Page 1-9
Spectra VX
3
User’s Guide
ness. This means you need to apply your own discriminator —
your brain — in deciding what the VDI responses are telling
you.
Ground Response
Unfortunately, buried metal is not the only thing the detec-
tor sees. Most soil contains ferric oxide minerals, and this min-
eralization looks like a target
2
. In terms of VDI, practically all
ground mineralization falls in the extreme negative range of the
scale, even beyond most iron targets. But it can vary somewhat
as shown by the gray range in the prior diagram. At most loca-
tions the variation is small, so you can ground balance at a par-
ticular spot and be very close for the entire area. Some locations
have significant variations and you should occasionally re-
ground balance as you hunt, or use automatic ground tracking.
Many locations have enough mineralization to create quite a
strong ground signal, often much stronger than that of a moder-
ately deep target. The VDI diagram on the preceding page uses
vectors to represent specific target responses, with the angle of
the vector representing the VDI value. We can also use the
length of the vector to represent the strength of the target
2. In this manual, we’ll refer to the signal resulting from ground
mineralization (including salts) as the “ground signal” or the
“ground response.”
0
o
90
o
-95
180
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+95
0
R
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VD
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Raw
Ph
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VD
I
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Ferrous
Non-Ferrous
Normal soil
S
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US Qu
arter
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S
N
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Nail
