Air Born Magnetic Particles or EMI

Hi Adrian,

I have a ferrite whatchmacallit clamped on my coil cable too.
I have no hard evidence, but feel there is a subtle effect.
No proof tho...

i bought some anti-interference spray when I took apart a coil
last year to repair the shocking lack of potting for the coil wire
but I left it up at the person's house where I did the repair, oops too bad.
It would be a fun experiment.

G'day Trev,

Yes, slight movement of a poorly contacting plug will cause false groans whilst swinging and bumping the coil. A loosely wound cable will make the problem more noticeable. The other problem that can develop from a loosely wound cable is where the cable enters the coil housing. Too much movement here can cause the cable to start to break. When this happens any slight movement of the coil cable(at the coil end) will cause a false noise.

Cheers Mick

@Mick,
yes thats what i was biasing towards,regarding the original post, and have noticed all over the net that individuals can be interpreting the problems associated with EMI in a way that cancels out other factors that are more relevant in a particular situation..of which seems to be a major factor in detecting because manufacturers like keeping certain info secretive..so most people out there would need years of field experience to have better clarification on the matter.my main purpose for researching is to have a much better base of knowledge to work from out in the field,as to give myself a headstart .( avoiding in field frustration as i see a lot of with many detectorists ).
rather than just the basic info supplied by Mfr's and people that dont like passing on too much info & or dont know how to..and thats where forums are good,but in saying that not all the info around is correct..Im an Information junkie when i'm interested completely in something.
Thanks Mick....................cheers.........Trev....

Mick & Trev, sorry i read it as it was posted....

The plating on the cables ends is another....if worn or badly scratched

As for the lead pins, i thought they were solid brass...not plated.??? Control box pins....iv never seen the plating warn off yet.?
I often file the plastic part back to meet the pins for a tighter fit if i feel the plug is causing mating probs.
The plugs admittedly have their faults, but EMI i doubt is one..movement would be the biggest concern with the plugs.
Im not trying to be a smartarse either, as a user of these things im very interested in problem solving if it has merit.
A to tightly wound cable has its down fall as does a to loosely wound cable, to tight and the small flex in the shaft has a pulling effect on both ends of the lead.
I have two fixing points on my otto shaft, the bottom near the coil as most do, leaving enough cable for the tilting of the coil...and the handle area near the c/box, but the cable in between is loosely wound where flex is more possible.
Coil cables should be mounted in front of the shaft a few inches, and on the angle of the shaft while its in use. This would allow for a small amount of cable to be fixed to the shaft for the tilting effect. Its time the manufactures of coils give us something new, instead of old technology in a new case.
Nugget Finder almost got it right with the first of the 8x6s. (my opinion)

Speculation on whats causing the EMI problems while the coil is connected to the detector is all good, but have a listen when the coil is disconnected, and much of the discussion is blowing in the wind. (pun intended)
The various timings will rx different levels of interference with no coil attached, more noticeable on the GPX models. (more susceptible timings)
Much of the EMI we hear is coil based sure, but not all of it. After all, we are walking around with an un earthed txmitter.
Placing an earth cable from the control box and or batt box has no effect either, at least the version i did had no effect........wire tacked to my boot. If it had merit, we'd all be doing it by now and the lead would be a part of the detector package, or sold as an accessory.

If ya realy wanna find out if a a wind can blow a magnetic field about just get a sealed compass and stick it in a big draft I reckon there would be a lot of lost bushies out there if that was the case.

OK guys thanks for your replys but I'll give you the info of what has happened today. I was in the same place as yesterday but this time running a 17" NF Advantage Mono Eliptical (spoked) but still the same problem with the wobbles every so offen with the breeze, even when the detector was on the ground when digging a target. I was getting it also when I placed a Coiltek probe on to checked a target. Now I'll try and explain the area were I'm working. It is bush and tree covered ground, and there are about 3 houses about 500 to 600 yds away and these are in the same direction as were the breeze is coming from, so it may be EMI from the homes. The breeze was blowing a bit stronger today than yesterday but in the same direction. All my connection were well tightened and the cable of the coil well rapped around the shaft with on slack movement, but still getting the wobbling noise. The probe is just a cable with the probe on the end that you put in the hole, but I was getting the wobble just the same. The breeze picks up and the wobbling starts for about 10 to 15 seconds then stops, and then you notice that the breeze has died down as well. This does not happen in most other places were I detect just a few, may be 2 or 3 areas only. There is nothing wrong with my machine as far as I can gather. I may get someone else down there with there 5000 as well just to see if they have the same trouble. I may also contact Minelab and see if they have any ideas of the problem.
Wombat

wombat hi
yeh happening to me today very bad. i was out at Moliagul. a few times i had to stop detecting until it settled down.i think there was a big storm somewhere.
i think when it is constantly happening to you , its your location. housing or industry.
cheers dave

@Narrawa,
"Placing an earth cable from the control box and or batt box has no effect either, at least the version i did had no effect........wire tacked to my boot." .
just a question dude,did you connect your "earth cable" to both boots,as to alleviate the walking and ungrounding effect..
Glad you worked it out in the end ..............it probably had no Merit but you tried it..
cheers...............Trev....
++++++++++++++++++++++++++++++++++++++++++++++++++++++
@jefgold why would minelab do that when they stand to make more money the way things are..and adding any new tech in dribs and drabs with each new model..but then again if they gave everything there wouldnt be a future market except in aesthetics....
cheers..............Trev....

did you connect your "earth cable" to both boots,as to alleviate the walking and ungrounding effect.. Question Question

Nope, to try two wired boots i would have felt like a puppet. as i thought the prospects of using just one boot was mute, getting carried away by using both was not entertaining.
I read that it had been tried by others some time back, but nothing is ever truly tried till you try it yourself.
Standing and working various targets for hrs on end tells you something....if it dont work motionless, it wont work walking.

Wombat wrote:OK guys thanks for your replys but I'll give you the info of what has happened today. I was in the same place as yesterday but this time running a 17" NF Advantage Mono Eliptical (spoked) but still the same problem with the wobbles every so offen with the breeze, even when the detector was on the ground when digging a target. I was getting it also when I placed a Coiltek probe on to checked a target. Now I'll try and explain the area were I'm working. It is bush and tree covered ground, and there are about 3 houses about 500 to 600 yds away and these are in the same direction as were the breeze is coming from, so it may be EMI from the homes. The breeze was blowing a bit stronger today than yesterday but in the same direction. All my connection were well tightened and the cable of the coil well rapped around the shaft with on slack movement, but still getting the wobbling noise. The probe is just a cable with the probe on the end that you put in the hole, but I was getting the wobble just the same. The breeze picks up and the wobbling starts for about 10 to 15 seconds then stops, and then you notice that the breeze has died down as well. This does not happen in most other places were I detect just a few, may be 2 or 3 areas only. There is nothing wrong with my machine as far as I can gather. I may get someone else down there with there 5000 as well just to see if they have the same trouble. I may also contact Minelab and see if they have any ideas of the problem.
Wombat

The only other thing I can think of at the moment is that as the wind blows it is carrying charged dust particales, and there would have to be lots of them (Ions) with it and these ions may become trapped in the magnetic field around the coil which would then create electric currents of there own within the field and this would produce random magnetic fields producing their own eddy currents in the coil and therfore EMI.

Field strength in close to the coil can be high as well as the electric field strength. I have measured upwards of 2000 volts at the surface of my Inf 10 x 14 so a few ions would have few problems being attracted to the coil and if the detector is very sensitive like the ML PIs, some EMI would result.
TA DAAA!! Problem solved, next please ..........Ang on a minit we az still gotta figure art ow ta fixit.

Vacuum cleaner Adrian....and its already been invented...but not a coil mounted one..
cheers...........Trev....

ARGH GEEEZ

Ang on a minit we az still gotta figure art ow ta fixit. Rolling Eyes

No one said anything about fixing it.??
Try this....get yourself a sensu (Japanese folding fan) ....its none electrical, dont weight much, and can be decorated in como if thats your thing.?
Serves the purpose of ...blowing away those nasty EMI infected dust particles as well as keeping you, the operator cool.

My bad.

Well I az thunk abart it and figure that if you can put the coil in a cardboard box that would have about a 2 foot clearance around the coil it would stop the charged particles from getting in to the densest part of the mag field thus reducing the likelyhood of creating EMI ORRRRR ya could use a less sensitive setting, orrrrr ya could use a smaller coil, oorrrrrr ya could get an Infinium orrrr ya could go home and have a beer or three.

G'day Narrawa,

That's an interesting observation you have had as far as firing up your machine with no coil connected. However it would be a bit hard to tell if the noise was actually internally generated or caused by the floating inputs to the preamps. I have a method to identify if noise is internal or external which could be done with a specially wired plug adapter, but you would only be able to test the DD preamp this way. To test it properly the machine would have to be pulled apart and the receive wires separated from the back of the coil plug(both mono and DD) and connected to the coil ground. Any noise heard then is internally generated. This is how I determine if I have made any improvements after fiddling, however I use a scope on the output of the filters which gives definite results/values vs just relying on your hearing.

Anyway it is my belief that the warbling noises heard are from electro magnetic interference from radio transmissions and the like. Little pops and farts are from lightning and static discharge. I like the idea of the earthing straps, but it would only solve the problems associated with static discharge, not emi.

Cheers Mick

Adrian ss wrote:
Well anything is worth a try. Maybe try wearing an pointy Alfoil hat.

Someone at Berkeley actually did a study on that.

http://berkeley.intel-research.net/arahimi/helmet/

Mick, if only there was a simple dummy load available for testing these things.

By wrapping the control box in shielding, would that suffice enough to make a better decision as to internal vs EMI.?

Geez Narrawa yu luv a bit of a stir eh??
Good to see you're not sick of this subject yet??? I don't think it will ever be solved.
That last suggestion of yours, wrapping the control box in shielding, I actually tried. I ordered some material from the US of A and made a purpose built skid plate for my coil that incorporated it and also got the bride to sew it into the control box cover. No reliable way of measuring the impact but kind of thought it helped. The then new NFA 14x9 made it even better and the Commando 8" is the last resort late in the year.
I think this noise/interference is something that we have each and every year at this time and it is diminished in the cooler part of the year. Luckily that is when it is best for detecting/camping. I doubt any of the companies will fix the problem so that you can detect all year round. I'm guessing the sun and wind combo will win out every summer.
Luckily we have golf and Jewie fishing to compensate during this time.
cheers
Brett

Approximately every 22 years, the sun erupts with very intense solar storms and those storms can have a severe effect on electronic devices on earth.

We are in the middle of one right now, which is expected to peak in 2013 and NASA scientists believe it might be a catastrophic event if precautions are not taken (take that with a grain of salt, given that NASA is looking for funding).

It is highly likely that our detectors are picking up interference from these solar storms. The last 48 hours have been particularly intense.

http://www.thestatecolumn.com/science/nasas-goddard-space-weather-center-increases-focus-on-major-solar-storms/

Geez Narrawa yu luv a bit of a stir eh??

mulgadansa, honestly i cant see where im stirring.?
Its a subject thats intrigued me for years as it would have others.
I questioned a coil manufacturer some years ago about putting a top hat above the coil made of shielding....i got 50 lashes for that.
I thought of wrapping the box in shielding once also, it came from playing with antennas many years ago and placing shielding behind the reflector and taking measurements with antenna test gear. I was wrapped in the results.
It was not me who smeared +30 sunscreen over his coil either, it was a mate of a mate who's friend worked for ML who told him of this.

By all means pull me up if you see my asking someone to pull my finger.

I run shortwave radios. yes from valves to Phased Locked loops. And Digital. Sunspot Cycle is blowing them all out from Approx 2 Mhz right through to 18 Mhz Now it could go higher in the Spectrum I haven't been up there lately. But What Im getting at is these these radios are very well shielded. And the solar crap is still blowing them away.

G'day Narrawa,

You could possibly try a 5w .5 ohm resistor in place of a mono coil(plyg hooked up like a mono coil), but do not know if it would work due to their safety cct's. Either you would get over current, or there could be some fancy interlock so when things aren't behaving right on the tx side of things, the front end stays switched off. The 2000 has this cct, but I am unsure on the gp's and gpx's.

I don't think additional shielding wrapped around the box would help. It is already in a grounded aluminum case which will stop static buildup from harming the cct within.

Cheers Mick

Gday

There are many sources from which interference can be recieved by our detectors, and after all a coil is only another form of antenna thats function is to transmit and recieve so it is doing what it was made to do, it should be of no surprise to any of us that different sources will cause havok on one day and not the next as weather conditions have always played a part in interfering with all forms of radio communications, any electronic device that is designed to recieve information through the air will be effected by external influences.

I believe heat is another factor that will have a further effect on the way our detectors react, observing that the most interference will most often occur on a day when it is both warm and windy, this I feel has more to do with with static discharges from surrounding sources such as dry grass and vegetation, other sources such as electrically charged particles from power lines also sound plausible, but only more likely when you are in the vicinty of high powered lines, not when like in many parts of WA there are no power lines to be seen.

Also I feel that transmissions from telecommunication sources, such as mobile phone towers, and also from things like trains, like we observed near Karatha, and also in some cases interference from aircraft radar, the reaction by our metal detectors has definately increased in severity and happened more often since the introduction of machines in the gpx series, prior to this the worst effects we would experience was from lightning which would often give us advanced warning of a possible weather change.

In my way of thinking this can be linked to the way that the electronics of the gpx machines has been designed or as a result of components that have been used that were not present in the detectors previous to the gpx ones, it may be in order to make the machine less suceptable to the effects of outside interference the machine may have to be dumbed down to achieve that, and personally I would prefer to live with the odd bad day and to have a very capable machine than to be using a machine that was no better than I owned previously.

I think we just need to learn to manage the machine better in the times when the interference is at its worst, and all you can really do is, re tune, and make manual adjustments to get the machine as stable as you can, and then change down to a smaller coil.

cheers

stayyerAU

Gday again Narrawa
Just jerking your chain re the stirring , your posts are always interesting.
The top hat idea you mentioned. Have a look in my photo album on this forum and you'll see a 17x10 mini ufo I made a double skin top skid plate for, with the shielding sandwiched between the two skid plates atop the coil. I don't have any gear to measure the results with but it did seem to make some difference. The coil also had a bottom skid plate that was cut out along the spoke lines and then siliconed on. Bit of extra weight but negligible really.
I was detecting full time back in the 70's and early 80's and when the temp was up in the high 40's we used to do a fair bit at night time (mainly with a full moon) and although the detectors were vhf, it vastly improved their performance and stability.
cheers
Brett

I have contacted Minelab and explained the problem to them and their reply was that EMI can be coursed by many factors. The chap that I spoke to said he had experienced the same thing from time to time, you could try and tune it out a bit with the manual tune but then your detector is not running at it peak and you may miss nuggets. If you are not experiancing it constantly and it comes and go's you may just have to put up with it. It is more proned in the Northern climates and in hot weather. So you have it, there is not much we can do about it except wear it and bush on. So thanks fellows for your help and reply's
Wombat