Ground Balance Number Meaning

[Relic]

The ground balance number on my X-Terra 70 is typically in the low 20s when auto-balancing. Is that considered low, moderate or high mineralization?

Thanks,
Relic

 

[TURNMASTER]

high-ish

 

[7centsworth]

The lower the number the more it is mineralized . Mine usually runs in the upper 40's to low 50's in KY.

 

[Goes4ever]

mine is normally in 30's in NW Ohio

 

[Beale]

I have seen mine as lowas 25 and as high as mid 60's.

 

[Relic]

Thanks for the feedback, guys.

Going farther, is there a relationship between mineralization and frequency, i.e. do higher frequencies or lower function better in high mineralization soils?

Relic

 

[David]

Thanks for the feedback, guys.

Going farther, is there a relationship between mineralization and frequency, i.e. do higher frequencies or lower function better in high mineralization soils? Relic

That is a very good question. I would think lower frequencies(LF's) handle iron better, so they should handle iron mineralization in the soils better than HF's.

Someone explained this=> The higher an operating frequency of a detector, the more sensitive it will be to small gold, but with the disadvantage of also being more sensitive to iron minerals. This can result in more false signals and difficult operation in high iron mineralized areas. Lower frequency detectors are generally less sensitive to small (gold)nuggets, but handle iron ground better.

BUT Minelab says the opposite, and seems to contradict this:

http://www.minelab.com/usa/consumer/knowledge-base/technical-notes
http://www.findmall.com/read.php?55,1068029,1068029#msg-1068029
9 Concentric
18.75 kHz Coil (HF)
X-TERRA 50, 70, 305, 505 and 705 detectors
Water proof
Has same properties as the 7.5kHz version, but more sensitive to low conductive targets. Also performs well when detecting for jewellery on ocean beaches.

9 Concentric
3 kHz Coil (LF)
X-TERRA 70, 505 and 705 detectors
Water proof
Ideal for highly conductive targets such as silver, copper, large rings and relics. Performs well in all soils with the exception of highly mineralised soil.


In this statement above Minelab made about the LF coil, maybe Minelab is referring to Concentric coils in general not performing well in highly mineralized soils(as compared to the DD's), but nothing is said about the HF. So it is a little confusing?

Like I said above, IMO I think the LF will handle high mineralization better than HF.

The LF 5 kHz Musky handles mineralization very well. Comparably how does the HF (~17 kHz) Tejon and other HF machines handle high mineralization. Like in the red clay in the southeastern US, etc. Besides Prospectors, Relic Hunters here should also have an opinion on this?

Maybe someone can add something to this.

 

[Digger]

As far as a direct relationship between mineralization and frequency, if you properly ground balance your X-TERRA, there should be no difference in how the frequencies function. The whole point of ground balancing is to neutralize the effects of the soil. However, different frequencies do respond differently to mineralization in the same soil. For example, when I properly set the GB at the same exact location, using both the 9-inch concentric at 3 kHz and the 9-inch concentric at 7.5 kHz, the adjustment required to neutralize the effects of the ground were a difference of 9. In other words, the 3 kHz required a ground phase adjustment of 29 and in the same exact spot, the 7.5 kHz required a ground phase adjustment of 38.

 

[Digger]

The transmit coil of a detector sends down an electromagnetic field into the ground, which induces eddy currents into a metal target. The target responds by generating another electromagnetic field that is picked up by the receive coil. The operating frequency of a metal detector is representative of how many times the electromagnetic field makes a complete cycel, per second. e.g. 18.75 kHz means it makes 18,750 complete cycles per second. The 3 kHz makes 3,000 complete cycles per second. Think of it as being similar to the difference in a 12 ga shotgun using number 8 shot compared to 00 buckshot. The pattern is a lot tighter with the smaller (and more numerous) #8 shot. As you might envision, the eddy currents of the higher frequency are much closer together than in the lower frequency. In this example, the 18.75 kHz coil has more than 6 times as many eddy currents being sent down into the ground, at any one time, as the 3 kHz. So they are more than 6 times closer together. Since targets are detected by the signal they produce, and that is determined by the electromagnetic field they emit, it stands to reason that a "tighter" network of electrical currents, the greater chance of them being induced into a smaller target. That is the reason that higher frequency coils are more sensitive to smaller targets. And, just as with the shotgun, the lower frequency will penetrate deeper.

[attachment 156313 freq.jpg] [attachment 156314 freq2.jpg]


As to the Advantage being an excellent detector in mineralize ground.....The only coils available for the 5 kHz Advantage are DD coils. Their ability to do well in highly mineralized soil is primarily due to the DD design and not necessarily the frequency.

 

[7centsworth]

That is some good stuff Digger. Thanks for sharing that.

 

[TURNMASTER]

Digger is one of them thar educated types.

 

[Relic]

n/t

 

[David]

I read it twice to let it sink in. An analogy parable, just like how Jesus got things across, is a great way to visualize the meaning. Great explaination Randy(Digger)!

There is more chance of hitting a small size red squirrel(smaller target) with a dense pattern of #7.5, 8, or 9 shot(HF) than there is with more spread out 00 buckshot(LF), and also the 00 buckshot(LF) will penetrate deeper into the ground or a tree if you miss.

Also someone said to me, "I have used alot of machines and I could not tell the difference in freqs, the difference I have noticed is that the DD coil works way better in hot ground............"

The DD coil sees about 75% less ground mineralization than a Concentric or Mono coil. Having a DD is far more important than a having a lower frequency for handling hot ground.

And as Randy(Digger) said, "As far as a direct relationship between mineralization and frequency, if you properly ground balance your X-TERRA, there should be no difference in how the frequencies function." Yes, after GBing he is right, being on normal mineralized soils for coin shooting there is no difference in how different frequencies perform. But still I think the Lower Frequencies(LF) handle very hot goldfields, very high iron mineralization soils and hot rocks a bit better when gold prospecting. This is not encountered in over 90% of coin shooting and so it is not usually a factor.