CTX 3030 13" Coil

[AngelicStorm]

Any word of a 13" coil in the makings? Seems that might would be my go to if they were on the market. Sacrificing a "little" separation in high iron areas and providing a depth advantage seems pretty enticing to me. What are your thoughts?

 

[Jason in Enid]

Never heard of one or rumors of one. I'm not sure it would gain you much. The depth increase from 11 to 17 is only 2 - 3 inches. I think a 13" would only add weight and lower separation, although you would gain a very small increase in ground coverage. For what a new coil costs, I don't think it would sell well.

 

[sube]

I think a 8 inch coil would fit good in there lineup good in between size coil . sube

 

[AngelicStorm]

Never heard of one or rumors of one. I'm not sure it would gain you much. The depth increase from 11 to 17 is only 2 - 3 inches. I think a 13" would only add weight and lower separation, although you would gain a very small increase in ground coverage. For what a new coil costs, I don't think it would sell well.

Seems like I saw a graph someone made on here a couple of years ago where a guy who works on them broke the numbers down with one side of the graph showing approximate depth advantage and the other showing coil size. What I remember is seeing that it peeked at around the thirteen inch range.

I think a 8 inch coil would fit good in there lineup good in between size coil . sube

Yes, it would be.

Edit: I found the post I was referring to. Here it is....

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

Link: http://www.findmall.com/read.php?86,2155440,2157772,quote=1#REPLY

So apparently the pics have been moved and Johnnyanglo was suggesting a 15" coil would have the best sensitivity.

 

[glenn3-88]

Everybody has their own opinions about coil size and depth. On my AT Pro I have the small dd coil and stock coil.
On my Safari, I have the small dd, the stock, and the big SEF coil that works great.
However, as I become more and more familiar with the CTX, I have found no situation yet
that justify me getting either a smaller or larger coil and before you guys start beating me up,
I dug almost everything when I first got it. As time has passed, I have proven to myself due to
items I have found that there has yet to be a situation where the smaller coil would have helped
me do anything but save a little time with the CTX. Time is something I hope I have an abundance
of but in my experiences thus far, (not saying I won't change my opinion in the future), I don't have
a use for a different coil than the stock one that came with the machine.