For the sniper I was going to get the Makro RC13 5" x 4.5" (12.7cm x 11.4cm) DD Coil, but the RC18C 7" (18cm circular) CONCENTRIC coil has just become available on the MDF shop https://www.metaldetectingauction.com/l ... m-7/104446
Seeing this I noticed the comments -
"Provides a cleaner target response and better discrimination on shallow targets.
However, it gets more affected by the ground compared to DD search coils in highly mineralized areas."
It then dawned on me (it can take some time!) that although I know what a DD coil is and what a concentric coil is that I have no idea what the advantages / dissadvantages are when compared
Can somebody please enlighten me.
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http://www.fisherlab.com/hobby/davejohn ... evised.htm
And from Minelab, this pdf:
http://www.minelab.com/__files/f/11792/ ... _Guide.pdf
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Try it for yourself. Very easy if your detector has a no motion mode.
Each has an advantage but neither is best for every situation. Personally I prefer the concentric as it runs slightly quieter.
Koala, thanks for your comments.
As with most things regarding coils "Each has an advantage but neither is best for every situation" is probably a good summing up.
After reading the links, searching this forum, and watching some videos I am starting to lean towards the RC18 (7" concentric) over the smaller DD sniper coil.
Main downside of the concentric seems to be in highly mineralised soil, fortunately most of my permissions are not to bad in this regard so hopefully this should not be an issue.
However, I will admit that this choice is in part to the concentric being larger and I can see it getting more use than the very specialised sniper DD as much as due to the technicalities of the coils. I also have the standard DD for the Racer 2 and a backup Ace 250 (which still gets some use) again with standard DD and the Nel Tornado DD so a concentric will give a wider range of options (although you could argue the same for a smaller sniper coil!).
Please note above statement is at time of post and I might well change my mind before order goes in!.
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The main advantage of DD coils over Concentrics is that they as a general rule far better on highly mineralized sites as they see about 70% less of the ground,another massive advantage is that the coil over lapping problem is almost eliminated with a DD coil.
I still prefer Concentric coils if i am honest,although on some of my detectors like the T2 and Deus they cannot run concentrics due to the way that the electronics have been designed.
When on a trashy roman/saxon site its situations like this that some of the older Laser/Tesoro and Whites machines like the IDX Pro with small coils come into a different league regarding iron rejection,this is why in theory its good if you can have a selection of coils ie smaller and larger both Concetrics and DD formats,you will then have almost all scenarios covered.
I have a couple of small areas where they are trashy, but finds do come up, so was looking for something to better deal with that.
Also been on the odd dig on stubble where a smaller coil would have been easier. But thought in this scenario that the genuine 5"x4.5" just would give to little ground coverage.
So combining the 2 points above the 7" concentric looks a good option.
"One major downside of course is the need for disciplined over lapping of coil swing so that targets are not missed." Sorry to say that as the bulk of my detecting is while taking Horrid Hound out that does not even happen with the stock DD
But should I ever find a scattered hoard I can soon change that and give a good overlap on each swing. .... and then go over it with the other coil, then in the other direction, then with the Ace 250 and the Nel Tornado for extra depth But I will worry about that at the time should it ever happen.