Manticore And Emi (and The Magic Word -- Depth)

[GB_Amateur]

(I'm starting a new thread because we may have been getting OT on this one and there are some things I want to say, in the appropriate place.  I don't know how to do the standard Quoting method of this site from a different thread so if you want the original post, please refer to the one I just linked/underlined.)

I wish I could talk from Manticore experience but I'm still patiently awaiting mine.  Maybe coming this/next week?  IDK.  But I still feel like there are some unemphasized things, maybe 'questions' is the right word.  Andrew quoted from Tom Dankowski's forum in the above linked thread and I'm going to start by cutting and pasting part of that post (taken exactly from the Tom D. forum):

If you (mostly) hunt sites that have little/no EMI...... stick with the EQX.
If you hunt the beach...... get the Manticore. It is MUCH deeper (especially on fine gold) than EQX.

I'm not concerned with the second sentence (since I don't beach hunt) so I'm focusing on the first.  When I think of Dankowski, the first two things that come to mind are some thoughts he's had quite a while ago and possibly (not sure) added some of the lingo.  1) Iron will sometimes mask non-ferrous targets ("masking") and even give no signal at all (! "silent masking").  2) EMI hampers detecting, and sometimes it affects things negatively even when you don't hear/notice it (! "silent EMI").

OK, let's go deeper into #2.  EMI isn't new.  For many detectors (especially older ones) you have two main options when encountering EMI -- A) live with it (i.e. "listen through the noise") and turn down your sensitivity/gain until you don't hear it.  (With selectable frequency you can try and find a quiter frequency to operate in.)   B) Recently(?) some detectors such as the ML Eqx 800 have a noise cancelling algortithm which can be activated by the user.  Sometimes that helps.  In my experience crudely 80% of the time it hasn't and other actions had to be taken.  But the silent EMI thing is one of those gremlins that scare me (not literally ) because just like silent masking, you don't know when it's happening.  Well, Tom says he does and the following is how he determines it.

In a quiet EMI environment Tom determines, for a given group of settings, the max distance from the coil he can detect a coin, e.g. 95% copper cent.  (I don't remember exactly the coins used but I think he just uses two different denominations for his calibration).  He also puts gradations on his shaft and remembers where the max distance is.  (Swinging an object above the coil is just as good as below the coil for an air test -- the coils magnetic fields are symmetric.)  When he goes to a site and breaks out the detector, after doing the typical tuning steps, he does a similar calibration to check if he's getting equal max distance.  If not he associates that with silent EMI.  He has standards for how much loss from this he accepts and since he carries multiple detectors, grabs another and starts over if necessary.

So what's my point?  I doubt very many people go to this much trouble.  I don't.  So when he says "If you (mostly) hunt sites that have little/no EMI..." I assume he means that YOU and I have done his calibration steps to determine that!  Last winter I actually considered building a Faraday Cage to block all EMI to do a baseline test, but I don't have a warehouse 😁 and didn't want to spend all that time just to have to tear it down afterwards.  And I wouldn't do a half-assed job, either, so project nixed.

 

[Dug D]

I will wade in just a bit on "depth", for me it should always be said "effective depth" and to me every part of the discussion becomes more clear. I received my NOX 800 went to my backyard and it could not hit my 6 inch buried dime, neither could my Ex 705. EMI is severe in my backyard everywhere close to home EMI was an issue, but I sure was finding a lot good stuff with my 800 that I didn't seem to find with the 705. I headed to dad's farm, (no EMI) placed a clad quarter in really clean ground at about 10 inches, both detectors hit it faintly (800 had some jumpy ID), 705 no number but faint tone, I would have dug both signals. 

You can't leave target separation out of the effective depth discussion, better separation also give you more effective depth. IMO

Seems simple to me (based on my use) the Nox 800 has better effective depth (including coins on edge) because it does better with EMI and separation, than the Ex705 in most situations. At Dad's farm in clean ground they were surprisingly close.

I'm confident with everything I've see and read that the M-core will have additional effective depth over the Nox, especially for me where EMI the limiting factor in most locations, not to mention the other detector upgrades.

Just my few cents on EMI / depth

[steveg]

GB_Amateur...

Couple things.

1.   I believe he uses a dime for the testing, and upon arriving at a hunt site, he would actually run through EACH of the noise-cancel channels, air-test-checking that dime, and seeing which channel would give him the most "depth" (air test), which he then determined was the best channel (at least at that moment, until/unless the EMI source changed).  And in checking that dime with each channel, there were sometimes INCHES of difference, and SOMETIMES inches of difference EVEN WITHOUT AUDIBLE EMI (silent EMI).

So, in this way, he'd KNOW that he was hunting the noise-cancel channel that best mitigated the EMI present at that time, on that site.  And yes, if even the BEST noise-cancel channel offered depth that was too far below what he had previously determined to be "max depth performance" of the unit, he'd switch to another unit if it offered better performance, relative to the existing EMI present.

But, recently, I was speaking with him, and asked him if the specific "LONG-PRESS NOISE CANCEL" method that he has described in detail, with the Manticore, REPLACES the need to do the "air-test-check a dime with every noise-cancel channel and see which one offers the best depth at a given location at a given time," and he said YES.  This is what the noise cancel on MC was engineered to do.  This specific procedure on the Manticore (not just press the button, let go, and let the unit do its quick, one-time, 1/3-of-a-second-per-channel check that occurs if you just press and release the noise cancel button) REPLACES the need to air-test-check every single channel to find the one that gives the best depth (i.e. the one that is affecting the machine's performance the least).

I found that very interesting...

Steve

[TampaBayBrad]

I've been doing the long press noise cancel several times during each 3 hour hunt. I don't move much, maybe 100 yards in each direction from my starting point on the beach.

I have found that it bumps usually between the same 2 or 3 channels each time I check it holding the coil steady 16" above the ground. I release when it settles for the longest time on a particular channel. Takes about 4 to 5 seconds of holding the button down.

So it looks like for me in my hunting environment, the long press noise cancel is only needed at the start of each hunt since I'm getting mostly the same channel result each time.

[JCR]

EMI is a relentless factor. We are subject to more of it than we think.

A few nights ago the power was out due to an Ice Storm at my house & a Large surrounding area, many square miles. I live in a semi rural location. There were a few small generators running in the distance but that's it. No 60 hertz power otherwise.  I wanted to see what difference this situation made in EMI pickup on a detector. Turns out not much.   The amount of non 60 hertz interference was surprising. I really could not tell any difference from what is normal day to day. I bet it would have been a lot different 20 years ago. There is a ton of new tech EMI out there no matter where you are with few exceptions.

I think one of the best chances for improved detector performance is in EMI mitigation. Minelab knows this too, hence the Long Press capability on the Manticore. NASA Tom has been preaching this for years.  I hope to see other manufacturers actively pursue this aspect.

[abenson]

If you want to see Tom's response to I believe Hugh's question about depth/EMI and how he arrived at the 23% increase over the Equinox, you can see it here. Again this applies to his mild Florida soil so may not apply to you.

https://www.dankowskidetectors.com/discussions/read.php?2,185174,page=19

[GB_Amateur]

53 minutes ago, abenson said:

If you want to see Tom's response to I believe Hugh's question about depth/EMI and how he arrived at the 23% increase over the Equinox, you can see it here. Again this applies to his mild Florida soil so may not apply to you.

https://www.dankowskidetectors.com/discussions/read.php?2,185174,page=19

As I write this there are two separate post/responses by Tom D. to Chase's question.  One is timestamped February 03, 2023 10:29AM

The second is timestamped February 03, 2023 02:30PM

I think those times are UTC so maybe 5 hour units different than USA EST (for example).  I also see that Chase has posted a followup question so more to come!

[Chase Goldman]

14 hours ago, Dug D said:

I will wade in just a bit on "depth", for me it should always be said "effective depth" and to me every part of the discussion becomes more clear. I received my NOX 800 went to my backyard and it could not hit my 6 inch buried dime, neither could my Ex 705. EMI is severe in my backyard everywhere close to home EMI was an issue, but I sure was finding a lot good stuff with my 800 that I didn't seem to find with the 705. I headed to dad's farm, (no EMI) placed a clad quarter in really clean ground at about 10 inches, both detectors hit it faintly (800 had some jumpy ID), 705 no number but faint tone, I would have dug both signals. 

You can't leave target separation out of the effective depth discussion, better separation also give you more effective depth. IMO

Seems simple to me (based on my use) the Nox 800 has better effective depth (including coins on edge) because it does better with EMI and separation, than the Ex705 in most situations. At Dad's farm in clean ground they were surprisingly close.

I'm confident with everything I've see and read that the M-core will have additional effective depth over the Nox, especially for me where EMI the limiting factor in most locations, not to mention the other detector upgrades.

Just my few cents on EMI / depth

When I asked Tom D about Depth vs. EMI on Manticore and his "nominal" 23% depth improvement vs. Equinox, this was basically what he was talking about Raw Depth is impacted by:  [Detector: Sensitivity + EMI Mitigation (coil power) + Recovery/Separation (processing speed) + Signal Processing(target identification/rejection)] + [Environment: Target Characteristics (conductivity, mass, orientation) + Soil Conditions + EMI present] = Effective Depth.  There are so many variables and interdependencies (e.g., you can increase sensitivity if EMI is less severe), there is no pat answer.  Tom appears to be saying - in aggregate Manticore provides about 23% more depth than the Nox on average for the range of conditions and targets Tom D encounters.  What is interesting is the "range" of performance improvement for Tom D's situations is 67% more depth to 2% more depth, depending on the combination of the above.

[Chase Goldman]

2 hours ago, TampaBayBrad said:

I've been doing the long press noise cancel several times during each 3 hour hunt. I don't move much, maybe 100 yards in each direction from my starting point on the beach.

I have found that it bumps usually between the same 2 or 3 channels each time I check it holding the coil steady 16" above the ground. I release when it settles for the longest time on a particular channel. Takes about 4 to 5 seconds of holding the button down.

So it looks like for me in my hunting environment, the long press noise cancel is only needed at the start of each hunt since I'm getting mostly the same channel result each time.

I have asked Tom for more insight as to what is really going on with long press noise cancel.  Is it just re-scanning what it thinks are the most quiet channels (after a "short press" scan) or is there some additional EMI mitigation going on.  I think it's the former and your experience tends to back this up.  If it's the latter, the question is "what is the downside then?" - because as Steve H always says, "There is no free lunch".

[Chase Goldman]

2 hours ago, steveg said:

But, recently, I was speaking with him, and asked him if the specific "LONG-PRESS NOISE CANCEL" method that he has described in detail, with the Manticore, REPLACES the need to do the "air-test-check a dime with every noise-cancel channel and see which one offers the best depth at a given location at a given time," and he said YES.  This is what the noise cancel on MC was engineered to do.  This specific procedure on the Manticore (not just press the button, let go, and let the unit do its quick, one-time, 1/3-of-a-second-per-channel check that occurs if you just press and release the noise cancel button) REPLACES the need to air-test-check every single channel to find the one that gives the best depth (i.e. the one that is affecting the machine's performance the least).

I found that very interesting...

Steve

And I wonder just how it manages to do that.   In other words, what is the feedback mechanism that accomplishes that.  Looking at Tom D's "contnuous "manual noise cancel" algorithm.  He manually gets air test depth data from every channel to determine which one is optimal.  I could see Long Press doing that if it had a target to calibrate from.  But that is not what is happening, from what I can tell.  I wonder if he has done side-by-side comparisons of his manual method and "Long Press".

From the Manticore User's Guide. (Note that "Long Press" noise cancel is officiall called "Continuous Auto Noise Cancel"):