jasong

Keep in mind that the 15x12 is specifically referenced in the Minelab 7k vs 5k performance graphs so I'm guessing that might be one reason why it was used. Anyone looking for evidence of claims on those widely circulated graphs now have a video to reference as well. Agreed, great video. Not an expert here, but my experience is that coils roughly scale in equivalence by area. The area of a 15x12" elliptical is roughly equal to the area of a 13.5" round. The DOD coil is 13x14 making it's total area almost exactly equivalent to a 15x12 if you do the math on it.

Thanks for the link Reg, I'll have to register there when I get off my phone, forgot my login.

I'll be around Reno this spring/summer if you want someone to film and edit vids. In exchange for letting me take the 7k for a spin every now and then.

Hmm interesting on White's, glad to see they are still in the game. Sounds like my night just got booked up with more reading, research and probably another patent deciphering haha. Interesting times in the detector world lately. I was too young (or not born yet) to take part in any of the early PI/VLF releases, glad to be around for whatever we see in this next stage of detector technology and being part of it this time around as it unfolds.

Ok, I can kind of see where you get VLF type sensitivity and PI depth from that general idea. I'm still trying to wrap my head around why that idea is so very different than the patent though. Is there another document that you are looking at that you could share?

Interesting Hotrock.... But now I'm even more confused. It sounds like you are describing full wave rectification like is used in most AC to DC power supply converters, or am I not understanding what you said correctly? There is definitely a big difference between that and what was shown in the patent though, so that patent is not the "big picture" if this description is on point, which may be why its so hard to determine what "Zero Voltage Transmission" actually is from the patent alone. I'd love to see an actual sample waveform, definitely looking forward to hooking a scope up to the 7k someday.

What I also meant to explain there was that even though the current is always non-zero with the GPZ, the voltage itself can be zero and probably is only non-zero when the pulse itself has some sort of modulation (some series of pulses, these are kinda like the timings we know) rather than a just the constant current portion of the waveform. Which is probably also why we still have the same timings. And makes me wonder if we might see timing upgrades via program updates rather than new physical models, but that is 100% speculation on my part.

If we're just dealing with DC then that would be true but even with a pulse you have reactant components to the coil since delta functions (perfect impulses) only exist on paper. The coil has both inductive and capacitive properties that are not constant and can change due to a lot of different factors. The mag field also rings to some extent which provides another AC component to consider, though a big part of their invention I believe is to reduce this effect so that the coil is always in a critically damped state, but even then we still have AC components since it the coil still has a finite decay time (it's physically impossible not to, I believe). So even in the case of a pulse we still have to look at the entire system from an AC perspective, and voltage and current can be out of phase with each over an inductor in AC and voltage can be zero when the current is constant. That's where you get V = L*(di/dt). di/dt is the derivative of the current with respect to time, in other words - what is the rate of change of current over time. I ignored L (inductance) for simplicity sake since it doesn't change the real important part of it all, which is that when current is not changing, ie has a rate of change equal to zero, then voltage must be zero. So, that's why in the sample waveforms you see the current staying at some non-zero value at all points during the operation of the detector. Another way to look at this, which to me was one of the most interesting things I ever learned in school, is from a Fourier perspective. Any pulse, and even more generally any waveform (even a square wave) can be broken down and described in terms of an infinite summation of sine wave of varying frequencies. I can almost guarantee part of the programming in the GPX and GPZ uses Fast Fourier Transforms to analyze the RX signal, a lot of MCU have the capability built right into the chips these days.

I like electronics like some like cars. Love driving them but love taking them apart and modding them too. Well actually im more like the guy that stands with a beer watching the real mechanics work and manages to pick something up here and there. Eurodigger - I couldnt even begin to answer that question with any authority or experience but if you want a guess I would say no. Or at least not without serious reprogramming and modding. But again im like the guy holding the beer not the wrench. And sometimes people manage to find a square to fit a circle hole, but more often something just breaks. Patents are intentionally vague and confusing so its also like trying to draw a recreation of a painting by only looking at small patches of the original. What may look like an orange could actually be a star among a galaxy.

I spent some time reading the US public patent document last night and I think I have a very basic idea and perhaps not fully correct of how that coil works now. They use one (or both, the patent isn't clear) of the D's to monitor changes in the TX coil due to varying ground permeability aka mineralization and then use a negative feedback amp to keep the current constant in the TX since the reactance of the coil changes as you move over different ground or targets. So that basically ground noise and effects are nulled out constantly at what the monitor sample rate is. I think that's also where they get the term Zero Voltage Transmission since V = 0 when absolute value of di/dt > 0, but I'm not sure about that and abs(di/dt) > 0 is only true when speaking in terms of averages which they do explain. I can't figure out if I am missing something on understanding the bigger ZVT picture though or if it's kinda a semantics thing? You can see in the provided sample waveforms there is always a non-zero current present which differs from traditional PI designs. The other net effect is that the coil remains in a critically damped state more or less constantly rather than changing as you swing and thus interefering with the decay time and thus the RX sampling period as with a traditional PI - a simple way to think about that is if your coil is still ringing during RX sampling then you have a hard time listening for target responses. It seems like that is where they are able to sample and detect lower conductivity or quick decay rate gold targets maybe? So it's kind of a mono coil but not, and kind of a DD coil but not. Looking at the sample waveforms and their description it looks like a PI in theory still, but kinda not too. Also, there is a point made about programs and updates in that document. Which leads to some interesting speculations about future models...maybe just program updates? No idea at all, just guessing. Am I understanding all this correctly or have I steered awry somewhere? Getting through the patent legalese speak is kinda tough in that document for me.

I wonder if we're gonna start pulling lots of deeper meteorites up now too that got missed with PI's with the increased sensitivity to lower inductance and lower conductivity gold seems like it might be a possibility. Wish I could sell them like gold.

Hey Klunker, I may take the plunge on a 7000, want a make a deal after I'm done cherry picking my old patches if so? Only semi-joking, I gotta pay this thing off quick if I were to buy it. I'm scared to see how much accesory coils cost because if I do buy it that 14x13 just doesn't cut it in a lot of places, and I won't have much to spend on the coils I need after that big purchase. If coils are like $1000 or something crazy that might kill it for me...waiting with crossed fingers.

BD, did you get your hardrock operation going? I have a question, I built a 4" impact mill and while my screens don't go down far enough to know for certain, I have a lot of 200- mesh crushed ore, maybe even closer to 400 mesh, it feels like very fine ground flour. Net result is it basically turns the water to a slurry even with stuff like Jet Dry, etc. It's hard just to pan, let alone sluice out so it's way slow going. Trying to stay away from amalgamation or cynadization since it's all free milling gold but I can't figure out any better solution. Mill pounds gold to tiny little spheres so something like a miller table is a no go since it rolls right off. Thinking of a wave or shaker table type setup but it's pricey and I'm not sure the slurry solids drop out in that a whole better than a sluice anyways. I remember the old mongolian miner threads with the pop and son sluices and stuff but I'm having no luck with those at all, can't get the slurry to drop out enough for any kind of riffle to be useful. Thanks for the refiner input guys, recommendations go a long way in businesses like that.

Thanks, coincidentally I'll be in Portland shortly so I can stop by in person which is preferred.

Thanks for replies. One last question, generally speaking how much better is the noise/interference cancelation abilities? If you still have the machine could you for instance tune out noise standing directly under or fairly close to a transmission power line?

I'm not prefacing it by implying I won't believe the answers at all, in fact I've been reading your detector reviews since you started writing them back on the AK forum. However, I've asked questions like these in many places and many forums for many machines and more often than not received responses from people saying depth tests mean nothing, or you can't fairly compare X machine to Y machine, etc without receiving an actual answer. Which is why I tried to tiptoe around it by saying I know these are controversial. But apparantly that approach doesn't work either.

I'm ultra sketched out mailing off big slugs but the time has come and needs to be done. Anyone out there using a refiner they've done business with and trust? Some of the joints I found online look fly by night and none are close enough to visit in person (actually some don't even allow visits). Hoping someone out there has some positive experience.

On normal nuggets that the old GPX series hits on solid and strong and in fairly neutral to mild ground, are depths/sensitivity essentially equivalent between the 5000 and 7000 given a 14" RM? Even if it's a slight difference is it more/less sensitive in these conditions? I do understand the point of the articles where the 7000 really shines on the stuff GPX's didn't hear and it's raising my eyebrows, but I still need to understand this bit here if it were to be my full time detector. I don't want to sell my GPX and then discover I'm missing stuff I used to hit with it and be back to square 1. I'm sure a number of other potential buyers are thinking the exact same thing even though I feel this question may be met with some reservation since I'm sort of side stepping the 7000's moment to shine as a unique star, but... Have any quantitative tests been done?

Very interesting, thanks to both of you. You stated PI had reached it's limits, knowing what you know about the 7000 do you think the ZVT technology has room to grow? Also, coils: whats the story with this detector and coils? Is there the potential for an aftermarket or is there anything like a chip that makes them Minelab only? Is there a limit to how slim an elliptical coil can be, does that main central winding need to be more or less round for some reason or another? How is it swinging this thing all day? Does the added weight bear down on a guy even with a harness and bungee? Having never used a CTX is the new form factor better at carrying the weight? For shallow stuff (small, spongy, crystalline, etc) how does the 7000 compare to a good VLF like the GMT or GB2? I know people won't like this question for a long list of reasons but it's inevitable so I'm asking.

Was thinking the same thing, free trip down under always wanted to try detecting there, plus a bit of room and board on top of that... Anyone know if there is like some sort of export tax or other hangup that'd raise the price?

Gold with a bad camera white balance setting? Maybe lead or rusty tin bits? Yep, notoriously hard to ID stuff from photos.

Wow, nice. Looking forward to trying one of your machines.

Judging by the lukewarm to cold response so far maybe the next contest question should be how many months until minelab lowers the price. And bonus question how many thousands of dollars do they take off? Really surprised the gag order is still in effect now. If you want to kick someone right in the wallet you should probably hang a carrot in front of their nose at the same time so they dont pay as much attention...

My bread and butter are nuggets 5 grams or under. In light of that and looking at this chart again, the SDC apparantly gets up to 25% depth increase over the 5000 w/11RM which is not far off from the performance they are quoting for the 7000. Is this like only for extreme boundary conditions like ultra spongy or specimen gold, or does the SDC actually hit deeper on a 4-5 gram normal nugget? The small text states "typical conditions" so I'm assuming no crazy ground. Finding that hard to believe but I've not used an SDC. Just curious because that metric also appears to be the same one they use for the "up to" 40% increase on the 7000.

Well, Kellyco has it listed today on pre-order for $9,999 USD. Hopefully that's just an error. Any other US dealers have a price today?