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DD Coil Center Receiving Shape Differences


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Makro Gold Racer GR40 is rated at 15.5" long and has a 14.5" center. And weighs 766grm.

Nel Thunder is rated at 14.5" and has no "V" in each end to shorten the center weighs 570. 

I will test both when I get them. I know, 2 different detectors. I'm only trying to see if there is a difference in the width and shape of the detection area. I really like how much lighter the Thunder is for the same coverage. 

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I re-read your post Steve. I think what you said is sinking in. I wondered why on a swing in one direction I would get a good number and the other direction I would get something completely wrong. It's the receiving coil side getting it right. That really clears up that question. The target must have been a little deep. 

   Also you mentioned getting coils that do different things or it makes no sense. That is what I'm trying to do. I feel like I'm waving a tiny coil with the 11". The Thunder increases my coverage by 50%. I like that. Also, it's way lighter than the GR40 I was swinging. So, I think I can get more enjoyable time in and cover way more ground. 

   I guess my original question was simply because of the odd straight style of the Thunder. I'm seeing what you are saying though. Its design probably won't matter much. And, it may just be the look that is different and not the performance. This is all actually ok with me. I just wanted a larger coil for the Simplex+. It's always fun to ponder some of the different builds and just ask questions about it. 

    Some forums have lots of folks who speculate and guess. Here though, I can rely on guys with the actual knowledge to share. Thanks again Steve. 

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I just uderstood another thing from one of the topics you linked Steve. The coils are transformers not antennae. So, the coils must overlap in order to be able to tell when the current from the target reaches equilibrium. I wonder then if it really matters, the small difference between the two middle shapes. Equilibrium for any target is in the middle. I'm sure there's so much more to it. That's what makes this interesting.

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As you’ve figured out, where the apparent signal is, and the actual technicals aspects, are not exactly the same thing. For most uses the signal runs up the middle. But there are cases where it is other wise, like with a DD coil on a PI detector. The receiver half properties become more apparent in that case. The main thing is this stuff is always a trade off. There are no perfect coils. What you gain in one way you give up in another. Long story short I’d probably get the Thunder coil myself if coverage was the goal.

Sorry if I seem blasé about it sometimes, but I’ve been detecting for 50 years now, and know that many detectors and coils will get the job done in the right hands. I’ve spent countless hours comparing different detectors and coils, and most differences are measured in fractions of inches. Researching out good locations, knowing your detector, and most importantly, putting in the hours, are the genuine keys to success in this endeavor. Good luck, but more than anything… have fun! :smile:

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I found out today that NEL jumped the gun making coils for the Simplex+. 

    I guess I'll wait for the Detech 15" which I heard is coming out soon.

   I asked Dilek if Notka/Makro had authorized NEL to make coils for the Simplex+. Here's her response.

Dear Tim,

The only company we cooperated with is Detech is Bulgaria for 3rd party coils for the Simplex+.

NEL has not approached us for any collaboration and thus cannot product coils for the Simplex  (or at least coils that would properly work) as they would need to board and the software from us.

Hope this helps.

Regards,

Dilek Gonulay

Director, Sales & Marketing

A Sıvatyolu Cd. Sakız Sk. No:4 Sancaktepe ISTANBUL

T +90 (541) 860 45 96 | W noktadetectors.com

 

noktamakrodetectorslogo

 

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I've decided to go with the SP35 after looking at the center construction. The coil is rated at 13.5x12.5. However, they did not do the same thing as the stock coil where the wires cross. So, instead of just 2 inches of coverage center line. It is actually 4" more. Thats about 30% more coverage. And, I noticed that the Notka SP28 original coil had much a better connection. 

   I'm going with Notka/Makro because it's the closest to the Thunder design. And, it is made by the same company as the Simplex+. 

   I will have a real warranty and I trust the build Notka/Makro puts into their products. 

 So, the middle shape maximized the coverage over the stock build style. And, it is actually less expensive too.

Here's a shot of them side by side. 

1775826649_Capture_2022-05-11-09-38-47.thumb.png.8c4b3b354d2003d6d014d5dcbcac32dc.png

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TG, the difference in overlaps is a trade-off between depth, coverage, and pinpointing. Yes, the straight overlap will be a bit more uniform in coverage but depth will still roll off as you get near the ends of the overlap. That is, it's not perfectly uniform all the way, end-to-end.

The football overlap has less coverage but will get a little more depth at the center. It's front-to-back roll-off is more severe which can make pinpointing easier when X-ing the target.

In severe soils, coils with harder radius changes will also exhibit a stronger lift-off effect. The Thunder will therefore be worse in that regard while a football overlap will be better. The double-0 SEF coil is even better as it has a very broad radius change.

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Thanks Geotech,

  What is the lift off effect? Is that when the target disappears when lifting?

Thanks for this explanation. I prefer to use the tip to pinpoint. Sometimes find on deeper targets the middle is where the stock coil pinpoints. 

If I understand correctly, the straight middle construction will give a consistent depth until the tip. For me, that would be ideal. I could therefore, find a target and pull back until the target disappears. The tip would be the pinpoint area, not the middle. I really would prefer this to having a little more depth in the middle. It frustrates me when I think I'm pinpointing on the tip and really, it's in the center. I dig and then pull out the pinpointer. Then I find the target. I would value consistent coverage over one area of depth. 

   So, I looking at the SP35 coil, it too has the straight middle construction. Notice the coil partially shown on the right. It has the wider middle construction and you can see the difference. 

   This confirms my suspicion of the detection area shape if I am understanding you correctly. Thanks, now I'm looking forward to putting this coil to the test.

I need something like a broom, a nice even coverage where I feel I'm not missing something unless I overlap all the way to the deepest point of detection. I think that since the sides are not straight as well, there is probably still a curve to the deepest detection area.

I'm sure I'm compromising a little depth in the middle, however, the functionality would be better for pinpointing and less need to overlap.

   We shall see! Once I get it, Ill check it out. TG

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4 hours ago, Tahoegold said:

What is the lift off effect?

As you lower a coil to the ground the ground signal produces a stronger & stronger response because it upsets the induction balance of the coil. When you get down to the last inch or so the effect can actually reverse and the RX signal decreases a bit. To make things worse, in some coils it also causes a slight phase shift that messes up the GB. This can produce ground noise. Generally only a problem in bad ground. Concentric coils are the worst because the TX coil and the bucking coil respond differently to ground vs height. DD coils are better, 00 coils even better. Mono coils don't have the problem at all.

Quote

I need something like a broom, a nice even coverage where I feel I'm not missing something unless I overlap all the way to the deepest point of detection. I think that since the sides are not straight as well, there is probably still a curve to the deepest detection area.

You are right, the curvature of the TX coil means that the TX field density (and curvature) changes along the length. Larger deep targets will respond best at the center and you might find that the tiniest targets are only detectable near the ends. Moderate not-too-deep targets will have a more even response. Speaking of brooms, the Tesoro CleanSweep coil is the only DD-style coil I know of that has both a straight overlap and rectangular coils with no curvature. It should produce the most idealistic response you want. Some people hang on to a Tesoro just because of this coil. I have.

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