Target Masking

[GB_Amateur]

Out for 3.5 hours yesterday with the F75:  5 inch coil, FAst process, gain 85 to start but turned down to 70 (still high compared to some detectors), 0 threshold (experimented cutting out iron @15 setting, but decided I liked it better hearing the iron).

No 'good' finds so won't bother with that.  But a couple things I noticed --

1) I found a few small bits (examples:  22 bullet and 22 casing) in an area I've search many times previously ('many' meaning at least 4 times) with other detectors and even the F75 with a different coil and settings.  There are multiple explanations for this, but "they weren't present before" is not one of them.  Still, I can't say it was because I didn't pick them up previously due to masking.  Also possible are:  a) didn't get the coil over them due to poor coverage/swinging, b) different ground moisture (we finally got some rain; YEAH!), c) inattentiveness, particularly when trying to find the signal in all the noise ('noise' being iron hits -- mostly nails), and d) just better technique, etc. due to more experience (including reading I've done, particularly here).

2) Although I still have a lot to learn, in general and about how specific detectors in my arsenal respond, I think I've picked up on some generalities but of course would like to hear what others have to say, either contrary or in agreement.  (Misery loves company.  )

A) I have a term I've toyed with (and I wouldn't be surprised if I've picked this term up from others):  'target confusion'.  Masking is included in this, but there are other things that I think enter in which may not specifically fit under that title.  One seems to be having two iron objects separted by several inches (let's say 8 inches as an example) and although either one ID's as iron, when you're between them you get a false signal that ID's above iron.  I end up digging the false signal and finding nothing.

B) Another related case of target confusion seems to occur when two objects are close enough in space that they don't seem to give separate signals, but give a combined signal whose ID doesn't match either one.  Also, when swinging off-center, you can get a positve signal from an iron target that shows up in its true 'bin' when you get centered over it.

C) Orientation of nails:  It seems that a perfectly vertical nail will give a high (non-ferrous) ID every time (unless it's super rusted to the point of not even holding itself together).  Certainly (if true) it doesn't matter what direction you sweep your coil because of the symmetry.  Horizontal nails can (depending upon size) give different signals/ID's depending upon the coil sweep direction, and sometimes give positive (non-ferrous) signals over their very tips.  However, I don't find there is a consistent signal for nails in general, because they can be bent, come in a plethora of sizes, and they are typically oriented randomly.  Very few are perfectly vertical but most aren't perfectly horizontal, either.  The ones at odd angles give signals which are like neither horizontals nor verticals.

D) Although under perfect conditions, a good target (e.g. coin) gives you a consistent signal with the proper ID, much of the time you have to deal with less.  I've read "just dig the consistent signals, independent of swing direction" and I'm pretty sure that will give you a high true positive result, but it will also give you a lot of false negatives.  (I want ALL the good stuff!)

What has happened to me (and I suspect many others) is when I first go to a site I find the 'easy' good targets -- the ones close to the surface or reasonably distant from other (bad) targets.  After that either one assumes there aren't any more goodies, or that they are too deep or too masked to find without Herculean effort.  After the low-haning fruit is picked, the remaining desirable targets are tough to discern without much better techniques (and maybe not even then).  And yet I suspect the truly expert detectorists can do a lot better.  (That's why I wish just once I could bring a more experienced detectorist to one of my locations and say "show me what I've missed.")

In summary, depending upon conditions, detector choice, coil choice, and settings, the response can be significantly different.  I don't think this is much different than many endevaors -- people (myself included) search for simple explanations when in fact, much of the time there is a 'conspiracy' of things going on, all of which interact to give a signal/indication/result which is quite different than any of the individual causes.  And the really expert are the ones who (maybe) figure out what is going on.  I think I'm headed in the right direction, and although I'll never get there, it's been a fun journey so far and I hope it continues that way.

 

[auminesweeper]

I think you did well to find those bits, So many people just have to run their machines flat out, Dropping the Gain down like that allowed the machine to see what is in the ground, Under a lot of conditions using high gain can be likened to driving in the Fog using high beam which in effect Blinds the detector, Lowering the gain might not provide maximum depth but it will unmask targets giving the detector a chance to see, Knowing when and where to do that is a Skill that many detectorists lack, So well done,

thanks for posting.

John.

[Tiftaaft]

51 minutes ago, GB_Amateur said:

B) Another related case of target confusion seems to occur when two objects are close enough in space that they don't seem to give separate signals, but give a combined signal whose ID doesn't match either one.  Also, when swinging off-center, you can get a positve signal from an iron target that shows up in its true 'bin' when you get centered over it.

All of your post was spot on GBA, and I will most likely read it again and quote it in future posts... but this portion highlighted a situation I had while hunting on Saturday.  I was in an old school yard that I have covered many times (at least 4 to match your comments).  I have pulled some wheats out of the area, but I keep going back because I am convinced there are at least a couple of silvers lurking (I plan to give this location the research and review treatment a la Deft Tones' "scouting a new patch" post in the jewelry forum.. shout out to DT!). 

But on this trip, I was thinking about the target masking discussion and started out with my ATX until the rechargables died in the first 20 minutes... I did manage to clean out several nails and pencil erasers, along with a 6" 1964 Jefferson nick before it went dead.  So I grabbed the Etrac out of the car and took another pass..  I came across a target that was pretty solid, at 12-30 in all directions.  Higher than normal pull tabs, but lower than zinc pennies.  I recovered a clad dime first... about 3 inches down, which confused me a bit.  I put my pinpointer in the whole and got a deeper target indication... I dug down another few inches and found a nickel.  The combination of the two targets gave me the 12-30 reading.  I have had this happen before, but didn't think twice about it... but I will be paying closer attention to those odd ID's... as they could be combined goodies. 

Tim.

[steveg]

Tim,

I have had this happen, also (two coins, screwy ID) but usually, there is an angle -- or sector of angles -- that as you rotate around the target, you get some indication in the audio that there might be two items present...like the machine (at that angle or sector) can't decide what it wants to report audibly so it kind of "reports both," and it has some semblance of a HIGHLOW or LOWHIGH blurb of tone.  That's not always true -- especially if the coins are touching, or right on top of one another (then, it's often just a cleaner, single tone representing the "conglomerate" of the two coins).  But often, I get this really weird tone -- hard to describe -- that I have come to recognize as co-located targets.  Did you get any of that, or was the tone "clean," and indicative of a solid 12-30 ID?

Steve

 

 

[Tiftaaft]

32 minutes ago, steveg said:

Tim,

I have had this happen, also (two coins, screwy ID) but usually, there is an angle -- or sector of angles -- that as you rotate around the target, you get some indication in the audio that there might be two items present...like the machine (at that angle or sector) can't decide what it wants to report audibly so it kind of "reports both," and it has some semblance of a HIGHLOW or LOWHIGH blurb of tone.  That's not always true -- especially if the coins are touching, or right on top of one another (then, it's often just a cleaner, single tone representing the "conglomerate" of the two coins).  But often, I get this really weird tone -- hard to describe -- that I have come to recognize as co-located targets.  Did you get any of that, or was the tone "clean," and indicative of a solid 12-30 ID?

Steve

 

 

I admit, I didn't spend as much time as I should have walking around the target, so I didn't notice anything but the 12-30, which was pretty solid and a single tone... though thinking back, it was a higher tone than I would expect for a "30"... whivh is probably as much the reason I dug it quick as any.  I was also swinging the stock coil, which is pretty great at target separation, but a sniper coil may have separated the two targets better.  In hindsight, this would have been a really good "in the wild" test target...  I will try to keep that in mind the next time I run across one similar.  

Tim

[steveg]

Tim, 

Gotcha.  I know how that is...can't tell you how many times I get "just enough of what I want" from the machine -- i.e. enough of a clue in the tones to make the "dig" decision, and then, once I have the target, I end up "surprised," and wished there in hindsight that I would have "interrogated" the target a bit more, from different angles, for the "educational" aspect the machine might have offered on that particular target.  I recall that specifically, awhile back, on the last half I dug.  I was hunting in trash, and had already dug a few rusty iron things, and got another tone that didn't sound all that great, but kind of hastily said "what the heck, I'll just dig it" and then, up popped a Walker!  My partner said "how did it read on your machine," and would you know, I couldn't even tell him?  Other than to say "kind of crappy?!"  Wished I would have been more careful, rotating around and listening to it...it would have been a good target to "get an education on," as it was certainly in no way CLOSE to the textbook air-test 00-27/00-28 (that they read on an Explorer).

BTW -- I didn't make it clear (for the sake of others), I am talking about FBS machines specifically, in terms of how they report co-located targets (especially that "HIGHLOW" or "LOWHIGH" blurb), because obviously each machine does things differently in terms of how they report co-located or close-proximity targets.

Anyway, Tim, I am going to guess that your two coins were probably on top of one another, or even touching, if you had a pretty stable ID and tones, at least as far as you can remember.  That "12-30" is obviously a clue, in that if it was stable, as you noted you recall it being, then the machine WAS treating it as a conglomerate, and not two separate targets...so they were likely touching, or close to it...

BY THE WAY, really good post just awhile back, GB_Amateur...

Steve

 

 

[Deft Tones]

Jacked around at a parking lot edge with the 4x6 shooter coil yesterday. Been there many, many times for fast 30 min hunts using larger coils.This time I slowed down to 1 foot per second sweep speed and went for co-located and masked

Dug two nickels and a dime. They were stacked and nearly on edge at 3-4". V3i read them as 64-62 depending on sweep angle. Nickels normally read 19, Dimes 72-74 (can't recall...lol) I find lots of targets like this and the read/soundsolid, generally.

Found a ringpull with no tail at about 4" - 2" under a medium sized bent nail. I could clearly hear a non-ferrous down there...again, depending on sweep angle. Solid ID coming from one direction, choppy from the other.

I used to analyze alot, but not nearly as much anymore. There is an intuition that comes with experience for sure.

[GB_Amateur]

17 hours ago, auminesweeper said:

I think you did well to find those bits, So many people just have to run their machines flat out, Dropping the Gain down like that allowed the machine to see what is in the ground...

I didn't even think of this -- that the reason I may have missed these small targets before but picked them up now is that I had the gain set too high previously.  Just another example of why it helps to post here:  others can point out details/reasons/etc. that I've missed.

When I was in Colorado a month ago and was able to pick the brain of an experienced F75 user he told me that he often runs at a gain of 50, which is just halfway up the gain scale.  He suggested I try that.  John, your post clarfies why he said that.  Thanks!

This also may be another emphasis of "simple isn't better" when it comes to understanding how an MD works.  In one of Dave Johnson's posts he mentions how unrealistic it is to think of the zone of detection of a coil as an inverted dome or cone.  He goes further to say something about over 24 degrees of freedom (>24 variables) that affect how a target will signal.  (The number he specified may have been 27.)  And I'm pretty sure he was talking about a single target.  How many variables when you add another target in range, and another....

Further speculating, suppose you have a small nail at 6 inch depth and nearby a dime at 4 inch depth.  The signal you get will not only depend upon where the coil is with respect to these targets and the direction and speed of motion, but also on the gain.  If you can reduce the effect of the nail more than the effect of the coin by turning down the gain then you come out ahead.  Is this (still an overly simple explanation ) a description of what is happening?

[auminesweeper]

Well GB what proved the high Gain issue to me, was me and a Mate were both using MXT's with the 12" coils, I was running mine just on the edge of the 10+ area remembering that the MXT's dial goes up to 10+3 and he was running his in the 6.5 to 6.7 yet he was digging them large English Penny's at over 13"and a half inches where all my finds were between 5 to 10" range and I put that down to the fact that I was Blasting ALL targets good and bad where he was just feeling his way through to each of the good targets,

Another thing to remember is running 2 high powered identical machines with big coils don't play well together because we could hear each others machine approaching from a long way away when the Gain is up around the 10+ area because they will cross talk from well over 2 to 300 feet away starting with a soft pulsing sound and then ending up sounding like a V8 with a couple of plug leads off, So there is a lot to be said for running lower gain settings,

hope this helps,

John.