question on trash, sensitivity, and coil "footprint"

Hi all, I have a question...

I recall NASA-Tom stating many times that with a CZ-3D, if you turn sensitivity any higher than about 5, you are not increasing depth, only increasing the size of the "footprint" of the coil.

This got me thinking. When I run a small coil on my Explorer (say, the SunRay X-5), I can easily run sensitivity much higher than I can with the 11" stock coil; I can even run it maxed out sometimes without the chatter/falsing being much of a problem.

HOWEVER -- obviously, if I am using the small coil, it's because I'm in and amongst trash -- trying to get separation and hopefully pull out some targets that may have been missed when using a larger coil. So, I began to wonder -- if I ran through a trashy spot running max sensitivity on the Explorer with the X-5 coil, and pulled out all the good targets I could separate/locate, would it then make sense to RE-HUNT the spot, at a much lower sensitivity level? Would reducing sensitivity on the unit to well below "maxed out" levels, likewise reduce the footprint of the coil (as has been mentioned for the CZ) -- such that I may get even BETTER separation, and possibly squeak out a few more good targets? I don't know if an Explorer/SunRay X-5 combination would behave like the CZ, in terms of higher sensitivity levels increasing the coil footprint, but I would suspect it's at least possible. Anyone have an advice on this?

Thanks,

Steve

Steve, strictly on a 'physical' level, I would say yes. As removal of targets is going open the ground up. But this would also be totally dependent on density of targets still existing after X-5 has done its work.

Terra -- I understand you on the "removal of targets" thing -- and thus opening the ground up. Makes sense. I guess my main question is if maxed-out gain is increasing my coil "footprint" -- and thus that I'm somewhat "negating" the coil's ability to "see between targets;" in other words, is using a coil to separate out closely-adjacent targets, and yet running at high sensitivity, somewhat "counterproductive?" Instead, would lowering sensitivity "shrink" the coil "footprint," such that the smaller footprint would make the coil MORE efficient at separating individual, closely-adjacent targets?

Steve

Steve, in addition to what Terra said, which I agree with, I think it might also be a bit relative with sensitivity and coil size. For example, if the coil footprint on a 8" coil increases 25% or so (to 10") and IF (big IF) a 6" coil increases the same percentage, then it's only a roughl 1" increase. You are already using a smaller coil so it will get in between the small stuff just fine. However if the trash is really really heavy then you are not going to get depth anyway and I wouldn't be running it hot as there is not point to get real depth in high trash areas.

At the same time, sometimes high sensitivity gets things "sparky" (like my T2 was) and if you can handle the noise, you might actually be able to pull out more targets with a higher sensitivitiy. I was no T2 expert, so correct me if you disagree.

I know from running the 6X8 SEF coil (not really a super small coil) on my E-Trac, I could run the sensitivity quite hot without problems regarding the footprint size and got GREAT depth with that coil.

DD coils are really nice in that the small ones don't lose that much depth. A small Concentric appears to lose more depth than an equally sized small DD coil. So, coil type (and you are talking concentric on the CZ) might change a bit of what I said above.

Albert

Steve, maybe an air test with the little coil will get an answer. Detector stationary and move a target around the coil measuring the distance while changing the sens.... checking the footprint. I see your logic, the smaller the footprint, the smaller the scalpel, thus better seperation to unmask.

Anytime you increase foot print you increase what the detector has to process and filter. Many of those near or deep targets you may have disc is going to cause coil shutdown.... which means you lost depth. Ive always found on my ML in trash a high gain so all targets sound the same and reduced sensitivity gets me in the target range and may increase depth and seperation. For me it seems to work. Even on the beach i notice there i a point of no real gain in depth cranking up the sensitivity. However, i do tend to pick up more surface trash.

Dew

There are so many variables to contend with.

Different brands of detectors provide different results. Some detectors work much better with max Sens settings in heavy trash areas. Other detectors may require lower Sens settings for better audio intelligibility.
Some detectors do not adjacent-separate non-ferrous "bad" targets from non-ferrous "good" targets very well.
Some detectors do not adjacent-separate ferrous targets from non-ferrous targets well.
Mineralization comes into play also.

You have to experiment with your specific detector........... your specific coil.............. your specific settings............. your specific dirt conditions. Head-t-head comparison is not easy! (((But a lot of fun))).

Thanks much everyone, for your answers. Gives me some things to think about.

Albert -- true that in trash, you usually won't get "max depth" anyway, so maybe running max sens. is not necessary. I guess my rule of thumb has always been to run as "hot" as I can without getting noticeably noisy/falsy; that X-5 will get really good depth when running high sensitivity (and if not in too dense of trash), just as you said about the small DD coils. Given that advantage, I never thought of NOT running it hot...but then I got to thinking about "footprint" (after thinking about what NASA-Tom always says about the CZ and sensitivity).

ozzie -- yes, you got my point...and maybe an air test would give some answers -- seeing how the coil behaves in terms of sensing the target on the fringes of the coil, at different sensitivity levels.

dew -- interesting that you say REDUCED sensitivity seems to do better for you, though I know what you are saying with respect to "picking up more surface trash." When I run the 11" Pro coil, it seems to be really "hot around the edges" when running high sensitivity, such that I pick up alot of targets way out on the fringe of the coil; however, I don't really notice that so much with the X-5 -- so I wasn't sure if higher sensitivity with that particular coil equals "larger footprint."

NASA-Tom -- sounds like there's not a "one size fits all" answer, but one thing your answer reminds me of, is -- if I'm trying to get the best separation I can in the trash, the Explorer is not the best tool ANYWAY...

Which brings me back to the "unmasking" discussion/thread awhile back (mainly regarding the F-75), with respect running disc up until the nails are JUST BARELY disced out, and then digging any target above that ID value (for maximum unmasking ability). I need to learn to do that with my Gold Bug Pro and 5" coil (though I still need to do that "depth test" on my 5" coil that we discussed.) That method sounds quite difficult to learn, and intimidating, to me...but there are times when it would be really nice to have that skill.

Anyway, back to the Explorer and X-5 coil, sounds like some sensitivity/footprint-size testing is in order (air testing, and test-garden testing...)

Thanks, all.

Steve

Steve .... a good way to tell with the SE is if you get screen feeze. I crank the sensitivity down until it moves normally...... but we are still using tome arent we.

Dew

Yes, I find myself using tones more and more, dew...I glance at the screen only when the sound of a target catches my interest. But I follow your point on the "screen freeze;" too much nulling often means too much sensitivity...so I'm with you on that...

Steve

Steve,

The GB SE with a 5" DD coil ......... (((config'd for "just barely" Disc'ing out the nails)))...... is a very easy unit/system to learn.

NASA-Tom --

Realizing that I'm speaking from ignorance (as I've never tried this method), I just can't imagine it being as simple as it sounds...seems like something that would work perfectly IN THEORY, but my mind says applying it effectively "in the field" would be quite difficult, and require a great deal of experience to accomplish any level of success.

What I mean is this -- I have a site I'd like to use this method on, which I mentioned before (an 1800-built church back home in PA that has burned and been re-built a couple of times; the yard surrounding the church is now filled with a blanket of square nails from the tear-downs/re-builds). I'm headed back home to PA for two weeks this summer, and plan to hit this site again (a couple hours there last summer yielded me a few Indian Heads with my Explorer from amongst the square nails, but I know there's much more there, hidden in the iron). While there, I dug up several of the nails, just curious to see what I was dealing with; of course, there were nails of many shapes and sizes, some bent, etc. Point being, my mind imagines that the reality of "just barely discriminating out" the nails, would not be nearly as easy of a task as it sounds "on paper" -- due to the non-homogenity of the nails (as I'm sure is the case at most sites). Given the various sizes/shapes, and the various juxtapositions (nails overlapping each other, etc. etc.) I would imagine they would ID all over the place in the iron range...and some of the bent ones even up into the "coin range" (they do on the Explorer, anyway). So, while I could "disc out" some of the individual "well-behaved" nails very effectively, it would seem that many would NOT be "disced out." Finding that theoretical "sweet spot" on the discrimination dial where the nails are "just barely disced out" would seem futile (again -- due to the various sizes, condititions, and orientations of the nails). And thus, I would imagine my attempts to locate and dig partially iron-masked coins IDing in, say, the "high iron" range (due to a nearby nail) would instead, in all actuality, likely result in a pouch full of nails that, for whatever reason, ID'd higher than they "should have."

I guess all I'm saying is that until I do it, and actually accomplish digging a coin or other good non-ferrous target that IDs as "high iron" or "foil" or something like that, I can't imagine that I could actually pull it off. It almost seems "mystical" -- a skill that only a NASA-Tom or a Keith Southern can actually employ with success! Again, I understand completely how this would work conceptually/theoretically; I just can't imagine this being a theory that I, in my inexperience, could effectively employ in a "real world" scenario. It will be fun to TRY, but I would bet dollars to donuts that I leave that church with a pouch full of oddly-shaped square nails that were unusually aligned/juxtaposed while in the ground -- and thus squeaked through my disc. level. And I really can't "practice" this skill much, as here in Oklahoma there simply aren't many "full of square nails" types of sites where this technique would be appropriate. My hunting experience has been confined to mainly "modern trash" sites, so I'd truly be a "novice" trying to deal with the iron in this way.

Is there something I'm missing, or something I'm mistaken about, in my mind's presumption of the difficulty of applying this knowledge effectively at my "church site?" Don't even you expert hunters end up, more often than not, with a pouch of nothing but oddly-shaped iron pieces at the end of the day, when attempting this "surgical" unmasking technique?

Steve

Steveg, It's not an easy method for me because of all the crackels, tics and pops. My thoughts were the same as yours. If I dig a few nails, scan over them and barly disc them out, chances are that there will be a bigger nail or bent nail or a bigger piece of iron, now what? My brain seems to distinguish better with 0 disc, 4 tones in a bed of nails/iron pieces.
Very slow process coupled with high consentration and swinging from all angles. Last week I pulled a 1836 half dime from a nail site w/ the 5". Lots of coil wiggeling with this approach and I've been over this tiny area (20'x20') many times.
Tom D. is way more experienced than I and his method is probably the best, I'm just not there yet, maybe more practice.

Steve,

I think once you find your specific Disc set-point that Disc's out most small iron............ the only other skill to be learned is: what type of audio response you receive as you rotate your body around a 'suspect' target. Bent nails, co-locate nails, rusty nails ....... present a certain 'audio signature' ; whereas.... a non-ferrous target in co-locate with nails ... presents a different response. This is also to say........... with small nails Disc'd out........... medium and large sized iron also presents a certain 'audio profile signature' that ALSO is highly discernable. Sounds intimidating (at first).......... and yes, you will dig plenty of iron (at first).......... but, your skillset will increase at a more rapid rate than expected. (((Especially when you witness success a few prideful times))).

Tom does one have to have acute hearing for this method? I can not hear the differences of a mono tone. I have good headphones (Grey Ghost) so don't think they are the problem. Is there a solution/remedy for not being able to hear the nuances of the same tone or just do my best with the hearing or lack of..... which is using 4 tones.
Steveg, please excuse the highjacking.

ozzie -- no need to apologize; "hijacking" is welcome; I learn from asking my own questions as well as from reading the questions -- and subsequent answers -- of others! You asked a good question, too -- and it's one I asked NASA-Tom awhile back when we were discussing this same thing. My question to him was whether my Gold Bug Pro's audio might actually offer some advantage over the F-75 monotone. Reason being, the Gold Bug Pro's audio has an adjustable set-point; once you choose your set-point, then any target that IDs below the set-point, it's just an "iron grunt;" ABOVE the set-point, however, it's "modulated VCO audio" -- and I had asked him if there might be "more intelligence" in "modulated VCO audio" (when attempting this technique) than there might be in a single monotone "beep" like on the F-75. Point being, I would, like you, think it would be somewhat tough in monotone. Having said that, though, I do know (and you do too, I'm sure) that with monotone, those "cracks and pops" you mentioned actually are, in fact, some of the clues that you are dealing with iron falsing, instead of an iron/non-ferrous target juxtaposition. I ran an F70 for awhile, and so I am quite familiar the "crackles and pops" you refer to ; I never perfected my understanding of all the "noise" on that unit, but I do know that those crackles and pops were iron most times -- which is probably part of how you learn to make your dig vs. no dig decisions using this method. While some of the clue may be in "nuances of the tone," as you asked about, much of it I am guessing lies in the crackles and pops (or lack thereof). If the response changes (breaks up, or gets more "crackly" ) AS YOU ROTATE 360 degrees, wiggling the target, vs. if the tone stays more consistent and repeatable. I'm sure you have learned that, too; I kno that's a HUGE clue to target type, on my Explorer, and I'm guessing some of that applies to the F75 as well.

Anyway, having said all that, I'm not sure how square nail-type responses in a VCO format will sound on the Gold Bug Pro, vs. a square nail/good target combination -- but obviously this is what I'll have to learn -- how to decipher the "iron clues" in a modulated VCO audio platform -- in order to make this method work for me.

NASA-Tom -- what you say makes sense...that for the iron that "sneaks through" the disc, there is a different, distinct audio signature (as opposed to a nail/good target combination) such that over time I will begin to recognize those differences. Some "square nail beds" here locally would sure help speed up the learning curve, BUT -- you say that learning it may not take as long as I think (especially if I can dig a few good targets and note the differences.) That gives me some encouragement/confidence. I look forward to trying.

Steve



Edited 2 time(s). Last edit at 05/29/2012 08:00PM by steveg.

ozzie - Monotone ........ in concert with "just barely" enough Disc to get rid of most of the audio of small iron (usually small nails) ......... this configuration creates the best unmasking abilities.............. and also creates a condition for a rapid learning-curve. You can ONLY find this Disc setpoint with actual local conditions. Throwing a bunch of rusty nails on a sheet of plywood.......... and setting Disc to 'just barely' Disc out the nails ..... is NOT the same as real-world 'ground conditions'.

Finding this set-point is fairly easy. Start the detector with too low of a Disc setting............. and see to it that you hear everything. Then, while sweeping the coil, start to adjust the Disc so the bulk of the sound is snap/crackle/pop/click/tick audio. Then........ dig a few targets that audibly break through the Disc setting. Determine if this is the Disc set-point that you want..... by the targets recovered. Keep in mind that......... you may have initially set the Disc point too high...... if there happened to be a non-ferrous target under the coil's sweep-path...... whilst you were initially setting the Disc.

Once you determine that the Disc point is about where you want it............. the next phase is human brain-train. This is the steep/fast part of the big learning curve. You will already know to ignore the snap/crackle/pop/click/tick audio reports. But........... you will find some targets breaking through the Disc and giving slightly more length to the audio reports............. so as to be longer in audio duration/length over the click/ticks. If Disc is set properly.......... bent nails,,,, and the tip of nails will give longer audio responses. NOW......... body-rotation becomes important. As you rotate your body around the tip of a nail (or a bent nail)..... the audio length ramps down very quickly..... as your approach angle into the target changes (due to you rotating your body around suspect target). You will also notice that the top-dead-center pinpoint location of a nail will shift/move.... as you rotate your body around the target. You will need to dig several of these...... for learning purposes. When you have a non-ferrous target in co-locate with a ferrous target................... THIS is where the audio delineation plays out. It will audibly respond quite differently than if it were just a bent nail..... or tip of a nail. When a non-ferrous target is in co-locate.......... the clarity of the audio report is greater............ AND the body rotation around the target allows for a greater (and/or different) degree of rotate. You will NEED to dig several of BOTH examples............ so as to instill the learning-curve process. Your confidence in carpets of iron will be tremendously increased........... and your success will be much greater. You will then be able to hunt areas that previously have never been able to be hunted/searched. Not only does this open up new areas................. but....................... the 'volume' of non-ferrous targets in these carpets of nails (where habitation existed the most)..... is maximum.

Thanks Tom, can't be more clear than that. Step by step on how to....like it!

The biggest concern here is: You MUST dig plenty of bad targets............... so as to enhance the data-bank on what they sound/react like. The more bad targets you dig............ the more intelligence you ascertain.... to draw from..... for subsequent decision digs.

I don't mind digging and learning. Mental notes are the key. My preference is; hanging out in the nail pits....more gratifying when a good target is located.

NASA-Tom, I much appreciate the detailed response regarding audio. Very, very interesting, and while the GB Pro has different audio, I can see where much of what you said will still apply...

Thanks!

Steve