Will The Next Gen Detectors Address Emi ???

[jasong]

The auto-adjustment on the GPX 6000 definitely uses sensitivity decrease to deal with EMI too. Down to unfortunate levels in some cases, it seems.

Hopefully better methods emerge, but I guess if R&D ends up decreasing due to less demand, they may not. I think the general idea with noise reduction in the future should be to lower the noise floor so you can boost sensitivity, not lower it. Approaches that lower sensitivity just seem like a temporary bandaid and not a longer term solution.

[GB_Amateur]

41 minutes ago, jasong said:

The auto-adjustment on the GPX 6000 definitely uses sensitivity decrease to deal with EMI too.

Does it reveal it's doing that?  This idea being blasted that Noise Cancel on the ML Manticore is secretly reducing the sensitivity (note:  on the Manticore the 2 digit sensitivity value is always on display on the left side of the screen and I've yet to see that value go down when I do a long Noise Cancel procedure -- has anyone??) seems over the top, to put it mildly.

A lot of the accusations being hypothesized here about the Manticore can be tested by the antagonists.  I'd like to see more of that compared to the current unsubstantiated accusations.

[jasong]

18 minutes ago, GB_Amateur said:

Does it reveal it's doing that?  This idea being blasted that Noise Cancel on the ML Manticore is secretly reducing the sensitivity (note:  on the Manticore the 2 digit sensitivity value is always on display on the left side of the screen and I've yet to see that value go down when I do a long Noise Cancel procedure -- has anyone??) seems over the top, to put it mildly.

A lot of the accusations being hypothesized here about the Manticore can be tested by the antagonists.  I'd like to see more of that compared to the current unsubstantiated accusations.

No, the 6000 doesn't reveal any specifics because all it's settings are hidden. But auto reduction of sensitivity, auto adjusting ground balance, etc that's the general concept behind "Geosense". Plus it's easy to test, and I've tested it and witnessed the sensitivity decrease firsthand. Anyone else could do the same with this machine, it's instantly observable, though the degree to which it auto adjusts and how long it retains those adjustments has so far been semi random from what I can tell.

That said, I'm just talking about the detectors I own and use, I don't know anything about the Manticore or any other recent VLF releases from other companies either.

I'm also not talking about noise cancels specifically in my prior posts, I'm talking about a range of topics. In terms of anything Manticore specific, I'm not the one to talk to. The topic was next gen detectors in general though, which is why I was speaking about machines other than the Manticore or whatever other VLF's people are talking about in the VLF world that I'm not connected to much.

 

[Digalicious]

59 minutes ago, GB_Amateur said:

Does it reveal it's doing that?  This idea being blasted that Noise Cancel on the ML Manticore is secretly reducing the sensitivity (note:  on the Manticore the 2 digit sensitivity value is always on display on the left side of the screen and I've yet to see that value go down when I do a long Noise Cancel procedure -- has anyone??) seems over the top, to put it mildly.

 

My suggestion was that the lowered sensitivity would be at base level, not the visible sensitivity. In addition, I suggested that noise cancellation may also be accomplished by heavily weighting the SMF toward 1 frequency. For example, let's say SMF is transmitting and receiving at 5 khz and 40 khz. So for noise reduction, instead of processing and adding together both of those frequencies equally (thus doubling the EMI) the algorithm could process 90% of the 40 khz, and 10% of the 5 khz. That should eliminate a lot of the EMI, while still maintaining some sort of SMF semblance.

[GB_Amateur]

50 minutes ago, jasong said:

No, the 6000 doesn't reveal any specifics because all it's settings are hidden. But auto reduction of sensitivity, auto adjusting ground balance, etc that's the general concept behind "Geosense". Plus it's easy to test, and I've tested it and witnessed the sensitivity decrease firsthand. Anyone else could do the same with this machine, it's instantly observable, though the degree to which it auto adjusts and how long it retains those adjustments has so far been semi random from what I can tell.

The 6000 is so unknown to me (Condor let me use his last June, but I didn't even try to change any settings) that I've gone far enough with questions about it here.  (Kinda like your lack of familiarity with the Manticore.)  It's not even obvious to me that noise reduction on PI's is similar to noise reduction on IB's.

FWIW, I point out that your scientific approach to testing and being able to back up what you say with more than just speculation (or you admit you are speculating) is the kind of approach that makes this site worth reading.  I can be (overly?) skeptical of posts as I may have sounded regarding meteorite availability but that is just an attempt to get some answers for questions that remain in my mind.  (And you're a good person to ask....)

[jasong]

Yeah I was just commenting in this thread because lately it's only recently that I've seen anyone but myself beat the drum for EMI/noise reduction in the forefront of newer detector tech developments on new machines and being something to really discuss. It's something I've been saying and asking for for over a decade though. And I'm passionate about it because after a tally, I'm around $25k spent on metal detectors at this point, and probably about to be $35k after the new 8000 (or whatever) comes out, so I'm getting impatient. 😄

So I wanted to add to the discussion here too because usually when I've mentioned similar things in the past it's mostly ignored or a few lukewarm responses at best, but now people seem to be paying attention. Maybe a manufacturer is too, who knows.

That said, I am going to buy a Manticore or 900 or something, maybe just an 800, here soon for gold prospecting and to detect old abandoned cabins and investment property yards. So I hope I can get a bit more up to date on them by this summer too.

[phrunt]

My guess is they're not lowering sensitivity with noise cancels on any of these SMF VLF detectors, I am sure they'll be using the old tried and true frequency shift method which for a SMF should be an easy task.  I'm sure Minelab added 4kHz single frequency to the Nox as 5kHz was a bad choice for EMI in many locations.  I can use 4kHz fine, 5kHz not so much. 5 and 10kHz seem to be my nasty EMI frequencies. 4, 15, 20 and 40 are fantastic.  Yet in SMF modes I can use them all and get near maximum sensitivity after a noise cancel, usually 23-24 out of 25.  The XP Deus has been really able to help me narrow down bad frequencies with it's fine adjustments.

If they are lowering sensitivity I sure can't notice it, I can find tiny specs on nuggets and deep coins with no noticeable difference in performance doing any number of noise cancels even in relatively high EMI areas.  I often detect for nuggets under high voltage powerlines and rely heavily on noise cancels on both PI's and VLF's and can't see any performance difference before or after a noise cancel. in fact often the performance improves after a noise cancel as less EMI for me = more depth or better tiny target sensitivity.

The GPZ appears very different, it has channels and just scans between them for the cleanest, and I honestly believe the GPZ noise cancel works very well, it's slow, but good.  Of course they can't use this method on a VLF being so different.

Note how they want it held up off the ground horizontal, and you are advised to stay still while doing it. 

[Jeff McClendon]

Back when I only used a VLF detector for gold nugget/follow black sand prospecting (I just didn't even consider coin/jewerly relic detecting...duh!), I used a Tesoro Lobo, then a bit later a Lobo Super Traq, then finally my first detector with a display-Garrett AT Gold. The Garrett AT Gold was also the first VLF detector I owned that had any kind of frequency shift. At the time, that feature was advertised as being added to help with multiple detector cross-talk. I also had a Minelab GP 3000 pulse induction detector for many years since I thought analog was just better...........it had an AutoTune feature that was specifically used for EMI mitigation even back in 2003. Other detectors may have had features like that before then. I just don't have any experience with them.

So, addressing EMI has been going on for a long time in detector land for those of us that use pulse induction detectors.

Completely eliminating the presence of EMI in the return signal.  I don't know if that is possible or even synonymous with high gain-highly sensitive detectors.

Has recent/current detector EMI mitigation engineering had trouble keeping up with the huge proliferation of human produced EMI? Absolutely.

Most detector manufacturers are making VLF and Pulse Induction detectors that are more versatile in terms of the wide range of target size and conductivity that they will detect along with the wider range of soil/beach conditions that they can handle easily. Some of that wider range of soil and beach handling is done automatically in the background by adjusting sensitivity levels like with the Equinox Beach 2 and with the GPX 6000. Then there are all of the soil timings, etc on some Minelab PIs. There are other detectors that can do that too probably that I don't know about. 

The GPX 6000's Auto and Auto+ automatic modes do regulate sensitivity without any input from the user. Reading through the GPX 6000 manual however and from my experience, the only tools for EMI mitigation are frequent use of the Noise Cancel button, lowering sensitivity and switching to its DD coil which automatically puts the GPX 6000 in Cancel mode with atmospheric interference versus salinity interference being the recommended nuclear option.

I rarely use the GPX 6000's Auto mode unless I am relic hunting in an area with lots of mineralization and EMI and I am just after multi gram sized objects. Using Auto is definitely a form of target size discrimination. If Auto and GeoSense by themselves were specifically designed to reduce EMI, I can't find any mention of that in the GPX 6000 manual or literature. The fact that Auto/GeoSense adjusts sensitivity to ground conditions is well documented. Turning off the Threshold tone can also reduce overall signal strength from any type of signal including EMI.

For me anyway, getting the GPX 6000 speaker mod done and using a smaller third party mono coil for shallower gold targets/shallow bedrock areas has made a big difference in EMI mitigation so I can stick with using the GPX 6000 manual operation instead of having to use its Auto modes and/or its lone, huge DD coil.

For extremely versatile simultaneous multi frequency VLFs that have gold prospecting capabilities, I want the hottest detector I can get. The hottest inherently means the most sensitivity to really small targets which automatically means EMI. These detectors already use DD coils for many reasons including ground handling benefits. They have frequency shifts- 13 (Legend), 19 (Equinox) and 49 (Deus 2 but its really only seven per main frequency/mode) (don't know about the Manticore)  depending on the detector model being used and the mode being used in order to try and find a less EMI effected frequency range. Most of them have smaller coil selections for reducing "antenna" surface area which can help with EMI. They also have the ability to lower recovery speed settings which can help with EMI too and can somewhat offset lowering sensitivity. In some instances where I was dealing with electric fence or underground wireless sprinkler system EMI, using single digit notching has really helped so I didn't have to either switch to a single frequency or notch out all ferrous and most low and mid conductor non ferrous targets. Sometimes just switching to a much higher frequency weighted mode really helps too.

So, dogodog, Jasong and Digalicious: I don't have any answers. I just use these detectors and try to find ways to get around EMI. I am sorry if some of my responses seem like I am ignoring you, don't want to talk about EMI or just don't care.

EMI definitely is an issue. On the other hand, I am not getting any younger and I am going to detect every day that I am physically able weather permitting whether there is EMI or not. I have "it" really bad and probably need some therapy. 

 

 

[Mike_Hillis]

Rutus Altrex has a screen that shows you what freq has the most EMI interference.

[jasong]

59 minutes ago, Mike_Hillis said:

Rutus Altrex has a screen that shows you what freq has the most EMI interference.

Cool...this is almost exactly the type of thing I was talking about wanting to see. 

So even with VLF's it is possible to basically do a real time background EMI scan, at least to some degree. So technically, you could have a "quick press" noise cancel button that just hops to the current best channel as it constantly analyzes in the background. 

It occurs to me (re: the coil up, coil down scan) that if external EMI is the problem, you don't technically need to use the coil itself to run a background scan. You could simply scan for EMI constantly with another antenna at the control box instead of the coil. This approach itself could be interesting because you could then run the coil signals and the EMI antenna signals through something like a differentiator so you could instantly know the difference between EMI and a target/ground noise (since the target/ground signals would be absent at the EMI antenna on the control box). Then cancel out anything that isn't a target/ground noise through standard signal processing.