If you are like most E-Trac newbies, you've probably read the manual,
and, when you turn the machine on, you hold it a foot off the ground and
do a noise cancel, as the manual recommends, and wait for it to assign
a channel. Or, maybe you don't bother at all, thinking it doesn't
really matter, and use whatever channel was set from before.
But, I think it does matter. Otherwise, why would Minelab give you the
option to change the assigned channel under the Expert Menu?
First, some background on why I think it matters (and that comes down to
three incidents I've experienced), followed by the noise cancel
procedure I use to select a channel.
Evidence of Different Frequencies on Different Channels?
The first was a subtle difference I noticed -- that TID (target ID),
seemed to be a function of channel. I had usually been running on
channels 9, 10, or 11, cause that is what the machine usually assigned
me (for some reason) when I followed the procedure in the manual. And,
as I hunted, clad quarters pretty much consistently came up with a TID
of 11-47. However, one day when the machine assigned me channel 2, I
noticed clad quarters pretty consistently came up with a TID of 11-46.
Big deal? Certainly not if you are interested in digging clad quarters;
everyone is gonna dig both of these. I like clad quarters as much as
the next guy, but I saw this as a clue into the inner workings of the
machine. Remember, TID is a function of both the transmit frequency,
and the target metal. The software will take the transmit frequency,
the response, crunch some numbers, and normalize it to a consistent
response to make it easy for the user, so that when the transmit
frequency is either X or Y, the TID will be the same, if the target
is the same.
But, there is bound to be some rounding error in this process. For
example, lets say everything normalizes to channel 9, and channel 9 transmits at 2KHz. When using channel 9, no computation is necessary,
blast out 2KHz, and report to the user what you see.
However, maybe channel 2 transmits at 1.5KHz. If so, to normalize to
the channel 9 experience, some math needs to be done, and its possible
that there is rounding error in that math. If so, it may report 11-46
instead of 11-47 on the same target.
The fact that I was seeing this allowed me to speculate that each
channel was causing the machine to send out different frequencies, and
that perhaps the difference was material.
Note: I understand that the FBS technology sends out multiple
frequencies. The above example is simplified. What matters to anyone
looking for silver is the low frequency; the lower the better. If you
know one channel is sending out a lower frequency than another, you want
that channel if you are looking for deep silver.
So, with this discovery and the inference that each channel may be
sending out a different low frequency, that led me to my second
Evidence That Channel Matters
Next was an actual in field test (not a test garden; IMHO, test gardens
are worthless -- if you want a test garden, find a deep silver in
the wild and don't dig it, remember where it is, and use it for your
test garden, that's what I do).
Eventually, I came to find a very deep silver in the wild, just
on the edge of detectability. You know the sort, quick,
coin-sized signal with that FE bounce, in the high zone. I
was running channel 9 when I found it.
I pinpointed exactly where the target was, placed a plastic marker,
and then went thru each channel (Expert Menu/Channel), to see if it
made a difference.
It did: I could only hear the target when running channels 2, 6, 9, or
10. While other channels may have given a threshold null or perhaps
an undiggable chirp or non-repeating signal, there was no mistaking
that channels 2, 6, 9, and 10 gave the best signal. I repeated this
test for quite a long time, and from different directions, to smooth
out any randomness. The results were consistent. Some channels didn't
even give a threshold null.
I had at least confirmed my hypothesis from above -- that, at least for
this target in this dirt, channel mattered. I don't know if it is
because of the transmit frequency, the software, or the phase of the
moon, it matters.
I dug the target (it was a merc), and vowed that I would run on channels
2, 6, 9, or 10 going forward, no matter what.
However, Some Channels Don't Work With Some Dirt
The third experience threw my worldview into a bit of a loop (why
does it sound like I'm writing drivel like the Celestine Prophecy?
I assure you I am certainly not trying to -- just my style, I guess).
Happily hunting on channel 9, I was pulling silver after silver
from a massive honeyhole that was giving them up at 1 per half
hour. Deep wheaties and clad on top of it meant the high
tone (low frequency) targets were frequent, and there were
very few shallow targets, due to, perhaps, the site being
hunted by weaker machines/weaker detectorists.
Then suddenly it stopped. I kept gridding out of the hot zone,
and couldn't pull more than a couple targets to save my life.
Not even clad. There is no reason that this section of the site
should have fewer targets than the section 10 feet over; I
remembered from the aerial photos that this entire section
contained an old baseball diamond, and that some dirt I was
digging here was orange, consistent with dirt often found in
baseball diamond infield baselines.
I got an iffy signal consistent with deep silver, but it turned out
to be a clad dime at only 4 inches. Ouch. Something was terribly
I got another iffy signal, and decided to do a test. I tried every
channel on this iffy signal, and all channels saw it loud and clear,
except channel 9, my preferred channel, and the one I was running
on earlier, and pulling silver after silver.
What was different? What was different was the orange dirt. Channel
9 was having a problem with the orange dirt, for whatever reason.
As an aside, I always run manual, and cranked, but noticed that the
auto rec was very low in the orange dirt section (what I mean by
"auto rec": what it shows you auto would run if you hit the right arrow
key to go into auto mode or look at the auto bar). I noted this.
So, I hypothesized that the orange dirt had different mineralization
characteristics than the normal dirt 10 feet over, and that target
response was also a function of the mineralization of the dirt and
the channel operating on that dirt.
I regridded that section on a different channel, and pulled targets
that channel 9 missed. Evidence that this stuff matters, at least in
So, my summary of these tests is this. Channels 2, 6, 9, and 10 are the
best channels to use if looking for deep silver, in normal conditions.
(Note that different channels may be better if looking for gold; my
tests did not look at that angle, tho rumor has it that gold hunters
like channel 4).
However, in abnormal conditions, such as strange dirt or variable
mineralization, one or more of the these channels may not be the
best; some channels may not like particular dirt or mineralization,
for whatever reason (I mean, heck, I'm an economist, not a physicist,
so who knows the reason?, but my tests and the silver don't lie).
Note: the ostensible purpose for the noise cancel/channel selection
function is to mitigate EMI. Therefore, it is possible local EMI will
render the above calculus useless. This is most likely to happen in
an urban setting -- you've got it all figured out that channel 9 may
not like the dirt, so use channel 2, but that powerline may neuter
channel 2. Ouch. In my experience, this is a very rare problem, and
to use the noise cancel function to worry about EMI noise should be
the lowest of priorities; do so only if there is an obvious EMI problem.
Finally, watch the auto rec and a sudden dropoff in deep targets. A
sudden drop in either is a red flag that you may need to change the
channel. I look at anything below 19 on the auto rec as a cause for
concern (tho some dirt is just bad, and auto rec runs low all the
time -- I'm talking about a sweet site where all the sudden drops for
Based on all that, here is how I manage channels at a site.
First, I follow the manual's procedure, and do a noise cancel holding
the coil 1 foot above the ground. This gives me a read of which channel
is most favorable to the local EMI conditions. I note the channel, and
hope it is 2, 6, 9, or 10.
Next, I do a noise cancel holding the coil flat to the ground. This
gives me a read of which channel is most favorable for this dirt. If
it is 2, 6, 9, or 10, I am happy and start detecting. If not, and the
channel from the above step was 2, 6, 9, or 10, I change it to that channel, and start detecting. If neither were 2, 6, 9, or 10, I use
what it gave me on the ground test, and do the above 2 steps in 10
minutes or so (under the logic that at this site, it may not matter,
and if I get a different answer next time, use the best one for
silver, and under the logic that the mineralization test is more
important than the EMI test).
Then, throughout the detecting session, I watch the auto rec, and watch
for a dropoff on deep targets. If I see problems with either (and
by that I mean auto rec below 19; if running manual, hit the right
arrow to see what the auto rec is, then remember to switch back to
manual), I repeat the above to see if I can get a better channel. Note
that some dirt is just bad, and auto rec will be bad regardless of
channel, and I believe that this is the case most of the time, but my
tests suggest that it matters some of the time. In some cases, the
auto rec is giving me a clue that this channel doesn't like this dirt.
Finally, in my log, I note the channel that seems to work best at a
given site, for next time, just so I know. Also, as an aside, I prefer
2 and 9 to 6 ans 10 when I have a choice (sometimes if the air
likes 9, and the dirt likes 10, I'll choose 9), but all of that
is further refinements of the model that go beyond the scope of
this article (and should rightly be ignored if you are a newbie to
all of this). Just notes for those who want to do more tests. That
said, there is one site that just loved channel 6, and that is the
channel I used to clean it out.
Disclaimer: And Does Any of This Matter?
My tests prove that it matters (at least to my satisfaction). The
question is, does it matter enough to think about it? For me, it does,
I think it helps me find more silvers. Maybe 5-10% more, that's my
good faith estimate.
Will it help you, who knows? I think the dirt matters alot. Where I
live, the mineralization is highly variable, and can be extreme.
Moreover, most of the silver is at urban sites (duh, population
density), meaning more EMI. So, it matters where I detect.
In other parts of the country, with cleaner dirt (and I've detected
in these places; you get more depth in this cleaner dirt without
thinking about this stuff), I think it matters less. As always,
YMMV, and FWIW. (and HTH too, this is just my experience, and
presented as food for thought).
Finally, I am not a physicist. I have no clue how metal detectors
work. All of the above is speculation and observation on my part.
Its just food for thought and a recollection of my experiences. Make
of it what you will, and do with it what you wish.