Gotta ask this question

[Cherry Picker]

The only differentiating factor in what I, Dankowski, and others have experienced, is the major difference in EMI between the test sites. If you know of any other factor that could explain the significant depth loss, I'm all ears.

BTW- I don't know anything about Dankowski. The first I heard of him was when I got back into detecting a few years ago after a long absence. I was taken aback at the amount of EMI noise and performance issues that I was experiencing, that I never experienced back in the day. So, I looked into the EMI issue, and that posting by him popped up. I remembered it, because I experienced the same thing.

I could name quite a few. Again, the term "silent EMI" is a generic term for anything that affects the magnetic field of the detector but does not cause noise. How about geomagnetic field of the earth? It changes according to the changes in the magnetic field of the earth. Far more feasible, and scientifically real, that would cause no noise, but cause the depth ability of the detectors depth to fluctuate. Much like how the moisture content of the dirt will dictate depth from day to day. But, I don't believe this is the silent EMI most are imagining. The way I see it described, and the way I disagree is that some electronic device causes an unexplained or measurable, or testable interference with the detector magnetic coils.

Geomagnetic field would not be classified as EMI because it is not interference, but changes in the natural magnetic field on the earth which in turn affects whether the Eddy current/field is strong or weak returning from the target.

I just believe any "interference" would cause an audble noise.

 

[GeoW]

EMI, is a factory defect, nothing more. Should be shielded.
We're being bombarded with more and more EMI as we defend ourselves from certain magnetic waves that aren't exactly from friendly sources.
When the metal detector signals travel through open air instead of wire, hitchhikers do take advantage.

 

[woodbutcher]

The only differentiating factor in what I, Dankowski, and others have experienced, is the major difference in EMI between the test sites. If you know of any other factor that could explain the significant depth loss, I'm all ears.

BTW- I don't know anything about Dankowski. The first I heard of him was when I got back into detecting a few years ago after a long absence. I was taken aback at the amount of EMI noise and performance issues that I was experiencing, that I never experienced back in the day. So, I looked into the EMI issue, and that posting by him popped up. I remembered it, because I experienced the same thing.

The Deus being wireless you'd think would open the door for more problems with EMI vs a wired coil.. I like Deus, just pointing out what makes sense to me at the moment

 

[Diga]

The Deus being wireless you'd think would open the door for more problems with EMI vs a wired coil.. I like Deus, just pointing out what makes sense to me at the moment

Just a guess, but maybe the coil to control box frequency is well outside of the typical EMI frequencies?

All I know is that all of my detectors suffer significant depth loss in sites with high emi compared to sites with low emi (even in the air). That depth loss also occurs when I'm in a mid to high SF and the emi noise is inaudible (compared to SMF modes in which the emi noise is intolerable).

 

[goodmore]

I had the original Deus. There were sites that made it almost useless. The Minelab units of the day like the CTX and ETrac did ok, but EMI was a huge factor. Power lines and even a red light a half block away was noise in my ears. I could hear every time the light changed in my headphones. That was not silent EMI. But the thing is you are only aware of the EMI you hear. I remember a story Tom Dankowski told about a hunt where he noise canceled every few minutes on a site. It made a difference. The technology exists to let the detector handle the EMI. Change frequencies until the interference is minimal all done in the background. The operator doesn't even have to know. If you don't hear the interference that doesn't mean it doesn't exist. To quote Tom.....you don't know what you don't know.

 

[Cherry Picker]

The Deus being wireless you'd think would open the door for more problems with EMI vs a wired coil.. I like Deus, just pointing out what makes sense to me at the moment

You'd think. I don't remember having any more issues with the Deus than any other detectors.

The only time I have ever noticed any changes in depth at any site is from moisture. After a good long soaking rain, it is obvious I can get from 1"-2"s more depth at the city park. I believe this to be from the same geomagnetic field that gets amplified by moisture. Just makes far more sense to me than some silent EMI concept. I could be wrong tho.

 

[Tony-Ok]

I was at an old home last year with a Detector that is almost immune to EMI …. A Fisher CZ 5. At the house next door was a person playing an electric guitar and my detector was extremely erratic. I wasn’t finding anything, and knew that the detector never acts like this. The person stopped playing the guitar and my detector went back to perfect operation. I managed to find a few nice targets. I new the detector was effected by the Amp of the guitar. CZs are analog and semi- digital. Most new detectors are definitely more digital and seem to be more susceptible to EMI . Manufacturers need to address this with better or best shielding possible. In todays World there are so many more electronic devices to cause EMI . It is a real thing. Noise cancellation is a must with all modern detectors and most offer that . Make it a habit to do and that should help. HH Tony

 

[IDXMonster]

I was at an old home last year with a Detector that is almost immune to EMI …. A Fisher CZ 5. At the house next door was a person playing an electric guitar and my detector was extremely erratic. I wasn’t finding anything, and knew that the detector never acts like this. The person stopped playing the guitar and my detector went back to perfect operation. I managed to find a few nice targets. I new the detector was effected by the Amp of the guitar. CZs are analog and semi- digital. Most new detectors are definitely more digital and seem to be more susceptible to EMI . Manufacturers need to address this with better or best shielding possible. In todays World there are so many more electronic devices to cause EMI . It is a real thing. Noise cancellation is a must with all modern detectors and most offer that . Make it a habit to do and that should help. HH Tony

Was he playing “Iron Man”??

 

[Coin-Saver]

Was he playing “Iron Man”??

I was thinking more like "Still haven't found what I'm looking for".

 

[metaladdict]

That's a weapon against the D2 that Minelab developed and went out with their latest Equinox update!

Nailed it! So we Nox hunters have an advantage around D2 users getting too close to us!

 

[Monte]

► EMI is simply a term to describe a 'type' of Interference. The key word remains and that is ... Interference.

► There are many websites I care not to visit because I don't like a particular individual or sometimes the type of content.

► Since we are using electronic devices to find metal objects, we know there is going to be a likelihood that something might influence improved or impaired behavior in performance. Technically, anything that affects the performance, one way or the other, might be considered 'Interference' or EMI.

► Someone called my attention to some character's "new term" of Silent EMI and I explained that I have referred to impaired performance for decades, back to the early '80s for example. An early era in this sport when most folks had no clue what EMI meant. And honestly, many still don't because it can mean several things depending on how we interpret it.

With many early detectors we didn't have the noisy behavior we might experience today because we have upped the performance over the years, changed frequencies, made these things more sensitive. Long, long ago, even in the latter '70s, I would experience some impaired behavior that cut in on my detector's performance at some sites. I could hear the noisy behavior so I dealt with it because it was Interference that I could hear that limited the detector's performance.

But there were times I grabbed a detector and noted that it was NOT performing as it typically did even though it had a fresh set of batteries and, as usual for me, was operating at full Sensitivity. Even doing a quick "air test" of by sweeping over a coin or pull tab on top of the ground, things were not quite right ... but it was quiet and there was no noisy behavior. What caused it? Interference. What 'type' of Interference? Certainly EMI since it was having a negative impact on my electronic device.

The fellow who called my attention to the other guy's website who boasted about "Silent EMI" asked how that could be because it didn't make sense if you couldn't hear it so I gave him two logical answers:

A #1.. Because I own and use multiple detectors and have since late '71/early '72, my approach today is to just swap to a different detector and make sure it is operating at full potential ... ie: no EMI that could or couldn't be heard. Most of the time that meant changing to a detector with a completely different circuitry OR one that operated at a different frequency which, apparently, was not interfered with.

I pointed out that someone who was using a Fisher F75 and referred to changing the "noise cancel" settings really wasn't. Yes, he was changing a setting that helped to deal with the noisy behavior he heard, but in reality that is a Frequency-Shift so all he was doing was slightly off-setting the designed operating Frequency so as not to hear the noise. But that also meant he was also likely changing to a slightly different Frequency that cut in on the full performance of the detector compared to the designed peak operating Frequency.

He agreed, and i pointed out that the detector then didn't create any audible noise to Interfere with the performance, but since he had changed the peak operating Frequency of the electronic device that resulted in slightly poorer performance but w/o noise, so wasn't that still EMI that had a negative effect but couldn't be head? That would maybe be called 'silent' Interference.

A #2.. Grab any modern, high-performance detector. Let's say you generally operate at a Sensitivity setting of about 85% to 90% for best depth and responsiveness to small desired targets.

If you increased the Sensitivity to maximum and found the extra noise you hear at full 100% Sensitivity was very annoying and limited the audio performance due to the noise you heard, what would you call that? EMI. Okay, so the overall performance was impacted or Interfered with because you, the operator, caused Interference that limited performance.

If you then reduced the Sensitivity to that 85% to 90% level and it was at the fringe of instability you would regain full depth and responsiveness to small targets without Interference. Great All you did was eliminate the noise.

What if you reduced the Sensitivity to a 15% to 20% level? Would you still get the best depth and responsiveness to desired small targets that were deeper? No. Would you hear any noise? No.

So you now have adjusted the Electro-Magnetic Field of the device to be 'silent' but still Interfere with the full-level performance behavior, right? Yes.

So I guess you could call that 'silent' EMI. Something folks do all the time but don't know they are Interfering with the Electro-Magnetic performance. That's why I always operate at full Sensitivity, or if necessary restore it to the fringe level just at the point of not 'hearing' any negative impacting EMI.

Monte

 

[Cherry Picker]

As someone who has also used a plethora of detectors since the early 70s, I think common sense trumps Bigfoot.

I'm not saying there cannot be any of this "silent EMI", only that it makes much more sense that the unexplained change in performance can be as simple as the geomagnetic field around the earth. Can be tested to influence the returning Eddy current used by a metal detector. Can't be seen, can't be heard, but can be scientifically explained and proven.

Interference, in my opinion, should cause some type of audio change. Now that is just my opinion based on the fact it has never been proven otherwise. For this reason, I find the concept of a "silent EMI", while possible, highly unlikely, and more plausible to be geomagnetic field changes.

 

[jmaclen]

As someone who has also used a plethora of detectors since the early 70s, I think common sense trumps Bigfoot.

I'm not saying there cannot be any of this "silent EMI", only that it makes much more sense that the unexplained change in performance can be as simple as the geomagnetic field around the earth. Can be tested to influence the returning Eddy current used by a metal detector. Can't be seen, can't be heard, but can be scientifically explained and proven.

Interference, in my opinion, should cause some type of audio change. Now that is just my opinion based on the fact it has never been proven otherwise. For this reason, I find the concept of a "silent EMI", while possible, highly unlikely, and more plausible to be geomagnetic field changes.

Monte had a great post above yours and made some valid points that were more for gaining other perspectives on "EMI".

Electromagnetic Interference can only be heard if our ears hear it. If our ears don't hear it through the speaker or headphones used with a detector, is it still there but "Silent" as far as our own hearing is concerned?

If my detector is acting up from electromagnetic interference, I can change the frequency and lower the sensitivity to reduce the effect of the interference. It is still there however and my metal detector's advanced noise reduction software algorithms cannot make it go away.

I also experience interference from the ground itself due to iron mineralization and hot/cold rocks. This ground interference acts like EMI in that it severely effects the overall depth of all VLF detectors and creates actual responses that are given different audio tones and target IDs. I can ground balance multiple times, turn up the recovery speed/reactivity and use VLFs with the latest simultaneous multi frequency tech like the Manticore, Equinox, Deus 2 and Legend that can reduce some of the effects of mineralization on depth and target ID accuracy. OR, I can take for instance my Equinox, put it in 4 kHz to 40 kHz single frequency and notice that my Nox is now very quiet......(the same can happen when I do this to reduce EMI interference). However, target IDs and depth are nowhere near as optimal/normal as they were using the Equinox in Multi. My detector was quiet with those settings.....I did not hear any interference but my detector's ability to actually detect where I hunt was severely hampered because I want to avoid so much audible EMI or audible ground interference. That interference is definitely still there. I just setup my detector so I won't hear it.

 

[Cherry Picker]

Monte had a great post above yours and made some valid points that were more for gaining other perspectives on "EMI".

Electromagnetic Interference can only be heard if our ears hear it. If our ears don't hear it through the speaker or headphones used with a detector, is it still there but "Silent" as far as our own hearing is concerned?

If my detector is acting up from electromagnetic interference, I can change the frequency and lower the sensitivity to reduce the effect of the interference. It is still there however and my metal detector's advanced noise reduction software algorithms cannot make it go away.

I also experience interference from the ground itself due to iron mineralization and hot/cold rocks. This ground interference acts like EMI in that it severely effects the overall depth of all VLF detectors and creates actual responses that are given different audio tones and target IDs. I can ground balance multiple times, turn up the recovery speed/reactivity and use VLFs with the latest simultaneous multi frequency tech like the Manticore, Equinox, Deus 2 and Legend that can reduce some of the effects of mineralization on depth and target ID accuracy. OR, I can take for instance my Equinox, put it in 4 kHz to 40 kHz single frequency and notice that my Nox is now very quiet......(the same can happen when I do this to reduce EMI interference). However, target IDs and depth are nowhere near as optimal/normal as they were using the Equinox in Multi. My detector was quiet with those settings.....I did not hear any interference but my detector's ability to actually detect where I hunt was severely hampered because I want to avoid so much audible EMI or audible ground interference. That interference is definitely still there. I just setup my detector so I won't hear it.

Don't get me wrong, I have the utmost respect for Monte's knowledge about metal detectors, and metal detecting. I also agree that "silent EMI" is a possibility, as I mentioned. I just think sometimes we tend to overthink and make things that can have a simple answer more complicated than need be.

My suggestion is that a perfectly feasible explanation could be the natural geomagnetic field. Even changed by the solar winds, some large metallic objects, tractor, etc. nearby, the detectors' abilities can be reduced, or enhanced. Ever go to some spot over and over yet the signals and ground noise seem to change? You could write it off as some "silent EMI" or the natural effect of physics. I just happen to put my chip on EMF (electromagnetic field).

The only problem I have with Silent EMI is the I in EMI. I believe Interference, cannot be silent. But hey, that's just me.

 

[AccurateCalls]

The only problem I have with Silent EMI is the I in EMI. I believe Interference, cannot be silent. But hey, that's just me.

I mean, EMI that the machine recognizes and subtracts from the signal, will produce no audible sound because the algorithm properly eliminated it. Thus, all successfully mitigated EMI becomes "silent". Yet it still exists and is not heard on the detector.

That is what noise canceling algorithms do, they silence undesirable tones generated by noise.

In my opinion, it's much more plausible it is an undesirable behavior (read bug) of the EMI mitigating algorithms. There is no other analog in physics in terms of natural phenomenon that I have ever heard of nor can find through research.

 

[Carl-NC]

Silent EMI is a real thing. Here is what's going on.

Metal detectors (from the 1970s on up) use "sampling demodulators" to convert the operating frequency (say, 10kHz) down to the baseband needed for processing the target phase. This is true for both analog and digital designs. Sampling systems are subject to aliasing effects, whereby other frequencies (say, 60Hz powerline or 600kHz AM radio) can end up right on top of the target signal, resulting in audible EMI.

The outputs of the demodulators have a low pass filter, usually around 20Hz. If you slightly shift the detector's operating frequency then you can move the aliased EMI just outside of this filter bandwidth and then you no longer hear it, or it's significantly reduced. You can also move the aliased EMI exactly on top of the detector's operating frequency and it will disappear. I intentionally do this in my security walk-through designs.

However, the EMI is still there all the way up to the output of the demodulators, so it can still affect the available dynamic range. In particular, weaker targets can get masked, so the overall effect appears to be reduced depth. It also may cause an error in target ID.

Conceptually, MF detectors will be worse with EMI (silent or not) because they have a wide-band front-end. SF detectors have a narrow-band front-end which helps limit the EMI that gets in in the first place. Digalicious noted that higher frequency VLFs had less EMI; that's because their front-end bandwidth was farther away from the 60Hz noise and did a better job of suppressing it.

Earth field is a similar issue but it occurs at 1-2Hz (the coil sweep rate) and is minimal when using short or slow sweeps with the coil maintained in a flat orientation. That is to say, you have complete control over how much effect Earth field has in masking. Earth field also changes on its own but is so slow it's not a factor.

Better shielding isn't the answer. Coil shielding is for electric field effects, not magnetic field effects, and if you apply magnetic shielding to the coil then the detector would no longer function. The only practical answer is to use an anti-interference coil, like the Bigfoot, a coaxial, or a butterfly coil like is on the GPZ.

 

[Diga]

Conceptually, MF detectors will be worse with EMI (silent or not) because they have a wide-band front-end. SF detectors have a narrow-band front-end which helps limit the EMI that gets in in the first place. Digalicious noted that higher frequency VLFs had less EMI; that's because their front-end bandwidth was farther away from the 60Hz noise and did a better job of suppressing it..

Thanks for the technical explanation, Carl

With further testing, I'm really beginning to think that it's not just a matter of frequencies alone, but rather the nature of SMF as well. More specifically, the "comparisons of frequencies", or something similar, when using SMF that makes it even more suspectable to interference.

For example, in my backyard, all SMF modes are very noisy, including the SMF Gold mode which I believe is a combination of 20 khz and 40 khz. Yet, if I use the SF's of 20 khz or 40 khz, the detector isn't nearly as affected by EMI as using the combination of 20khz and 40khz. In other words, that Gold mode should be quite as well, but it isn't. So either, the combination and comparison of Gold Mode's 20 khz and 40 khz in of itself, is more prone to interference, or???

 

[Carl-NC]

Probably you are right. In a MF detector the different frequencies are channelized just before the demods and each channel includes a filter that alters the EMI differently. When the results are later combined it is possible that the noise in each frequency channel adds to a worse overall EMI.

I should add to my prior post that EMI and silent EMI affects even old TR and VLF models. It is only coming around as a notable issue because (1) EMI is getting worse and (2) raw detector sensitivity has increased.

 

[Cherry Picker]

OK, I see where I was looking at "Silent EMI" differently. I understand if you're referring to silent EMI as silencing EMI. As in turning down, silencing, the EMI noise. I was thinking some mystical undetectable interference that the only way to know it exists is your detector having poor performance.

How turning down the sensitivity makes the EMI chatter go away. The Interference is still there, just now silent.

I'd probably would had picked up on it, but it wasn't until someone suggested the algorithm. Now I understand that yes, the detector would be still producing the EMI chatter if not being "Silenced" by an algorithm, demodulation?, or adjusting the detector to silence the EMI noise. The interference would still be there, just no noise. "Silent EMI.

 

[Carl-NC]

No, not really. Silent EMI is interference you cannot hear. It is literally "undetectable interference that the only way to know it exists is your detector having poor performance." OTOH, yes, silent EMI is EMI that is still there, just no noise.