DD Coil vs Standard Coil

[TractorNut57]

Fairly new to this hobby and have been looking at several metal detectors, I was wondering about the coils. The way I understand it is the DD coils penetrate or send signal into the ground the same size as the coil it's self and does not narrow down into a cone shape. In other wards, say a 8" coil is sending a signal 12" deep, are you covering that entire 8" coil all the way down to the 12" depth, or does the signal reduce to a inch or two? I understood that the standard coils on the less expensive detectors located in a cone shape fashion.

 

[The-Bone]

think of the DD coil as emitting a field from toe to heel on the coil about 2 inches wide that does not diminish in strength until it reaches it's peak. So, if you have a 10" coil with a 2" wide field you are covering about 20 square inches of ground AT DEPTH....with a concentric coil the field is indeed coneshaped and diminishes with depth...so at max depth you are only covering about 1 sq inch of soil

 

[Goes4ever]

with a DD coil you cover more ground more quickly, don't loose the depth like the standard coil, the DD separates targets better as well

 

[liftloop]

answer this...my 5900 di pro with the 15 persission scan in non motion can detect a 5 pound piece of copper 6 inch in front of the coil and at the same time it 6 inches deep...so if a round coil diminishes as it goes down.. then were is the starting point...or does it gust throw field around the hole lope a 360 degree effect both ways like a ball.....is that's how they come up with this cone..idea..and can you rim a tar with a dd like a circular coil...or does the target have too be under the dd for it to see it.... liftloop

 

[U.K. Brian]

If you conduct in ground tests you soon find that the claimed "wiper" effect of the DD's doesn't extend down to the full detection depth whilst concentrics don't act in an inverted cone shape but more of a squashed ballon.

I prefer a good concentric but they do target mask more so suit your coil choice to the amount of rubbish in a site.

 

[Frankn]

The concentric coil will go deeper than the same size DD.
The concentric coil will pinpoint better than the DD.
The DD will cover a wider area than a concentric.
This is true using the same detector, same size coil, and same power output adj. on detector.

P.S. The "cone" projection on my concentric is wide enough to excede 2' for large objects.

 

[dwatson4]

With DD's you don't have to overlap your sweep pattern as much while covering the same surface area. consider your cone shape penetrating into the ground, the tip of the cone is the coils deepest range. you have to overlap to keep the consistency of depth if you dont overlap your swing enough then your missing targets on either side of the cone

just my opinion

flame wawy

 

[Frankn]

If you really believe that cone theory, check it out! Try detecting next to a metal fence. Oh my gosh it picks it up! That coin is wider than you think! Now consider how deep you can go. MY XLT will pick up a license plate at 2' in the ground as proven by an actual find. Let me tell you that cone point is awful deep! That concentric cone is MUCH bigger than you think.

​

 

[TractorNut57]

Thanks for all the info fellas, sorry I had got away from the post for so long, had computer problems and then a trip to the hospital after I posted this question and just never got back to you all. Didn't want everyone to think I just bailed on you and I wanted to make sure I thanked you all. I have done a bunch of research here lately on different detectors and I am liking what I hear about the Garrett AT Pro (which I think comes with the DD coil). Maybe able to swing one around the end of the month, what ya think?

 

[Sandman]

These two pics are almost what the fields look like but they extend out from the edges of the coils some inches. This is why you can not get near metal fences with either DD or conc. coils. The larger the coil the more out to the sides the field goes.

I would hold off on getting the AT Pro more to summer and let the supplies dwindle. Most sold now have to be sent in for adjustments and a change of coils. Mine is being updated as we write.

 

[TractorNut57]

Do you fellas think if I get this AT Pro with a standard DD coil, then order a seperate coil for it so if I get into a bunch of trash I can change the coil out in the field? And if so, what should my second coil be? Thanks again, you guys are welth of info.

 

[neuseman]

From what Ive read and seen you may need the sniper coil for those trashy areas.

 

[Badger 5]

We use the big mono coils out in the desert for gold Were trying to get as deep as we can but the ground can't have to much mineralization or the coil gets to noisy,Then we have to go back to the D D coil. That's only for gold.

 

[Treasure_Hunter]

Of course it is going to detect a fence, it is a huge metal object right next to it, the cone narrows as it goes now, not at the start. A license plate is huge, if your not picking it up at 2 feet there is something wrong with your detector. I have pulled up dimes at 15 inches with the WOT, I have no doubt I could detect a license tag well over 2 foot, only problem is it is iron and I usually don't bother to dig iron.........

I have been using the WOT coil for years, I have no problem pinpointing with it at all and I use the WOT for land hunting many times too when I am hunting with my Sovereign GT........

There is no doubt you get lot more coverage with the DD coil as you do not need to over lap the coil 50% like you should do when using the concentric coil......You get a slight more depth with the concentric, of the same size but you lose a LOT of coverage. I make up for the loss of depth by going to a larger coil which goes deeper. A 15 inch WOT DD coil, beats the heck out of a 10 inch concentric coil, I get more depth, and I get almost 3 times the coverage with my WOT coil than you do on a 10 inch concentric because I am not over lapping it.

The coverage and depth I get on my 15"x18" SEF Butterfly coil is amazing.....

 

[U.K. Brian]

All thats needed is a few tests.

You need to get a few lengths of dowl. Glue a small coin of the same or slightly smaller diameter to the end. Cut a few more and do the same but each should be a few inches longer. Tap into the ground until almost flush with the surface. You need to be able to see exactly where the coin is.
Easiest to use a non motion setting and approach the most shallow coin. Measure and note the distance from the dowl when you get the first hint of audio response.
Repeat with the next deepest and so on.
Most concentrics will show a "squashed ballon" detection area so a ten inch coil might well be detecting a 14" swath at a few inches in the soil.

An air test doesn't give a true representation but on a Nautilus with an 8" coil and a small coin swept a few inches from the bottom sounds off (both in all metal and discrim. mode) when the coin is three inches from the coils edge. So your getting in theory a 14" sweep. In theory because ground effect brings the distances down on all coil types. Move the coin further out and its not until twelve inches that the width of the hot area of the coil drops to the width of the coil itself.

Some concentrics detect wide and deep, some DD's don't act in the windscreen wiper manner the manufacturers suggest.

The plus of the DD design is that there's less area picking up ground effect, on the other hand many concentrics allow fairly accurate I.D. of ferrous in the all metal mode.

 

[Frankn]

Treasure_hunter, If your picture of a concentric coil is correct how is it possible to pick up a chainlink fence 1' to the side of the coil. Your DD pattern is also wrong. the DD is two coils and projects two cones with a slight dead spot near the surface in the center. You were stacking a 15 "DD coil against a 10" concentric. Lets even up the playing field. A Whites Sierra Madre/ULA-3 with a 15" concentric is rated at 5' dept. I think that beats your 15"DD. Frank

 

[TractorNut57]

I can see that this a deep subject, most likely over my head at this point until I can get my hands on a detector and learn all this good info. Sort of reminds me of what I call the blacktop driveway vs. the concrete driveway issue, lots of good in both. I for the most part understand what you fellas are talking about, but I can only cross over my exsperiance with locating untilities. The type of locators we used would go to 13-14 feet deep, but the deepth read most true in the 1' to 8' range. And when using them, the rec. end or the wand if you will, was normally hot a foot or two from the boom. I remeber the really old Goldac unit I use to use was a split box type, and tech had not be around yet for the new push buttom depths, you use to find your signal (which is the object, pipe, cable,ect.) make a mark, then the locator had a bubble that would tilt the rec. at an determined angle and move it 90 degrees left or right of the pipeline, when it nulled out, make another mark, the distance between the two marks was the depth of your pipeline. I remember back then that was state of the art, sorry did not mean to get off subject with the thread, the whole depth and interferance with fences and that made me think of those issues. One thing for sure, I can see were this hobby is much more then grab a detector at your local hobby shop and jump right into detecting. Thanks for the info. it is priceless.

 

[Treasure_Hunter]

Treasure_hunter, If your picture of a concentric coil is correct how is it possible to pick up a chainlink fence 1' to the side of the coil. Your DD pattern is also wrong. the DD is two coils and projects two cones with a slight dead spot near the surface in the center. You were stacking a 15 "DD coil against a 10" concentric. Lets even up the playing field. A Whites Sierra Madre/ULA-3 with a 15" concentric is rated at 5' dept. I think that beats your 15"DD. Frank

On my WOT I can pick up a metal fence a lot more then 12 inches away. How far past your coil's edge does it detect coins in the ground, I have detected targets to the side of the WOT that was not even under the coil yet, all 3 of my WOT coils are hot coils, all 3 have detected coins that are not under the coil yet, but were a couple inches outside the coil, and several inches deep, and were just outside of the sweep..........

As far as the fence, it is the same way you can pick up a car 3 feet away, you have a huge metal target..... I understand it is 2 coils back to back, point is the DD sees the same width all the way down. I will stack my 15X18 DD coil against the 15" concentric coil.....

Even on the 15 inch concentric coil you still have to overlap your sweep 50% to get coverage, you don't on the DD's....

My Whites BHID, Whites Classic ID, Whites 6000 XL PRO, Tesoro Comparade, and Troy X2 all had concentric coils. I found I prefered the DD's over the concentric coils....Not putting anyone down who choses not to, or does not believe in DD's....

In the end it's each to his own, I will stick with the DD's when I hunt because they have proven theirselves over and over to me........

 

[TractorNut57]

Hey Treasure Hunter, that AT Pro comes with a 8.5x11" PROformance DD Search Coil, so this will be a good all around coil? And when you say the one coil you have will pick up even before the coin gets under the coil, does it tone slightly and then gets better after it is actually under the coil?

 

[Treasure_Hunter]

Hey Treasure Hunter, that AT Pro comes with a 8.5x11" PROformance DD Search Coil, so this will be a good all around coil? And when you say the one coil you have will pick up even before the coin gets under the coil, does it tone slightly and then gets better after it is actually under the coil?

I can't say it is the same for all DD coils, I can only speak for the WOT and SEF Butterfly coils..... All 3 of my WOT coils are hot coils and I get a signal on the outside edge left and right side.... Best I have see is a couple inches depth. I was pleasently surprised when I discovered this. Yes the tone was lower, like a deeper target, but it was there and it gets louder as the coil gets closer to it............

I hunt 100% of the time using the DD coils..... I just bought an almost new Minelab Safari and it comes with a 11" DD coil, I will use the stock coil till I am confident with the Safari, I may then buy the 12"x15" SEF Butterfly for it, but that is down the road......

I have never used the AT PRO so I can't speak for its performance, but I have read good reviews including from respected hunters for it except for it's early minor problems.... I had one hunter tell me he wasn't happy with it, but that could be he didn't take the time to learn it, or it is an early model and he is not aware of the early problems.... I think you will be happy with it and the stock coil from what I have read, you may want to get a waterproof headset if your going to hunt water, just incase a wave knocks you over or you step in a hole...

There are far more experienced AT PRO hunters here who can speak for it, but from what I have read you should be very happy with it.........