Target Masking

[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.

[Steve Herschbach]

A simplistic way to look at it is imagine the sensitivity control as making your coil larger or smaller. Going to smaller coils can help in dense trash as it reduces the number of items under the coil at once. Making the coil “smaller” by reducing the gain or sensitivity can have similar benefits. Some detectors also overload easier than others. Nokta/Makro detectors are very high gain and overload easily in close proximity to surface trash so reducing sensitivity to very low levels is critical when using those detectors in dense trash.

[Tiftaaft]

2 hours ago, Steve Herschbach said:

A simplistic way to look at it is imagine the sensitivity control as making your coil larger or smaller. Going to smaller coils can help in dense trash as it reduces the number of items under the coil at once. Making the coil “smaller” by reducing the gain or sensitivity can have similar benefits. Some detectors also overload easier than others. Nokta/Makro detectors are very high gain and overload easily in close proximity to surface trash so reducing sensitivity to very low levels is critical when using those detectors in dense trash.

This and GB's and AU's comments should really be part of Detector 101 training.  So many hunters go into their settings and crank everything up as high as they will go in an attempt to "go deep" - then wondering why their machine is falsing all over and they are digging so much trash.  I am guilty of leaning that direction on occasion... but these comments remind me and hopefully others, that detecting at the "next level" requires a finesse and patience... not a sledgehammer approach on a sprint through a field. 

I am embarrassed to say that I was hunting last week and pocketed several beautiful sounding bent rusty nails from an old park... then I realized I had bumped my gain up to 10 on the SE Pro at the end of a previous hunt and forgot to reset it to 7 where I feel the sweet spot is for my ground.... I didn't dig another bent nail the rest of the day. 

Great comments guys... #tip of the hat#  Tim.

[Swampstomper Al]

Good discussion..

Swamp

[johnedoe]

Hadn't really given this a lot of thought .... I have always run my gains anywhere from 1/3 to 2/3 ..... Just seemed natural I guess... Also I am in western Oregon where the soil is pretty highly mineralized.

I am of the school that More is not always better.

[GB_Amateur]

Got out for 6 hours today (which is about my limit, currently) running the Fisher F75.  I started with the 5 inch DD at gain of 50 in a schoolyard which has produced Wheats and one Merc.  It's typically not that noisy (in terms of iron) and I decided to switch to the 5x10 concentric after about 1.5 hours.  That didn't help.  I ended up finding several modern coins (clads, Zincolns, and copper Memorials) but nothing with age after a total of 3.5 hours.

The last 1/3 of the day I switched to a 43 year old park established on a piece of property oringinally composed of two 19th century homesteads.  I went back to the 5 inch DD and after about 30 minutes with a gain of 50 I decided to drop to 40.  (Note:  max gain on the F75 is 99).  I was searching in my most hunted (by me) section which has produced a Merc and and a couple Indian Head pennies, where I've been at least half a dozen times with all my IB/VLF's.  I ran mostly in FA(st) process but occasionally I switch to other processes and even into all-metal to get a better reading on ID, location, etc.

What I noticed (and it's not a figment of my imagination) was that with the lower gain I was getting more clear non-ferrous signals.  That doesn't guarantee a non-ferrous target since (for example) vertical nails will masquerade as solid non-ferrous in my experience.  But I was digging non-ferrous (unfortunately nothing either old or valuable) that I have passed over previously.  BTW, my F75 ground balance is in the ballpark of 60 (between 56 and 64 depending upon location) at all my sites.  I consider that mild to moderate but you be the judge.  (Different values but similar quality ground balance figures with my other VLF's as well.)

Another thing I notice with the gain lowered: the FA(st) process of the F75 has fantastic recovery time.  I'm sure experienced F75 users know this, but when you see (for example) the video from England last month of the Equinox ripping through a series of closely spaced nails, I gotta say the 8 year old F75 can do that, too, without a hickup.  In extremely noisy (again I mean loaded with iron) soil it sounds like an automatic weapon going off.

Unfortunately I don't have any prize trophies to show (so far) with my new settings.  So in some sense this is a hollow post.  They will come.  Again I thank all those here on this site who have enlightened me on the complications, challenges, and solutions of hunting in heavily iron enfested locations.  I just wish&hope I can pay you back.