Page 3-5
Spectra VX
3
User’s Guide
erratic operation and noisy audio. Secondly, in highly mineral-
ized ground excessive gain can cause the input amplifier to
overload or operate at close to overload due to the large ground
signal, limiting the available range for target detection. Finally,
the quality of the loop null can also push the input amplifier
toward overload. White’s V-compatible loops are designed to
minimize null limitations, but third-party loops typically have
wide variances in the quality of the null which can require a
lower Rx Gain.
EMI affects the lower end of the signal range, which more
directly impacts target sensitivity. Both ground signal and loop
null affect the upper end of the signal response range, which
usually results in a quicker overload. Ground signal and loop
null affect target sensitivity only so far as the Rx Gain must be
reduced to prevent overload.
All-Metal Sensitivity
All-Metal Sensitivity (sometimes called
DC sensitivity
)
determines the responsiveness of the all-metal channel. All tar-
get signals cause an all-metal audio response regardless of sig-
nal strength, but a higher all-metal sensitivity setting will
increase the response rate to targets. This setting affects all-
metal modes including pinpoint and mixed-mode, but does not
affect normal discrimination mode. Setting this too high will
make the all-metal audio chatter. See Chapter 4 for a more
detailed discussion of audio responses.
Tip:
VX
3
uses induction-balanced loops which rely on a
“null” between the transmit coil and the receive coil. The
quality of the null may determine the point at which the
detector overloads, especially when running high Rx Gain
settings. Null quality varies loop-to-loop, so some loops
may overload at lower gain than others.
Tip:
Always address EMI noise by first adjusting the transmit
frequency offset. See the
Frequency
section for more info.
