Truth about MF and SF

[crane]

There are at least two types of "hot" ground. The worst Oz ground gives a very high X signal and a very high R signal. The ground in the USA can also give a very high X signal but it usually gives a very mild R signal. This is one reason why a VLF and PI detector that works okay in the USA needs to be fitted with a ten turn GB pot here in Oz. A high X signal is usually associated with highly susceptible ground such as magnetite and its cousins. It readily sticks to a magnet but often has a very low R signal. In other words it may give a negligible phase shift on a vlf and a very low amplitude decay on a PI.

We have another type of ground that is highly mineralised and also conductive because of wet salt and this can be a true nightmare.

Another type of ground gives an unpredictable signal and therefore can't be cancelled by using any of the methods discussed on the forum. Apparently this ground is also common in some parts of the USA.

[mickstv]

Another type of ground gives an unpredictable signal and therefore can't be cancelled by using any of the methods discussed on the forum. Apparently this ground is also common in some parts of the USA.

Can you tell us more about this type of ground ?

[crane]

Ground that behaves predictably gives a log decay, the decay would be exponential only for the fact that the ground retains some remnant magnetism as it decays.
It's amazing that most ground is as well blended as it is. The unpredictable ground apparently isn't well blended. The exact reason is probably complicated but, according to Bruce Candy, it is one reason why some ground can't be cancelled by using any of the known methods.
An old PI patent filed by Poole states that any object can be cancelled by simply subtracting a late scaled sample from an early sample and cites a steel block as an example, but this isn't correct because it only applies to the block at one distance and orientation. Change the distance and orientation and we need to readjust the GB to obtain a null. This doesn't apply to predictable non-conducting mineralised ground.

[mickstv]

Thanks for the reply. Do you know of any places in Vic that has this type of ground and could you share the location's ?

[Qiaozhi]

With KRinAZ's MPP modifications, he's not trying to cancel the ground response completely. The ground signal is still there, but is nullified somewhat. As Crane correctly states, you cannot completely reject ground where the composition is non-homogeneous, so maybe these mods can provide an alternative solution. It might be worth trying.

[M.D. prototypes]

There are at least two types of "hot" ground. The worst Oz ground gives a very high X signal and a very high R signal. The ground in the USA can also give a very high X signal but it usually gives a very mild R signal. This is one reason why a VLF and PI detector that works okay in the USA needs to be fitted with a ten turn GB pot here in Oz. A high X signal is usually associated with highly susceptible ground such as magnetite and its cousins. It readily sticks to a magnet but often has a very low R signal. In other words it may give a negligible phase shift on a vlf and a very low amplitude decay on a PI.

We have another type of ground that is highly mineralised and also conductive because of wet salt and this can be a true nightmare.

Another type of ground gives an unpredictable signal and therefore can't be cancelled by using any of the methods discussed on the forum. Apparently this ground is also common in some parts of the USA.

Hello Crane,

As you can see in the video on the thread: http://www.geotech1.com/forums/showt...eriments/page2. # 37 , we have experimented with different grounds.
Where can these different grounds in been subdivided, in terms of x / r value? And in which countries can you find them in your opinion?

Thanks for your answer.

[crane]

Thanks for the reply. Do you know of any places in Vic that has this type of ground and could you share the location's ?

Sorry, I'm from NSW and haven't been to Vic for about eight years.
It is easy to pick because the GB won't null when the coil is bobbed up and down, it requires a different GB setting if the distance between the coil and ground varies.
It shouldn't be confused with pre-amp saturation where the GB works well but results in an instant loud noise when the coil is close to the ground. Magnetic saturation is much the same but no instant loud noise, the GB works well at height but begins to fail when the coil is very close to the ground.
Sampling too early can also cause the GB to fail.

With some ground the response varies as the coil is swept horizontally over the surface and would normally require at least two different GB settings to null, but it (and hot rocks) can be cancelled simultaneously with one GB setting if you have a GPX4000-5000.

Most of these problems only become apparent at very high gains.

[crane]

Hello Crane,

As you can see in the video on the thread: http://www.geotech1.com/forums/showt...eriments/page2. # 37 , we have experimented with different grounds.
Where can these different grounds in been subdivided, in terms of x / r value? And in which countries can you find them in your opinion?

Thanks for your answer.

I don't have any data for X and R in other countries (Eric Foster published figures for Oz and the USA) but the fact that most vlfs can operate in some countries with a single turn GB pot, and at least one seems to work with a tuned resonant receive coil, suggests a small to relatively high X signal but a very low R signal.

I don't think anyone has built a detector that handles our soil without spending some time here.

[tragac]

Is it possible targets which would be detected with MF detector sometimes can not be detected with SF detector ...also there is statements from owners on SF detector that they can detect all targets which are detected with MF devices......Also WM6 posted same article for Minelab and old Goldmaster II


Also like to share text bellow:

Why are newer metal detectors the key to older coins?

07/04/2009



*

This is a follow up to the question, “Are newer machines the key to older coins?" Online forum posters brought up operating frequencies and gold, so this addresses these two topics.

Looking at some online resources:* "Lower frequencies penetrate more deeply but higher frequencies are more sensitive to smaller targets." "Different metals respond better to different frequencies which is why all gold detectors run at 15 khz and up." "The lower the freq. such as 3 Khz will be sensitive in detecting copper and silver targets. Higher freq. such as 15 to 60 Khz will*

be sensitive to gold targets. That's why most gold detectors sold have a freq. starting at 15 Khz and higher. The detectors sold with general hunting in mind have operating freq. starting from between 5 to 10 Khz."**

Minelab’s E-Trac*and*Explorer*use FBS which simultaneously transmits, receives and processes 28 frequencies from 1.5 kHz to 100 kHz.*
White’s V3*uses three frequencies 2.5 kHz, 7.5 kHz & 22.5 kHz and operates in the frequency domain only.*
White's MXT*is 14 kHz
White's XLT*is 6.5
White's DFX*is dual frequency 3 kHz and 15 kHz*
Tesoro*models use various single frequencies:
10kHz, 12kHz, 14.3 kHz, and 17.5 kHz.**
Tejon*ranges 17.2-17.6 kHz.
Garrett Ace 250*uses a 6.5 kHz operating frequency.
Fisher CZ3D*and*Fisher CZ20*are both dual frequency, 5 kHz and 15 kHz
Fisher F5*- 7.8 kHz.
Fisher Gold Bug*- 71 kHz

So, if you're looking for gold only you want a machine that handles the higher frequencies.* Hence, the Fisher Gold Bug at 71 kHz, and PI (pulse induction) units, but let's not get into PI units as most of us do not want to do old coin hunting in trashy sites on land with a PI.**

The multiple and dual frequency machines should always be able to turn up more targets than a single frequency machine.* Theoretically, if you have "cleaned out" a site with your 6.5 kHz White's XLT, and then come along with a 17.5 kHz Tesoro Lobo, you will find targets you missed and that were undetectable with the 6.5 kHz White's machine.

The result of this is that a newer multiple frequency machine will be able to find more targets than the single frequency machines (not necessarily older coins).* So the newer multiple frequency machines, including the old Fisher CZ and Minelab FBS machines will do better than a single frequency unit.**

This is where I start thinking about accuracy of target ID - beeping over metal is not enough, I need to know if it's worth digging or not.* How does the number of frequencies affect the target ID?* Is a dual frequency (or more) machine going to ID targets more accurately than a single frequency unit?* It seems like this would be the case.* Certainly in my experience I have found that my Minelab FBS machines are the most accurate ID machines I have ever used, and they are accurate at good depth as well, though any machine will start to drop off on target ID at the edge of it's detection range.* I have seen some reports that users of the White's V3 are also reporting more accurate target ID.

[Funfinder]

What you suggest for peat/clay soil with grass


It it true that MF
multifrequency BBS/FBS machines get better ID at depth, better discrimination, can handle ground minerals better, and so on...because of multifrequency.

From my experience for such conditions ONLY non-motion VLF induction-balance goes reliable really deep -
also concerning discrimination - if someone looks for non-magnetic metal only etc.

The more and massive ground-distortions, and such heavy-mineralized soil works almost like a shield or metal-reflector,
the more the user itself must handle the signals the detector spits outs. Which is far more easy with non-motion VLF
and by working with a fixed GEB-level incl. reset-button if the signal is wrong or the coil comes to close to ground.

For PI there should be some reduction of the EM-pulse-energy and at the same time increase of detection-sensitivity
otherwise the detector even may get completly overloaded, comparable with holding the coil 20cm over some
copper-roof-layer.

And there should be somewhere tables how much % 1,5,10 kHz penetrates the ground better at iron, bronze, silver etc.
compared with higher frequencies (at which mineralization-strenght).

[Carl-NC]

Is it possible targets which would be detected with MF detector sometimes can not be detected with SF detector ...also there is statements from owners on SF detector that they can detect all targets which are detected with MF devices......Also WM6 posted same article for Minelab and old Goldmaster II

Different detectors have different capabilities, and while MF is generally better than SF, it is not necessarily the best. Two examples are: Minelab BBS/FBS which, despite advertising claims of using 17/28 frequencies up to 100kHz, in reality have a weaker high frequency of 25kHz and are well-known to have poor response on small gold, so many SF detectors will outperform it on those targets; and White's V3 which has good detection across all targets but not stellar depth, which can be demonstrated by switching it to SF mode and picking up 1 to 1.5 inches in depth.

If you're expecting a MF detector to outperform everything else on the market, you're gonna be disappointed. They only do that in salt water.

[Nupi]

............ They only do that in salt water.

This depends on what kind of criteria you use.
If you accept that all the "little gold, and more" with certainty will miss then you can say that the MF is better in saltwater than else on the market.
Many people I have spoken prefer the White's V3i above the minelabs in such situations.

[tragac]

Thank you on answers

[tragac]

What is you opinion about clay soil to use VLF or PI
I also posted tread with similar name ...because on this way probably more users will read mentioned tread and give more answers...

[Qiaozhi]

What is you opinion about clay soil to use VLF or PI
I also posted tread with similar name ...because on this way probably more users will read mentioned tread and give more answers...

Please don't make duplicate posts in different threads, as this dilutes the conversation and makes it difficult to follow the discussion.