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Geotech

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Geotech last won the day on November 9 2023

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    Republic, WA
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    Designing metal detectors

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  1. Apparently Republic is the gold capital of Washington State. 8 million ounces and still going. But few places for prospecting, it's all deep hard rock stuff. Almost ended up in White Salmon, gorgeous area.
  2. I posted a reply to Woody's video. The ferrites shield the solder connections so they don't light up with sudden changes in ground mineralization. Woody mentions this late in the video but doesn't seem to think that's what they're for.
  3. The core purposes of VFlex were (1) to transmit coil parametrics (like "this is a 10" DD coil optimized for 18kHz") to the control box and (2) to use a security check to limit 3d party coils. Whether or not #2 was an afterthought I don't know, but I suspect it was planned and deliberate, as it was for printer cartridges. A great way to limit competition. Otherwise, a simple resistor in the coil could be used to ID the coil type. The inclusion of a preamp in the coil might be considered part of VFlex, but in reality it has nothing to do with the micro that is the at core of VFlex. That is, you can do VFlex without the preamp in the coil, and you can put a preamp in the coil without the micro. But if there is no micro in the coil, then there is no VFlex. I don't recall that the original Go-Finds used VFlex, but the newer models apparently do.
  4. LMAO, I like that the coil appears to have a metallic housing. I would design it with vibranium, besides being durable it does not support eddy currents so is not detected.
  5. Placing the preamp in the coil improves noise immunity because the RX signal from the coil to the control box is now driven by a low impedance and has also been gained up. Minelab started this with the original X-Terras (30/50/70) and I assume all their detectors are now designed this way. I'm not sure if Garrett or Nokta do this, and XP obviously does.
  6. Looking for an 8x9 and 10x12 that will run on the 10/12 kHz models. Might also consider 17kHz coils.
  7. No, digital components don't change with age. The newer detectors still have 3 elements that can change, though: the coil, the preamp, and the ADC. The ADC and the opamp used in the preamp are pretty stable. The coil can shift over time, but that will mostly change the null and affects the point where it overloads, but depth should not vary. The preamp has resistors and capacitors, and that's mostly where depth variation can occur. Ironically, many newer designs place the preamp inside the coil so replacing the coil might be the solution if depth degrades.
  8. Some fantastic caches have been found hidden in old homes, in walls and floors, attics, and buried in crawl spaces. Especially if it dates to the Great Depression. I know a guy who metal detected a burned-down house site, found gobs of silver coins and ingots that apparently had been in the walls. Another fellow I met had purchased an ex-grocery store building, found a big cache of silver dollars that were hidden by someone who worked there, went off to WWII and never came back. I would turn the sensitivity down to a minimum, even a small cache in the wall will sound big. A large coil will help minimize small targets like nails. Look for a strong localized target that seems out of place.
  9. I've never seen a screen cover "go bad." However, the display might. It's not clear when you say "the face don't light up very well" whether you mean the backlight isn't working well or the display itself is faded. But both can happen. Also, indoors it can be hard to read without the backlight. So first, I would take it outside or make sure the backlight is on. Next, I would pop off the pod faceplate (it snaps on) and look at the screen without the screen cover.
  10. In a detector with only a single GB channel (like the TDI), it is possible to find a small range of conductivities at the conductivity transition point that are severely suppressed. When I air test the SDC with a continuous array of conductive targets, I can easily find the two transition points between the three regions. I could not find any range of suppressed targets with the SDC, target detection through both transition points was quite good. This tells me that the mathematical target holes are filled in. Again, that's in air. If particular targets are then lost in particular ground, then that could be due to the way the tracking algorithm is working, rather than the mathematical target hole. I suspect the same thing would happen in a multiperiod detector. In other words, you can eliminate the mathematical target hole with either multi-TX or multi-RX, but you will likely still face the same issues with certain targets in certain ground. I can see calling that a "target hole" but it may be a completely different issue.
  11. Just saw this thread, and then read the older thread with Brent Weaver's video. I disagree with Brent (and so does Minelab, apparently) and posted a response in the older thread. In any case, once you have a "hole-less" detector, the channel responses can be used to extract a conductivity VDI, as the E1500 apparently does (I don't have one so I'm speculating). But this does not necessarily give ferrous discrimination as ferrous eddy responses can mimic nonferrous eddy responses. Steel bottle caps, ferinstance. But I'm keen to learn more about what the E1500 can do.
  12. This was linked from another recent thread, and I don't recall reading it before. So another better-late-than-never reply. This is not necessarily true. The SDC2300 is a single pulse detector and it has no target hole. The reason for a target hole is that eddy responses have an exponential curve and viscous ground responses have a power law curve. A "single channel" GB detector takes 2 samples of the response curve, and 2 samples (basically a straight line) are not enough to distinguish the two types of curves. Therefore, there will always be a 2-point eddy response that matches the 2-point ground response, and this gives you a target hole. The target hole can be moved around in a number of ways. Changing the TX pulse width will do it, but so will changing the sample timing or even the bandwidth response of the preamp. So, as Brent says, you can create a detector that transmits 2 different pulse widths, with their own RX channels, and they will have target holes at different places so that, when combined, there is no overall target hole. But you can do the exact same thing with a single pulse detector, by creating 2 RX channels that place the target holes in different places. Again, this can be done by using different preamps, or by simply creating 2 channels with different sample timings. Normally, each channel takes 2 samples but they can be combined. Above I said that 2 samples are not enough to distinguish the two types of curves... but 3 samples are. You can create a first channel that takes Sample1 and Sample2 and this will give you a target hole, call it Hole1. Then you take Sample1 and Sample3 and this gives you a different target hole, call it Hole2. Combine the 2 results and there is no hole. You can actually hear this result in the SDC as it gives a wee-woo response for very low conductors (below Hole1), a woo-wee response for medium conductors (between Hole1 & Hole2), and a wee-woo response again for very high conductors (above Hole2). All with a single TX pulse width.
  13. Offhand, I can't think of a PI design that will be damaged by turning it on without a coil connected. In fact, it would be engineering malpractice to release such a design. In designing and building PI circuits, I hot-swap the coil all the time and don't think twice about it. That said, I suggest following the manufacturer's recommendation.
  14. I just checked out the new forum. There are 6 threads, and 3 of them are spammers. If you're gonna run a forum, you gotta stay on top of it. Not only being vigilant with spammers, but also by stimulating conversations and keeping the personal sniping under control. I enjoyed Dankowski's forum in the past but it's really lost the plot and everyone seems to have left. I doubt a new forum script will fix that.
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