Page 4-3
Spectra VX
3
User’s Guide
mode, except that salt responses are subtracted out. This elimi-
nates salt signals while still allowing
VX
3
to track ferrous min-
eralization. This technique is only possible in multi-frequency
detectors, which is a second reason to use multiple frequencies.
The Salt Beach program uses this mode.
A small downside to salt compensate is that a narrow range
of VDI’s are notched out and targets in that range won’t
respond. The VDI for salt is 4 to +5 which is normally
the area for bits of foil. However, very small gold nuggets and
some jewelry can also fall in this range, which is why
VX
3
has
the added option to run a normal 3-frequency with salt subtrac-
tion disabled. Some
V
-users have reported situations where the
salt-compensate mode helps reduce EMI noise.
Single Frequency
With any multiple frequency detector, the total transmit
power must be divided among the active frequencies.
VX
3
offers the ability to transmit only one of its three frequencies. In
single frequency mode, the transmit waveform is optimized to
focus power to the selected frequency, resulting in slightly bet-
ter depth but for a more narrow range of targets.
Usually the VDI responses for targets vary with frequency,
which means that a particular target will have completely differ-
ent VDI numbers at each of the three frequencies. For example,
a US silver quarter has the following raw VDI responses:
Trivia:
White’s DFX is always in salt compensate mode.
Trivia:
The single frequency modes in White’s DFX do not
use optimized transmit waveforms.
Frequency
VDI
2.5kHz
70
7.5kHz
85
22.5kHz
91
