Will The Next Gen Detectors Address Emi ???

[jasong]

3 hours ago, GB_Amateur said:

What's the replenishment timescale, though?  (You know better than I that...)

...

I read a  decent book (Field Guide to Meteors and Meteorites by Norton and Chitwood -- for some reason I can seem to find the link atttach icon in the post headings...) on the subject and it surprises me the low number of estimated falls and even recovered samples listed for the various known finds by classification.

I don't know much really, I don't specifically look for them, I find them by accident. The people I know who meteorite hunt seriously spend a lot of time looking for fresh falls though, so it must be at least somewhat frequent.

But from prospecting in general I can say I've found meteorites in 2 states that were unknown falls, cold discoveries while prospecting for gold (both were clearly old though, 100's or 1000's of years). I haven't reported any of them to be classified. I don't really want my full name out there for the bad elements to know, and I don't want some places I'm actively working to be known either, so no classifications for me. I suspect there is a good number of meteorites found that go unreported for similar reasons, I personally know other people who've also made finds and not reported them for those reasons. 

While they are rare, I doubt the slim number of recorded instances represent the actual occurence/distribution of them on the Earth. The amount of land people have run coils over is diminishingly small. Both cold finds I made were in places no one would ever metal detect, and probably never will again, because there was no indicators there of prior habitation or gold mineralization.  Endless more land like that available... That leads me to believe that meteorite hunting probably could be a fairly doable hobby with a metal detector, for people with a ton of patience. At this point, if I had to really make a living off detecting and didn't want to mess with jewelry, I think I'd probably choose to do meteorite detecting as it gets me into the wilds and exploring and away from people same as gold. 

That said, I doubt it will ever be a significant source of revenue for detector manufacturers....but it's something I guess. 

[FloridaSon]

UT Dave good report. Do you use the ‘long press’ when noise canceling? I have found a quarter about 12 inches deep directly under the power lines behind my house. I have noticed the EMI from power lines changes throughout the day.

Regards

[GB_Amateur]

12 hours ago, jasong said:

While they are rare, I doubt the slim number of recorded instances represent the actual occurence/distribution of them on the Earth. The amount of land people have run coils over is diminishingly small.

Yes, even though we think of primo sites (whether for native gold or coins and relics) as seriously picked over, that is a small fraction of the earth's non-ocean surface.  The deserts (including Antarctica) presumably have the exposed and shallowest meteorites; seems less likely for plant covered areas, though.

I know it's been mentioned before, but still an interesting thing to contemplate -- how many meteorites, small fragments in particular, have been detected but ignored as simply hot/cold rocks (by native gold detectorists) or even nails or other waste iron bits (by coin&relic detectorists)?

Coincidentally when the 11:00 news came on last night the first item covered was the reports coming in from Central Indiana of a bright flash and sonic boom that had occurred a few hours earlier.  Most skies in the area were unfortunately overcast but a morning news program (see the link I just posted) shows a perported image -- I initially am a bit skeptical that this is the event, given the sky conditions I was experiencing as well as some people's unscrupulous efforts to get their 15 minutes of fame.  Hope I'm wrong and if so there should be other videos showing up to confirm that one.

[phrunt]

I watched a TV show on Antartica meteorites once, it's the easiest place to find them, dark colours really stand out on white and it's not soft snow, it's often rock hard ice.

If I encountered one I'd likely call it another stupid hotrock and kick it away, I doubt I'd recognise one.

We've had a couple of them in NZ already this year caught on CCTV cameras with the bright flash and object flying across the sky.  I've only seen two in my lifetime, one quite big one in Brisbane, Australia at about 3am after getting off a plane, we were driving back from the airport to the mother in laws house, no cars at all on the road, most properties with lights out, the place was asleep and a massive flash that I thought a speed camera got me, then we see the object flying in the sky but it's angle looked like it was going to hit the ground pretty close, it wasn't going across the sky more coming downwards..

The other I was just sitting in my Spa at night time again in Brisbane and there was a much smaller flash and an object flying across the sky on a downwards trajectory.    Nothing at all like the previous one I mentioned though.

I'd love to find one, I doubt I ever will.

I think EMI mitigation is the final frontier for metal detectors, many in the know have commented depth levels have been maxed out for years, target ID stability was maxed out with the CTX and now we are heading backwards to less stable to improve other aspects of detector performance I guess, tiny gold performance peaked with the GB2 back when I was a school kid.    EMI seems one area where improvements could be made, and in a way have to be made as EMI gets worse every year for almost every detectorist.  Frequency shifting to me seems the best solution for VLF's, and now with most modern detectors being multi frequency they have coils more suitable for moving frequencies.   They should be able to establish during a "EMI noise scan" procedure which frequencies in their pre-programmed modes are being affected by EMI and shft off them slightly until the noise clears while leaving the quiet frequencies alone.   Older detectors like the T2 where I do my frequency shift in a previous video on this thread perfectly demonstrate how well frequency shifts work, even tiny ones like the T2 has under 1kHz can make a huge difference.

I don't think we should get used to these lightning fast 3-5 second noise cancels though, good things take time and the most effective detectors at the moment for noise cancels take time, the GPX 4500 seems like it takes about a minute if not more to go through its 254 channels while you're holding your heavy GPX coil up in the air.  The GPZ 7000 although slightly quicker still feels like about 30 seconds.  Both these detectors recommend you hold your coil up above the ground.

I personally have found noise cancels most effective holding coils above the ground in maximum sensitivity to get the most EMI into the detector, then after it thinks its done as good as it can with the noise cancel I move my sensitivity to the desired level. 

 

 

[jasong]

1 hour ago, phrunt said:

I don't think we should get used to these lightning fast 3-5 second noise cancels though, good things take time and the most effective detectors at the moment for noise cancels take time, the GPX 4500 seems like it takes about a minute if not more to go through its 254 channels while you're holding your heavy GPX coil up in the air.  The GPZ 7000 although slightly quicker still feels like about 30 seconds.  Both these detectors recommend you hold your coil up above the ground.

I think they could have 0 second noise cancels if someone spent the time to incorporate such a feature. There is enough CPU power to run a program that does nothing but scans noise/channels constantly when the detector is on. And either auto adjusts to the quietest channel, or gives you the option to adjust to current quietest channel instantly with a button push.

The holding the coil thing in the air is to direct the detector to the loudest EMI source. But that also puts it with the coil 90 degrees off from other sources of EMI that might actually affect the detector more when using it on the ground. So while it often helps, I don't think it's absolutely necessary to have the coil in the air and an automated scanning program could probably do about as well with the coil flat on the ground as you detect too.

I can't say for certain because I have no idea what they have going on in the actual detector software or how many resources they are using. But even if they have the FPGA maxed out, a 2nd FPGA only costs like $10-15, so they could easily add another dedicated to nothing but noise/signal processing. 

[Digalicious]

Perhaps one of the reasons the manuals often state to "Keep the coil away from the ground when noise canceling", is to avoid ground mineralization and / or metal from interfering with the noise cancel.

[phrunt]

7 hours ago, Digalicious said:

Perhaps one of the reasons the manuals often state to "Keep the coil away from the ground when noise canceling", is to avoid ground mineralization and / or metal from interfering with the noise cancel.

Yes, to the detector EMI is just another target, it can't tell the difference, if it could the EMI probem would be resolved already 🙂 you'll also often notice holding the detector in the air makes EMI worse, especially with Pulse induction and the GPZ detectors that are far more prone to EMI than VLF's.

[Digalicious]

7 hours ago, phrunt said:

Yes, to the detector EMI is just another target, it can't tell the difference, if it could the EMI probem would be resolved already

Yes Phrunt.

That's exactly why I've been saying current EMI mitigation technology can't theoretically work properly. In other words, the detector is seeing a multitude of targets with multiple of IDs (EMI). IF noise cancel filtered those out then all those IDs would be filtered out as well. Also meaning that if noise cancel works, then it's a software illusion by reducing the base (hidden) sensitivity, or weighting the SMF almost exclusively at 1 frequency, so that the detector is actually running more like a EMI resistant SF detector.

[jasong]

It's hard to know what's going on inside some of these modern detectors specifically without just guessing, but from a wider noise cancellation perspective, you can tell the difference pretty easily between some EMI and a target just by looking at periodicity (for instance, a sine wave) - a 60hz power signal, etc. VLF's I'm less sure about than PI's, but I imagine you can differentiate by frequency too, similarly.

Harder would be to tell the difference between a target and random noise, spherics for instance. You could enable some of this potential on a detector by the inclusion of an accelerometer so that it knows when the coil is moving, and if it's not moving (in the case of a PI anyways), then noise should be noise and not a target. In these cases the transient time - speed of signal - can be used to differentiate between a target and a noise event. Again, an accelerometer in the coil would help here since the target "size" could be esitmated as function of swing speed (targets would be "wide", lightning would be "short"). This would enable some degree of effective noise cancellation with the coil on the ground. Smoothing does this.

The problem is that more noise cancelling = more potential for noise cancelling a target. That's what Smoothing does on the GPZ, even without accelerometers to gauge coil movement or not. There are definitely times to use Smoothing, and times to know when not to use it. The key is understanding what it does and when it helps or hurts.

Minelab has recently patented designs incorporating accelerometers, so I suspect they might be able to improve smoothing and general noise cancelling with the coil on the ground, using some ideas like these.

[Digalicious]

It seems the "go to" for dealing with EMI, is to reduce the sensitivity, and often reduce it significantly. However, that's a poor way of dealing with EMI, due to the amount of depth loss. It's akin to the proverbial, "Throwing the baby out with the bath water". BTW- Who ever thought of such a morbid phrase? lol

I honestly think that's what Fisher did with their DSP, and also why so many were saying that DSP "dumbed down" the detector and caused it to lose its depth, and sensitivity to small targets. I also kind of think that the Manti's long press does the same thing, and/or the long press weighs the SMF heavily toward a single frequency that is more or less outside the range of the EMI.