| The MXT FAQ - Part 2 |
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The MXT FAQ and Operation pointers PART 2 (FAQ Questions Nos.
8-15): 8) How accurate is the depth reading in the VCO pinpoint mode? The depth reading is excellent if the target is a coin or coin sized and fairly close to the surface. At the maximum detection depth of the MXT, the estimated depth readings are not as accurate. Also, remember that the depth reading on the meter assumes a coin sized object - if smaller, the target will be shallower, if larger than a coin, the target will be deeper. I regularly hunt a park where there is a buried brass head sprinkler system at about 4-5 inches. These brass heads sound out clear as a quarter and read on the meter as being at 0 depth. However, although they pinpoint sharply like a coin, they also pinpoint much larger than a quarter. It takes about 2 seconds to shove my screwdriver in far enough to find a large object at 4-5 inches, then I know its a brass sprinkler (I've dug enough of 'em to know). Its safe to say if you've dug a 4 inch hole for a target indicated that is supposed to be at 1 or 2 inches, and the hole is correctly centered over the target, that the deeper target is much larger than the coin indicated. On the other hand, a target smaller than a coin will usually be found shallower than the meter's depth indication. |
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9) I am having problems in the VCO pinpoint mode. Any tips for a better technique? With the 950 concentric, most targets, including coins, make a significant tone change when the target crosses over the edge of the inner opening of the coil. It is easy to get the target under the inner opening based on the tone, and after that one can find the exact location by doing an X pattern over the target and listening for the sound change when the target passes across the inner edge - out of the opening and under the coil. This technique can be used to both locate a target as well as measure its size. Using this technique, I can usually find a near surface coin on the first try with my probe - if I don’t hit it on the first try, I am usually not far off. The DD coils are a bit harder to pinpoint with, but still not a problem. The sensitive area under a DD coil is blade shaped, so by making an X pattern over the target, it is possible to pinpoint a target using the DD to a fairly tight area. When pinpointing with either the DDs or the concentric coils, practice is the key to accuracy.
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| 11) My MXT is noisy in wet sand on saltwater beaches. How can I improve its
performance? A lot of folks assume that all beaches are the same and that there is one "correct" or one "good" setting for beach use. Unfortunately, like parks, all beaches are not the same. I've hunted on coral sand beaches in Hawaii - very low iron content. These are easy quiet hunting, where one should push up the gain beyond the recommended setting to get the maximum depth. However some nearby beaches have Hawaiian basalt rock mixed into the sand, and the iron laden basalt chunks become hot rocks in comparison to the low iron coral sand. This makes these beaches rather noisy - chirping and popping all the time. Yet to go from one situation to the other may only require a walk of a few hundred yards. Some beaches in California have fairly high iron, causing problems for any VLF detector in wet areas when it tries to balance out the low end salt response with the high end iron response. So, like going to any new area, you need to figure out what is the best setting for that particular area, on that particular day. On dry sand, there should be no problems. There can be noise and chatter issues in wet sand and with the head underwater. On a low mineral beach soil, the MXT may operate just fine in wet sand. However, on beaches with significant iron content, the MXT must adjust both for any iron sand or rocks in the soil, as well as the salt. Unfortunately, back sand and salt balance out on opposite ends of the scale, so it is hard to adjust for both at the same time. The standard 950 concentric coil is fairly sensitive to mineralization. If there is any iron, any variance in conductive soil moisture, or if the coil head actually goes under water, this will cause the coil to make lots of soil noise. The auto balancing switch needs to be set in the "salt" mode for these conditions, but most users find they also need to switch to one of the DD coils to get the best results on the wet sand, where the sand has some iron mineralization present. The DD coils are less sensitive to the salt or iron mineralization than the standard 950 concentric. The last option in these conditions is to turn up the discrimination (usually not desirable since beaches are prime ring hunting areas and it is easy to loose potential finds turning up the discrimination too high) or to reduce the gain which still allows ring detection, but lower gain reduces the depth at which a target could be detected. |
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| 12) What happens if I turn the gain down below the recommended preset level? The MXT is a high gain unit, made to be able to find small gold flakes. When you are just coin shooting, you can turn the gain down some (say to about 7-8) with no big problems if you are willing to blow off the deepest stuff. (hey, you don’t need to worry about those 6 inch deep barber dimes when you are hunting at a school built in 1972 on a clean site). When you are new to the machine, try dropping the gain to 8 and then cranking the discrimination up to about 7 to eliminate most trash. You can increase the gain and lower the discrimination later as you get to know the machine better. However, the deepest detection (of coins, etc) and the detection of the smallest objects (small nuggets, small earrings) requires the highest gain. Unfortunately, the highest gain also means the greatest noise from the MXT. For ways to deal with that noise, see the noise question (#18) below. |
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| 13) I took my MXT out and it was acting strangely. I noticed one of the switches had been
bumped. One thing I have noticed it that it is easy to accidentally bump a switch and change a setting while putting the MXT away or getting it out. Every time you take out your MXT out to the field and turn it on, check to see that all the switches and knobs are set exactly where you want them. Otherwise you may find that you are hunting in a mode which is undesirable for the conditions you are in. 14) I was testing a target and it just disappeared. A few seconds later it was back. What gives? When you are in automatic ground balance and making multiple passes over a target to ID it, be careful not to stall over the target and let the system track into the target and adjust the ground reading to include the target. This can give bad or unexpected results. The auto ground balance adjusts quickly and may adjust out a target faster than you might expect. |
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| 15) How can I tell what the mineralization level of my ground is? What does it mean? Here is how to use your MXT to determine your relative level of soil mineralization. When you are out hunting, flip the MXT into prospecting mode when the coil is over some target-free soil. In the upper right hand corner there is a label, GND = 78 (or some other number). The ground reading number tells what the MXT is seeing as far as soil mineralization. If your number is 30 to 50, you have low or no mineralization (lucky you!). Readings of 50 to 69 are found in moderately mineralized soil. A reading of 70 or over is highly mineralized soil. In general, highly mineralized soils are much harder to hunt in, often tend to have more hot rocks, and as a result are noisy to hunt over. Some areas with moisture and a high alkali or salt content can cause their own set of problems. They read on very low on the ground scale and give ground readings in the 20s. The MXT has a separate salt adjustment on the ground balance settings for work in these areas. Soil mineralization that reads high on the ground scale is caused by iron minerals in the soil, and can have a very significant negative effect on the operation of your detector. Unfortunately for us detector operators, the earth's crust averages a little over 8% iron, and some of us seem to have a just a bit more than our share! This is why all modern VLF type detectors have the ability to adjust and compensate for increased iron in the soil. The automatic adjustment the MXT makes to compensate for mineralization is not just a simple reduction of gain, but the net result of ground balancing to hunt in highly mineralized soil is reduced sensitivity. Reduced sensitivity means reduced target detection depth. The MXT (and all other VLF type detectors) will detect much deeper in dry sand that reads 40 on the MXT ground scale than it will in soil that reads in the low 80s. There are a number of factors that affect target detection depth, including soil density, soil moisture, salt content, and others. Soil mineralization is just one of these, but it is one that is common, and does have a significant effect. Here in the Reno, Nevada area, soils typically vary from the high 70s to low 80s. |
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MXT FAQ -
Part 1 |
MXT FAQ -
Part 2 |
MXT FAQ -
Part 3 |
MXT FAQ -
Part 4 |
Basic Placer Gold Prospecting |
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