3 coils / depth comparison

[Diga]

Compared using SMF in low mineralized ground, high EMI, max sensitivity, a 6" round DD coil, a 9.5x6 DD coil, and an 11" round DD coil.

I started with the 6" coil and buried the coin to a depth in which the 6" just barely gave me a repeatable "dig me" tone, then tried the 9.5x6 and the 11" coil on the coin. The 9.5x6 went about 1" deeper than the 6" round, and the 11" round went about 1.5" deeper than the 9.5x6.

However:

In the EMI with max sensitivity, the 6" was quiet, the 9.5x6 fairly quiet, but the 11" was ear piercing noisy. When I reduced the sensitivity on the 11" so that it was fairly quiet, I could not detect the coin at all.

What this means, is that with having to significantly reduce the sensitivity when using the 11" coil, both the smaller coils will at least match the depth of the 11", and often exceed the depth of the 11" coil. In addition, with the smaller coils, I get far superior unmasking and separation performance, and I don't have to worry about my arm falling off

 

[Diga]

To be clear, the 11" coil will detect a coin sized object approximately 3-4" further than the 6" coil, and approximately 2" further than the 9.5x6" coil. BUT, that is in the air (no ground mineralization) and without reducing the sensitivity due to EMI and possible ground mineralization. To get a quiet and stable detector in EMI, the sensitivity has to be reduced a heck of a lot more with the 11" coil, compared to the smaller coils. When that sensitivity / depth loss due to EMI is taken into account, the 11" loses its depth advantage. On top of that, the depth loss due to ground mineralization should be higher with the larger coil.

EDIT: By saying "going deeper" in my first post, I meant I could raise the coil by that amount off the ground and still get a good repeatable tone.

 

[Jose159]

Great info! The smaller coils are much easier on the body to swing also. I find myself using the 6 inch coils almost exclusively.

 

[Diga]

Great info! The smaller coils are much easier on the body to swing also. I find myself using the 6 inch coils almost exclusively.

Thanks.

Does Minelab have a coil around the 9x5 size for the Nox, or does another manufacturer make a similar sized coil for the Nox?

On a side note, My 11" is collecting dust for the reasons I explained, and I'm not using the 6" very often since getting the 9.5x6 elliptical. I do occasionally encounter sites that are "ludicrous" trashy, and that's when I'll use the 6". Other wise, it's the 9.5x6 all the time.

EDIT: As soon as I posted this and checked for new posts, I saw the post about the Coiltek 10x5 for the Nox

 

[AirmetTango]

I’m not super familiar with coil sizes for machines other than my own - is this for the Nokia Legend, XP Deus, or something else?

 

[Diga]

I’m not super familiar with coil sizes for machines other than my own - is this for the Nokia Legend, XP Deus, or something else?

Hi AT.

I was using my Legend for the test.

I didn't mention the specific detector, because I fully suspect the results would be similar with any other SMF detector. More specifically, in EMI, on any SMF detector, the sensitivity has to be reduced significantly more with a larger coil, compared to smaller coils.

 

[AirmetTango]

I didn't mention the specific detector, because I fully suspect the results would be similar with any other SMF detector. More specifically, in EMI, on any SMF detector, the sensitivity has to be reduced significantly more with a larger coil, compared to smaller coils.

Agreed…in general, I believe all the points you made can be considered accurate across most, if not all, SMF and SF detectors where EMI, mineralization, and/or target density are issues.

I never took the time to do an in-depth comparison between coils on my EQ800, though at one time I owned 4 coils simultaneously for the machine (6”, 10x5”, 11”, and 15”). I ultimately parted ways with the 6-inch round coil - for me, I could never get used to the change in swing that was necessary to achieve full coverage using the tiny coil. I felt that any gains I was making against EMI or mineralization was getting mitigated by the unshakeable feeling that I was missing targets because I either wasn’t overlapping my swing properly or I was running out of time because it took 4 times longer to cover the same area In my case, the larger elliptical 10x5 was a better compromise, matching the shape of the 11” and 15”, so there wasn’t as noticeable of a difference in swing to achieve the same coverage, but still getting improved performance in EMI/heavier mineralization/target dense environments when needed.

Edited for: clarification of last sentence

 

[Diga]

Agreed AT.

I don't use the 6" much anymore, and my use for it is becoming less and less. Like someone else said, "Using the 6" feels like painting a wall with a toothbrush"

 

[Diggndabeeps]

Thanks for posting Digalicious...very informative.

Just to add a bit; I hunt mowed yards along with fields and heavily wooded sites. My primary 'go to' is the 10 inch on my Vanquish. 8 inch if the brush is just to thick for the 10. Really like the 10 as a good general purpose.

 

[MasonDixonMding]

I change my coil according to the site I’m hunting. I hunt a lot of fields. For that kind of hunting the bigger the better. If I find a heavy patch of nails I’ll put my smallest coil on. If I’m hunting a yard than I’ll go to the stock coil. I just look at it as they are tools for different jobs.

 

[Dave_e]

If I find a heavy patch of nails I’ll put my smallest coil on.

Yes, yes, and a 3rd yes.

I've got a detector that I'll mount a 4.72" concentric coil on and painstakingly, patiently, paint through the trashiest spots unmasking good targets.

There are trashy times when the 4.72" CC is a must.

 

[Jose159]

Agreed AT.

I don't use the 6" much anymore, and my use for it is becoming less and less. Like someone else said, "Using the 6" feels like painting a wall with a toothbrush"

LOL I'm just the opposite. After mainly using the 6 inch when I put the 11 inch on it feels like I'm swinging a manhole cover.

 

[Diga]

LOL I'm just the opposite. After mainly using the 6 inch when I put the 11 inch on it feels like I'm swinging a manhole cover.

Agreed!

I should have added that I don't use the 11" at all. My go to coil is now the 9.5x6.

 

[JAC]

Good info here for a new guy like me. Thanks, all!

 

[longbow62]

This is my experience with small coils. They seldom meet the hype and praise heaped on them. I'm not just picking on small coils. I think the same can be said for the coils bigger than 10"-11". They should be a last resort in my opinion. I never found not one silver with the 6" Nox coil when I re-hunted areas with it. I've had two and I got rid of them both. The CoilTec 10x5 I would put above the Nox 6" as far as usefulness goes, but even it does not get left on the detector as an everyday coil.

I have found silver with Coiltec 10x5, and if EMI is horrible, yes I used to put it on as a last resort. Yeah if I had a place where there was potential for more finds I would try smaller coils, but to me they are strictly specialized tools, or a last resort thing.

Most of the silver I find is deep. I seldom find any silver that is not at least 6" deep. Most is a lot deeper. Even the 10x5 is no match for the Equinox 11" coil when it comes to depth. I have a quarter buried very deep in my back yard. Nox 800 11" hits it fine with a good solid I.D. in Park1, 20 Sensitivity, and a Recovery of 4. There is EMI in my yard. Not horrible, but there. You can't make the 10x5 hit that quarter no matter how much you turn the Sensitivity up, or the Recovery down. When you turn the Sensitivity up and the EMI makes the 10x5 worse than it is with the 11".

I have a buddy who used an Etrac exclusively for a long time. The NEL 9.5x5.5 lived on his Etrac. He didn't even carry the stock coil. He found a lot of silver with it, but I firmly believe he would have found more if he had used the 11" most of the time, and only put the smaller coil on after he had hunted with the 11" first. More than once we got into to places he just couldn't get the depth he needed. I've pulled many deep silvers behind him.

Yeah I'm going to grab the M8 for the Manticore as soon as I can, but it's only going to get used in certain situations. I'm all for having small coils. I just think they are overrated.

 

[Dave_e]

Coil type can matter just as much as coil size, at times.
Here's a Paystreak video showing that the concentric type coils sometimes unmask targets measurably better than DD coils, even if the DD coil is on a $1500 machine and the concentric is on a $200 machine.

Concentric vs DD

 

[marcomo]

Hi AT.

I was using my Legend for the test.

I didn't mention the specific detector, because I fully suspect the results would be similar with any other SMF detector. More specifically, in EMI, on any SMF detector, the sensitivity has to be reduced significantly more with a larger coil, compared to smaller coils.

True that the bigger the coil the better the depth and the larger the ground coverage. The smaller the coil the better the separation and the higher the emi resistance.

But where I've seen a difference is in what size and type of coils work better on different detectors.

I've been using the Equinox as a primary detector for a little over 4 years. I've found that the Nox is at it's best with the stock 11" coil assuming EMI permits. The depth difference between the 11" and either the Coiltek 5X10 or the 6" is substantial. Also the Nox 11" separates well for a big coil. The biggest downside to the 11" is how prone it is to EMI. The 5X10 is a bit less susceptible and the 6" a lot less. I can't comment on the 15" because the type of detecting I do isn't conducive to the huge coils so I have no experience with them.

One the other hand, the AT Pro which I used primarily for 8 years was at it's best with the 5X8 coil as opposed to the stock 11". The depth trade off was only around an inch and the 5X8 had a lot better separation and crisper audio. It was also way better ergonomically. The AT Pro felt bottom heavy and clunky with the 11"

I used a F5 as a primary detector for 3 years and although I didn't have one back then, I'm guessing the 8" round would have worked best for me on it as it has on the other Greek platform detectors I've used, the Omega and the Eurotek (Minuteman).

Never tried a larger coil on the CZ-3D, but the 8" round was super deep on a proper unit (many were NOT proper) and I didn't find the sniper coil for it to my liking at all.

 

[Diga]

The depth comparison comes down to how much the sensitivity has to be reduced for each coil size due to EMI, while taking into account the separation and unmasking performance of each coil.

 

[marcomo]

The depth comparison comes down to how much the sensitivity has to be reduced for each coil size due to EMI, while taking into account the separation and unmasking performance of each coil.

With some of the detectors I've used, sensitivity seldom needs to be reduced due to EMI. As a general rule, analog and lower gain detectors are a lot less prone to emi issues. And certain kHz frequencies are more likely to be compromised by EMI. When EMI forces me from multi to single frequency on the Equinox, 10 or 15 kHz usually does well, 4 or 5 kHz usually doesn't. With the detectors I listed in my post above, the Nox, F5, Omega and AT Pro were most likely to have EMI force lower sensitivity in that order. The CZ-3D was seldom affected by EMI. I've never had the Eurotek affected, but I've used that one less than the others. The worst EMI I ever experienced was with the pre-DST F75. That detector was an EMI magnet!

 

[Diga]

That's why I specified "SMF" in my original post. SMF is inherently noisier in EMI compared to SF, due to SMF accumulating the EMI of (typically) 3 frequencies.

In my worst EMI power line sites, SMF is out of the question, and so is up to around 15 khz in SF modes. 20 khz is usually outside the EMI range, and 40 khz always is.