Let me start by being clear in my opinions about the MX-7:
I own and use TWO of the MX-7's in my Regular-Use Detector Team and enjoy them for many reasons and they are a great complement to my TWO Nokta CoRe, TWO Nokta Relic and TWO Makro Racer 2 devices. I have TWO of each of these models because I like the detector, and I hunt moderately littered to very dense debris sites and I have a smaller size and mid-size coils for each pair of my favorite detector models.
For the MX-7 I keep the 6½",
measured, or 6" labeled Six Shooter Concentric coil on my most-used unit as the 'smaller coil', and the 7" Double-D made by Detech for White's on the others as my mid-sized coil for modestly littered sites. Actually, my 6½" was Ian initial prototype coil for the MX-7/MX-Sport that has the earlier style rounded 'bowl-shape' bottom half and I need to get a new flat-bottom and thinner-looking Six Shooter for it.
JEF contacted me Wed. evening and stated he had the '79' numeric VDI respond from a US Quarter, but the display read DIME, and it just so happened that early that day when hunting a former CCC / Japanese Internment Camp / County Park site I found a 25¢ piece at about a 4" depth. It was a moderately trashy site and I could hear the annoyance of the close-by junk targets. I only got a half-decent signal on a couple of sweep directions that caught my attention with all the low-volume rejected trash audio I was hearing, and the VDI read-out, with a short-length wiggle of the coil, gave me a '78'/'79' response occasionally also showing a '77.'
Checking, I had a sizing indication is was a narrower, coin-like target-size response and hoped for a silver dime or quarter. I seldom glance at the printed coin denomination type, just refer to the numeric VDI read-out with the MX-7's because that how I use all my other makes and models. When I used to use the MXT All-Pro and MX-5 I did the very same thing, only referencing the VDI numeric report and not the detector's guess of a coin or object label.
I had noticed the periodic errant target read-out when I first started evaluating the MX-7 and the 6½" Concentric, 7" DD, and standard 950 Concentric coils, but I didn't fuss much about it because most of my time is spent in Relic Hunting environments where I am dealing with high mineralized sites and very dense debris, especially nails, other iron objects, and various sizes of hunks to bits and pieces of rusty tin.
Most places I hunt, even a lot of the urban Coin Hunting locations, will have some challenges such as working close to metal structures or in areas with higher trash levels. Doing so we will have the masking effects of nearby objects that can, and will, throw off a good target's TID reading with a slightly up-scale or down-scale numeric report. That's normal.
Targets that are located a little deeper or are canted at an odd angle can also throw off the visual, and audio, Target ID we might get, and that simply suggests that nothing is going to be perfect. We know, or learn, that in a variety of hunting environments and when dealing with various hunting challenges, such as various ground mineral conditions or nearby masking offenders, the TID response might not lock on perfectly. Numeric VDI information should be used as a general reference to an object's conductivity level and we can mentally associate desired objects with visual responses we get in testing as well as in-the-field searches.
North of us those Canadians get to find a lot more $1 Loonies and $2 Twoonies that I wish we had, and those coins are made of mixed metals. Most Canadian coins today, and for quite some time, have also been made of similar metals such as Nickel, Steel or other 'blends' that are predominantly a ferrous or magnetic-based metal. They don't get rock-solid and consistent VDI read-outs like we do with the better metal coins here in the USA. And when you consider all the other countries where White's products are put to use, you will see a wide-range of coins. Alloy metal types, various sizes and shapes and thicknesses, and other things that can influence a located target's numeric VDI response.
Thus, many different denominations of coins and metals used to make them that there is going to be a lot of different VDI responses. Everyone from every country learns those target read-outs. They have to learn what the numeric response might be from THEIR coins, and then know those responses can vary at least a little bit for several reasons. I don't have my MX-7 Owner's Manual at hand, but I looked at the MX-7 manual on-line at the White's website. The manual is in English [size=small]
(American English, if you will)[/size] and Spanish for our other neighbors to the south. Refer to both sections on Page 17. I can only read the one in English, however, note the graph on the left-hand side.
It is the same graph that the Canadians and Mexicans can refer to that gives a general
Numeric Reference for Low-Conductive 'Iron', a Mid-Conductive 'Gold' range that runs from high iron to include the USA 1¢ and 10¢ range, and then 'Silver' for the High-Conductive range. Mentally, folks in those countries use the VDI numeric responses in general reference to a Low, Mid or High conductivity target they might be searching for.
But they look at this graph and then at the MX-7 and MX-Sport Display and see a US Coin Reference for Zinc Penny, Copper Penny, Dime, Quarter, etc. Those denomination names do them absolutely no good and are there simply because Target ID, as we know it, got started here in the USA way back in '83 with the Teknetics Coin Computer and manufacturers were quick use our US coin references for the majority of metal detecting Hobbyists who are Coin Hunters. That was back in the day where a lot more people were into the hobby here in the US, and when we had more detector makers, more clubs, more dealers, and
were one of the more active countries where metal detecting took place.
Not so today. The metal detecting industry has really grown a great deal in many other countries, and we're seeing more foreign metal detector manufacturers who are sharing the upper-end of the quality detector market. And they are not tailoring their detectors to specific tight-range categories intended to be specific coin denomination with a word association, but simply relying on having a nice VDI numeric display that a consumer can use to learn where the targets they are after might respond.
Back to search coils for a minute .....
It is important to have a coil that is tuned or calibrated to work well with a detector, and it's also important to have a detector that offers Ground Balance to get the best performance with any coil and in any search mode used. And, as with other brands, we also notice that it is not unusual to change a coil on a detector and have a sample target produce a slightly different VDI read-out by one or two numbers either higher or lower. That's normal and expected from possibly happening with either a detector maker's search coil or one from an after-market search coil..
I don't have, but want to get, the new flat-bottom Six Shooter Concentric coil. A very functional search coil that is light weight and handy for many applications. I hope they might find a slight calibration to make to get that coil to produce a little better response, but let's use caution in our wishes. It's best to just refer to the numeric response and, in my opinion, it would be better to eliminate the wordage that describes what a coin might be. Just do away with it.
Consider this. A Dime range is from '75' to '79' and the Quarter range starts at '80.' A clad dime, with the 6" Concentric coil and sometimes with the 7" DD and other coils, usually gives a '74' read-out that says CPENNY. So, let's say they remedy that by making the common US Dime produce a '77' VDI that is right in the middle of the Dime's numeric range. Great! Until someone happens to sweep over a silver dime instead of clad and the VDI response is then '79', which is a DIME or maybe the silver Dime drive the response to '80' or '81.' What then???? Is everyone going to be bothered because the display then
'says' QUARTER when it isn't?
So, in the end, the VDI might be off
slightly on
some coins with
some coils by 1 to 3 VDI numbers. No big deal to many savvy Detectorists because there's more tellable information in the audio Tone, audio response, VDI read-out and consistency, and quick sizing and classification when using the Pinpoint function that lets us know the target is a likely desirable find and needs to be recovered. Me? I'll stick with my very good MX-7, my preferred 6" Concentric and 7" DD coils, hunt in a slow and methodical manner and pay attention to the VDI numeric read-out.
Get a reasonably good to questionable 'iffy' response, then rely on the proven
'Beep-DIG!' method for success. Recover the target, and
then check it out ...
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