Today I headed out to an old favorite spot of mine that has produced a lot of good coins and other items in the past. I've absolutely hammered this location with my prior machines, including my Explorers. While I've pretty much gridded most of the large mowed grass field there, one particular spot near a large tree has been really gridded hard from several directions using my Explorers. This is the spot where a while back my GT and 10" got the two deepest coins I've ever dug on any machine, a V nickle and an Indian in separate holes that were somewhere near or around 11" deep. Both gave loud/clear/correct signals.
Anyway, today I once again decided to hit this spot but with my 15x12 SEF coil. I decided to start the hunt by doing what I'm prone to do now for optimum depth and performance, sticking a silver dime in the ground to use as a guide to calibrate sensitivity. I buried the dime at about 7" and then first tried Auto. No response from the target, not even a null. Now, I have dug silver coins at almost 8" in Auto, but something freshly buried is of course going to give less depth. Then I dropped sensitivity all the way to it's lowest and swept over it. No threshold change as expected. Brought it up to about 4PM and now the threshold would null here and there with a slight target break through. Turned it up to 3PM and now it's loud and responding, but the ID was "weak" and low, staying in the low 120's to 130's for the most part and not really locking anywhere. Bring it up to 2PM and now it's climbing in the 140's, 150's, 160's, and some into the 170's here and there, with the occasional 180 hit and good audio. I was doing the "Sovereign Wiggle", which most know is wiggling the coil as short and as fast as possible directly over the target.
It was for sure something I would dig because it sounded good and was making it to 180 when I got it just right. Very rarely, like maybe every 9th or 10th "wiggle" or so, the VDI # would jump into the negative numbers (iron). Brought the sensitivity up to about 1PM and not the VDI is not as easy to get to climb, being slightly more erratic and not steadily moving through the 150's to 170's. It was more jumpy and also more prone to showing negative numbers a little more often. Raise it up to noon and the same above qualities are getting more pronounced. Hit 11PM and now the ID is even less uniform, more all over the place, and the negative VDI #'s are happening much more often now, like probably every 3 to 5 wiggles of the coil. In other words, had I not known this was a coin I'd be more inclined to believe it was iron. Cranked the sensitivity up to full blast and not only is everything just described in full force now, but I'm also getting nulls over the target sometimes with no ID or threshold response at all (other than the null).
Swung around the site and about five feet away I get my very first hit, which turned out to be a decently deep and good "penny" signal of 176, but it was a little hard to get there, just like the above dime was when set just perfect. Dug down about 6 to 7" and I see something silver that at first I thought might be a half dime or 3 cent piece because based on the glob of dirt it was in I knew it couldn't be too big, but I also knew by it's shine that it was silver. Turned out to be a little star-like silver pendant somewhere between a 3 cent piece and half dime in size. Very small, very cool, and from the looks of it and the depth I would guess also very old.
So what have I concluded thus far? That sensitivity can be too high or too low, and that a high sensitivity setting that seems stable in threshold is NOT getting you deeper based on soil conditions. Some sites you can go higher, some lower, but I'm making darn sure I calibrate the machine for each specific site. Seems like 2PM is the most common in my soil, 1PM the second most, and 11PM is third most in better soil. Too high of sensitivity setting often produces nulls and much more in the way of negative numbers and an erratic ID. I think the negative numbers are perhaps due to the coil running hotter and thus seeing more iron or minerals in the soil, washing the target quality down a bit due to that.
By the same token, too low of a setting will cause the number to stay in the lower range more and be much harder to get to climb to it's true identity. Too low can also cause targets to null just like too high, though too high seems more prone to it. In moderate to heavy minerals, at least with this coil, around 6 to 7" seems to be a good starting point to bury the silver dime at. I try to get it at just the right depth where the window of "perfect" response in sensitivity is narrowed down on the dial. If you've got the coin too shallow and it hits decent from say 3PM to 11PM then you obviously can't tell as easily just what the "best" calibration is.
What I've also learned is more about coins at the fringes respond versus say iron or other trash trying to pretend to be a coin. The coin will have decent tone and go 140's 150's 160's. If you hit it just right and wiggle right there it may climb into the 170's and hit 180, but a coin just a hair deeper might not make it all the way there. You should see very little in the way of negative numbers when doing this. Say one out of 7 to 10 wiggles or around there should be negative. The more a negative number appears the more your odds are that it is iron, IF you have the sensitivity calibrated properly.
With further testing on targets before I dug them up that are sort'a like the above I found this...If let's say it's real deep and doing the above but keeps getting to about 146 and staying there mostly. You think you may have a deep nickle. However, doing the wiggle the target occasional spikes up about 146 to something like 151 here and there. You can almost be assured that it's not a nickel then, because a deep fringe target will almost never spike above it's true ID, even for an instant. If it's below the true ID and trying to get there, and especially if it sometimes does, then that's the ones I'd key in on. Again, if the negative numbers creep in too much then odds are otherwise.
I would recommend doing the above sensitivity calibration at any new site, not only to set it for best depth/performance/ID lock, but also because it will keep you in practice to listen, see, and learn exactly how deep fringe coin signals act. The way they act IS different than most trash or false coin spikes off iron. To further test what might be iron go into PP and see if the target moved much. If it did then I'd say it's iron, but it could be a coin next to iron. I like to PP in discriminate from two directions on the target myself, and if they both give me the best response in the same spot then I'm digging regardless if PP mode says it's moved, because I feel it might be seeing the junk and not the coin next to it. It's rare for a false coin hit to ID in the same spot from two directions. However, I'll warn you that a fringe coin in my tests may sometimes be easier to get to ID swept one direction than it is the other. For that reason, if it sounds good and "gets there" from one direction you'll pretty much know by the way the ID reacts (140's to 170's with not too many negative #'s) that chances are good it's a coin. Swept the other way it may only get into the 130's to 150's, but again the key is the lack of excessive negative numbers.
One final note...If the target at the fringes of depth seems to say keep getting up to like 152 for instance but never past that, and you keep seeing that "152" from two different directions after your work the target with the wiggle, then chances are it is a "152" target since it's "resting" there if you get the wiggle just right. If, however, it keeps climbing, 160's, 170's, and maybe hits 180 when things are just perfect here and there then it's more likely to be a 180 target. You CAN notice a distinct pattern in the VDI and the audio for the most part staying good that should tip you off to it being a fringe coin, versus how iron or other trash reacts. Also, another tool is to note how deep the target sounds. If it doesn't sound all that deep then chances are it isn't a deep coin trying to behave since it shouldn't be giving you so much trouble to climb to the proper ID. On the other hand, it could be a shallow coin mixed in with iron or other trash, but there are other tools to help ID those which I've covered in my mask test thread in the past and will probably add more to here in the near future. The "iffy" more shallow coin signals require a different set of tools in the way you see and hear the target to decide which is which. I'm mainly just covering the coins here at the fringes of depth that are getting iffy, as well as how and why sensitivity should be set properly in order to max out depth, performance, and response. Keep running around running sensitivity at full blast or as high as it seems to sound and run "stable" and I guarantee you that you are costing yourself depth and response quality on the deep stuff, not improving it.
Also did some playing around with the volume. At it's highest it gives me no further detection depth. So long as the machine is hitting on the target at the fringes the audio is more than loud enough for me to hear, and as said I think the quality degrades a bit if I run it at full on these Sony Studio phones anyway. However, since this spot seems to have hardly any shallow trash I decided to hunt with it at full. After a while I got adjusted to the slightly change in tone quality that full volume does. Now I wouldn't say it degrades the audio but rather changes it slightly, so you just have to give yourself a little time to adjust to it. Still, after hitting a few deepies in full volume at the fringes I went to lowest volume and could still hear the target perfectly. Yes, volume was lower, but still well within my hearing limits. I wouldn't have missed those targets regardless....on these headphones....with my hearing. I might add that I don't have the greatest hearing in the world either. I was told that I have high frequency nerve damage, but I've never noticed myself.
One more note: 2PM to me on the GT is where the dial is pointing directly at the middle of the "C" on the word that is above and to the right of the sensitivity dial. The name of that control escapes me at the moment but you'll know what I'm talking about when you look to 2PM on the sensitivity dial. It's an easy way for me to set it just right at a site when I don't feel like sticking a dime in the ground, though I would suspect with changing moisture conditions a site I have previously done this at might change it's sensitivity setting from one hunt to the other. Still, the vast majority of my sites thus far (medium to heavy minerals) are turning out to be 2PM, at least with this coil.
