at 12" depth and 12" coil radius). Thus, if you were searching for a coin at 15" depth, the best coil would have a radius of 15" (diameter of 30"), beyond this coil size sensitivity would be lost.

Well, this is just speculation and playing around. Try not to take it too seriously.

Johnnyanglo

 

[CZconnoisseur]

I would think that target conductivity and operating frequency would alter the K values moreso than coil size...While hunting in 12 khz I can get deep zinc pennies reliably at 7-9" (provided they are not too corroded), but copper Memorials peter out at about 8" unless I lower the processing speed of the detector while keeping operating freq. the same.

Switch to 4 khz with all other settings equal, and now the zinc pennies are hard to pick up beyond 6" but copper Memorials hit reliably at about the same 8" mark. I think this may be why Indian cents are easier to locate in 12 khz with my settings...

But you guys are using FBS technology and this is something I'm not versed in. At all. So my observations may not hold any water compared to the CTX 3030...