White’s Electronics Spectra VX3 - Manual (Page 17)

Page 1-11
Spectra VX 3 User’s Guide
Any error in the ground balance point can result in an error in
the target VDI response so it’s important to maintain a decent
ground balance point.
Ground Tracking
In order to better handle variations in ground mineraliza-
tion, many detectors now incorporate automatic ground track-
ing (White’s uses the term AutoTrac
® ). The detector attempts to
determine what part of the signal is due to ground and continu-
ously track the phase and strength of that signal, and eliminate
it. One trick is to limit the range of VDI’s for normal ground
(the grayed area in the VDI scale) and consider anything else a
target. This works for most soils, with two caveats.
Besides “normal” ground mineralization, some areas con-
tain rocks or small pockets consisting of material with slightly
different mineralization than the surrounding ground. The dif-
ference in VDI between these anomalies and the surrounding
ground isn’t enough to consider them a true target, but they are
small enough to act like a target to the detector’s ground filters.
These so-called “hot rocks” can create annoying responses in
many detectors.
Another situation concerns soils with significantly conduc-
tive salts. A pure salt response lies all the way in the non-fer-
rous region of the VDI scale, roughly in the midst of foil. Some
salt-water beaches are close to having a pure salt VDI, while
other beaches include black sand mineralization that creates a
Weak
Quarte
r
-95 +95
0
New Origin
Strong Grou
nd
-95 +95
0