Jeff McClendon Posted April 21, 2023 Share Posted April 21, 2023 I don't like how metal detector companies have used the words Noise Cancel for a process that at best is only Noise Reduction. I have owned single frequency VLF detectors that operate at 15 kHz or less that were absolutely unusable at some local sites even 10 years ago. These detectors only had very slight frequency shifts which helped very little. Using them now would be a joke. The same goes for all of the pulse induction detectors that I have ever owned. If you think EMI is bad using a VLF at a site, try using a pulse induction detector with a mono coil at that same site. The only recourse is to try an Anti Interference DD coil which will significantly reduce EMI interference but also overall sensitivity too. I have used all of the Vanquish models, the Equinox models, the Legend and Deus 2 at the same sites I referenced in the previous paragraph. If I insist on running them at maximum sensitivity, I won't be able to distinguish between random EMI audio responses/target IDs and actual target responses no matter how many times I do a noise cancel (reduction). I can switch to 20 or 40 kHz single frequency and crank up the sensitivity some BUT due to ground mineralization, I will lose a ton of depth and target ID accuracy. So, instead of freaking out or thinking a bunch of negative thoughts, I just lower the sensitivity and stay in the most quiet simultaneous multi frequency mode available that I can find and start detecting. 3 Link to comment Share on other sites More sharing options...
Past Member Posted April 21, 2023 Share Posted April 21, 2023 Jeff, The more posts I read of yours, the more I'm grateful that I don't have to deal with the hot ground that you do. It seems that under your ground conditions, and on the high EMI sites, using a single frequency to stabilize the detector due to EMI, isn't even a viable option. Ouch. In your EMI sites and SMF mode, by about how much are you having to reduce the sensitivity to stabilize your detectors? Link to comment Share on other sites More sharing options...
Jeff McClendon Posted April 21, 2023 Share Posted April 21, 2023 1 hour ago, Digalicious said: Jeff, The more posts I read of yours, the more I'm grateful that I don't have to deal with the hot ground that you do. It seems that under your ground conditions, and on the high EMI sites, using a single frequency to stabilize the detector due to EMI, isn't even a viable option. Ouch. In your EMI sites and SMF mode, by about how much are you having to reduce the sensitivity to stabilize your detectors? I can run them between 70 to 90% of maximum and they will be quiet enough to detect with using most of their SMF modes. Running Deus 2 at 90% using the 9" coil is like running my Equinox and Legend at 80% using their 11" coils as far as the EMI interference experienced. I can run the Legend and Equinox up to 85% using their smaller elliptical coils at those sites. All three detector models do not have the same base sensitivity/gain just like they don't have the same sensitivity increment levels. The Equinox models in general are much more sensitive to actual smaller sub gram targets (which includes EMI and ground noise) with the Legend being a little less sensitive to the same targets and Deus 2 even with the 9" coil being significantly less sensitive to the same sub gram targets. So, it doesn't surprise me to hear Deus 2 users reporting less EMI compared to the Equinox and Legend. Whether that is because Deus 2 has better shielding, lower overall gain, a combination of both or some other X factor.......who knows. 1 Link to comment Share on other sites More sharing options...
Past Member Posted April 21, 2023 Share Posted April 21, 2023 10 minutes ago, Jeff McClendon said: I can run them between 70 to 90% of maximum and they will be quiet enough to detect with using most of their SMF modes. Running Deus 2 at 90% using the 9" coil is like running my Equinox and Legend at 80% using their 11" coils as far as the EMI interference experienced. I can run the Legend and Equinox up to 85% using their smaller elliptical coils at those sites. I previously mentioned coil size in mitigating EMI. In my experience, going from the 11" round coil, to the smaller elliptical, has a huge impact on reducing EMI noise. I would estimate a 75% reduction. For example, when I do EMI tests in my backyard near those three high power lines, I pretty much have to use the round 11", becuase the smaller elliptical coil picks up so little EMI to begin with, that testing with it wouldn't provide very tangable results. With that said, I also wonder why exactly the smaller coils are less suspectable to EMI. More specifically, is it simply a matter of the small coil's much tighter field being more "closed" and impenetrable to the EMI? 2 Link to comment Share on other sites More sharing options...
CPT_GhostLight Posted April 21, 2023 Share Posted April 21, 2023 3 hours ago, UT Dave said: So far, for me in my urban parks the Manticore does seem to handle EMI quite noticeably better than my Nox 800. I have not had them both out at the same time to compare though. But in a couple of parks where I have had to run the Nox in 20Khz and lower sensitivity below 20, I have been able to run the Manticore in SMF at 20+. Actually have not had to leave SMF in a park with the Manticore yet. Which is quite different than I was accustomed to with the 800. I speculate it's got to be more than just the long press, which I believe simply automates the process of running through the channels looking for the quietest one. Pure speculation but because the Manticore does seem so much better, I think there has to be more to it. Perhaps the increased TX improving the signal to noise ratio? I was expecting Manticore owners to chime in here as much of the new patented coil design of the M-Core was designed to help fight EMI. I suspect a lot of their new designs incorporate EMI mitigation to compensate for their higher transmit power. 1 Link to comment Share on other sites More sharing options...
CPT_GhostLight Posted April 21, 2023 Share Posted April 21, 2023 28 minutes ago, Digalicious said: I previously mentioned coil size in mitigating EMI. In my experience, going from the 11" round coil, to the smaller elliptical, has a huge impact on reducing EMI noise. I would estimate a 75% reduction. For example, when I do EMI tests in my backyard near those three high power lines, I pretty much have to use the round 11", becuase the smaller elliptical coil picks up so little EMI to begin with, that testing with it wouldn't provide very tangable results. With that said, I also wonder why exactly the smaller coils are less suspectable to EMI. More specifically, is it simply a matter of the small coil's much tighter field being more "closed" and impenetrable to the EMI? There has been much discussion posted about how small coils handle EMI better. It's mostly physics. Smaller coil, less ground and EMI samples to analyze, less filtering required by the processor, more efficient operation. Link to comment Share on other sites More sharing options...
Past Member Posted April 21, 2023 Share Posted April 21, 2023 4 minutes ago, CPT_GhostLight said: There has been much discussion posted about how small coils handle EMI better. It's mostly physics. Smaller coil, less ground and EMI samples to analyze, less filtering required by the processor, more efficient operation. Ok, but doesn't all that fundamentally come down to the effects of a tighter and smaller field? On a similar note, I see so many posts on other forums and Facebook pages, in which the hunter is using a stock 11" round coil (or larger) in a high EMI and park like trashy site, then asks what to do about the EMI noise. The typical replies I see to such scenarios, is to lower the sensitivity or use a SF. But a better solution for that scenario, would be to use a smaller coil such as a 9x6 or 10x5. Those coils won't be nearly as suspectable to EMI as the 11" round coil, will have much better unmasking and separation characteristics, and the sensitivity won't have to dropped nearly as much. Link to comment Share on other sites More sharing options...
Jeff McClendon Posted April 21, 2023 Share Posted April 21, 2023 16 hours ago, Digalicious said: Thanks for the video Vanquish / Nox video Phrunt, but honestly, I'm not sure what it accomplished ? EMI audible noise is often reduced when the coil is on the ground, and you keep moving the nox's coil from on ground to in air. You also do a noise cancel, then as soon as it is finished, you immediately start pushing buttons / changing modes / settings...whatever. A true test of noise cancel abilities, is having the coil away from the ground and stationary (which is exactly what the manual says to do). Then, press the noise cancel button, and without moving the coil or pressing any buttons, see if the noise is reduced. That's the type of video that I can't find. In fact, all I have ever seen from the You Tubers, is that they do the noise cancel correctly, but it does basically nothing. Granted, if someone did post such a video, I would also wonder if the noise cancel is actually "cheating" in one, two, or both of the ways I described in one of previous posts. Like Chase mentioned, I would rather detect than make a video and suffer the consequences of having someone critique it the way Simon's was above. I am not seeing anything wrong with Simon's videos by the way. They do show a noticeable reduction in audible and visible effects of EMI. Thank you Simon for posting them. 3 1 Link to comment Share on other sites More sharing options...
jasong Posted April 21, 2023 Share Posted April 21, 2023 56 minutes ago, Digalicious said: With that said, I also wonder why exactly the smaller coils are less suspectable to EMI. More specifically, is it simply a matter of the small coil's much tighter field being more "closed" and impenetrable to the EMI? It's because coils are antennas too, meaning they can couple with both magnetic and electric fields. Generally, with loop antennas for receiving EM radiation, the rule of thumb is that bigger diameter = more sensitivity. It's more complicated than that since certain sizes/shapes are more sensitive to certain frequencies, 1/2 frequencies, 1/4 frequencies, etc, but that's a basic idea anyways. Close to a loop, the magnetic field dominates, and sensitivity is a matter of flux density, so smaller coils are more sensitive to smaller targets, but less sensitive to EM. Well, with PI's anyways, I don't know a lot about VLF's, but a loop is a loop. I think a lot of research could be put into reducing noise just with proper coil design. Some detectors seem to still be using generic sorts of coils from decades ago that appear to have very little modern design consideration for EMI reduction included. For top tier detectors (definitely the $6-$10k gold detectors anyways) I think the entire control unit should be carbon fiber too. Both for weight reduction, but also because it's conductive and thus has the potential to act as a shield itself. I can detect my phone while off next to the side of the 6000 control box, it clearly lacks any shielding at all. Same for coils, for PI's anyways, I'm curious if carbon fiber tops/sides and plastic bottoms might be a good method to shield without gaining weight - maybe even losing weight. This is stuff I've mentioned for over a decade though - knowing Minelab reads the forums - and they don't seem to do it ever though, so maybe it just doesn't work. I think the whole concept of a "noise cancel" button is obsolete though. Modern computing power is in abundance for cheap on chips today. No reason EMI filtering/noise cancelling/channel scanning can't go on in the background 24/7 and auto adjust as needed rather than press a button. IMO anyways. 3 Link to comment Share on other sites More sharing options...
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