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au,

I am NOT saying this is THE explanation, just A POSSIBLE explanation...

Falsing off of the plough itself.

Another, possibly more LIKELY scenario?  Detecting and then mis-IDing (and thus allowing to sneak through the discrimination) the iron plough?  Not uncommon at all, of course, for large iron to not be "discriminated," as the large size of the iron fools the detector into IDing it as non-ferrous...

Steve is correct, detectors cannot see "through" iron. 

Steve

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This whole discussion on masking reminds me of a silver quarter I found in an old school playground a few years back.

I was running my V3i in the area of the swing sets and off to one side I get a banging quarter hit... Nice high VDI and a good solid signal... so I dug the target and out pops a flattened bent up aluminum soft drink can... And a silver quarter in the plug as well... Now which did I detect?

I really didn't care because I found the silver, but that bent up aluminum can read very similar to the quarter... Did the V unmask the quarter? I doubt it.... I was just fortunate enough they both came out of the hole at the same time...

When I am in a new area that I deem has potential I dig a lot and ALWAYS recheck my holes so my unmasking is more technique than electronic.

Just my thoughts and experiences in the matter.

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Very good point, johnedoe.

I have obviously read, and heard, several people showing a pile of nails, and a coin, and say "I dug out all these nails, and then finally the coin, at the bottom...my machine heard the squeaks of high tone to clue me in that the coin was down there."

My question always was -- and how do we know that the squeaks weren't, in fact, just the nails falsing, and that it was just fortuitous that a coin was down there, too?

I am sure that is not ALWAYS the case -- sure, you can pull a nail and a coin from the same plug, having had the machine see both targets.  But when it's a handful of nails?  How can you really know?  I have dug more than my share of bent, rusty nails that sounded like there should have been a coin down there, only to dig the plug and find "nope, only a bent rusty nail."  If I dig another similar-sounding target, and find a bent rusty nail, and then a coin two inches deeper, should I assume my machine heard the coin, or just the nail falsing (and the coin was a "nice accident")

Steve

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SteveG, you really hit the "nail" on the head with that post.

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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.  :biggrin:)

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.

 

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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.

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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.

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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

 

 

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