Coil question.

[Mick in Dubbo]

Hi all.
Just wondering. Is it normal for a concentric outer coil to lack any real sensitivity? I have found that the coil on my Xterra can't pick up a large coin at any more than 2 inches. That will in reality make for a small coil in real terms. Appreciate any feedback.
Thanks.
Mick Evans.

 

[Andy Sabisch]

Mick,

What you are finding (if I understand your question) is a fact about concentric coils. Now if you are saying your concentric coil gets NO sensitivity to coins deeper than 2 inches ANYWHERE across the coil then you probably have a bad coil.

This link is to a "Tech Sheet" from Garrett Electronics . . . . they have always put oput great information in a format that we can all understand it.

http://www.garrett.com/hobby/techsupport/techsheets/searchcoil.pdf

Hope this helps,

Andy Sabisch

 

[Mick in Dubbo]

Thanks Andy
The explanation was very good.
What I have been finding, is that only the outside part of the coil is not very sensitive; had hoped to get about 4 inches before it would drop out.
The middle of the coil works very well.The end result is, that in order to cover the ground that I am detecting properly, makes for snail pace coverage(50% overlap each sweep=4.5 inches). As a result, I've been seriously considering something with a DD coil on it for better ground coverage. Just read a comment you made about the possibility of just such a coil becoming available for the X-terra's(page42 of the instruction manual).
Find your posts quite informative.Thanks for coming on-board.
Best wishes,
Michael Evans.

 

[BarnacleBill]

that's the transmit part of the coil, it sends the signal down into the ground. It is only the inner coil that receives/hears the signal from the ground. The further out from the inner circle you go, the less depth, it has nothing to do with the outer ring. And yes to get ultimate depth you should overlap your swings by 50%, as is stated in just about every metal detector instruction manual ever printed. That is simply how a concentric coil works.

But a DD is not going to be the cure all that you are hoping for. They are variously reported to, when compared to concentric and depending on soil. A. Have less depth. B. Be less sensitive to smaller items. C. Be harder to pinpoint with.

And like most things in detecting, you have people who swear by them, and others who swear at them. I use both types, but they're times when it's best to use a shovel, and others a rake.

HH
BarnacleBill

 

[Mick in Dubbo]

Thanks Bill.
Still in early days of the hobby. It's good to get feedback like this.Guess I might have been getting my hopes a bit higher than I should on the DD's.The X-terra's are a great little unit. It has given me a lot more confidence than with my first two detectors,just hoping I could cover more cover more ground than I do, as the sites I like to go to require permission and or a lot of travelling.
Keep up the good posts.
Mick Evans.