Cache Test

[Ferric Toes]

Apology accepted. I had a bad day trying to sort my quarterly tax return, so got fired up quicker than usual.

A ferrite pot is an extreme example but, in Australia some ground is nearly as bad. Often there are stories of nuggets being detected, that in the ground give weak signals and poor range, but once dug up can be detected at double or three times the distance. This is attributed to the pulsed field from the coil being diverted in a more horizontal path, before looping back to the coil. This ground also has a strong viscosity component, which has to be nulled out.

I'm sure Carl's cache situation is nothing like this, although I do think that if the transmitter and receiver parameters (PI) are correctly adjusted for high conductivity objects, then it should easily be detected.

Eric.

[Carl-NC]

(Carl is using the same set of worn out batteries in all
the detectors)

Ah, so that's the problem! And I thought all my detectors were just "silent search" types!

[Unregistered]

JC1

Hi Eric,

Wow! thanks for the support, but probably don't

deserve it. Been a bit of a Pratt, no doubt.

Hey, some of it is bait.

Carl is too smart to fall for it.

Some of it is for interest.

Most is for fun.

But alas, the tests are probably correct.

And good information before someone

wastes alot of time cache hunting with

something that will never find it.

Still at depth a "cache" at two feet could

sound like a coin at 4 inches.

So how do you tell the difference?

without digging.

You use your 700 watt coil to inductively

heat up the cache until steam starts to rise

from the ground (helps with pinpointing)

In fact you don't even need the "receiver electronics".

But you will need gloves.

[Unregistered]

Apology accepted. I had a bad day trying to sort my quarterly tax return, so got fired up quicker than usual.

A ferrite pot is an extreme example but, in Australia some ground is nearly as bad. Often there are stories of nuggets being detected, that in the ground give weak signals and poor range, but once dug up can be detected at double or three times the distance. This is attributed to the pulsed field from the coil being diverted in a more horizontal path, before looping back to the coil. This ground also has a strong viscosity component, which has to be nulled out.

I'm sure Carl's cache situation is nothing like this, although I do think that if the transmitter and receiver parameters (PI) are correctly adjusted for high conductivity objects, then it should easily be detected.

Eric.

I have done some experiments with ferrite ring. It introduces more negative phase shift than iron nail. I would say about -60 to -90 degrees.
As far as I remember the worse ground (in theory) will introduce phase shift no greater than -10 degrees.
That`s why I think a ferrite pot is exessive exampel.
Perhaps those conditions in Australia are not exactly to be considered as the soil in the traditional sence, but just as minerals with high metal content which in average conditions are not often found.

[Ferric Toes]

I have done some experiments with ferrite ring. It introduces more negative phase shift than iron nail. I would say about -60 to -90 degrees.
As far as I remember the worse ground (in theory) will introduce phase shift no greater than -10 degrees.
That`s why I think a ferrite pot is exessive exampel.
Perhaps those conditions in Australia are not exactly to be considered as the soil in the traditional sence, but just as minerals with high metal content which in average conditions are not often found.

I am open to correction by someone more versed in induction balance detectors, but with a ferrite material that is non conducting, I would expect the phase shift to be approaching 90 degrees, as you say. Any conductivity, as in soil, would add a 180 degree component, so you would end up with the vector sum of these two.

PI's do not measure phase, although there is a relationship between the decaying target signal and the phase response of a sine wave system. Scan a PI over a ferrite core or rod (provided it is a magnetically soft ferrite) and it will give no signal. Scan a balanced coil sine wave detector of the same ferrite, and it will give a large signal, that is, until the phase detectors are adjusted to the null point.

In practice, soils and rocks that contain magnetic minerals are both permiable and have magnetic lag. Now, magnetic lag shows up on a sine machine as a frequency dependant phase shift, so you would have to dial in some additional phase compensation to null this. The amount would depend on the operating frequency of the detector. Add in soil conductivity, wet, dry, or salt and you have quite a complex sum of different and varying phases to sort out.

PI's do not respond to purely permiable targets, or to ground conductivity, unless it is sea water. What you are left with is the magnetic lag, which decays away, similar, but not identical to a metal target. Most soils and rocks have a permiability/viscosity ratio which is constant between certain limits. This higher the viscosity signal, the higher the permiability, or susceptibility as we call it. A straight PI cannot be used in most inland areas of Australia, because of the viscosity signal, and even the Minelab SD's and GP PI detectors, with their auto tracking ground balance circuitry are unuseable in some extreme areas. This circuitry balances out the viscous signal but the permiability of the ground is still there, and doing everything it can to prevent the TX signal reaching the deep nugget, and the return signal getting back to the coil. Hence the extension of thought to a ferrite pot.

As far as has been reported to me, even the strongest mineralised ground in the US, does not approach that in much of Australia, and it is purely ferric oxides that are responsible, with little or no metallic iron content.

Eric

[Unregistered]

Ah, so that's the problem! And I thought all my detectors were just "silent search" types!

Hi Carl.
Have you found some detector capable to pass the cashe test so far?
Georgi

[Carl-NC]

No, but I haven't been messing with this lately. Woodworking has taken over the last few weeks.

[Tinkerer]

Halo effect

Interesting thread, many years ago I faced a similar problem with gold chains. I was really amazed that a 5 pound gold chain gave less of a signal than my gold tooth filling.

About the “Halo” theory:
I have two explanations, just theory, but based on somewhat parallel observations.
Many years ago, when I was doing a lot of magnetometer search for shipwrecks in Florida and the Bahamas, I kept finding these magnetic anomalies that looked just like a cannon or anchor, big. We dug many holes, but there was no metal at all. Once we dug a hole 30 feet deep and 100 feet wide, the only thing we found was some discoloration of the lime stone bottom. So I explained it as possibly a meteor that buried itself in the coral sand before that turned into limestone. Still, I kept wondering, so I started to make systematic observations and here we come to the parallel of the “halo” effect.

This region was above water some 10-20 thousand years ago. In those times ”sink holes” formed. Such holes form by leaching of the limestone by an acidic solution. This kind of solution can easily be created organically by mixing vegetation, biomass, with water and letting it rot. It turns quite sour and dissolves limestone easily. Fill a hole in the limestone with that rotting biomass, replenish it continuously with new leaves etc. and it will eat an ever deeper hole in the hard substrate.
So what does that have to do with a magnetic anomaly?
Rotting biomass, acidic in its nature, thousands of years old, we called it peat moss, was the stuff we found in the holes in the lime bedrock. The surrounding limestone is alkaline in its nature. Add saltwater for a conductor and you have a voltaic cell. Since you have current flowing, you have a magnetic field.
Looks just like a cannon on the magnetometer.
Enigma solved.

This is getting too long, If you are not bored to death yet, I will tell you in a future post how silver or copper can make a “halo”, that could possibly be detected.

Tinkerer

[michael]

Hi Tinkere, very interesting for me, good. please continue your comments and write more especially about "how silver or copper can make a “halo”, that could possibly be detected." of course I know little about it, but it seems your comments are complete.

[Carl-NC]

Agreed, very interesting. Yes, please continue with halos... I've long considered detectable halos to be mostly a myth, except for iron.

- Carl

[digger barns]

Halo Sailor

A man goes into a metal detector shop and buys a metal detector. He read in a brochure and a field test report that it will find coins up to 12 inches. A couple of days later he goes back to the shop and says. Here if I bury a coin in my garden this detector only detects it down at 4 inches is there something wrong with the detector. There's nothing wrong says the salesman. Coins have to be in the ground for at least a 100 years so they creat a Halo, then you can detect them at 12 inches. The halo affect in metal detector bollocks like a lot of other stuff.

[Esteban]

The halo is the electric field around metal buried for long time. Nothing rare in this world... This field is detectable by non intrusive magnetic field like agressive metal detector oscillator very near, so a simple microvoltmeter with antenna can show the difference in the terrain at some distance. The magnetic field of the coil "eat" this low energy.

[hung]

Diggerbarns: Absolutely correct.

Esteban: Just comçementing to the general reader, that's why if you run a regular MD in a certain spot prior to the use of the Mineoros, you will ruin the ionic fields around it.

[Esteban]

From Charles D. Rake's book (pages 56-57):

[Tinkerer]

Halo Effect

Halo effect

In the ocean, a silver or copper object can create a halo of hundreds of feet over a certain amount of time. How does this work?
Sea water is a very aggressive environment. It oxidizes most metals and leaches ions out of coins. Not only the surface, it actually manages to penetrate deep into metal surfaces. To remove the salt from within silver coins that have been submersed a few hundred years, demands a lengthy electrolytic process. If not done that way, the coin will tarnish again within a very short time.
Anyway, the water at the bottom of the ocean is in constant movement.
Most marine life takes advantage of this movement. One organism in particular, commonly called a sea fan, always grows perpendicular to the prevailing currents and nourishes itself by filtering the sea water.
Over a lifespan of filtering the water it accumulates many minerals but also metallic ions that are floating in the current.
With the use of spectrometry ( saw a used HP one for sale at $5000 on the net) one can detect higher than average concentrations of metals in the samples taken in alignment with the prevailing currents.
OK now the secret is out. This method has been known used with success by very few shipwreck treasure hunters.

Next post, about how a silver or copper coin creates a halo on land.

Tinkerer