Fisher F19 Ground Balance Question

[Geotech]

Rick is correct, and there is an explanation. If you are in mineralized ground then it is important to have a correct GB to minimize ground noise. If the ground is not mineralized, then you won't hear ground noise no matter the GB setting. In this case, if you set the GB negative there are some designs that will produce a slight increase in target sensitivity. These are designs that create a "G channel" by adding a slight amount of X channel to the R channel; G = R + kX and we select k so that G = 0 for perfect GB. G then becomes our target indicator, since anything other than G=0 means we have a target.

But if there is no mineralization, then by increasing the factor k we are adding some X target signal to the R target signal. This gives a stronger overall target signal, and it benefits high conductors more than low conductors. If there is a slight amount of ground mineralization, then this setting will make it respond negatively as you lower the coil to the ground. However, even with some nulling effect from slight mineralization you might find that this tweak still gives more depth.

Some people run the GB slightly positive on the theory that it avoids the nulling effect you get with a slightly negative GB. However, either a slightly positive or a slightly negative GB produces the same nulling effect, the former as the coil nears the ground and the latter as the coil recedes. Since ground is not always even, and coil sweeps aren't either, I've always considered a tight GB setting to be preferable, unless the ground is weak enough that the whole explanation above prevails.

Sorry, this is one of those things that really needs pictures.

 

[EL NINO77]

Carl...thanks for explaining the matter...can you expand on this topic?,,, I think it will clarify a lot of things...

Another thing is that the Tek G2 / Fisher F19 platform itself hides a strong "all in one" potential.

[Rick N. MI]

I like all metal on the F19 and the T2/F75.

[Mike_Hillis]

Hi Rick,

I don't remember if the F19 ground balance circuits will allow the operator to see the gb hole (deadspot) moving around.  Most do though, unless the design engineer specifically focused on eliminating it.  The Fisher GoldStrike comes to mind as one where the design has no target sensitivity loss due to gb settings as he specifically focused on removing this.

Your gb setting is discriminating the ground's phase number(s) but it also has a deadening affect on the nearby numbers too.  You can actually mask target responses based upon your gb settings when the gb setting are at or near their extreme ranges. 

You can test this yourselves with a silver dollar and a very small gold ring.  Max out the gb setting on either end of its range while air testing the two target's depth and responses and this will clearly manifest itself in most detectors.

I look at it as a useful feature that can be deployed when hunting for target most affected by it.

HH

Mike