When would you choose a concentric over a DD if ever?

[iskirkra]

I have some dimes in my test garden that are beneath junk, mostly nails and I can hit more of them with my concentric coils that with the DD's. I have always used DD's but am starting to play with the concentric coils. NASA Tom gave the following explanation for why this could happen.

Let's say a coin is buried at 7". And let's say that a very small piece/sliver of nail is 4" deep.......and directly above the coin. ((( This would be 3" above the coin ))). ,,,,,,,,,,,, It would be common that a very tight footprint DD coil would place MORE FOCUSED energy on the 4" deep sliver that is directly above the coin........and possibly miss the coin; ................. whereas........... a concentric coil....of which does NOT have 'focused' energy............would place less energy on the 4" deep sliver.......and poses a wider angle-of-attack envelope footprint; subsequently lending a better chance of detection of the coin.


For you experienced guys, would there ever be a location where you would choose a concentric over a DD and what would the reason be?? Thanks for any help. Randy

 

[go-rebels]

I use my small elliptical in any sites contaminated with rusty steel bottle caps; much better audio ID compared to the 5" DD.

 

[Elton]

n/t

 

[iskirkra]

Thanks guys, the place I am starting to hunt is loaded with pull tabs, nails, wire, aluminum etc. I know what you mean about the audio, when I put the concentric on the LTD it reminded me of the audio on my F5, which I thought was the best audio on coins of any detector i have ever used. I am going to take the 5"DD next time just to compare. Thanks for the help.

 

[Monte]

"Simple" means a sort of easy to explain answer, "Experienced" means dealing with iron nails and trash for 46 years snow, and "Opinions" means that's really all it can be because we each use different makes and models of detectors, search coils, control settings, sweep techniques, and encounter a variety of ground and trash target environments. In short, there is no rock-solid correct answer, but I'll offer this:

I have some dimes in my test garden that are beneath junk, mostly nails...

ALL metal targets within the search coils EMF will be detected and have some bearing on the overall performance potential of other metal targets in near position to them. Unwanted junk, especially iron-based targets, can impede or mask the detection of a desired metal target on the same plain, or if the trash is above or below the better target. Nails, mainly iron types as a rule, might be out biggest, most common offenders.

... I can hit more of them with my concentric coils that with the DD's.

by your statement, that you can "hit more of them" with the concentric coils Vs the Double-D coils also noted that there are some which do NOT respond. Thus, target masking is complete on those. How about partial target masking? On those that do respond, what do you get in the way of audio tone or response and how about visual target ID info? Odds are it is not going to be a 'proper' TID or audio, and that suggests the iron nail trash has partially-masked the desired target, and it doesn't matter which search coil type is used.

I have always used DD's but am starting to play with the concentric coils.

Through the years I have preferred a concentric type coil design. In the earlier years, when using IB's or other TR type models, many used a Double-D design from Compass and Garrett, especially, with their TR's, while others used a differently looped coil design. the Douible-D or wide-scan coil does provide good coverage, but when Discrimination models came along makers found they usually didn't discriminate as well. Concentric sear coils became the more popular trend with all of them because they provided us with better discrimination performance, and pinpointing was easier for many hobbyists than with the D-D designs.

Also, most often, a similar-size concentric coil might produce slightly better depth than a D-D coil. We do see many differences in the way of performance, in many ways, since we've gone to our motion-based discriminators since the mid-to-latter '70s. Motion discriminators do not reject bottle caps and similar junk (like rusty tin) like a good old TR-Disc. model, which adds an additional challenge to getting the most out of performance in trash regardless of search coil type.

Today, even with some of the very good DD coils on models I presently use, I still favor a good concentric coil for most applications I prefer to hunt in. Unfortunately, not all manufacturers make a good set of concentric coils, and the past few years we've seen a growing trend for them to offer only, or mostly, DD coils. Of that move, I am opposed.

For you experienced guys, would there ever be a location where you would choose a concentric over a DD and what would the reason be??

My favorite models over the past 10-15 years have served me best with a concentric coil. During this period I have used (owned or evaluated) a number of Double-D coils as well, and when hunted side-by-side with a similar-size concentric coil, I usually still preferred the concentric designs. In years of hunting with both types on modern detectors in many different conditions I can state the following. Note that this isn't 100%, but overall my best depth of detection came from using concentric coils. My best and most consistent Target ID/VDI numeric read-out came when using a concentric coil. Best discrimination, overall, favored the concentric designs, too.

However, there is a category or two where I lean in favor of a good D-D coil. For some coverage on beaches and open fields, I do like the Fisher and Teknetics 11" DD coils, but with some makes I did okay with a 10" DD coil, and sometimes a 10X12 DD, but seldom ever got the better performance with any DD coil that was 12" or larger. I have done okay with a 12" round concentric using some White's models, but most often, anything over the 10"/11" coils mentioned in DD haven't benefited me.

I am partial to smaller-than-stock coils for most of my hunting needs because I am often working in trashy conditions or around brush, building rubble, metal structures, or a blend of these. I have used a lot of smaller coils and here is where I do like what I get out of some models with a D-D design. I am referring to the 5" D-D FTP products coil I use on my Teknetics Omega and G2, mainly, and I am sure they would server well on the Fisher-labeled models. Yes, I favor a concentric most of the time, but the depth and separation of this 5" DD design has been impressing me in nasty littered sites.

So, when do I prefer one coil over another? 1st, I consider the make and model detector I have in hand. 2nd, I give thought to the targets I anticipate finding as well as the site conditions I am going against. 3rd, I factor in how a particular size and type coil will serve me. With that in mind, with the Teknetics models or similar modern Fisher models, I like the 5" DD coil. Personally, I would like to have a true, 6" diameter concentric coil to work with and try, but the sub-5" DD does take care of most of my needs.

We don't have an assortment of concentric and D-D coils to compare with the F-75 or T2 models and therefore we can't really make a decision which to use. On some of the other model, I like the 8" concentric, as found on the Delta and Gamma Teknetics, but I actually prefer the elliptical sub-10" concentric to the 8" on my Omega for most average-size coil use.

In closing, I'll go back to your earlier comments about hunting in a site with trash (iron) associated with good targets. I am not concerned if a coil type will or won't locate a target below or above iron like nails. The simple fact is that whenever you're hunting in any trashy site, you need to keep the Disc. level as low as you can tolerate and recover all good and iffy signals that could be a good target. For total success in recovery efforts, just remove all metals in an area, ferrous and non-ferrous, wanted or not. Beyond that, if our allotted time to hunt a site is limited and/or our desire to 'dig-it-all' or the practicality of doing so just doesn't fit, they do what you can with what you're comfortable with.

Monte

 

[iskirkra]

Monte,
Thanks for taking the time to respond and letting me learn from your experiences. I guess what started me on this was the way the detector responded to 2 dimes in particular. Using the F75 LTD with disc= 6 sens=80 and using 3 tones with the 11" DD or 5"DD I could not get a good tone or TID on either of the dimes, I could hear iron grunts and maybe 1 time in 10 swings a high tick from 1 direction. But when I put on the 6.5 concentric I got a good ID and good tone from all directions on both using the same settings. I also tried my explorer XS and could not get a good tone or ID. I guess these 2 particular dimes just happened to fit the way the concentric works as opposed to the DD. I had just not thought about using the concentric in the field. I did use it Sunday in a very trashy area and found a 64 Rosie and some other coins and was happy with it. I am going back hopefully next weekend and take all the coils and see what happens going over the same spots with different coils. I guess that is why they make different detectors and coils because there is just not one that does it all and then you have to factor in experience. Trying to figure this stuff out makes this an interesting hobby, thanks for helping me along. Randy