Geotech

All the last-generation Tesoro designs had digital audio.

I can't speak to what coils might be available. The only ones mentioned so far are the 8" (stock, I assume) and a 12", both solid disc style. There is nothing to prevent aftermarket coils but they are difficult to make and with a much smaller market share we'll see if anyone jumps in. But right now we need to finish the design and then see if FTP can manufacture it.

No,we will at least build out the remaining 40 or so we have parts for and then decide where to go with it.

The beach version is what Alexandre had focused on and was ready first. It did not have the small sensitivity of the (e.g.) SDC2300 and we didn't know how tough that would be to solve. Turns out dropping delay from 7us to 3us wasn't as hard as I feared, although it remains to be seen if FTP can manufacture it.

It is light and a breeze to swing. No idea on the price, that hasn't been decided yet. I've lobbied for $2k. No discrimination, it happily finds those rotten can flakes. In most places I did not find the manual GB to be an issue. But in one locale the ground varied by the meter and I found myself tweaking the GB every few swings. Once I swap the locations of the fine/coarse knobs then it will be fairly easy to use the thumb to tweak the GB control on-the-fly. As I recall, the QED has to be placed in a particular mode to adjust GB which makes it difficult & tedious. Impulse GB works in any mode.

It's strictly manual, no grab. GPX coils might work (I haven't tried it yet) but you won't get the minimum delay of 3us using them.

It's my understanding that the AQ will resume in the next 1-2 months. It will not have the drop-in batteries but will still have the clip-on NiMH pack. I finally got the green light to take the Impulse/Gold out for a field test, did so a few weeks ago in N. California. No gold but numerous small lead and quite a bit of rotted tin can flakes. Found some rough edges that need polishing but overall it performed very well. Very light & balanced, a pleasure to swing for hours. It does have the tube batteries, per Joe's photo above, and 8" solid coil. Small gold sensitivity is pretty much tied with the SDC2300, Impulse may go a little deeper on gram+ nuggets. Biggest drawback is the Impulse is currently manual GB only. Question is whether to finish what we have & release, or develop ground tracking for it.

I lived in Greensboro for many years and walked the tracks in the McLeansville area. Quite a bit of the trackside property is wooded so you're not gonna drag a PI mat around very well, and all of it is private land. But the biggest obstacle to finding this treasure is that the story itself is fake. There was no Civil War gold train and there are no pots of gold. The story originated in 1969 in True Treasure magazine which published mostly fabricated treasure stories. People like Jameson repeat those stories for the purpose of selling books.

It's a souvenir shop ring, off one of those carousels that have a couple hundred common names. Next to the keychain carousel and fridge magnet carousel.

No idea, I don't have one.

Please don't tell anyone (we're trying to keep it under wraps) but that spiffy new coil is available on Amazon: https://www.amazon.com/Fisher-inch-Coil-Triangulated-Bi-Axial/dp/B09SNVRXHC Apparently only at Amazon, as far as I can tell. Limit 2 per person. If anyone can purchase, on the open market, the new Fisher MF detector in 2022 I will send them one of my paychecks. Offer good for the first person who can show proof-of-purchase. I'm not sure why we keep aiming for the foot and pulling the trigger but it sure makes for sore feet and a red face.

I still like lead shot for a target standard though it certainly has more variation than I expected. I recently made another batch of test paddles and measured the pieces to find close-to-nominal weights, ferinstance 0.75gr for #9. Lead shot does have a few percent antimony so, no, it's not pure. BTW, lead shot is made by dropping molten lead inside a tall "shot tower." Making tiny solder spheres by hand is durn near impossible. And you'd still have to make a whole bunch and weigh them all to find the perfect size you're looking for, assuming a standard gets established. Copper wire bits will also work for test targets. Alloy and diameter are nicely consistent but length may not be, especially for very short pieces. As a piece gets longer, orientation can make a difference and orientation effect can differ with mono, concentric, and DD coils. I also use aluminum foil pieces, 25x25mm squares stacked to various thicknesses, plus 10x10mm and 5x5mm for "tiny" targets. To compare results with someone in, say, New Zealand would require that our household aluminum foil has the same thickness. Not sure that is so. All-in-all, coming up with a perfect target standard ain't easy. Everything has pros & cons.

As you lower a coil to the ground the ground signal produces a stronger & stronger response because it upsets the induction balance of the coil. When you get down to the last inch or so the effect can actually reverse and the RX signal decreases a bit. To make things worse, in some coils it also causes a slight phase shift that messes up the GB. This can produce ground noise. Generally only a problem in bad ground. Concentric coils are the worst because the TX coil and the bucking coil respond differently to ground vs height. DD coils are better, 00 coils even better. Mono coils don't have the problem at all. You are right, the curvature of the TX coil means that the TX field density (and curvature) changes along the length. Larger deep targets will respond best at the center and you might find that the tiniest targets are only detectable near the ends. Moderate not-too-deep targets will have a more even response. Speaking of brooms, the Tesoro CleanSweep coil is the only DD-style coil I know of that has both a straight overlap and rectangular coils with no curvature. It should produce the most idealistic response you want. Some people hang on to a Tesoro just because of this coil. I have.

TG, the difference in overlaps is a trade-off between depth, coverage, and pinpointing. Yes, the straight overlap will be a bit more uniform in coverage but depth will still roll off as you get near the ends of the overlap. That is, it's not perfectly uniform all the way, end-to-end. The football overlap has less coverage but will get a little more depth at the center. It's front-to-back roll-off is more severe which can make pinpointing easier when X-ing the target. In severe soils, coils with harder radius changes will also exhibit a stronger lift-off effect. The Thunder will therefore be worse in that regard while a football overlap will be better. The double-0 SEF coil is even better as it has a very broad radius change.

If you have the 12" coil it floats like a cork. And because it's air-filled you only need to take it a few feet down for it to flex, crack the seam, and flood with salt water. Then it's a goner. The main case is pretty stout and as long as you take care of the Hexseals on the controls it will probably survive 100 ft. For a while White's made a diver version of the SMPI with a weighted loop. I had one but sold it.