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My Observations Of Eqx Update 2.0.1 And Iron Bias F2 At Daytona Beach


ColonelDan

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1 hour ago, schoolofhardNox said:

So...... could you wrap the control box in anti- EMI cloth to cut out the interference?? How about the coil? Would some form of cover on the top of the coil (not the bottom obviously) work as well, or would it cause chaos with the signal sent into the ground. I would love to shield my whole machine in some way. 

The display screen makes an effective control box shield problematic (though not impossible, I suppose).  Partially shielding the coil would be ineffective.  I am not really seeing this to personally be worth the trip as I am seldom EMI limited with Equinox.  Sounds like it is more problematic for you, though.

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3 hours ago, Chase Goldman said:

The display screen makes an effective control box shield problematic (though not impossible, I suppose).  Partially shielding the coil would be ineffective.  I am not really seeing this to personally be worth the trip as I am seldom EMI limited with Equinox.  Sounds like it is more problematic for you, though.

Oh, I should have said it was for the GPX 😄 I have a beach that the train is about 20 feet from the top of the beach. EMI like you have never seen. When those tracks are energized, no machine can operate there. You can use quiet modes or on the Equinox you can use 20K or 40 K, but depth is reduced significantly. I was just wondering if covering the top of a coil would hinder the signal emitted from it in any way?

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2 minutes ago, schoolofhardNox said:

Oh, I should have said it was for the GPX 😄 I have a beach that the train is about 20 feet from the top of the beach. EMI like you have never seen. When those tracks are energized, no machine can operate there. You can use quiet modes or on the Equinox you can use 20K or 40 K, but depth is reduced significantly. I was just wondering if covering the top of a coil would hinder the signal emitted from it in any way?

Maybe some folks in the general Minelab forum would have some idea's then.  I really just keep my GPX away from power lines (and other GPX's) or use low noise coils.  But other than that, not much you can do.  If EMI is untenable then I go to the Nox.

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In my case there are no visible sources , cell towers , power line etc. , I thought of my cell phone , which was on the other side of me from the detector , and I set it down on a picnic table about 50' - 100' from  where I was swinging .

Of course there are many sources of EMI , I was hoping that some specific / known frequencies were the cause ?

In ham radio we deal a lot with this issue and in doing we note the frequency being use or interfered with HF , UHF , VHF , then use various gear that operate on those frequencies to find , as an example for HF [ high frequency ,

Band (meter) MHz
HF 160 1.8 - 2.0
80 3.5 - 4.0
40 7.0 - 7.3
30

10.1 - 10.15

The copy & past didn't work to well , the band meter should be over the 160 column , MHz over the 1.8 - 2.0  column 

One device a common transistor radio set to AM is used a lot .

Not sure if some of the comments meant this , but many misunderstand that not all RF - Radio-Frequencies affect all electronics , there has to be some resonance between the transmitter & the device being affected , depending on a number of factors , quality in design  , in both the transmitter & device receiving / being affected  , one of those is if chineeze junk that operates outside of there intended bandwith , called a number things like spurious emissions -

A spurious emission is any radio frequency not deliberately created or transmitted, especially in a device which normally does create other frequencies. A harmonic or other signal outside a transmitter's assigned channel would be considered a spurious emission.

Now have to add to one of my things-to-do-list 😉

Bring out some extra gear to pindown some of this ,

A phrase for MA & PA KETTLE - " I'l have to fix that one of these days "

Dang and now winter is near - do not want to dig in frozen ground , and do not think I'l make it south this yr. , DOGGEY DEW   

  

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3 hours ago, KD0CAC said:

In my case there are no visible sources , cell towers , power line etc. , I thought of my cell phone , which was on the other side of me from the detector , and I set it down on a picnic table about 50' - 100' from  where I was swinging .

Of course there are many sources of EMI , I was hoping that some specific / known frequencies were the cause ?

You didn't previously say whether you conducted a noise cancel for each of the modes (each mode needs to be separately noise cancelled) or whether you ensured there were not other sources of non-EMI chatter such as proper ground balancing (the fact that your coil was stationary and still chattering probably rules this out, but nevertheless, thought I would mention it).  You also didn't discuss your sensitivity settings or any possible mitigating actions you took like lowering sensitivity.  EMI sources are not always obvious or visible even in rural settings.  Unless there is absolutely nothing nearby I can make the Equinox chatter after a noise cancel simply by cranking sensitivity from the default of 20 (quiet) to 25 (chatter) and that is why I rarely every need or want to raise sensitivity more than a couple points above the default.   More about resonate frequency EMI sources and why that is a tough nut to crack, below.

3 hours ago, KD0CAC said:

One device a common transistor radio set to AM is used a lot .

Not sure if some of the comments meant this , but many misunderstand that not all RF - Radio-Frequencies affect all electronics , there has to be some resonance between the transmitter & the device being affected , depending on a number of factors , quality in design  , in both the transmitter & device receiving / being affected  , one of those is if chineeze junk that operates outside of there intended bandwith , called a number things like spurious emissions -

As an electrical engineer involved in power electronic and small signal sensing equipment design including EMI mitigation and as a previously licensed amateur radio operator, I do understand this and where you are coming from and how an AM radio, for example, can be used to locate a noisy light florescent light fixture or spark gap (loose electrical power connector) as near field EMI.  A metal detector is basically a near field induction balance machine vs. a radio transmitter/receiver.  And even though the operating frequencies of interest lie in the EM VLF radio spectrum between approximately 5 and 50 khz in the case of the Equinox, that alone cannot be used to really ascertain the offending resonant EMI frequencies as it does not necessarily tell you the frequencies that both the front end signal processing circuit resonances or what the microprocessor noise susceptibilites are and the degree of self shielding used.  Here's why:

The mental model you should think of for a metal detector is a transformer rather than a radio transmitter/receiver.  The target represents the core of the transformer and the transmit and receive coils represent the primary and secondary windings of the transformer, respectively.  On the Equinox, however, unlike many other VLF induction balance detectors, the output is a spectrum of frequencies rather than a discrete frequency like most single frequency machines.  The power vs. a radio transmitter is relatively small because the near field only has to penetrate some number of inches into the ground.  The Equinox receive circuitry is designed to process inputs from a number of different frequencies and is basically looking for a tell-tale phase shift and magnitude from which it can infer the nature of the metallic target and display it's guess.  Since the Equinox is a relatively wide spectrum transmitter and receiver it is highly susceptible to both generation of harmonics and interference from EM harmonics across a wide spectrum so it is difficult to pin down a single resonate frequency or group of frequencies that are the worst offenders, as you wanted.

This EMI can enter via the "front" end with the coil effectively acting as an antenna.  To mitigate this, ML has incorporated the noise cancel feature that selects the quietest spectrum "channel".  Recognize, that this channel does not represent a single frequency but a spectrum of frequencies that appear to be least susceptible to local interference.  Again, this is why it is difficult to give you specifics on the "resonant" frequency you discussed.  Note that this is best suited to steady state interference sources such as other Equinoxes (BTW Equinoxes spew out so much EMI themselves that I have found that in contest hunt situations where many detectorists are co-located in a small hunt area, hunt masters are starting to ban operation of the Equinox in multi-frequency mode.  Pulse Induction detectors which put out a broad spectrum pulse are already usually banned), constant noise from transmission lines or transformer boxes, or the continuous carrier wave (loose sense of the term) of a nearby transmitter (broadcast radio transmitter, WiFi Hot Spot, Cell Tower, electric fence or wireless dog fence, or cell phone) or fluorescent lights.  Note that noise cancel needs to be performed separately for each search mode (as mentioned previously) as each search mode transmits a different frequency spectrum.  

If noise cancel is ineffective, you have eliminated ground noise feedback and chatter through a proper ground balance or mode selection (beach in the case of wet salt sand and water environments - some of the higher weighted frequency spectrum modes (e.g., Park 2, Field 2, and Gold) can be less susceptible), and you are concerned about having to turn sensitivity down too low (i.e., much less than 12 or so), then another alternative is to use the single frequency mode and to try to find the optimal quiet operating frequency.  As I said previously, in general, the higher operating frequencies tend to be less susceptible to the most commonly encountered EMI while detecting.  I cannot give you the definitive science as to why this is the case, but it is generally true.  But there are always exceptions so situational testing of the lower operating frequencies (e.g., 5 khz and 10 khz on the Equinox) should be positively ruled out rather than assuming they are not going to work. 

Transient noise sources are much harder to deal with and the best you can usually do with that is turn down sensitivity as necessary or switch between modes or go to single frequency. 

The other issue is the microprocessor components within the control head and I think this is probably one of the most susceptible and is the one that is most susceptible to cell phones and nearby Equinoxes.

Finally, to protect it's intellectual property, ML gives us very little information or specifics on the frequency spectrum used for each mode and how it generates that spectrum or even how many discrete frequencies and what frequencies are used to generate those spectrums, so we are basically in the dark from the get go.  Some have hooked the Equinox up to O-scopes and spectrum analyzers but the results are far from conclusive and even if they were, may not actually tell us the susceptible resonant noise frequencies.

Not a very satisfying answer as to the "resonate" problem frequencies question, but I hope this helps to explain why that answer is not so straight forward.

HH

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Thanks Chase ,

Since I just got the Nox 800 , I have not been tuning , just in presets on these fresh water beach's I mostly work with Parks 1 & 2 - I did do the noise balance , but may have forgot when switching from Park 1 to 2 .

As I get to know the detector later I will adjust settings and build my own profiles .

I've been spoiled by ham radio , most equipment come with wiring diagrams / schematics spec.s etc. -- unlike almost any other consumer gear .

I do have a lot of test gear , but mostly oriented to ham bands , but then look at adding outside ham bands to work on WIFI , blue tooth , but that means new / more expensive gear , mostly look for broken test equipment & then learn enough to repair , get to have fun twice that way .

Also mostly self taught books & internet .

I may be wrong , but kinda keep the idea of motors , magnetic & edde currents  to imagine how metal detectors work . 

Thanks again John

 

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40 minutes ago, KD0CAC said:

I may be wrong , but kinda keep the idea of motors , magnetic & edde currents  to imagine how metal detectors work .

Nope, you are right, those are the basic principles for metal detecting.

Another advantage of the 800 vs. the 600 is that you can do a "manual" noise cancel, where you step through the channel settings and choose the one you feel is the quietest.

So, to recap re: noise 

1.  Avoid obvious sources of noise, if possible (transmission lines, cell towers, cell phones, etc.).

2. Noise cancel (can be done auto or manual (800 only), but is search mode specific)

3. Ground balance, as necessary.  (Also mode specific).

4.  Lower sensitivity as necessary to remove chatter.

5. If still experiencing noise, shift modes, if possible (don't forget to noise cancel for each selected mode)

6.  If still noisy, try shifting to single frequency mode, and look for a quiet operating frequency.

HTH

 

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If your Equinox is picking up your cell phone,  an easy solution is to put it in one of the many phone cases that shield you from EMF - probably not a bad idea in any case.

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  • 5 months later...

I have some beaches in my area where the EMI seems to come from the lighting installation at the promenade. Switching to single frq. helps in those spots.

 

 

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