Question for the F75 owners

[JG]

Hello all F75 owners!

The question has to do with VDI numbers on targets that are near the edge of detection with a VDI.
It also deals with the Discrimination mode and All Metal Mode/Stat.

Observation:
AMM gives a tighter range of VDI numbers than say in JE. What I mean to say is the VDI has (can have) a broader reading in JE Vs. AMM. Not necessarily a bad thing because,..
It has been noticed AMM (buried target) can give a VDI above the air test VDI, but very close. JE sometimes a bit more exaggerated. I call it VDI overshoot.



Here is the question: Have anyone of you noticed a solid or an air VDI greater than the overshoot (MAX) VDI in AMM? How close was the max VDI to the best repeatable 'true' VDI?
This may help in unmasking iron and better target identification.

Again, this applies to targets at the edge of detection with VDI information. It can also apply to masked targets. Any targets producing a range of VDI values at the edge of detecting a 'true' repeatable VDI.

Thanks,
Jim

PS. maybe VDI overshoot is too much gain? any comments?

 

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[gmanlight]

I just did a quick test in the house in disc mode on 6
A quarter hit 82 A nickel hits 30 both at same time read low 60s
A quarter and a nail with a inch or 2 between them jumpy read low 70s
I think AM would do the same I try to use tone mostly and know i will dig
even before i see the #s

 

[Charlie P. (NY)]

I'll have to play around and see. I really don't use all metal mode ever (well, I guess pinpointing switches to all metal but that doesn't count). I've been running at disc "6", which is near-nuff all metal except nails. In that setting if I get an odd squeaky audio hit with no VDI it's usually iron/chain.

In the discrimination side I see very consistant VDI values . . . though old & deep coins tend to read a few points further down the scale.

I was running along a river-bank and hit a "70" right at the water's edge. Went down 8" and found a dime - a clad 1982 dime! RATS! I figure ice gouged a hole and it silted back in over it. Clad dimes read 70/71 right at the surface, so that's a pretty consistant VDI. But, as I said, in disc mode and not all-metals.

By coincedence, within a few yards of that dime I found an Indian Head cent on the surface - on a shale outcrop & worn smooth on the obverse and almost smooth on the reverse so I don't know the date.

Riverbanks are odd places to detect.

 

[JG]

Thanks guys,

Trying to get outside the box with the F75 here. I view the VDI as very important information when available. JE can give some wilder values as can AMM when there is masking, shape anomalies and distance. I have seen the AMM give better real, high-end VDI numbers to air test/close proximity readings. AMM reads in truer in it's ranging than JE in situations where the VDI is not a narrow range and repeatable. >>JE is jumpier than AMM at the limits of detection. AMM seems to give a better reading that is closer to true VDI at the same limits. This is a tell.

This can help in evaluating these questionable targets, one step at a time. Maybe like a flow chart for troubleshooting. Looking to find some rules and procedures everyone can use to evaluate a target better. Sometimes a feature of a machine is considered only for what it does, but what does not happen is equally important as a tell, like upward trending VDI numbers that indicate a small, low conductor (gold, lead, etc) saying there is something to investigate that is not looking confident to be iron. You cannot always count on the confidence meter at the edge of detection, so we look again for more tells. If confidence hits in the high and low VDI's then we ask ourselves "which is it"? What is the next step(s) in the flowchart of evaluation?

Maybe we all can establish a checklist for target evaluation using features of the F75 normally viewed as insignificant in the particular application. Sounds weird, but Charlie's PF and FeO evaluation is a big step forward in that direction. The FeO meter can give tells on a target. It might be limited to how much rust there is, but rust can give false high readings and the expanded iron range of the F75 gives us the ability to better evaluate a target, be it good, bad or both. The FeO also gives information that may confirm iron or not. This is extreme detecting on targets that report but are somehow questionable. I think there is more to discover with the F75 and we are getting close to seeing some of it strength's shine brighter.

Thanks and let's see if we can sort this out one aspect at a time for evaluating questionable targets. It might take all the modes, smarts 'n parts of the F75 in and outside the box.


JG

 

[Charlie P. (NY)]

Just a side note on interpretation - The Fe3O4 scale measures Magnetite ("Hot Rocks" - as opposed to just rusted iron, which is Fe2O3). Both are forms of oxidized iron, but whenever you have a large iron object you get a substantial amount of impure Fe3O4 in with the plain old rust. This may be a fine distinction, though if you think about it the longer an iron object is exposed to water and salts the more of both compounds will be present.

If you are in an area that was logged or farmed, as opposed to a CW battlefield prior to being logged or farmed, you may want to pass on the high Fe3O4 readings. Most often they will be chain and broken soil implements.

On the other hand, it could be that old steel toolbox filled with Morgan Dollars.

 

[JG]

good point Charlie on the difference.

I busted up a hot rock that was not a hot rock because the signal I was getting was the rust stain in a very fine circumferal fracture.
I got a VDI in the teens and that is worth looking at in the field. I only wish I had looked at the FeO meter instead of the VDI.

The old saying of the Spaniards is that "Iron Caps Gold". They would hunt with the first metal detector hundreds of years ago, the Spanish Dip Needle. A real instrument. It was developed using the scientific method #1, observation. What was known to them was the interesting action of a Compass as iron nears. The Dip needle was a compass on it's side. Dipping down toward iron in the ground. Next to the compass, the first strictly geological tool based on magnetism.

In gold country you find all kinds of Fe2O3 and Fe3O4 . The question is, Does the meter respond to it? Does the F75 respond to it and in what ways. What is it about Fe3O4 and the meter interaction that is reported and excluded? How can we use the information in evaluating a questionable target?

Unmasking iron with the F75 is getting legendary, but are there more 'tells' to see and listen to?
We can detect both metal and mineral!



JG

 

[JG]

Yes Charlie,.

"Both are forms of oxidized iron, but whenever you have a large iron object you get a substantial amount of impure Fe3O4 in with the plain old rust. This may be a fine distinction, though if you think about it the longer an iron object is exposed to water and salts the more of both compounds will be present. "

One is made in the presence of water and the other air. Two different compounds. If buried, there should be much Fe3O4, the black rust. This can be detected on the meter, and at best in low mineralization earth.

Both types of rust (the basic two, there are 16 or 18 different types) are ferromagnetic. So we have an instrument that registers this on the fly.

For nugget hunting, the amount of iron trash in tailings can be troublesome and if disturbed can give some wrong impressions. Impressions that a nail could give similar to that of a small and or distant irregularly shaped nugget. The same impressions I might add, are targets that register at first in the mid to upper iron range and into the high teens. And those targets being masked or not are sometimes good targets, normally passed by. The rub is, how do we evaluate those targets better with what we have in the F75? Anybody have a clue?

Thanks
JG