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VLF salt & black sand ground balancing question.

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I've heard that a single frequency VLF detector can NOT simultaneously balance out salt water and black sand. IS THIS TRUE?

Would this also apply to wet & dry alkali washes which contain black sand? I believe that a "salt" or "alkali" switch merely changes the ground balance point, which might not solve the problem!

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Personally, I don't know any VLF single frequency or multiple frequency that can balance out both salt and black sand at the same time. PI's don't balance it out either. What happens on a PI is the signal from the black sand is gone before any signal is processed, so black sand isn't heard. This is why a PI can pass over black sand without any signal. At least, that is what happens on my TDI.

As for VLF's, the detector will generate a signal over black sand which is quite different of an adjustment of that from an alkali based soil. So, the VLF can be adjusted to balance out black sand but that never is perfect or it can be adjusted to something else such as an alkali based soil. Move from a black sand base to some alkali base, which isn't a salt base, and the offset in the ground balance will be more than enough to cause a signal. Fortunately, the alkali base can be balanced out also. This may happen either as a manual adjustment or automatically, depending upon the detector.

Salt mode, which is on some detectors is just for that reason, working in a saltwater environment. Saltwater is conductive much like a weak signal and differs greatly from any alkali signal, phase wise.

One more point, on a VLF, it is possible for the detector to be operating in a form of motion discrimination mode that may cause it to appear that neither black sand nor alkali soil will cause a signal, so the detector may appear to be balancing out both at the same time. That really isn't the case. Both may be causing a signal but that signal is such that it is ignored sort of like setting the disc mode on a discriminating detector, thus giving the appearance of a multiple balance system. Unfortunately, the unheard signals can still cause problems and cause good targets to be ignored if they happen to occur at the same time as a signal from black sand or the soil. The reason is signals from black sand or even typical soil is generally much stronger than any similar size non ferrous object. This also amounts to a strong black sand base can easily create a signal stronger than a much weaker non ferrous target signal that is buried.

Years ago, I used to have fun showing how easily, for what appears to be a simple rock, could cause a large nugget to "disappear" even though one actually could see the nugget. In the case of my demonstration, the rock contained heavy concentrations of magnetite that wasn't that obvious. The strong signal from the magnetite would create a very strong negative signal which would overpower any weaker signal from the gold. Actually, this masking effect can be shown even in the all metal mode on most VLF's.


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