Interesting observation with a specific target -- would love NASA-Tom's thoughts...

Hi all!

I had an interesting experience with a specific target, that I've been pondering for the past day.

Yesterday, I was hunting with my hunting buddy, both of us swinging Equinoxes. He -- running FE = 5, and the 6" coil, me running F2=0, and the 11" coil. All other settings the same (recovery speed 3, sensitivity 23, 50 tones, Park 1).

We were busy "comparing signals," as we've had some interesting "differences" recently, while listening to each others' located targets -- with him running the 6" coil, and me running the 11".

I hit a target that I figured was probably a moderate depth (6" to 7") wheat cent; repeatable low to mid 20s, from all rotation angles around the target, and very little iron grunting (just an occasional grunt -- but solidly non-ferrous). So, I called my buddy over for a listen, but quite surprisingly, he said "nothing but iron grunts." I was shocked, and said NO WAY -- so I let him listen to my headphones, and he said "oh wow." So I listened to his. Yep, iron. An occasional chirp of a high tone, but basically solid iron grunting.

So, I assumed that since I was running FE=0, the only reasonable conclusion at that point was that I must be somehow getting fooled by a falsing nail, since my buddy, running much higher iron bias was getting nothing but grunts (which I assumed would probably be the more "correct" answer). Still, that signal sounded too good to me, to be iron -- TOO good, to be "explained away" by an iron bias setting. I was very intrigued, therefore; upon digging, it turned out to be a 7" deep wheat cent. But I said to my buddy that there is NO WAY the 6" would have called that target iron; I said "there HAS to be something else in this hole, that was throwing off the 6" coil." So, I probed around the wall of the hole with my pinpointer, and located another target in the wall, roughly 3" or so off from the actual location of the coin, similar depth -- and I retrieved that target. It was a tiny, circular piece of rusty iron -- about the size of the head of a thumb tack, and about the same thickness. It is possible that that is exactly what it was, missing the "shank." I didn't find any other iron in the plug, or the hole.

SO -- I can only come up with about three possibilities for how to explain this...and I don't feel like any of them are very reasonable...

1. his iron bias being set high, was to blame; it saw the two targets as a somewhat "combined target," BUT, with his iron bias set high, it called it "iron." Mine, though, with bias set as low as it would go, favored the "high tones," and thus correctly suggested "coin." I'm not sure about this, though. It doesn't seem like iron bias settings should have this much effect. With the small coil, he SHOULD have been able to get "separation" of those two targets AT LEAST as well as I did, with the 11"...so even with his iron bias set high, I would still think it should have been able to "see" the high-toning coin at least reasonably well. We both worked the target pretty thoroughly. What I would have expected, would have been for him (with the small coil) to have been able to maybe have isolated TWO targets, an iron tone, and a high tone. But this was not the case.

2. he accidentally "locked on" to the iron target "by accident" -- thinking he was sweeping over MY target (the coin). We were both interrogating the target using very short/choppy sweeps -- ala the "Minelab wiggle," so perhaps he was centered over the iron target the whole time, and never fully got a good pass over the wheat cent itself? I don't think this was the case, but we weren't being careful enough at the time (as much as we wish we WOULD have been, in hindsight, after the target was dug and turned out to be a coin) because NEITHER of us were thinking "there are two targets here." If we had thought so, we would have worked harder to try and isolate the two targets. But that's not what it seemed like. It seemed to us BOTH like ONE target -- his "iron," mine "non-ferrous."

3. his small coil, which may prefer smaller targets, simply had a "preference" for that small, round piece of iron, as opposed to the larger, nearby coin, and thus tended to report the iron more readily? This doesn't sit well with me either, though.

None of these "possibilities" are very satisfying to me, intellectually; I know it is near impossible to ask someone else to help "figure this out" without having "been there," but still -- I thought maybe NASA-Tom might have an insight, since this at least theoretically could be pertinent to the FE vs. F2 discussion...

Steve



Edited 3 time(s). Last edit at 01/07/2020 05:28AM by steveg.

My guess would be that the small coil simply wasn't getting the same depth as the big coil and ID'd the coin as iron, or the adjacent piece of iron had a bigger influence on the small coil than the coin did compared to the big coil and masked out the coin.



Edited 1 time(s). Last edit at 01/07/2020 08:02AM by Badger in NH.

Badger,

I tend not to think it was the first option; I think the small coil should hit that 7" wheat, without that kind of trouble. Your second thought seems possible/plausible, but if that is the reason, I'd like to understand the WHY -- WHY did the adjacent piece of iron would have affected the small coil more than it did the large coil?

Steve

Um,
This has happened to me before. When comparing Deus 9” vs 11” dd coils. Using the same exact settings as well as different (trying to get the coil that was struggling) to detect target.
Has happened once while employing the big Eqx Coil.

The cause?
Relationship of Tx winding to Rx winding. This what happens when we compare bigger to smaller coils, it’s not always a depth difference or one would think oh the little coil is not out flanked by iron like the bigger dd coil. It does happen. Funny thing though, Eqx useage with stocker coil, if I ever had to wager (with all all detector models) being entered, would Eqx see a target with stock Eqx coil that was located with 6” Eqx coil. Would be a bad bet to bet against stocker coil not detecting find located with 6” Eqx coil.

Now if we try this betting using other model detectors and switched off between 11” dd and 6” dd coils, one betting likely would not lose as much money. Those ML engineers really honed Eqx and 11” dd coil to be used as a pair.

Steve , you’ll see this happen again I am sure of it.

Mr Dankowski has said here at one time he had some test fixtures where he had poured acrylic. To freeze the articles used in place. He gave these I think he said to First Texas. Using one of his fixtures he indeed may have been able to duplicate what you and your friend experienced.

Thus far comparing the 11” and 6” coil head to head in the wild. It was modern trash where 6” coil seemed to excel moreso over 11” coil, not a nail environment - odds wise. With goal to get say a more proper ID to place better odds on digging say higher conductive target like a coin be it silver or copper.This doesn’t mean there’s is never no advantage for the smaller coil vs stocker in nails.



Edited 4 time(s). Last edit at 01/07/2020 08:47AM by tnsharpshooter.

The 6 inch on the Equinox is the coil I thought I would use the most and the 15 inch is the one I thought I would use less of. It turns out to be the opposite. I was impressed with the air test figures of the 6 inch coil but it got nowhere near the air test figures in the ground for me. In fact, 4 to 5 inches was tops for it in my ground on coin and button size objects. The 11 inch seems like it can separate just as well, and goes much deeper to boot. I sold my 6 inch...had no use for it. So I'm inclined to say it was probably a depth thing, as that would be what I found to be the case here.

Id say the larger coil sees around the iron better to targets below it, you see that when you try the nail test where the nail is elevated above the coin, the big coil does better.

I believe your iron bias setting helped quite a bit. I have also mentioned on various occasions and posts my dissatisfaction of the 6 inch coil. Some people feel the exact opposite, and that's fine by me. I just know what works for me. And one other thing.....I know for a fact that 50 tones will report on good targets that the other tone settings will not report on. It is hard to explain and replicate, but in have experienced it.

I think the most likely is that he wasnt centered over the coin and instead was detecting the iron.

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That's why I rarely use the 6 inch coil unless I'm hunting surface trash in a desert ghost town where there's little chance items are going to be more than 3 inches deep. Big coil gets deeper and sees around the iron better with the wider RX/TX windings. Heck I wouldn't even be able to hit a 7 inch wheat penny in my soil with a 6 inch coil, even the 11 inch would struggle to ID it properly. When targets are located on the same plain, small coils see in between targets better. Once you add dirt and a 3D environment where targets are on different plains, the big coil is going to do better. Interesting to see what Tom says though.

That's saying something if an 11" coil unmasks and I.D.'s better than a 6". Goes around our old way of experiences and knowledge.

With that said...I think the target (wheat penny) for the 6" coil was overwhelming the field AND too deep...It picked it up, but identified it as iron. If you removed the penny and swept the area with either coil, a low tone would sound or ID as iron. I do not own or run a EQ, so that unit is unfamiliar to me.

Very good answers, EVERYONE. This is exactly what I had hoped for -- some thought-provoking comments, even though I know it's hard when you weren't "there," to figure out what may have been going on.

Badger, I see that several others mentioned (as you did) that they felt that at least a PART of what my have been going on there, is that the coin was getting down toward the limits of what the 6" coil could accurately ID, and so that skewed the ID toward "iron." I was skeptical of that, but maybe I was too quick to dismiss that as at least a part of the answer. While I wouldn't have expected a 7" wheat to be "fringe depth" for the 6" (though admittedly, I personally haven't used the 6" much), I do know that with single freq. VLF units, in this dirt, that's EXACTLY what happens...a deeper coin will be ID'd as iron. However, in my dirt, FBS/Multi-IQ both do a pretty good job of not consistently calling a deep coin "iron." Sure, with a fringe-depth coin you may get grunts mixed in, but you will hear the high tones, also. That's one of the main reasons I USE FBS/Multi-IQ -- their ability to "hold onto" reasonably good ID through the entire depth range of the unit. As such, I have not experienced that "solid iron ID, every sweep," phenomenon on a fringe-depth target, using the Minelabs (like when running a single freq. unit). My old F70 was NOTORIOUS for that. It could hit a 13" deep coin, but beyond 6 or 7 inches or so, a dime was a solid "13" iron ID, every sweep.

BUT -- with all that said, several of you nonetheless mentioned that you felt that "depth" may have contributed, so perhaps there's some truth in that -- at least such that it is a PART of the answer. In other words, maybe depth PER SE wasn't entirely the issue; given the same target, but without the nearby iron, perhaps the 6" would have ID'd it correctly. BUT, perhaps when combining that depth (admittedly a pretty deep target for that size of coil), PLUS the iron there, all together that may have led to the iron ferro-magnetically being a substantially "stronger" signal to the 6" coil than the wheat cent was, such that it thus "favored" the iron target. So, with that, plus combining that with the rather high iron bias setting my buddy was running (and possibly the other points about how the EQX really "favors" the 11" coil being attached, etc.) -- perhaps all these factors combined to yield the observed resultant.

Great stuff, guys...

Steve

Steve...……. a 7" deep penny is childs-play for the 6" coil...… (in fairly mild dirt). It is well within the depth range of the small coil. Depth is not the issue.

6" coil whilst on FE6...…… vs. 11" coil whilst on F2-0 .,.,.,.,.,.,., does indeed present partial culprit..... as to your resultant; however, only to a degree of about 25%.

The real culprit lies herein: "Coin signal-strength" (((vs. mineralization & iron/iron-oxides signal-strength))).
I'm going to use a scale-of 0-10 analogy to illustrate:

11" coil sees the coin as a Signal Strength = 7.0
6" coil sees the coin as a Signal Strength = 4.0
Per expectations. (No problems yet).

Now we interject the variables:
The 11" coil sees the iron-nail/mineralization/iron-oxides as a signal strength of = 6.0
The 6" coil sees the iron-nail/mineralization/iron-oxides as a signal strength of = 4.3

If you understand the physics principle of RF (Radio Frequency) and/or EM (electromagnetic) energy dissipation...…. the energy off of an antenna (or coil) dissipates at a negative (root). (((Ten to the negative sixth [--root--]))). Also said: 6th-root.
Said differently...….. if you get closer to an antenna...… the radiation energy increases (at a rate of) "to the 6th-power".

So...…………… in our case: The larger coil still sees the 7" deep penny as a fairly strong signal. The iron-nail/mineralization/iron-oxides is also a fairly strong signal; yet, is weaker than the coin signal. Subsequently...…. the coin 'wins'.
The smaller coil sees the coin as a fairly weak signal...…… and sees the iron-nail/mineralization/iron-oxides ALSO as a weak signal strength; yet, the signal strength of the coin is SOOOO much weaker...….. that...….. by now...……. the iron-nail/mineralization/iron-oxides remains the trump-card. . . . . and the coin loses.

A 3" deep coin...…..and a 7" deep coin ….,,,,,,, is a very strong signal..... to a 11" coil.
A 3" deep coin to a small coil...… is a 55-gallon drum HUGE target to a small coil. A 7" deep coin to a small coil...… is starting to push its limits...… and is a weak signal. (Closer targets..... even if they are fairly small...…. will appear to be ---proportionately--- larger.... to a small coil).

I speculate that IF the 6" coil equipped EQX was switched over from FE6...…. to a setting of F2-0...….. would have 'probably' resolved on the coin. If you would have witnessed this...…. you would have been 'sold' on F2-0.

There is a correct time & place for smaller coils. They can be very beneficial. But...…. one problem is: The 'unsuspecting' variables that we encounter whilst hunting...…. is what dictates efficiency (or inefficiency) usage of a smaller coil.

NASA-Tom,

Thank you, for the very thorough response. Makes complete sense, and is very satisfying (intellectually); I don't like having these "questions" in my mind, that I don't quite have the knowledge or experience so as to assign a "likely to be the reason" explanation for them. Your information -- very clear and understandable -- allows me to do so.

I, too, now wish we would have switched my buddy's machine over the FE=0; he hasn't updated yet, so as to allow F2=0, but he intends to update, and I will share this info with him which will probably hasten his decision to do so.

Thank you for taking the time to explain!

Steve

That's a brilliant read Tom.

Specifically with the EQX...…. I find about 11% 'different' targets with the 6" coil. This is not as much as you would expect (nor I); yet, if you are in a fairly-trashy productive area...….,,,,,,,, 11% more targets can be a godsend. Don't underestimate.

Steve,

"I think I might have been there with you!"

In between making soup (bad flu last few weeks) I tried re-creating your conundrum!

Had to use my 'E Trac' as I no longer have my 'Equinox600' but, I do have an actual Minelab made 6" coil for the 'E Trac' as well as the standard larger coil. (we experimented with a 6" design housed in X-Terra 6" housings and I have a few For Sale brand New if anyone wants one PM me) (I love anything to do with 'small coils' cos at one time they became my 'baby', and I pushed for and helped design/create/test small coils right up to the CTX period from '09-'11)

Test Objects:
1. 1953 wheat penny
2. a small rusty nail
3. a rusty flat piece of tin (Boer War find from SA Karoo region)
4. a piece of detected coke l

The large coil had no issue with multiple detections beyond the 7" 'window', with various objects 'in hand passes' across it sometimes two objects e.g. coin and nail, coin and coke, coin and tin piece (watch face size)

However, the small 6" coil had a definite 'cut-off' point at the 7" window using a standard sweep speed i.e. going along as you would. But with a much slower sweep speed the 'cut-off' "dirty sounds" became a decent signal.
It's imperative to employ 'slower sweeping' when using a small 6" coil for two reasons: (a) too fast and you will miss something (b) the coil might not get "to see" the target if you miss its edge beginnings by a few inches even if large.

The reason I used the coke and the nail was to measure the detections possible at the magic 7" window and it was still possible to detect the coin with both the nail and the coke in hand using the slower sweeping (as shown to me by one of Minelab's top physicist's many years ago - in fact I was quite surprised at the 'slowness' of the target manipulations)

When prototyping all the Minelab detectors and coils I always tested in 'the worst-case scenario' site that I had been detecting since 1977 and it was a fantastic piece of ground (sadly sold now and overgrown)
Steve, I had situations as you described weekly (why I said I was there with you) and I always remember prototyping the CTX' small coil and digging in a really iron noisy/black soil/mineralised spot, digging three targets from a hole: a piece of coke, a small rusty nail and a thin copper ring blackened in color and large enough to fit the thumb not the finger. (we find these regularly and could be medieval?)
But, the previous week I had a 'blurp' dirty signal with the standard coil and had an 'a-ha' moment and said before I dig that I'll check with a smaller coil and the 'blurp' turned into a 'blip' and up came the three targets.

Where am I going here? I'm thinking your friend swept the spot too quickly: missed it: and zoned in on some "extra ferrous" particles that when dug by you ceased to signal. It was so rusted it disappeared and blended into the coil leaving just a tiny part you referred to. You locked onto the 'wheatie' which was an easy target as you had no bother hearing it while your friend didn't. He had gone past the 7" window the small 6" coil is capable of by sweeping too quickly and missed it. At this point the signals can go from GOOD to 'Dirty' to 'Non Detection'

That's my take, any thoughts?

Des D

PS: may I take this opportunity to Wish Happy New Year to you all and Good Hunting and may all your dream finds come up in 2020...(me...I'm still playing the Lotto...Lol...)



Edited 1 time(s). Last edit at 01/08/2020 04:25PM by Des D.

I just posted a video on this topic...

Thanks, Des -- for the post, and the New Year wishes; same to you, sir!

Interesting info, about the sweep speed thing, from back when you were testing the small coils Minelab. I totally agree with you on the need for SLOW sweeps, as I've been able to glean, from my own experience, that very thing -- when working in iron, work SLOW. Not ONLY to improve the chances of getting a good tone on a non-ferrous target, but ALSO to "quiet down" the falsing. Slow sweep speed REALLY helps, in that regard.

Not sure it was totally a "sweep speed" issue, though, in this specific case, since I located the target first, and then called my buddy over to sweep it. I pointed roughly to the location of the target, and asked him to "give a listen," so he already knew it was there. We BOTH used the "Minelab Wiggle" over the target, while we were "interrogating," and incidentally he "Minelab wiggles" MUCH more slowly than I do (just a difference in style). No matter what he did, no matter which angle he approached the target from, it was saying "iron" on his unit. Really, really a stark contrast to the report I was getting from my unit and 11" coil.

Good to hear from you, Des!

I hope you hit that Lotto!

Steve



Edited 1 time(s). Last edit at 01/09/2020 12:11AM by steveg.

Steve,

Did you and Mike (I am assuming you were hunting with Mike) happen to switch detectors or just listen on each others headphones? That would have eliminated any swing speed scenario. My best guess is all down to coil control. Level, smooth, slow, very controlled 360 degree swing.
Now you will just have to get out again very soon and replicate the scenario. LOL

Later,
Joe

“Never approach a bull from the front, a horse from the rear or a fool from any direction.”

Greetings, my good friend with the "Cherokee" forum name, LOL!!!

Yep, 'twas Mike I was hunting with!

No, we didn't switch machines, just listened on each others' headphones. You are right, that would have eliminated any "swing" variables.

Yep, we DO need to get out again, soon; ironically, he and a couple of others are headed out tomorrow; I had to turn down the invite (work schedule).

Also, I need to chat with you soon, re: your prototype carbon-fiber sand scoop handle is about ready to ship!

Steve



Edited 1 time(s). Last edit at 01/09/2020 04:39AM by steveg.

Steve,

"Throwing out a few scenarios and after hearing you are positive it wasn't "sweep speed" I'd say it was more the 'very rusted ferrous particle' that was present, you pulverised but a piece that hadn't corroded fully remained!"

Can you guys get back there easy enough? There might be another example just like this one???

Des D

Thou shalt not compare targets with different detectors!

Confusion will rule the day.

g