What Difference Does 1khz Have On The Equinox From 5khz To 4khz?

[Digalicious]

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[Digalicious]

21 minutes ago, Chase Goldman said:

Taking the time to read the technical references reveals that the rule or generalization or whatever you want to call is applicable mainly to power line noise sources.   But given the growing proliferation of 5G transmitters and WiFi 6, solid state switching power supplies, and LED lighting, even detectors with higher operating frequencies will be affected more in suburban and even rural areas as time goes on as evidenced by Steve's anecdote about his noisy 19 khz detector. 

Yes of course. He mentions how his previous 19 khz detectors were almost immune to EMI due to the higher frequency, until that pesky LED light paid a visit and 19khz didn't like it.

When I talk about EMI, I usually add that "it's only getting worse". Meaning, both the intensity of the EMI and its frequency range is getting worse. I don't expect it will be much longer before even 20 and 40 khz won't be immune to EMI.
 

[Jeff McClendon]

What difference does 1 kHz make? I have no clue why Minelab added it. It does make it easy to tell if a Nox 600/800 has the latest update.

At least in my yard near way too many sources of EMI including my neighbors 40 foot short wave tower, I can actually stand to run my Equinox 800 at 4 kHz with sensitivity on 20. Switching to 5 kHz it is absolutely impossible for me to listen to the racket at any sensitivity. The 800 at 5 kHz might as well be a pulse induction detector with a 14" mono coil on it at full sensitivity!

I have had similar 4 kHz vs 5 kHz results at other high EMI locations.

So for me, that is my experience and I don't want to argue about it or go off on any tangents. It just is what it is at least for me.

[GB_Amateur]

20 hours ago, Digalicious said:

nor do I believe that the Manti's long press does anything more than what the F75 and that other Minelab detector did. Although with the Manti, it's also possible that the long press could change the SMF to be ludicrously weighted toward 1 single frequency. That would significantly reduce EMI noise, but also lose the advantages of SMF.

I believe that LGM (that's "little green men") are running around inside the Manticore waving magic wands to accomplish the noise reduction.

So how do we decide which one of these competing hypotheses is correct (if either)?  Not be repeating it over and over like Dorothy when she tried to get from Oz back to Kansas ("There's no place like home; there's no place like home;...").

Short of getting a Minelab engineer to tell us (not holding my breath) it's going to take experimentation.

[Digalicious]

1 hour ago, GB_Amateur said:

 

So how do we decide which one of these competing hypotheses is correct (if either)? 

I've presented many valid reasons to consider that the Manti's long press might only give the illusion of EMI mitigation. Just one of those reasons is that Minelab themselves have already done it with reducing the sensitivity on at least one of their previous detectors. But alas, experimentation would be required to prove it either way.

I've mentioned two ways in which the illusion of the mitigation can be accomplished. One of those is the proven technique of reducing the hidden sensitivity, and the other is changing the algorithm so that it looks like the detector is running in SMF, but is actually running in a mode that is far closer to a single SF, which of course would significantly reduce EMI noise.

For the former, the Manti should be at the highest sensitivity, in high EMI, the coil stationary in the air, and then an air depth test done. Then do the long press and if (and only if), the EMI is gone after the long press, then immediately do the air depth test again.

For the latter, well, that would require highly mineralized ground. Basically the same EMI noise reduction procedure would be done, but the targets would be a deeply buried high conductor and low conductor. Check the before and after on depth and target ID accuracy of those two targets.

 

[GB_Amateur]

The Manticore manual gives a description of how the Noise Cancel is done.  I paste here the pertinent snippets:

Note it says "slightly shift transmit frequency" (emphasis mine).  It also explains what the continuous method (holding down the key until a stable channel is seen) to "find the quietest channel".  Nowhere does it say the sensitivity is adjusted nor the frequency weighting is adjusted.  Those would be significant adjustments affecting performance (probably in a negative way compared to quiet operation) and to hide that from the user would be egregious, IMO.

3 hours ago, Digalicious said:

Minelab themselves have already done it with reducing the sensitivity on at least one of their previous detectors.

Which detector is that, and was it done surreptitiously or did they tell the users about it (e.g. in the user manual)?

[Digalicious]

GB,

Fisher's DSP on the F75 modified the sensitivity (possibly other settings as well) to give the illusion that EMI was being mitigated. In a recent thread, I was made aware that Minelab did the same thing on?? If I remember correctly...SD "something"? I'll try and find that thread.

In addition to that, there are other good reasons to suspect that EMI noise reduction is "software sleight of hand", or put another way, "an algorithmic illusion". That's all discussed in that other thread I mentioned.

 

[Digalicious]

I found the thread...all 9 pages of it 😁

Will The Next Gen Detectors Address Emi ??? - Metal Detector Advice & Comparisons - DetectorProspector.com

 

[GB_Amateur]

15 hours ago, Digalicious said:

I found the thread...all 9 pages of it

I read it.  Didn't see a lot of "other good reasons", rather a lot of speculation like (paraphrased) "EMI can't be alleviated so they must just be toning things down to fool us into thinking they are" and people pretending that a one-size-fits-all oversimplification of EMI is the whole story.  How about a spectrum (intensity vs. frequency) graph/plot of just one example of EMI let alone the different spectra from multiple sources.  Hand waving is cheap.  Evidence takes effort.  It's one thing to consider possibilities but to dogmatically then jump to unfounded conclusions -- that's what annoys me.  There's a difference between "it could be possible" and "it can't be done because I say so."

I'm tired of conspiracy theories about why things in the real world don't conform to someone's preconceived, oversimplified views and AFAIC that's how that thread quickly evolved, and this one has been turning into.  EMI is not one-size-fits-all and solving the problems it causes isn't something we can just theorize about and then conclude we are right.  (When did Descarte's "I think, therefore I am" devolve into "I think, therefore I'm right"?)  And then conclude that since the problem is insolvable the detector engineers are resorting to behind-the-back slight-of-hand.

When my Manticore shows I'm operating at a gain that's displayed on the screen (two digits on the left side when in search mode) and I do a Noise Cancel and it doesn't change, the Occam's Razor conclusion is that it didn't change.  When the screen simultaneously shows me the mode I'm in (top of screen) and that icon doesn't change after a noise cancel then I'm not going to assume that the weighting of received&utilized frequencies has been altered past what the manual has indicated -- "...slightly shifts the ...transmit frequency".

[Digalicious]

Speaking of evidence, I would sure like to see the empirical evidence that EMI noise cancelling that actually seems to work, does so without detrimentally affecting performance in one way or another.