Ground material susceptibility

Quote from you article Beneath the Mask
"When you discriminate iron with any detector (Minelab calls it "iron mask") you have achieved nearly nothing. (Simply, there will be no audio response reported in the headphones). The detectors electromagnetic signal is still disrupted by the iron. It does not matter if you transmit one frequency, two frequencies or 17 frequencies into the ground - electromagnetic energy is electromagnetic energy, and iron will always disrupt this energy. This is not a fault of any detector, only an indication of where technology is at today. There is not a detector on the market today that can "see through" iron. And I think I could safely say that less than 20 percent of the coins in the schoolyards and parks have been recovered because of masking, silent masking and deep depths."

Can I safely say that any kind of material that will attract to a magnet will disrupt the signal from a metal detector?

I've posted this problem a year or so ago.
I have several old school yards where they dumped the coal cinder waste on top of the ground. This material attracts very easily to a magnet. There has been some very good machines used in these area. Minelab E-Trac, whites V3, Fisher F75, Tesoro lobo supertrac, Tejon and Vaquero. Very few keeper targets have been found in these area.
In your honest opinion is the material waste preventing these detectors from finding hidden targets just under the top of the ground.
Do you have any work arounds for this type of problem?

Masked & Silent Masked.....they will be!

.....ANY metal object, ferrous or non-ferrous......will disrupt/block EM energy. This is also to say that coal/ash (coke) can also attenuate electromagnetic energy. Currently.... no electromagnetic-principle apparatus is (or will be) the magic wand. PI's are interesting (possible future hope; due to EM decay-rate).....but still; no-joy.

Since most of this waste material is BB size, what do you think about taking a small area, say 10' x 10', scraping it clean of the surface material and hunt.
My thinking is if I can clean this material I might be able to pull some goodies up. This old ball field was used almost ever day for more that 40 years prior to 1965, there should be something there.

This will help "some"; however, it is more the norm that these flecks/flakes are interdispersed at all various depths.......not just on the surface. It is not uncommon to detect a 5' x 5' area of property (usually at old Forts) and find one non-ferrous 'keeper' item/target with a metal detector. Then..........start to dig a pit in this same 5' x 5' area.......maybe by digging the first 2" - 3" of sod/grass/root-structure off of the top/surface. Then........... swing the coil (now at a 2" - 3" depth advantage) in the 5' x 5' pit.......and STILL not detect any more non-ferrous targets.
After a full excavation of the pit.....and running a Rare Earth magnet through the dirt...removing all ferrous 'maskers'........only to find 17 or 18 more 'keeper' non-ferrous targets.
Yes, scraping off the first few inches of topsoil in ANY area .... can be advantagous........especially if the dirt is NOT riddled with iron. At old homesites.....iron/rust/nails/flakes are most certainly "unsuspectingly" more crippling than most would ever suspect.

Tom

After watching the following video I'm wondering if the AT Gold and it's ground balance window will help in these areas. Watch the entire video especially toward the end.

[www.garrett.com]



markg Wrote:
-------------------------------------------------------
> Quote from you article Beneath the Mask
> "When you discriminate iron with any detector
> (Minelab calls it "iron mask") you have achieved
> nearly nothing. (Simply, there will be no audio
> response reported in the headphones). The
> detectors electromagnetic signal is still
> disrupted by the iron. It does not matter if you
> transmit one frequency, two frequencies or 17
> frequencies into the ground - electromagnetic
> energy is electromagnetic energy, and iron will
> always disrupt this energy. This is not a fault of
> any detector, only an indication of where
> technology is at today. There is not a detector on
> the market today that can "see through" iron. And
> I think I could safely say that less than 20
> percent of the coins in the schoolyards and parks
> have been recovered because of masking, silent
> masking and deep depths."
>
> Can I safely say that any kind of material that
> will attract to a magnet will disrupt the signal
> from a metal detector?
>
> I've posted this problem a year or so ago.
> I have several old school yards where they dumped
> the coal cinder waste on top of the ground. This
> material attracts very easily to a magnet. There
> has been some very good machines used in these
> area. Minelab E-Trac, whites V3, Fisher F75,
> Tesoro lobo supertrac, Tejon and Vaquero. Very
> few keeper targets have been found in these area.
>
> In your honest opinion is the material waste
> preventing these detectors from finding hidden
> targets just under the top of the ground.
> Do you have any work arounds for this type of
> problem?

Most certainly! When electromagnetic (EM) energy is utilized to 'attempt' to detect metal items in the ground...... whereby magnetic/electromagnetic dirt is the medium............... it will attenuate the EM energy from the coil......... limiting/preventing the ability for detection.

Due to the 'decay rate' of this ferromagnetic material............ a PI will perform much better; yet, remembering PI's (as of current-day technology) do not have ID capabilities.

Tom, do you have an technical explanation for the 'ground balance window? And can it be replicated on other detectors via settings/adjustments?

If I am understanding you right........... IRT the 'ground balance window'. ""Where"" the window is... on the Grnd Bal knob (or numerical range on a digital unit)...... is dictated by the TYPE of dirt being detected. In other words............ Are you on the high-end of the knob rotation..... or low-end of the knob rotation.......... when you achieve Grnd balance.

Now............ how "TIGHT" the window is (((how much can you rotate that Grnd Bal knob.....and still be 'reasonably' Grnd balanced))).......... is dictated by the VOLUME of mineralization in the dirt that is being detected. The higher the volume of mineralization...... the worse the mineralization level (volume) is.............. subsequently............. the 'window of acceptability' is a much tighter window on your metal detector. You will know this by..... a slight adjustment on the Grnd Balance knob..... will easily place you in a condition of NO LONGER ground balanced. A very 'narrow' (or tight) window......... indicates BAD ground.

I know I've said this before; yet, is worth repeating:

Using a electromagnetic detection medium/principle (((our current-day metal detectors)))............... to detect electro and magnetic items................ in a electromagnetic core Earth (and dirt)...... seems intuitively counter-productive.

But, did you notice that there was no change in response when he passed the coil over both the original dirt and the pan of highly mineralized dirt.
I don't think you could replicate this with a typical ground balance adjustment.

NASA-Tom Wrote:
-------------------------------------------------------
> If I am understanding you right........... IRT the
> 'ground balance window'. ""Where"" the window
> is... on the Grnd Bal knob (or numerical range on
> a digital unit)...... is dictated by the TYPE of
> dirt being detected. In other words............
> Are you on the high-end of the knob rotation.....
> or low-end of the knob rotation.......... when you
> achieve Grnd balance.
>
> Now............ how "TIGHT" the window is (((how
> much can you rotate that Grnd Bal knob.....and
> still be 'reasonably' Grnd balanced)))..........
> is dictated by the VOLUME of mineralization in the
> dirt that is being detected. The higher the volume
> of mineralization...... the worse the
> mineralization level (volume) is..............
> subsequently............. the 'window of
> acceptability' is a much tighter window on your
> metal detector. You will know this by..... a
> slight adjustment on the Grnd Balance knob.....
> will easily place you in a condition of NO LONGER
> ground balanced. A very 'narrow' (or tight)
> window......... indicates BAD ground.
>
> I know I've said this before; yet, is worth
> repeating:
>
> Using a electromagnetic detection medium/principle
> (((our current-day metal
> detectors)))............... to detect electro and
> magnetic items................ in a
> electromagnetic core Earth (and dirt)...... seems
> intuitively counter-productive.

Hmmmmm. I just watched the video for the very first time. What a well orchistrated, educational video.

What interests me the most is............ I fully understand Ground Balance..... (in this case.... it was '85')..... and the purpose of Ground Balance. BUT..... I have never heard of a Ground Balance 'window'. This is a new feature for a metal detector (to the best of my knowledge). I do understand it's principle...... and commend the intent and invention. The window allows/compensates for larger (or smaller) delta's (differentials) in mineralization 'change'. I do not own a AT-Gold..... and cannot comment on it's effectiveness...... nor can I comment on its performance attributes..... especially if it is set incorrectly. For single frequency VLF IB units............ it seems like a near-mandatory function. For true multi-freq units...... this feature becomes less necessary. For a PI unit....... it would have no value (understanding PI units have enough limitations to begin with).

Very interesting.

*** But, did you notice that there was no change in response when he passed the coil over both the original dirt and the pan of highly mineralized dirt.
I don't think you could replicate this with a typical ground balance adjustment. ***

First he ground balanced for the slightly mineralized soil. This means, usually, that the reactive X signal was measured and subtracted from the soil resistive R signal. The darker soil has a larger X signal reaction. I think that by increasing the window 2 points he is subtracting an additional 2% (or some amount) more of X out of the R to silence the reactive soil. A PI detector simply would have delayed sampling until the X signal died away - then its just pure R (except for soil R - such as wet salt and any iron hysteresis with slow magnetic relaxation. Minelab measures these late when it is the only signal left and then subtracts this ground signal out too).

It might be said that though the A/T Gold's threshold isn't reacting to the neg phase of the soil it is still reacting to the negative phase of the soil. It just isn't heard.

Having removing more of the soil phase from the target probably does decrease sensitivity, sorta like being somewhat poorly ground balanced. But it still can find a 2-3 gram sized gold nugget at ~3-4" in the video through the ironstone chips - which is good. But to be sure how good it would be interesting if he had tried to detect the gold with the preset gb of the 250 - and it hit on it.

Since the highly mineralized dirt in the pan will easily attract to a magnet, I am wondering how it might compare to the coal cinder waste I am accustomed to in Virginia. This cinder waste is from the size of a bb down and will easily attract to a magnet. In these areas, it is very difficult to detect anything over a couple inches deep. Short of a PI machine, the AT Gold might just be an improvement over the typical VLF machines in these areas. This new “ground balance window” feature is both interesting and very thought provoking. It would be nice if Tom could get his hands on one to test.
Hint, Hint…….

Very intuitive Johnny. Yes....... with two different 'types' of dirt mineralization ....... and with a very distinct localized delineation/differentiation between the two types of mineralization................. sweeping the coil over the abrupt differential.......... you can see how a regular ACE-250 (and nearly all other detectors) will respond.......... when this Ground Balance "window" is NOT brought into play.

I would like to know the phase-shift angle differential between the two differing dirt samples. It may not be as far apart as we would suspect; hence, the enlarging of the window span (phase bandwidth) not being that large. BUT...... I have no 'base-reference' to gauge upon.......... in reference to: span-width window of '0'....... or span-width window of '1'........... span-width window of '2' (which is where many/most of the testing gave a quiescent end-resultant).......... and the span-width window of '3'....... which is where the last testing presented the most (quiescent) stability. Yes......... 'how' desensitized did the detector become to targets with the setting of '2'..... and '3'. We can certainly see how much of a pleasure (less audibly fatiguing)..... the unit becomes with this adjustment employed. BUT...... (and I'm not a prospector)...... does the real-world truly present such dramatic/abrupt differentials in dirt mineralization......... so as to quantify/qualify/justify such a conceptual architect. I know the intent of the video was most probably.... to show just how 'effective' such adjustment can be...... by the utilization (and demonstration) of a exceptionally severe condition........ for video demonstration purposes only. The real world may not pose... quite this severe of a abrupt delta. Extremely bad dirt; yes. Extremely bad dirt 'delta'........ maybe not too often. Jim Hem/Humble Pie........ I'd truly honor your input on this one!

Yes, the magnetic susceptibility (via permeability) and subsequent hysteresis of ferromagnetic and paramagnetic materials........ vs...... diamagnetic materials when exposed to a external source (in this case.... a metal detectors EM coil energy) ............ does have a completely different decay rate ((when the source is removed))...... that a good PI can delineate/differentiate between..... via the rapidity (timing) of the decay. Hence/subsequently; a VLF IB unit would need to employ a different type of architect to overcome. BOTH have advantages. BOTH have drawbacks. (((As to be expected))).

From a prospecting point of view, you could eliminate hot rocks. If you had this feature on a high frequency unit like the GB2, it may be possible to hunt the wet saltwater sand for the small gold most detectors are blind to.

No......... small gold and saltwater are nearly identical in phase-shift angle and conductivity.