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Will The Next Gen Detectors Address Emi ???


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1 hour ago, Digalicious said:

On both my Vanquish 540 and my Legend, noise cancel does basically nothing. I've also watched countless detecting videos, and it didn't matter if they were using the 540, 800, Legend, or D2, because not once in any of those videos did the noise cancel do anything either.

Easy-peasy, I took the liberty of starting the video right at a spot showing noise cancel on the Nox working.  It's an old video I did some years ago showing the Vanquish working better in high EMI than the Nox, so you could go from the start if you wanted also, it's only a short video.
 

Noise cancel is also highly effective on the older GPX series detectors and the GPZ and I can easily be demonstrated working on them.

I still think frequency shift on older single frequency detectors like my T2 works best.

 

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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.

 

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39 minutes ago, F350Platinum said:

One day I found that Rattlehead's Silver Slayer program dealt well with harmonics, I was right under some really noisy power lines, switched to his program on a whim, and wham - gone. Really freaked me out.

 

Doesn't that program notch out everything but very high conductors? If so, that could very well explain why it is much more quiet. More specifically, most of the EMI was notched (filtered) out.

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47 minutes ago, F350Platinum said:

 

One day I found that Rattlehead's Silver Slayer program dealt well with harmonics, I was right under some really noisy power lines, switched to his program on a whim, and wham - gone. Really freaked me out.

 

 

4 minutes ago, Digalicious said:

Doesn't that program notch out everything but very high conductors? If so, that could very well explain why it is much more quiet. More specifically, most of the EMI was notched (filtered) out.

I just went out in my backyard and confirmed this.

I have 3 high power lines running parallel to the back of my yard. I set up a custom program that notched out everything below silver/copper. In no disc, ground disc, or ferrous disc mode, the detector was noisy with a jumpy ID. I switched to that custom mode which notched out everything below copper/silver, and the EMI noise was gone.

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3 hours ago, dogodog said:

Erik, Thanks!!! I had a feeeeeeling this was the Evil that haunts us all. My soil is bad enough, the extra noise is horrible. And I hunt with average sensitivity. Now go make someone's day!!!!?

4 hours ago, Erik Oostra said:

I reckon you're spot on Dogodog with the issue being WIFI related.. Both my Nox and D2 go mental on a beach near a backpacker hostel when their WIFI is on.. There's also a powerline with a box nearby which never causes any interference.. 

I must point out that this is the only spot on the island the D2 does this.. I've used it around a huge telecommunications tower which drove the Nox crazy but not the D2.. Maybe the hostel's got an extra large WIFI transmitter to beam down to their private beach? It's weird that it only happens here but I know for sure that when their WIFI is turned off both the Nox and D2 behave themselves..  

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24 minutes ago, Erik Oostra said:

I must point out that this is the only spot on the island the D2 does this.. I've used it around a huge telecommunications tower which drove the Nox crazy but not the D2.. Maybe the hostel's got an extra large WIFI transmitter to beam down to their private beach? It's weird that it only happens here but I know for sure that when their WIFI is turned off both the Nox and D2 behave themselves..  

Yep. The intensity of the EMI changes from minute to minute, hour to hour, and day to day. That means a valid comparison of noise cancelling abilities would most importantly entail both detectors being compared on the same time and day, and less importantly, both detectors using a similar weighted SMF mode. For the latter, in high EMI, the SMF mode used wouldn't usually matter, because all SMF modes would suck lol...BUT, if you're in an area in which the high EMI is mainly around a particular frequency, then the weighting of the SMF can matter when it comes to EMI mitigation.

But wait, there's more! The recovery speed can also have a huge impact on EMI mitigation. So, the detectors would also have to be using similar recovery speeds.

EDIT:

I worded that last paragraph imprecisely. I should have said that changing the recovery speed can give the illusion of EMI mitigation. Meaning, the recovery speed doesn't legitimately reduce or increase EMI noise.

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4 hours ago, Chase Goldman said:

Yes, I would.  Deus 2 seems to deal with it better than any other SMF machine

Yes. In my limited EMI world, the Manticore works as the D2 does.  

As a side note. I hear very few people using Manticore and EMI in the same sentence. 

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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?

One of the absolute worst parks for EMI is the one closest to my house.  I have to run the Nox at 20Khz and sens 16 to get it to quiet down.  Maybe I'll take them both over there this afternoon and do a side by side to satisfy some of my curiosity.

- Dave

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45 minutes ago, UT Dave said:

 

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?

One of the absolute worst parks for EMI is the one closest to my house.  I have to run the Nox at 20Khz and sens 16 to get it to quiet down.  Maybe I'll take them both over there this afternoon and do a side by side to satisfy some of my curiosity.

- Dave

You have to reduce the sensitivity to 16 even in 20khz? Wow. That's some serious EMI. In my worst EMI sites, all SMF modes are terrible, 5,10, and 15 are almost as bad, 20 khz does much better, and at 40 khz the EMI is virtually gone. BUT, that is with maximum or close to maximum sensitivity.

Regarding the noise cancel (sometimes called frequency shift).

To the best of my knowledge, all the detector is doing, is sampling the signal at very slightly different frequencies. I'm not talking differences as large as let's say 5 khz, but rather more like differences of 0.1 khz. So if there is 13 channels, the actual difference in khz among those 13 channels is very little. If the frequency shift was significant, then it's no longer noise cancellation. Rather, it's avoiding EMI by using a completely different frequency.

On a high EMI site, flipping through the different channels manually, will in general, show that each channel is noisy. Granted, sometimes a particular channel may seem slightly more quiet, but that's only temporary due to the randomness of EMI in frequencies, harmonics, and intensity. As such, sampling the channels for a longer time, doesn't change that fact, nor should it make the EMI mitigation any better. If the long press does make it better, then I suggest it is done via software "trickery" using one or both of the software trickery methods that I previously mentioned.

Detector manufacturers have been trying to address EMI for many years. I would think that if one of the manufacturers succeeded in a way to legitimately accomplish that, then not only would they profusely advertise the new noise reduction software technology, but also patent the crap out of it. I haven't seen either of those occur. 

It seems to me that with all the random aspects of EMI, claiming to mitigate EMI via software, would be like claiming to be able to count the bubbles in a boiling pot of water. So for all the reasons that I've mentioned here and in my previous posts in this thread, I believe that any metal detector noise reduction that seems to work, is actually an illusion based in software "slight of hand" tactics.

 

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