Ground balance

[markg]

Ok, here goes.
I'm using the Tejon.
Done some test in my planted garden of US coins ranging from fifty cent piece to pennies. Several coins were buried flat and at 3" deep. On edge coins were also buried about 2" deep. These coins have been in the ground about a year now.
Tried checking each coin with the GB perfect. Noticed if I raised the coil off the ground 4" I would loose the signal on the quarters, dimes and pennies.
Adjusted the GB to full positive and this made the targets loose response with the coil at 4" off the ground.
Then set the GB to full negative and to my surprise all coins hit well with the coil 5" off the ground.
My question is this:
Why would being negative help with target response in my situation?

 

[basstrackerman]

i would like to know also.

 

[tabdog]

That's very interesting Mark.

I can't go out side because of the wet ground with snow on top of it.
So I did an air test inside with my Euro Sabre. I set the 3 3/4 turn
ground balance to all the way negative, then two complete revolutions
to the positive. That's what Tesoro recommends for an air test.

I then tested a quarter with sensitivity at 9 and disc at min. Tested
both disc and all metal modes.

I turned the GB all the way positive and and suffered a minor amount
of loss. Maybe 1/4" less.

I then turned the GB all the way negative and gained at least 1" over
the first setting.

Does this mean that we may gain 1" or so of depth by turning our
ground balance to the negative? If so, under what conditions?

 

[Canewrap]

The true test is with coins that are at 8" deep. This test you're doing has a lot of the distance as in the air. Of couse, without any ground to balance against for more than half of your distance, it won't work right. The ground balance is meant to cancel out the ground as a target. That's why air tests are only potential depth and often don't come close to reflecting actual depth unless you have really good ground, and even then you'll lose some depth because the signal travel differently through ground than it does air.

 

[JB(MS)]

The ground balance control is actually a discrimination control for eliminating ground effects. With it set at the point the threshold doesn't change as the coil is lowered to the ground and raised in the air ground minerals are being discriminated out, but setting it so the threshold has a slight increase when the coil is lowered to the ground will usually result in smoother operation. With the ground balance set negative it will air test farther, but in actual use the ground effects, mineralization, will be detected and result in numerous "false" signals. If there's enough range in the ground balance control it can be set to a point the receive circuits overload and the detector sees the ground as one giant target. Setting the ground balance too positive has the opposite effect. Since the ground balance control is a discrimination control it affects depth the same way the normal discrimination control does. The more discrimination that's dialed in the more depth that's lost, except with the ground balance control it's kind of a reverse effect. As it's set more positive it begins to lose depth on higher conductive targets like dimes, quarters, etc., before it does on lower conductive targets, and the more positive it's set the more depth is lost. Again, if there's enough range in the ground balance control, it can be set to a point that half dollars are discriminated completely out, then quarters. The optimum setting for most ground conditions will be when there's no threshold change, or only a slight increase, as the coil is lowered to the ground and raised in the air. Do some experimenting outside in real hunting conditions by changing the ground balance settings from one extreme to the other and you'll see the effect it can have. You might not have enough range in the ground balance pot to discriminate out half dollars or quarters, or for it to overload the receive circuits, but unless you have absolutely mineral free ground you should see the difference in positive versus negative settings.

 

[JB(MS)]

n/t

 

[tab-nabit]

I read something about this somewhere before - can't recall all the details - mind ain't like it used to be
But I do recall the condition you mentioned in reference to the ground balance setting and air gap between the coil .

If I come across this information again, I'll try and remember to mention it in a post.
Just afraid I'll get it all screwed up if I try to put it down the way I remember it and the mind ain't like it used to be

 

[tab-nabit]

I have read something before to the effect of what you have mentioned.
Setting the ground balance for air tests also in the center as a reference point because the soil conditions are removed.
Also the center position if a ferrite sample is not available for air tests.
Then it went on and on, but there were conditions where a negative affect can result depending on the soil conditions and outside interference sources.

 

[tabdog]

Thanks JB, I think I got a handle on it now.

HH

 

[Mikel]

I know on my Tejon with the 12x10 coil you can get rid of alot of ground noise if you turn the GB knob as you sweep the coil.

 

[rmptr]

Thanks JB!

The more often I see a good explanation the better change it gets driven into my head!!!!!
hh

 

[John LA]

Thanks for the post. It helps me understand. JohnLA

 

[markg]

Gaining a little better understanding of the subject is what I'm looking for.

 

[peter-d]

my deepest 10c i dug from a sand pit this morning was 6" under sand and a further 2in under mud. the signal was strong. i ignored the smaller signals...

some of the tiny wire, smaller than fuse wire, and tiny bits of foil i dug was unbelieveably small.........the compadre sounded them out eeaasssyy.....

 

[Wayne/TX]

Thanks JB, for that perfect explanation. Being in the hobby since the
60's, I too well remember how sweet it was when the engineers finally
gave us true ground balance controls, along with VLF's too of course,
though I'll always have a soft spot in my heart for Garrett's great
old hard working BFO's! They were fine for their time, but handling
mineralized ground was just not their forte`..!
And truly, I've always accepted the fact that the GB control was
invented specifically to combat the effects of Ironized soils and all
that's necessary is to set it where it just begins to cancel those
effects, with a slightly positive threshold to better hear those
"deeper beepers". The dedicated threshold controls were another
welcome innovation!
..W