No offence intended here.
But a manual ground balance is very much like a discriminator.
Some of the older ten turn machines could even discriminate out
iron.
I am going to describe the process of manual ground balancing.
When using a three and one half turn manual ground balance,
turn the knob counter clock(-) wise four complete revolutions. This
will be all the way negative. Then turn it two complete revolutions
to the right(+). That will set it a little positive.... This will be close for
most soils.
When adjusting the GB over metal-free ground, you can get four
different reactions as the search coil is lowered toward the ground.
I will discuss three for now.
This ground balance process requires that the search coil be held about 8" above the ground. Use a slight audio hum, or more if
needed.
Then, as the search coil is lowered toward the ground, to within one
half to one inch to the grounds surface, you listen for any change in the threshold audio and use that information to make any necessary
ground balance adjustments. The threshold audio might decrease as
the coil approaches the ground, suggesting that the GB setting is too
negative. Naturally, the hint here is to increase the GB setting.(+)
Or, as the coil approaches the ground, the audio threshold might
increase, this suggesting that the GB setting is too positive. Naturally,
this gives you the clue that you need to reduce the GB setting(-).
A third response is, well, no real response at all as the coil is lowered
toward the ground. In essence, a "perfect" GB whereby there is no
increase or decrease as the coil is lowered toward the ground from about a 8" height. The threshold audio remains the same as the coil
is lowered to about ?"-1" from the surface. This would be the ideal
GB adjustment to achieve because you can easily hear any slight
change in the threshold during the search.
Happy Huntin,
Tabdog
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