Air Born Magnetic Particles or EMI

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Post  Wombat on Sat Feb 04, 2012 1:51 pm

I do not know if this topic has been brought up before, but with the sensitivity of our detectors of today does anyone have any idea of how to handle Air Born Magnetic Particles. Every so offen out in the field my coil stars to get a wobbling sound come through the ear phones then about 30 seconds later you get a light breeze. Soon as that has passed the wobbling stops. What I have heard it is magnetic particles riding on the breeze. Is this true and what can I do about it. It is very annoying as you can not swing the coil until it stops as you can not distinguish between a target and the wobble. Right now I'm using the 11" Mono Commander on my 5000.
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Post  nero_design on Sat Feb 04, 2012 2:30 pm


There have been articles published before that describe how larger magnetic fields will drift slightly from their anchor points with strong wind. It's not likely that the particles themselves could form a strong enough field to affect your detector as they drift past. Some have noticed that when working near large HV power lines, the magnetic field will drift from them in the direction of strong wind. So some prospectors will operate on the side of the power lines where the field is less as the breeze blows.

I would expect a larger coil to be susceptible to this effect compared to a smaller one.
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Post  Guest on Sat Feb 04, 2012 3:40 pm

I doubt it would be air born particles either, May be heat waves moving about screwing with emi's, or as suggested in another topic, "Their following you" affraid
Probably didn't help!

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Post  Kon61gold on Sat Feb 04, 2012 3:44 pm

Don't you love EMI - Electrical Magnetic Interference.

Since the 4500 and the 5000, with their advanced electronics, they seem to be more susceptable to this interference. When the sun gets up and the wind starts to blow you can almost stop detecting due to the interference and noise.

Now I did try a large coil which they say acts like a radar dish and the EMI gets so bad you change to a lot smaller coil which is a vast improvement and reduces the noise. Has anyone else got any other suggestions on how to get over this problem?

Jeff
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Post  Nohave on Sat Feb 04, 2012 4:16 pm

I thought this source of interference exist on my antique ML only. Rolling Eyes


Well I use Anti Interference coil to combat this problem and it's working very well. Very Happy

However the downside is it's not so sensitive when compare to the same size mono coil.


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Post  Guest on Sat Feb 04, 2012 7:07 pm

A magnetic field that can be blown about by the wind.........Hmmmmmm, yez blokes az bin suckin too many magic mushrooms Suspect
A dense dust storm made up of iron ore dust might build its own magnetic field which miiiiight be able to cause some emi but just wind on its own,not a chance.
There would be more likely the possibility of the wind/moving air mass being electrostaticaly charged due to dry or stormy conditions and this could cause EMI. But the wind on its own cannot move a magnetic field that is within the earth or surounding your detector coil.

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Post  MS on Sat Feb 04, 2012 7:18 pm

Marco's right with the drift from HV power lines, we were taught that at trade school years ago, there is a field generated around the power lines and when the wind blows there are extra losses of voltage flowing through the HV power lines
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Post  Guest on Sat Feb 04, 2012 7:37 pm

maybe a cuppa in the shade would stop the wobbles
regards
jackson

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Post  Wombat on Sat Feb 04, 2012 7:49 pm

Adrian ss wrote:A magnetic field that can be blown about by the wind.........Hmmmmmm, yez blokes az bin suckin too many magic mushrooms Suspect
A dense dust storm made up of iron ore dust might build its own magnetic field which miiiiight be able to cause some emi but just wind on its own,not a chance.
There would be more likely the possibility of the wind/moving air mass being electrostaticaly charged due to dry or stormy conditions and this could cause EMI. But the wind on its own cannot move a magnetic field that is within the earth or surounding your detector coil.

Sorry Adrian but I was getting it on and of all day. I live in and was detecting around the Maryborough area and there was no pending storms today and it was completely dry. But every time a breeze came through my coil started to give out a continues wobbleing sound until the breezs settled down. What ever it was coursing the problem, was driving me nuts. (no jokes please Smile ) I have heard that if you spray anti-static spray on top of your coil that may fix it scratch
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Post  paulf on Sat Feb 04, 2012 7:57 pm

MS wrote:Marco's right with the drift from HV power lines, we were taught that at trade school years ago, there is a field generated around the power lines and when the wind blows there are extra losses of voltage flowing through the HV power lines
Mark


Use to work an area in Bendigo a couple of years ago that ran along power lines. Used a Commander 10"x5" DD coil to minermize interference but found on the days the wind was blowing away from me I could get real close but when the wind was blowing from the powerline direction towards me I had to keep further away.
Paul

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Post  Guest on Sat Feb 04, 2012 8:03 pm

sorry wombat , could be gb , stabilizer , tuning or just another noise sent to test us all .
regards , jackson

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Post  GREENnuggetCONVERT on Sat Feb 04, 2012 8:33 pm

gday folks,
The most susceptible part of your detector to EMI in (natural occuring) forms and conditions is the Cable from the Coil to the Control Box,and
therefore during periods of Wind or Gusts of Wind this ( WEAK LINK ) can be very problematic to detectorists...Also with that being said the slightest knick cut or indentation on a poorly maintained Cable will also suffer from major EMI..Another thing to note with EMI during periods of heat/humidity and the like is that yor Cable also suffers from Elastasisation which also brings into the equation (another) weak link..The plating on the cables ends is another....if worn or badly scratched..One other susceptible part during windy and hot conditions is the cable from your Battery to the control box and any movement from it.........
Just thought this would be relevant and useful to those who are not tripping on mushies...its nearly mushie time too 10 weeks affraid .mmm So........
getting back on track i have a question:::Has anyone ever tried using any kind of ( EMI Shielding ) over their shafts and Cables Question Question :?
during these trying conditions............

Cheers............Trev..... cheers
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Post  Guest on Sat Feb 04, 2012 10:29 pm

There is an electric field of charged particals surounding all HV power lines which can be blown about causing electrostatic charge build up in the ground the grass the trees and your metal detector, your clothes, everthing. This can cause EMI. I have measured this field at up to 450 volts per mtr beneath some local HV lines and it does vary from place to place depending on atmospheric conditions. But as I said earlier, You can huff and puff until the cows come home but you aint never going to be able to blow a magnetic field about unless you use another magnetic field or some other moving inductive material, and even then you will only change the field shape and/or density.

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Post  slimpickens on Sat Feb 04, 2012 10:54 pm

How about an anti static strap from the coil body to the ground, so the static doesn't build up and release when your coil touches some grass or the ground? Would it help? scratch
Air Born Magnetic Particles or EMI Strap_10
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Post  Guest on Sat Feb 04, 2012 11:09 pm

Look out where all starting to use the computer for more than looking at what we like!. You don't need the earth belt, Bare feet will do just fine and dandy with a good spray of Mortein. Very Happy
I'm going now-Bye

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Post  Guest on Sat Feb 04, 2012 11:28 pm

shiraz wrote:How about an anti static strap from the coil body to the ground, so the static doesn't build up and release when your coil touches some grass or the ground? Would it help? scratch
Air Born Magnetic Particles or EMI Strap_10


Well anything is worth a try.

Maybe try wearing an pointy Alfoil hat. lol!

I will say that I have never noticed any noises due to windy days while detecting but there was one day at the beach with the Infinium, that the detector went nuts every time the coil touched the sand, just on one small section of the beach. I Have no clue as to what was causing that

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Post  Guest on Sat Feb 04, 2012 11:32 pm

That's because your trying to answer questions about the GPX 5000 when you only own a Infinium, My pay back to you.
Cheers Chris

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Post  4rd on Sat Feb 04, 2012 11:49 pm

Perhaps the recent increase in CME activity (solar flares) including what was reported as being the largest in several years in the past week may be causing some grief? Considering what happened back in 1989 also....
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Post  Guest on Sat Feb 04, 2012 11:57 pm

What ever you reckon, I know of a different scenario?? About had enough??????????????

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Post  Narrawa on Sun Feb 05, 2012 12:44 am

The most susceptible part of your detector to EMI in (natural occuring) forms and conditions is the Cable from the Coil to the Control Box,...

Take a coil cable from any of the leading brand coils, and wave it over the coil of a switched on detector....no sound. (plugs excluded)
Not such a week link to EMI if the detector coil cant hear it.
The plating on the cables ends is another....if worn or badly scratched
Not electrically connected to cable.???

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Post  Flakmagnet on Sun Feb 05, 2012 7:36 am

I definitely pick up moments of EMI-sounding interference on dry windy days.
Not everywhere I go but in certain desert areas and they are far from power lines.

I have solved innumerable little glitch problems by fitting coil cable stabilizers
much like the 'cable thingy' that has been discussed in the forum.

i am interested to hear from someone knowledgable
if spraying anti-interference spray on a coil will have an effect,
that would be cool.
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Post  Guest on Sun Feb 05, 2012 8:58 am

someday wrote:That's because your trying to answer questions about the GPX 5000 when you only own a Infinium, My pay back to you.
Cheers Chris

Only own an Infinium! Only own an Infinium!!! You have cut me to tha quik. Sad Ya big narthty Meanie.
I have heard that some ML coils are pretty tacky and donot have good Electrostatic shielding, Like Throwbacks to tha ole BFO days Laughing Razz

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Post  Guest on Sun Feb 05, 2012 9:16 am

4rd wrote:Perhaps the recent increase in CME activity (solar flares) including what was reported as being the largest in several years in the past week may be causing some grief? Considering what happened back in 1989 also....

I have Electric field, magnetic field and Nuclear radiation monitors running continuously.
The past two days has shown an approx doubling in my local mag field strength and for an as yet unknown reason my radiation monitor has been reading random spikes in the back ground radiation levels.

Normal BG radiation in my area is 0.17 microSv/h with the high average being approx 0.23microSv/h but has been spiking randomly to 0.57 microSv/h for the past few days. pale pale pale

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Post  Guest on Sun Feb 05, 2012 9:23 am

Flakmagnet wrote:I definitely pick up moments of EMI-sounding interference on dry windy days.
Not everywhere I go but in certain desert areas and they are far from power lines.

I have solved innumerable little glitch problems by fitting coil cable stabilizers
much like the 'cable thingy' that has been discussed in the forum.

i am interested to hear from someone knowledgable
if spraying anti-interference spray on a coil will have an effect,
that would be cool.

I have fitted ferrite cable doverlackies to my Inf coil cable (like those on computor cables) to try to reduce EMI but as yet I have not noticed any changes.

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Post  Guest on Sun Feb 05, 2012 9:31 am

Flakmagnet wrote:I definitely pick up moments of EMI-sounding interference on dry windy days.
Not everywhere I go but in certain desert areas and they are far from power lines.

I have solved innumerable little glitch problems by fitting coil cable stabilizers
much like the 'cable thingy' that has been discussed in the forum.

i am interested to hear from someone knowledgable
if spraying anti-interference spray on a coil will have an effect,
that would be cool.

Anti static coating is always worth a try.
Check to be sure that the detector does not respond to it before you spray. Put a bit in a dish and run it past the coil.

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Post  GREENnuggetCONVERT on Sun Feb 05, 2012 10:31 am

@Narrawa said ????????????????????????????????????
because it is a part of the TX / RX circuit.that is why the coil cable gets wrapped around your shaft..
its no different than tv antenna cable flapping in the wind freely...
no different to a coaxial lead that is SWR"d in on a CB / UHF radio etc...........doing same......
but you may believe differently as you wish......
cheers...............Trev....
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Post  Mechanic on Sun Feb 05, 2012 11:58 am

Narrawa wrote:
The most susceptible part of your detector to EMI in (natural occuring) forms and conditions is the Cable from the Coil to the Control Box,...

Take a coil cable from any of the leading brand coils, and wave it over the coil of a switched on detector....no sound. (plugs excluded)
Not such a week link to EMI if the detector coil cant hear it.
The plating on the cables ends is another....if worn or badly scratched
Not electrically connected to cable.???


G'day Narrawa,

I would have to agree with you on this. The interference is picked up by the coil itself, not the cable between the coil and detector. This is why when you are using a large coil and things start to get a bit too noisy, eg detector wailing when the coil is slightly tilted, bolting on a small coil then quietens things down.

As far as wind blown charged particles go, they would not cause the warbling described by the original poster, it would sound like a lightening strike, just a sharp blip. These sharp blips are more than likely caused by static buildup in the detector coil/detector case(they share the same ground) discharging into the ground or shrubs. I have also seen a carbon fiber shaft build up static charge and discharge into the coil cable on a hot dry windy day(perfect for static buildup.

The coil cable is not tuned like a 2 way radio antenna lead. If it was it would be a hell of a lot longer than what they are. I figured it out once and the wavelength was well over a kilometer!

I would put the interference heard by the original poster to that of an approaching aircraft. This starts out as a slight warble, increasing until the detector is unusable and then dies away back to the original quiet threshold. Just because you can't hear or see the plane does not mean it will not interfere. Many a time I have heard the warble, stopped detecting heard the plane, waited for the plane to pass and so did the interference.

Narrawa, perhaps he meant the plating on the pins in the plug? This will have an effect but only when the coil plug is moved, once again, not what the original poster experienced. CLEAN YOUR PLUGS Very Happy

As far as magnetic fields moving causing interference, they would have to be moving extremely fast to cause interference as the ML detectors have a method of removing effects of slow moving magnetic fields.

Cheers Mick

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Post  GREENnuggetCONVERT on Sun Feb 05, 2012 12:48 pm

I'm not trying to be a smartarse or anything ,,
yes i did actually mean, the actual pin contacts in the plug..( caused by coil switching and assembly/disassembly )..
and no i didn't mean for the cb comparison to come out the way it may have be interpreted:
through research i have done on EMI the (following paragraph) is an extract from one published paper on the subject,of part of my research into it but mine version was shorter and in my own words....everything we read on a forum still has individual interpretation.................
.........................................................................................................................................................................................
Cable wiring and harnessing is a significant EMI concern. Cables are required to distribute electrical power and transmit electrical signals for the operation of various systems. Since cables are usually routed to accomodate its function, it is often difficult to quantify its environment and it usually varies over both frequency and electric and magnetic field amplitudes. Cables can be EMI radiating sources if they act as radiating antennas, or be susceptible to EMI if they are receiving antennas. Cables can also be coupling paths. In addition, cables are sometimes harnessed together, so interference can also be between two cables that are close in proximity. Therefore, their performance is very difficult to predict. Many specifications classify wiring or cable types into four to six categories but these classifications are generally qualitative in nature. More quantitative classifications should look at levels of power transmitted, or susceptibility of termination.
.......................................................
Environment/EMC/EMI
Carnegie Mellon University
Author: Eushiuan Tran
.......................................................
cheers................Trev....

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Post  Mechanic on Sun Feb 05, 2012 1:32 pm

G'day Trev,

I see where you are coming from, and what you say is true for capacitive coupled antennae but our coils(antennae) are inductors. The coil is approximately 300uh, the lead ?? .1uh? The coil is going to pick up much more emi than the cable. The cable is shielded the same as the coil which reduces/eliminates capacitive coupling. Then the preamp inputs are impedance matched so common mode noise picked up on the cable is cancelled there too.

As far as the coil cable being wrapped around the shaft for tuning purposes, this is not correct. The coil cables are so long to accommodate tall buggers like me who need a long stem to keep the coil out in front of them vs a shorter person with a short coil stem. The excess cable has to go somewhere!

Trev, I mean absolutely no disrespect with my answers. I hope we both learn from the outcome of the discussion....

Cheers Mick

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Post  GREENnuggetCONVERT on Sun Feb 05, 2012 2:21 pm

Mick, all is good and always will be,
with the cable being wrapped around the shaft ,you are correct(thats pretty obvious) what i was trying to say is this.
With the cable on (some) owners detectors not being (firmly wound) around the shaft this may also be a part of the problem due to the actual
cable having some movement which in turn (at the back end of plugs) could cause some (instability)because the wires/pins/plug arrangement
is always classed as one of the weak points in any electronic device,due to this factor i was tending towards (movement) that would be unable to be detected by the naked eye and only be able to be accurately eliminated from the equation by diagnosis with test equipment
such as an oscilloscope and EMI test gear.even though plugs are a secure way of attachment there are still those susceptible areas of termination and contact...
the above may make it a little clearer as to where i was going with that...sorry but im useless with a keyboard / typing and it takes me forever so i try and keep things short and sweet,otherwise i get timed out and sent back to the home screen having to type everything all over again,which really frustrates the crap out of me lol! .........................
cheers..............Trev....
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