Here in the NW, more specifically NW Oregon where I live, we have-had/are-having some of the nastiest storms in a long time! Rain unending, wind to make it worse, and some serious flooding in many areas.
It's been so nasty blustery that it's been hard to get in any appreciable amount of time with the new 18.75 kHz coil, and the forecast is for more of the same for the next 7-10 days. But, I have managed to get out a few times and work with the coil, but the time was shared with comparisons against the X-Terra w/stock 7.5 kHz coil, and a couple of competitor's models in the higher frequency range.
And I said the delay has been due to some "scratch-my-head" performance because I have been pleasantly surprised in the field results. But I also haven't had the chance to get to the sites I want to compare the two coils in a black sand environment. My favorite river beaches are under 2-4+ feet of water so I am going to have to head off to some volleyball sites this weekend. Their sand is downright ugly!
I did manage to get out to a few woodchip playgrounds where I have had decent success finding gold jewelry and I have a nice #3-reading gold neck chain I'll try and attach a photo of. As others have commented, there is a little 'shift' in the segment/numeric TID of the higher-conductive coins, but it's no big deal. The mid-to-lower TID range doesn't seem to have any shift in ID but what you do notice is a little 'hotter' or better performance on the lowest of the conductive range targets. The smaller gold rings and such.
Clad Quarters, which are always a '42' with the 7.5 kHz coil, drop down one segment and ID at '39.' Clad dimes (most) and silver dimes gave me a '36' reading and a copper penny read '33' with a flicker to '36' if within a certain range. Zinc cents, were usually '27' with an occasional flicker to '30.' Most of these coins were detected in locations that had a good deal of nearby electrical interferences and that might have added to some 'flicker' responses. My Peace dollar still registers a solid '45.'
After some hunting and not having but one gold item for comparison, I gathered up some of the gold rings I had left from last years and did some on-ground comparisons between the 7.5 kHz and 18.75 kHz coils. Here is what I used and how they read:
14K baby ring w/heart .. #3 with both coils
10K ring w/Chinese writing .. #3 with both coils
14K neck chain, made in Israel, .. # with both coils
10k ring w/yellow stone .. #6 with both coils
14K 'CTR' ring .. #9 with both coils
10K ring w/blue stone .. #9 with both coils
14k w/heart & sml. diamond chip .. #9 with both coils
14k wide and thick, 2-tone ring .. #15 with both coils
I was very pleased to see the consistency in TID read-out between the two coils. The only thing I have to mentally account for are the one-segment off-reading quarters and dimes, but if I am hunting for gold jewelry, that doesn't matter.
If I am working some of the woodchip playgrounds where I average 12 gold rings a year, at least a half-dozen other gold items (bracelets, pendants, neck chains, etc.) a LOT of sterling silver jewelry and have averaged over 6400 coins per year over the last 9 years of records, then it isn't going to matter what the reading is. The woodchip and sand-filled playgrounds are easy to hunt, easy to recover targets, and produce a lot of 'keeper' finds. I usually don't use Target ID and I recover everything above iron nail rejection. With the X-Terra 50 I hunt in Pattern 1 and am only rejecting -9 and -6.
What I did take notice of in the woodchip play sites where ground mineral isn't usually a problem is that the smaller, thinner, lower-conductive targets produced a much better audio 'hit' with the 18.75 kHz coil. A very noticeable difference! Not only a brighter audio hit, but better depth on the low-end conductive targets.
As I said, most of this was done with targets on the ground and/or in the woodchip play sites. Where I had to pause for some head-scratching was when I went to hunt a more mineralized site. There are a couple of places I like to hunt for older coins and not only is the adjacent dirt mineralization high, but the site is on a rocky bluff with a lot of the rock exposed here and there through the grass.
Ground Balancing here can get a little 'touchy' with many makes and models, and with the X-Terra 50 I need to use a GB setting of #2, which is quite positive. The interesting thing I noticed was that while the 18.75 kHz coil also GB'ed at the necessary #2 setting, it was a much smoother sounding GB.
If you haven't used a Minelab X-Terra 50 and done the GB thing, then you won't know what I'm talking about, but if you have, and if you're NOT hunting in a low to moderate 'mellow ground' environment, it is quite noticeable. Mind you, due to the weather I haven't had a chance to check this out in a wide assortment of sites, but where I have been hunting with the new 18.75 kHz coil, during the GB procedure it was not as pronounced a 'warbly' sort of low-high compromise audio. All of this, by the way, was done at a sensitivity setting of '12' due to power transmission lines overhead for a large plant.
Now, I am not a dealer for any brand so I don't have to use caution when discussing different models I have compared with in order to remain 'forum specific', but I can tell you this. I am NOT going to part with my excellent Troy Custom Shadow X5 even though the 18.75 kHz frequency coil comes close to the Shadow's 19 kHz operating frequency. Nor am I going to part with my also versatile White's IDX Pro with Bill Crabtree's modifications, even though it's 6.59 kHz frequency is close to the X-Terra 50's 7.5 operating coil frequency.
Both those units have accessory coils that are smaller in size, or elliptical DD types, that provide some versatility not yet offered by Minelab for the X-Terra's. I'd love to see a nice 5"-5
