Interesting observation on the question of "see through" and coil options:

[Tom_in_CA]

Hey gang, A week or so ago, I posted a question about which coils see through nails best. For ghost-townsy iron-ridden type conditions. And I had assumed that the vote would be towards the HF coils. Especially the smaller ones, obviously, to see-less-ground. Because:

a) I had seen a local fellow with a 505 and the 6" HF coil kick b*tt in seeing conductive targets amidst, and through nails, &

b) that in the old days, the very HF all-metal TR's, were known to see through nails better than later generations of VLF machines.

But the feed-back I got from that post, was that you guys didn't see any particular merit to solely HF coils, versus the MF or HF, for that task. And were instead favoring MF or LF coils. As if to say: The "hat-trick" I witnessed my friend pulling off, wasn't necessarily d/t his having a HF coil on there. But also perhaps just the machine itself's inherent characteristics.

So while I don't have a LF coil for my 705 handy so far, I do have the 9" MF coil. And decided to do some tests:

The HF coil does indeed have a better ability to see through iron, IN AIR TESTS. To determine this, I switched back and forth, with the exact same target combination: A given size rusty nail, with a dime held behind it about 1/2". Ie.: separated. Then in any mode I chose (AM versus disc. with only the bottom 3 ticks edited out), only the HF coil could get a conductive hint. While the MF coil would mask entirely. So there does seem to be some merit to the HF coil seeing through iron better.

HOWEVER, I found the following odd characteristic:

I performed the same series of tests, with the task of seeing through low conductors, to reach high conductors. This would be good for if someone is working underneath old bleachers/grandstands, to where they can't be-a-hero trying to get nickels or gold. Where they're going to content themselves with just looking for silver, amidst a sea of foil, tabs, etc....

On a lot of today's power-house machines, if you knock out pulltabs, you will not get a penny or dime hiding underneath it. The machine will mask because it's seeing the tab. For this test, I knocked out progressive ticks till I eventually found the level-at-which both round and square tabs were edited out. When I went to pass a dime behind a tab, with the 6" HF coil, it continued to remain a blank. It was not averaging the two, to enable it to be heard. HOWEVER: when I took the exact same combinations of targets, placement, etc... for the 9" MF coil, to my surprise, it effortlessly got the positive signal. Granted: It didn't read on penny/dime, but it was still high enough to register above tab.

I'm looking forward to trying an LF coil, to see if this tendency isn't even more pronounced, for the favoring of high conductors and beneficial averaging.

 

[Tom_in_CA]

So far, as it pertains to iron-see through, it seems the HF wins. Not sure if the LF would fair any better, for iron see through. If anyone has both coil type of commensurate size, can you try this test:

1) get a piece of cardboard square. Scotch tape a rusty nail to one side. Scotch tape a copper penny to the reverse side, so it's behind the nail. Try passing it, in air test with your HF coil, so that the placement (and size nail, etc...) are such that you can begin to get a certain clue of conductive there (versus a nail alone which would be a certain iron signal to pass). Granted, it might not be a penny TID, but at least get it so that the signal is repeatable, and knowingly to where you'd discern a conductive target. Next....

2) try the exact same test, with the exact same fixed placement on the cardboard, using the LF coil of commensurate size. Does the LF coil equally get the hint of a conductive target? Or does it take more playing with it, to keep from nulling out and/or masking ?

 

[Tom_in_CA]

3) Now try the same tests with tab versus penny. Even increasing to double tabs over a single penny. Which coil does the test better: the LF, MF, or HF, for you ?

 

[CampCache]

Just wondering if it could be that the MF coil is concentric and the HF is a DD making the DD "see" the coin better? Really not a level playing field with two different style coils instead of just different frequencies. I too would be curious to see which is better in iron trash. The other day I was running the 9" MF coil on the X-70 and my nephew was running the AT Pro with DD which is around 15 khz. He killed it with the finds in the iron trash. But was it because of the higher frequency or because he had a DD coil? I know if I run my 6" HF DD in iron trash I can do much better than I can with the 9" concentric MF coil. Is it because of the frequency or the coil style? I would love to hear results from people that have used the 15" WOT in all three frequencies in iron trash. This way the playing field would be level on what the actual frequency "sees" in iron trash. Just some thoughts.

Another thought is that my sniper coil for my Ace250 does really well in iron trash. It is a small concentric coil but has a small beam that will work in between trash.

 

[Tom_in_CA]

Just wondering if it could be that the MF coil is concentric and the HF is a DD making the DD "see" the coin better? Really not a level playing field with two different style coils instead of just different frequencies. I too would be curious to see which is better in iron trash. The other day I was running the 9" MF coil on the X-70 and my nephew was running the AT Pro with DD which is around 15 khz. He killed it with the finds in the iron trash. But was it because of the higher frequency or because he had a DD coil? I know if I run my 6" HF DD in iron trash I can do much better than I can with the 9" concentric MF coil. Is it because of the frequency or the coil style? I would love to hear results from people that have used the 15" WOT in all three frequencies in iron trash. This way the playing field would be level on what the actual frequency "sees" in iron trash. Just some thoughts.

Another thought is that my sniper coil for my Ace250 does really well in iron trash. It is a small concentric coil but has a small beam that will work in between trash.

thanx for the input Camp-Cache! Yes, I had forgotten that it's more than an issue of HF vs MF. It's also possibly an issue of DD versus concentric. Hmmmm.

Ok then: forgive me for my ignorance, but....... is the 9" coil (and the other coil sizes like the 6", etc...) available in BOTH DD and concentric ?

As for the observation about the Ace 250 with sniper coil: Don't confuse the "separation" issue with the "see through" (aka averaging) issue. 2 separate things. My main concern with this post is more about how a machine averages, when the targets are one-on-top-of-the-other. Such that separation becomes a moot point, since there is no "peak" at the object beneath, in the first place.

 

[Old Longhair]

There are no redundant coils. Currently we have 9" concentrics and 15" DD coils in all three frequencies, 10.5" HF & MF DD coils, a 6" LF & HF DD, a 6" MF concentric, and a 5"10" HF DD.

 

[Tom_in_CA]

Huh ? I am sooo confused. What coils are available in what frequencies and configurations (dd vs concentric) ?

6", HF, MF, LF , concentric vs DD (6 different combinations, right ?)

5 x 10 (I've deduced is only only availabe in DD HF, right?)

9" HF, MF, LF , concentric vs DD (6 different combinations, right ?)

10.5 HF, MF, LF , concentric vs DD (6 different cominations, right ?)

 

[Old Longhair]

9" concentric = LF MF HF
6" concentric = MF
6" DD = LF HF
5x10" DD = HF
10.5" DD = MF HF
15" DD = LF MF HF

That's it. Twelve authorized coils. And only the 5x10" and 10.5" coils are not waterproof.

 

[CampCache]

Never knew there were that many coils. Neat experiment for sure though. It's a shame there hasn't been more research posted on coils by Minelab. It would make buying a coil easier for some of us that are still on the fence about what would be the best choice for us. Looking over a chart on another thread it confuses me even more and the poster has not gave real world experiences on his post only air tests in the original thread.

 

[Old Longhair]

Lots of info on coils in the FAQFAQ pinned thread near the top of the forum page. Things like this 4-part blog that Randy wrote.

Which X-TERRA coil is best for me? part 1
http://www.minelab.com/usa/treasure-talk/which-x-terra-coil-is-best-for-me-part-1

Which X-TERRA coil is best for me? part 2
http://www.minelab.com/usa/treasure-talk/which-x-terra-coil-is-best-for-me-part-2

Which X-TERRA coil is best for me? part 3
http://www.minelab.com/usa/treasure-talk/which-x-terra-coil-is-best-for-me-part-3

Which X-TERRA coil is best for me? part 4
http://www.minelab.com/usa/treasure-talk/which-x-terra-coil-is-best-for-me-part-4

 

[CampCache]

I have read that blog and it made perfect sense to me. That was until I read this thread: Target response comparison of the three 15" All Terrain coils Unless I am reading that wrong the HF coil seems to go deeper than the MF coils and the LF coil goes deeper on larger gold than the HF coil. This is from air tests but there is no follow up on it so we have no real world results on this from the larger coils.

 

[Tom_in_CA]

n/t

 

[Tom_in_CA]

One drawback there is to ever having some sort of definitive "chart" for results, is that there is WAY too many tasks/desired outcome needs for folks. For example: Have you ever noticed, that the minute any discussion (video, thread, consumer reviews, etc...) starts on pitting coils-against-each-other: That the FIRST thing they all do, is zoom in on depth. Ie.: which "goes deeper". Well that's commendable if you're doing something where depth is the primary objective. However, that fails to take into account, that often-times depths comes with other draw-backs. Ie.: less see-through ability, less separation, perhaps less TID, perhaps only works in mild-soils, etc... etc....

Or coils said to be "better on small gold", woohoo ! Who can argue with that? But then the thing is perhaps weak on ability to reject iron.

So you see, it's no simple task to develop a consumer review chart, since there's sseeooo many venues/needs/tasks, for each type area, soil, objective, etc....

 

[Tom_in_CA]

thanx. Good read. He doesn't really address the "iron-see through" discussion, in any of those links. But good info none-the-less.

 

[CampCache]

One drawback there is to ever having some sort of definitive "chart" for results, is that there is WAY too many tasks/desired outcome needs for folks. For example: Have you ever noticed, that the minute any discussion (video, thread, consumer reviews, etc...) starts on pitting coils-against-each-other: That the FIRST thing they all do, is zoom in on depth. Ie.: which "goes deeper". Well that's commendable if you're doing something where depth is the primary objective. However, that fails to take into account, that often-times depths comes with other draw-backs. Ie.: less see-through ability, less separation, perhaps less TID, perhaps only works in mild-soils, etc... etc....

Or coils said to be "better on small gold", woohoo ! Who can argue with that? But then the thing is perhaps weak on ability to reject iron.

So you see, it's no simple task to develop a consumer review chart, since there's sseeooo many venues/needs/tasks, for each type area, soil, objective, etc....

You forgot a couple of other drawbacks.... bigger holes, digging a deep hole with a small opening and then hitting what you were after or spending several minutes digging a hole and not finding what you were after only to fill it back in and move on. Maybe that was in etc.... etc...? LOL! To me depth isn't the biggest deal on larger items but I would like to get better depth on smaller items. I do really well on bullets over 12" when I happen to swing the concentric coil over it and the stars and moons aliegn perfectly. But I have to overlap my swings really close too and it takes forever to cover ground. So If I could get the depth I am getting on bullets, cover more ground and find smaller targets deeper I think I would have the field licked. So when my soil is a bit above 30 to 50, I don't have to worry much about trash and I want to go with a large DD... looking at the chart in the link I posted the 15" HF might be better suited for my needs since it does get better depth then the MF on smaller items but will still get great depth on the larger items as well but then I am not sure?
No trying to hijack your thread because to me it seems all a little relative since it all bled together.

 

[CampCache]

Another thought on this. The other day my nephew and I were out hunting a battlesite. There was an old house place on some of the ground. Over the years this place has been picked over by me as well as others. We decided to suck it up and hunt the old place because it's one spot that most people will avoid due to the amount of trash. He runs an AT Pro with the stock coil. I was using the X-70 with 9" concentric. He found 5 bullets and I found 2. He found so much more other smaller brass and copper items than I did. Not sure if he was able to see more, get better target seperation or both. Not sure since again it still wasn't a level playing field. It still impressed me though.
I borrowed the machine to play with ait a bit to see if I might want to purchase one. What I found was that airtesting I could get the same amount of depth with the X-70 as the AT Pro could on bullets, silver and such but gold was a different story. I tried a few rings and found that no matter what ring I ran under each machine the AT Pro would hit 3 more inches on it than the X-70 with the 9" MF coil. I was really impressed with it. This was probably due to the fact that the AT Pro runs at HF and I was running MF. Either way it got me wondering about which frequency coil would suit me best because of being more sensitive to gold and raising my chances of finding it better.

 

[Digger]

But you can equip your detector to help identify conductive targets scattered among ferrous objects. A metal detector isn't a magic wand. A metal detector does exactly that.....detects metal. We can't look through one target to see the other, no more than we can look through a wall to see what is on the other side. But, we can look around the corners! And in the case of a metal detector, we can learn to recognize ALL signals coming from the coil, and sort out the ones we want to investigate further.

For the sake of simplicity, lets say that all metals have two properties....ferrous (magnetic) and non-ferous (non-magnetic). Sometimes we refer to non-ferrous as conductive, although there is more to determining the conductive value than simply the conductivity of the metal. Regardless, to keep us from digging up everything metallic, most modern detectors have some sort of discrimination capability. Some makes and models have variable discrimination. Others, such as the X-TERRA series, have what we refer to as notch discrimination. Without going into great detail about variable discrimination, let me just say that when you set a certain level of discrimination with a variable discrimination detector, everything with a ferrous value greater than that level will be rejected. Anything with a ferrous content less than that level will be accepted. IMO, notch discrimination has several advantages over variable discrimination. In detectors with notch discrimination, the entire spectrum of metallic objects is represented by a series of "bins". Typically, the lower the bin or bin number, the more ferrous the targets will be. And the more conductive (less ferrous) the targets are,the higher the bin or bin number. For example, targets that register a negative number on the X-TERRA series are the most ferrous targets. As the ferrous level of specific targets decreases, and the conductive properties increase, the higher the number will be. Those targets with the greatest conductive properties will be at the top of the number range. So when you consider that the notch discrimination system uses notches (bins) where targets are categorized, you can see how a notch detector will allow you to "pick and chose" which bins you accept, and which bins you reject. If you were to reject pull tabs on a variable discrimination detector, you could also be rejecting lower conductive coins and a variety of gold jewelry. Where as with the notch discrimination, you could reject the "bin" that represents the pull tabs, and still accept bins (above and below that level of rejection) representing lower conductive coins and gold jewelry. Regardless of which type of discrimination you have on a given detector, you are still going to detect all metal targets. The difference between passing over one that has been set to reject, opposed to passing the coil over one that has been accepted, is simply whether you set up your detector to provide an audio response on targets with those metallic properties. If you set nails to be rejected, you are still going to detect them. You just won't hear an audio response if they have been set to reject. Instead, they will only null out the Threshold. As I've said many times, I prefer to hunt in either zero discrimination or All Metal. By doing that, I hear virtually every target the coil passes over, allowing my ears and my brain to alert me to the ones I want to learn more about. There is quite a bit of information regarding how I like to hunt, in my FREE eBook. If you've not read it, there is a link to it at the top of these pages.

As to coils...one of the posts I made regarding the three Coiltek All Terrain coils has two charts. http://www.findmall.com/read.php?55,1800848,1800848 By comparing the information in those two charts, and by recognizing what role frequency has in relation to the metallic content of a target, you can get a pretty good idea as to which frequency of coil would serve you best.

Generally speaking, lower conductive (higher ferrous) targets respond best when inducing a higher frequency. Conversely, higher conductive (lower ferrous) targets respond better to lower frequencies. You can see this represented in the second chart provided in the link above. When you look at the TID numbers generated by the various frequencies, you see that the LF and MF coils provide very similar readings on the higher conductive targets. You will also see that the HF coil provides a much more accurate TID reading on the lower conductive Jefferson nickel. You will also note that the HF coil has a higher Ground Phase number than the MF coil. And a much higher Ground Phase setting than the LF coil. The simplest way to analyze that is by recognizing that a proper Ground Balance was obtained with each coil. Therefore they are all set to detect that specific piece of ground with their maximum capabilities, based on the software design. In other words, the end result is the same.....they're set to go. But by noting the numbers, we can see that there is a difference in how the software written for each frequency of coil analyzes the magnetic mineralization properties of that soil. And if you look at the mineralization readings, you will see that the HF coil was able to "neutralize" the effects of this particular site, to a lower magnetic number than the other two frequencies.

If you look now at the chart with the "distances from the coil" numbers..... (NOTE: I don't use the word depth because there are too many variables in the places we hunt, our detector settings and the techniques we use) Notice in the chart that the HF coil had the best results on the low conductive gold ring and the nickel. And, the LF coil had the best results with the higher conductive coins. The MF coil is usually somewhere in between the LF and HF, which is what we'd expect. You will also notice that the highest conductive target provided the most "spread" between distances from the coil when comparing the different frequencies. So, it all reinforces what I said earlier, the higher conductive targets respond better to lower frequency coils. And lower conductive targets respond best to higher frequency coils. There isn't a lot of difference between the LF, MF and HF coils on targets with "mid-range" TID readings. But as their properties migrate either higher or lower, the choice of frequency becomes more important for accurate TID and "distance to the coil". HH Randy

 

[Tom_in_CA]

I think you/we are getting bogged down in semantics digger. I mean, SURE, "no detector can see through". But that's just a convenience of words, and ... no , I don't think anyone thinks you can "see through". When I use that phrase, I'm referring to : Some machines have a better ability to AVERAGE two targets. While another tends to "see" the object on top only.

Example: Take your 9: MF coil. Set the machine's bin to knock out tabs or a given-foil-wad. So that it nulls (yes yes I know it's "still detecting" it, but just "not sounding over it", blah blah). Ok now take a dime or quarter, and put it squarely behind that tab or foil (so there's NO "peak" of the target visible to the eye). Notice that you WILL now get a signal. Yes yes I know it won't TID as "dime" or "quarter", but it's still up higher enough so as to register as above tab ! So in THAT sense, yes: It's seeing through. Or "averaging better" or ... whatever you want to call it.

There are other brands & makes of machines that don't do this test as well. Same for nails: Some machines will mask at a nail over a coin (even if your disc. is so low that you *only* have small iron knocked out). While others can get a clue of conductive target hiding under one, two, or even 3 nails for some machines (like a 77b )

 

[CampCache]

I went with the High Frequency 15" coil just because I would rather have a coil that's hotter on gold, small silver and buttons because while bullets are cool to find I would rather find coins, jewelry or buttons. If the larger coil will get about the same or a bit deeper on bullets than I am getting now I will be pleased. Thanks!

 

[Digger]

I think you/we are getting bogged down in semantics digger. I mean, SURE, "no detector can see through". But that's just a convenience of words, and ... no , I don't think anyone thinks you can "see through". When I use that phrase, I'm referring to : Some machines have a better ability to AVERAGE two targets. While another tends to "see" the object on top only.
There are other brands & makes of machines that don't do this test as well. Same for nails: Some machines will mask at a nail over a coin (even if your disc. is so low that you *only* have small iron knocked out). While others can get a clue of conductive target hiding under one, two, or even 3 nails for some machines (like a 77b)

I don't think I am getting bogged down in semantics. Several years ago, I would have agreed with you when you talk about target averaging or "seeing" the top target only. But having been deeply involved in development of the CTX3030, I know that the technology to see multiple targets simultaneously is not only possible, but being witnessed by CTX users every day.
[attachment 310940 screenshotwithtwocoins.JPG]

Does the X-TERRA have that capability. No, not with visual indications. But by using a combination of discrimination, all metal and pinpoint, and passing over the targets from multiple directions, you can do one hell of a job separating targets when they are directly adjacent to each other. But if there is a large ferrous target directly over the top of a small conductive one....it won't happen, regardless of coil size or frequency.

As you indicated, some machines will sort through multiple target signals and separate each target fairly well. And with the proper coil, using proper techniques, the X-TERRA is one of them. But not if the target response of a larger ferrous target negates the attempt of the conductive target to create their own eddy currents. Even if the coin is on top, a large piece of iron can "neutralize" the coin signal. JMHO HH Randy