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Gmt: Hotter Than A Pistol!


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I was surprised, never having run a high kHz machine before, I nearly went off the road at first!

Got my machine last week and got to hunt about 6 hrs. this weekend. Got skunked but was happy I got the feel for the machine and kept it on the road.

I really got to see the difference between my PI machine, my AT Gold and this GMT (my red hot poker).

This is the first time I've had two VLF machines with kHz ratings this far apart and the first time running 48 kHz. 

I'm laughing about it now. I was totally caught off guard and figure I might have been a little to cocky, so it makes me laugh. Another life lesson learned.

And, I picked the river where I knew the hot rocks covered the bottom, shallow overburden and lots of exposed bedrock. So, how's that for cocky?

So, I went up the river hearing, boing, boing - boing, boing - boing, boing - Ha! I loved it! (I was thinking, "I know you and.......I know you and.......I know you"!

One thing I found concern with is, the Thold wouldn't run smooth till I turned the gain to 2 - 2 1/2. I need to do some testing to see how much I am losing by having to do this.

Are there other tweaks to smooth the Thold without losing gain?

It was a beautiful early fall day. Clear sky, light breeze and in the 70s. It was a great outing and the first outing with my GMT. So far, so good.

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It sounds like the definition of hot ground so stick with the stock DD coil. A concentric (the old Longscan) will just make things worse.

You have reduced gain but do not mention the V/SAT control. This is the other half of the equation. The Variable Self Adjusting Threshold control smooths audio responses at higher settings but with a trade in that it also tends to smooth target responses. The trick is to find a mix of gain and V/SAT setting that best smooths the hot rock response while still allowing nugget signals to stand out. This is best achieved through some on the spot trial and error with a test target. Gold nugget is best but lead shot a decent substitute.

From page 21 in the Owners Manual by Jimmy Sierra:

"GAIN and VARIABLE SAT (Self Adjusting Threshold) Speed: The (-) and (+) Ground Balance pads compensate for common ground minerals in the area. The VSAT control compensates for the consistency of that ground mineralization. The greater the degree of inconsistencies, the more SAT is needed to quiet ground noise. If the THRESHOLD becomes too erratic or noisy, it might be necessary to use the VSAT feature and/or reduce the GAIN control. This noisy behavior will make it difficult to recognize a true target (possible nugget) from pieces of mineral, commonly referred to as "hot rocks". It is not wise to keep a high level of GAIN if the detector will not operate smoothly. This is a false sense of security. Recognizing a true target is the most important part of detecting. This is an example of when less GAIN will produce more nuggets. You must be the best judge of just how much noise you can tolerate and still identify nuggets, as well as the combination of V-SAT and GAIN which produces the desired results in your area. Therefore, if you have been operating your GMT at the full level of GAIN (10) and you determine that this is too high because either the threshold is erratic or the detector is giving false signals; always begin by reducing the GAIN toward the Initial Setting triangle of (7 to 8). If this does not correct the problem, start adding some SAT speed by turning the SAT control slowly clockwise. If this does not correct the problem, go back to the GAIN and reduce it a little more and add a bit of SAT. As I mentioned earlier it is sort of like seasoning a pot of soup. Some salt and some pepper. Remember any drop in GAIN below (7-8) will result in some loss of depth. Any increase in SAT speed above the Initial Setting of (3-4) will also reduce overall depth. However, every ground condition has its optimum setting. Overall depth is not the ultimate goal. Finding nuggets is! Unless your threshold is constant and as smooth as possible. and free from false targets which confuse the picture, you will never be able to tell the ground from the gold. We like to use the analogy of driving on a straight road versus a curvy road. The object is to get from point A to point B. 65 mph might get you there on a straight road, but you will have to slow to 35 mph if the road is curvy, or you will end up off the road. The straight road is like low mineralized ground and the curvy road is like heavy mineralization. High Gain and slower SAT will not get you the Gold in heavy mineralization as well as lower GAIN and a bit of faster SAT."

A trick that can be used in conjunction with this is to use manual ground balance. Then ground balance to the ground itself and note the ground balance number. Now ground balance to a hot rock and note the ground balance number. Then manually adjust the ground balance to a number more or less midway between these two extremes. This can make the audio responses less pronounced. In other situations just running in tracking does a better just smoothing the responses so you have to experiment.

You have chosen the worst place possible to learn the machine. The GMT can compensate very well for high levels of mineralization where the mineralization is consistent. High frequency machines are very sensitive to changes in mineralization and so places like river bars with mixed cobbles of highly variable composition can be difficult if not impossible to deal with depending on your expertise level. I highly recommend you chose to work on normal ground or bedrock and stay off the cobbles until you get more familiar with the machine. Truth also is, some places just call for a PI detector or at least a lower frequency machine to take the edge off.

The tuning tips in the GMT manual starting on page 18 are worth reading several times, once after each use of the machine as use makes things it discusses clearer. 

I do not know if your unit was new or purchased used and so maybe you did not get the excellent operating video. If not, it is available in 6 parts on Youtube. V/SAT is discussed in part four around the 7 minute mark.



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Hey Steve , could you please giv a little detail in your responses? Your kind of vague bud.

Just kidding of course! This is what makes your forum such a pleasure...and Im not even much of a nuggetshooter. Thanks.

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Thanks a bunch Steve - Yup, I've got some learning to do!

I've watched Jimmy Normandy demonstrate the use of the GMT. Hard to digest it all but getting out to use it then rereading and watching the info is how I learn. Also, asking questions and taking one step at a time is best for me. 

Funny, when I was looking into buying the GMT and asking questions on forums, answers I got were pretty simplistic. "Just set to initial settings and go hunt". That is what I heard most. I knew there would be more to it than that!

I am "that guy" that goes to the school of hard knocks. Yup, I choose the hottest ground I could find. That is where I will learn to use this machine, the ultimate test. If I learn there I will be ready for the hot grounds in big nugget country out west. However, being up here in Northern Vermont, I am looking for crumbs, making it necessary to learn the fine tunings of this machine. 

Not having been able to put the V-SAT and the gain together for smoothing the Thold (great to get that info after this hunt) my objective for this hunt was to see how smooth it would run. I had a low gain setting and ran the SAT at the initial setting, not wanting to take to much on at once. (never mix two variables when experimenting) So now I can take one step forward. I am happy with the smooth Thold experience I had, hearing the different tones, using the Iron ID trigger and, most of all, knowing the hot rocks I was hearing. Running in auto track was really cool and altho it didn't completely cancel every hot rock, it gave a good ID tone and nulled them enough (with 2 - 3 pumps) so I knew what they were. 

It's a "new" machine bought from that dealer in Florida. 

Fall is here! In six weeks the ground will be a frozen block of ice, as well as the rivers. No hunting for 5 - 6 months after that. I need to cram a lot in over the next few weeks.

Steve - I hope you know how much you are appreciated - Thanks again.

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