18. My MXT seems a lot noisier than
other detectors I have owned. Why is
this?
There
are very few complaints about the MXT, but one of the few that is
regularly heard from new users is that the unit is too noisy, chattering and
chirping on tiny bits of hot rock, foil and soil iron. These folks would strongly prefer a detector
that is just silent until an acceptable target is found. This situation is most often noted in
strongly mineralized ground. Most of the
MXT's ability to get deep items or
small gold nuggets is due to its higher than normal
gain (and the circuitry to handle that higher gain). This higher gain, the fact it does not
average passes over targets, the greater operating KHz of the MXT, plus some other features of the detector, do make it more chattery than most.
Dave Johnson, the design engineer for the MXT (and a very talented one) spells out why the MXT makes more noise than most detectors in his engineering
report. In the simplest terms, the
increased noise of the MXT is the trade off for the
increased sensitivity, both to small targets (nuggets) or deep targets (old
coins). However, even in very highly
mineralized soil, I have found that with the right adjustments, I can get used
to the chatter and pick out the coins, other good targets, etc.
The
two tone feature of the relic mode also works real well for this type of
situation. The relic mode is best used
in these situations by setting the discrimination at just a hair under 4 (or
higher where appropriate) and pushing the handle trigger forward. This makes the low (iron) sounds go away, the
general noise becomes a medium tone (same as the normal tone in coin mode), and
the good targets are the high tone. this makes it easy to ignore the medium tones and focus on
the highs. It definitely takes some time
and practice, but one can get used to it.
There are also some other techniques that can help reduce the noise,
though none are a perfect answer.
Locking the ground balance over clean soil can help, especially in areas
where a large amount of man made iron trash is present, such as at ghost town
sites. Use earphones with adjustable
sound settings, and turn them down until it is not painfully loud when
pinpointing over a near surface target.
Using DD coils rather than the standard 950 concentric also helps quite
a bit as the DD design is less sensitive to soil mineralization as a whole. Unfortunately, the DD coils are also a compromise
as they get slightly less depth than the 950 concentric coil. The threshold sound level can be turned down
a bit below the edge of hearing, and this helps a small amount, but the real
problem with noise is in the gain.
Although turning down the gain will cut down the noise significantly, it
will also significantly reduce depth and sensitivity. In order to get those deep coins others have
missed, or to pick up those small nuggets, the gain needs to be up at +2 or
+3. So to get the full performance from
the MXT one needs to learn to get used to the chatter and learn to pick
out those good targets from the background noise. With practice and a little tweaking, one can
find the best balance of coil and other adjustments to make the targets as
distinct as possible from the background chatter. The goal is to get the target response that
is easy to distinguish from background noise.
This means that sometimes, a little less gain can actually give a better
response, as the soil noise will not obscure the weaker target responses. You have to test to see what works best at a
particular site.
For
a new user, I'd turn the gain down to about 8, and discrimination up to about 6
for a while when you are first learning the unit. That makes a huge effect to reduce the noise,
and you'll still have no problem getting coins within 5 inches of the
surface. After you get a little more
practice, you can turn the gain up and disc.
down to get the full performance from the MXT.
19) What is the best
operating mode to choose when using the MXT?
There
really is no one best mode for the MXT. There are 3 completely different programs,
and the three modes are there to give you pre-made programs for a wide variety
of conditions. The MXT performs quite differently in each mode. The prospect mode goes a hair deeper, but is
the least stable toward ground noise or iron junk, so it is the worst choice
for working trashy areas like parks. The
prospect mode has an iron ID feature, but does not have a true discrimination
setting. In Prospect mode, iron trash is
dealt with using the iron grunt tone and the interpretation of the screen
output by the operator (only the Relic and Coin modes have a true disc. setting). The Relic mode (dual tone mode) is next
deepest, and is preferred by some because of its two tone
ID. The coin mode sees targets a hair
less deep than the other two modes in air tests, but it is also the most stable
mode.
It
is not always necessary to hunt in what would seem to be the "right"
mode for that application. Some folks
like to prospect in the Relic mode where there is lots of trash with the
nuggets. I've heard of folks who beach
hunt in prospect mode to get a slight increase in depth. The best choice depends on the application
and your personal preference. Here's my
opinion on some possibilities in different applications: I think the coin /
jewelry mode is best in areas like open fields without large amounts of
trash. The relic mode is best for high
trash areas, like old parks or ghost towns, it works well there with the
alternate mode, trigger forward to disc out the iron trash. Prospect mode is best for nugget shooting .
Prospecting is the most sensitive mode (though only slightly) and as
noted, is best where there is not too much iron junk or other trash,
because it lacks a discrimination mode.
20) What should the gain
setting be when detecting for gold?
One
of the main keys to detecting small gold with the MXT is cranking up the gain to the +3 MAX. Having the 6 inch DD is also very worthwhile,
both from the stand point that with its small size it is more sensitive to
small gold, but also because it allows higher gain settings than the 950 coil
under mineralized conditions. It is also
less susceptible to changes in soil mineralization than the 950 standard coil. In doing some
tests in my yard, I found I could barely detect a 0.5 grain flake with the 950
coil at a gain of +1 (with the flake right on the surface about 1/2 inch below
the coil) - the signal was there but was so weak that in the field, honestly I
probably would have ignored it, or not been able to distinguish it from hot
rock / background noise. A gain setting
of +3 gave a much better response. The 6
inch DD gave a better response to the 0.5 grain nugget at all gain
settings. At times, high and variable
mineralization may make it necessary to reduce the gain, but when that happens,
sensitivity to small gold will be reduced.
21) What does the iron
probability reading in prospecting mode really mean?
When
using the prospecting mode, probably anything that does not make the
"grunt" sound (80% iron probability) should
be dug. The target ID on the MXT is excellent, however it is not perfect. The ID does not work as deep as the detector
will detect. In high iron soil areas, it
is possible for small nuggets near the edge of the detection limit to score as
high as 70% iron probability. In my
experience, most junk iron gives a reliable signal with the special
"grunt" sound. However, it you
are looking for meteorites, the "grunt" noise may indicate a
meteor. Use of a magnet to collect
surface iron is also helpful. On the
other hand, many small nuggets below about 2 grains weight do not give any ID
indication. Tiny bits of iron or lead
can also fail to give a VDI or probability response. Repeatable targets which do not give any ID
should be investigated. If passing a
magnet over the surface does not cause the target to go away by picking up any
iron or small hot rocks, the target needs to be dug. The ID will not detect to the deepest and
smallest of targets. The key is that if
the target is repeatable, the magnet does not remove it, and it does not seem
to move around as the coil is passed over it, it probably is not iron (it is
most likely lead or gold).
The
iron ID in the prospecting mode should probably be interpreted as follows:
10 to 30% iron probability - The MXT is reasonably sure the target is not iron, dig these for
sure.
40 to 60% iron probability - The MXT just can't tell - you will need to dig these targets or you will
loose gold.
70%
iron probability - In
low mineral areas, you may not need to dig these, in a high mineral area, dig -
use a test nugget to see.
80 to 90% iron probability - The MXT is reasonably sure the target is iron and probably can be ignored.
When
you are testing a target, be sure the coil is centered right over it. You may get inaccurate iron probability
readings if the coil is not properly centered.
This could cause you to loose nuggets.
The
use of a test nugget to see how the MXT responds in a particular
area is highly desirable. Bury a test
nugget of about 2 grains size about an inch deep at the site you are testing,
and see what the response is. In order
to be sure you do not loose the nugget, most people will glue the test nugget
to some small plastic piece like a plastic poker chip. Some detector owners have a full set of test
nuggets of various sizes that they use for this purpose.