Atmospheric EMI interference

[Hawkear]

Asking for a bit of advice and opinions.
Went out two days ago successfully with the 5 just purring. Today was horrible with false signals coming in thick and fast. Both days were in the same (although difficult) ground so why the difference.
Has to be atmospheric EMI but although the skies both days were cloudy no evidence of lightning activity although it sounded very much like it with signals coming every few seconds at times. Just gave up in the end.
My question is why does there appear to be so much atmospheric EMI activity some days but not on other days with similar weather conditions.
A second question might be are there any forecasts that can predict that so that I might find other things to do?

 

[fwdoz]

I had a lot of false signals & EMI chatter yesterday also (a lot more than usual). Put it down to the intense moisture & heavy air with yesterdays fog along with the lovely wet red clay.

A few pockets were not as bad, but it still made detecting far more difficult.

 

[Hawkear]

Yes was very foggy in the morning so settled for the Talbot market, and didn’t get out until the afternoon when things had cleared. Still cold damp and overcast without much wind.
The redder coloured clays were much noisier than other patches but that does not explain why two days earlier those same red clays were relatively quiet.
I have heard of “sprites” which are electrical discharges in or above clouds which are unseen from the ground.
Maybe if we have some meteorological informed people among us an opinion could be offered as to why some cloudy days seem more active EMI wise than others.
Edit Possibly an electrical potential difference between earth and atmosphere manifesting itself more so in the more electrically conductive patches of earth? If so can this be measured?
Edit 2 Could it be Cosmic caused by interaction with Cosmic rays or Suns activity?

 

[user 4485]

Solar flares are also thought to cause issues.
https://www.sws.bom.gov.au/Solar/1/10Here's some previous threads on EMI issues:
https://www.prospectingaustralia.com/threads/emi-in-the-gt.24104/
https://www.prospectingaustralia.com/threads/wind-emi.15131/
Another cause can be static electricity discharges from yourself & on conductive vegetation in low humidity.
https://www.minelab.com/__files/f/11043/KBA_METAL_DETECTOR_BASICS_&_THEORY.pdfSection 2. More Advanced theory. 2.1 Environmental magnetic noise sources has some info under atmospheric sources but it leans mostly towards lightning & long conductors (fences etc.) being the most common & likely cause.
I have had issues with EMI spikes with no obvious location cause only to find out later there were storms, but hundreds of kilometres away, so my thoughts are this storm activity doesn't have to be localised for the issue to be present. Obviously just gets worse as the activity moves closer.

IMO wind can contribute to the static discharge too (although Minelab say it's minor/rare) but there isn't much to support it only my observation that windy days can be problematic.

 

[Hawkear]

Solar flares are also thought to cause issues.
https://www.sws.bom.gov.au/Solar/1/10Here's some previous threads on EMI issues:
https://www.prospectingaustralia.com/threads/emi-in-the-gt.24104/
https://www.prospectingaustralia.com/threads/wind-emi.15131/
Another cause can be static electricity discharges from yourself & on conductive vegetation in low humidity.
https://www.minelab.com/__files/f/11043/KBA_METAL_DETECTOR_BASICS_&_THEORY.pdfSection 2. More Advanced theory. 2.1 Environmental magnetic noise sources has some info under atmospheric sources but it leans mostly towards lightning & long conductors (fences etc.) being the most common & likely cause.
I have had issues with EMI spikes with no obvious location cause only to find out later there were storms, but hundreds of kilometres away, so my thoughts are this storm activity doesn't have to be localised for the issue to be present. Obviously just gets worse as the activity moves closer.

IMO wind can contribute to the static discharge too (although Minelab say it's minor/rare) but there isn't much to support it only my observation that windy days can be problematic.

Thanks for that.
That is a wonderfully informative article written by Bruce Candy and certainly answers a few of the EMI observations I have noticed.
Why when detecting close to a big town EMI picks up at certain times of the day usually later - maybe because people getting home start turning on appliances en masse.
Static discharges when just touching dry grassy clumps on low humidity days
Sferics as he calls them being multi sourced from near and far electrical storms.
He certainly allows for sferics to be manifested not only as transient signals to be heard clearly from lightning up to 1000 km away But also from far wider afield as threshold instabilities.
Maybe the lesson is to keep an eye out on the wider weather forcast for lightning activity and just be thankful for the better days or if there is the chance of major lightning activity within up to 500 or 1000km, just go somewhere else where you can engage in detecting that requires less gain.

 

[Hawkear]

Went out yesterday afternoon with weather conditions similar to the previous day when there was significant interference.
I checked the BOM site for lightning activity and all being clear for thousands of km was hopeful of better EMI conditions.
Unfortunately there was still EMI sferics activity, although not as bad early, it did worsen as the rain band came closer.
There was no apparent lightning activity going on while I was out and on checking the BOM website when I got home no activity was showing there either even though the rain band was showing directly over the GT. So if not lightning what is causing the EMI sferics?
After a bit of googling, I found information on TLEs (Transient Luminous Events) such as sprites which are electrical interactions by storm clouds with the ionosphere. Fascinating stuff about atmospheric electrical activity we are just coming to grips with. Here is a link.

Probably not responsible for the sferics I encountered as they are associated with severe electrical storms, but makes me wonder if there are more mysterious electrical relationships between the ionosphere, clouds and the ground that may be responsible for some of the bad EMI conditions we encounter during detecting.
Maybe nothing that could ever be controlled other than learn when to go out or not to go out with my sferic detector.

 

[OzzieAu]

Another potential source is wind generators in the vicinity, not just big windfarms, but smaller domestic units that may be on nearby private land.
I experienced a emi issue one time in the GT that would come and go relative to the wind speed and direction.
It wasn’t till I crested a hill and saw cleared land and a dwelling in the distance with a large tower and wind generator spinning and oscillating with the wind direction.
I lifted the 17 x 13 Evo on the 5000 and pointed at it and knew it was the source of my EMI.

 

[Hawkear]

Another potential source is wind generators in the vicinity, not just big windfarms, but smaller domestic units that may be on nearby private land.
I experienced a emi issue one time in the GT that would come and go relative to the wind speed and direction.
It wasn’t till I crested a hill and saw cleared land and a dwelling in the distance with a large tower and wind generator spinning and oscillating with the wind direction.
I lifted the 17 x 13 Evo on the 5000 and pointed at it and knew it was the source of my EMI.

There was a house with a windmill nearby but when doing a 360 with the coil there didn't seem to be any noticeable direction to the sferics. I was in the Talbot area so probably about 25k to the big Waubra wind farm so worth a thought there.
Was the EMI interference from the wind generator regular in nature or just randomly spaced signals.

 

[OzzieAu]

Was the EMI interference from the wind generator regular in nature or just randomly spaced signals

I could hear the EMI increase in intensity with the wind speed and direction ( I was basically down wind from it).
The interference was noticeable just before the gusting wind hit me, sort of like...... hear comes the wind.
It was one of those blustery days and that wind genny was intermittently speeding up and slowing down.
Needless to say I didn’t hang there for long...

 

[Hawkear]

Thanks OzzieAu. Still googling and there seems to be a possibility of the build up of static electricity in wind turbines that self discharges periodically. That could create a broad spectrum radio emission if large enough. Certainly worth a thought but I suppose maybe broad spectrum EMI is overall too complex an issue to see a solution at this stage.
I'll resolve to take a bit more notice about the environmental situation in future occasions other than letting off a few expletives and heading back to the car.

 

[Hawkear]

Just picking up on this earlier post.
Noted that NASA warned of a solar storm observed last Friday. Initially the ejected solar particles were expected to hit the Earth on Tuesday but now expected Thursday or Friday, as they have been observed moving slower than expected.
Went out yesterday (Tuesday) and the detector was very quiet but this afternoon (Wednesday) even with a clear sky and little wind, lots of EMI even when well away from a town.
Wondering whether this may have been the result of the solar storm reaching earth
Wondering also if other prospectors noticed bad EMI this afternoon and possibly over the next day or two. If similar EMI conditions are noticed Australia wide at the same time that could be telling.

 

[Hawkear]

Just picking up on this earlier post.
Noted that NASA warned of a solar storm observed last Friday. Initially the ejected solar particles were expected to hit the Earth on Tuesday but now expected Thursday or Friday, as they have been observed moving slower than expected.
Went out yesterday (Tuesday) and the detector was very quiet but this afternoon (Wednesday) even with a clear sky and little wind, lots of EMI even when well away from a town.
Wondering whether this may have been the result of the solar storm reaching earth
Wondering also if other prospectors noticed bad EMI this afternoon and possibly over the next day or two. If similar EMI conditions are noticed Australia wide at the same time that could be telling.

I have to post an embarrassing retraction.
On the way home from the GT today I couldn't help myself when passing some diggings releasing the 5. I soon experienced dismay at the same seeming EMI conditions as the day before.
Felt that this couldn't be right and checked the settings and found that the the switch on the front panel of the 5 had been somehow had been knocked to deep. Explained everything.
I switched it back to normal and everything was OK.
Looking for something to rationalise my failure, I remembered my mates similar incident some years ago, when he accidentally knocked his switch to Cancel and had a lovely mornings detecting with a remarkably stable threshold but unfortunately no target sounds at all.

 

[Syndyne]

We've all been there Hawk! Had days where I'd just wander off with the mobile still switched on in the pocket rather than on airplane mode, or left in the ute. I soon know what's happening though and then have a bit of a chuckle (after a good face palm moment).

We had a real nasty week of EMI in 2018 after an X-Class (X8 if I recall correctly) flare from the Sun. It was Earth facing and hit the planet directly. That was the worst EMI I've ever experienced with the Zed. Almost enough to make me turn it off and wait a few minutes at times. No tuning through the channels removed it either. I could see others chiming in here on the forums from around the states with similar complaints that week. Very nasty.

Another time in the years previous to that I was detecting with the SDC (possibly with Heatho at that time?) and we were hearing earthworks going on about 5 or 6 kilometres away. The bulk of that was coinciding with the impacting of a large hydraulic hammer on an excavator working on a rock dam wall. We could hear it in the distance so knew what it was immediately.

The strangest of all the signal peaks for me came from a night swing with Reeks a few years back and we both copped a very loud ping at the exact same time (could hear it on both modules even from a good distance apart) from a small asteroid burning up upon entering the atmosphere. I saw it visually overhead. Made me jump actually!

Funny the things that crop up during a day's swinging.

Regards,
Shauno.

Edited for missing word.

 

[Jaros]

Weird these astronomical phenomena we have these days-in our time that is.

 

[Hawkear]

Started this thread to see if there might be ways to predict when atmospheric EMF interference (man made or natural) would be bad. Have been out detecting on occasions when it has been so bad as to make detecting impossible.
I bought this little lightning detector to see whether it could help. We just had a fierce electrical storm pass by home and it was going berserk even when the storm had passed and no lightning to be seen or heard.
Not quite sure if that’s going to be a lot of help as usually the weather forecasts can tell you that.
Anyway will continue to monitor it especially before heading out for a day and see if anything predictive significance shows up.

 

[Davent]

where did you get that from? the lightning detector.

 

[Hawkear]

Hi Dave.
I bought it on eBay to go with our Pantech weather station (Pictured). Unfortunately it does not seem compatible with our model But it still works as a stand alone unit and indicates lightning when the led glows.
Can’t remember how much I paid for it but there appear similar units on eBay now Around 70 odd dollars.
We love our weather station, had a couple but this one although expensive (approx $300) is the best and I see newer models that would probably be comparable with a lightning sensor.
Great gear to have just because you can.

 

[user 4386]

Started this thread to see if there might be ways to predict when atmospheric EMF interference (man made or natural) would be bad. Have been out detecting on occasions when it has been so bad as to make detecting impossible.
I bought this little lightning detector to see whether it could help. We just had a fierce electrical storm pass by home and it was going berserk even when the storm had passed and no lightning to be seen or heard.
Not quite sure if that’s going to be a lot of help as usually the weather forecasts can tell you that.View attachment 7401
Anyway will continue to monitor it especially before heading out for a day and see if anything predictive significance shows up.

An expensive lightning detector like Boltek’s detect lightning up to 400 km away. Cheap ones will detect up to 40 km. You can't hear thunder beyond about 25 km away. So no thunder but it will still detect distant lightning.

 

[Calico]

You guys are probably already onto it but the app My Lightning tracker is free. Shows real time position and klms to nearest strike. We use it for work and you can zoom way out to 1000’s of klms. Just click on the closest dot(strike) to get distance and time. Cheers.

 

[Moneybox]

I just switch on the GPX6000 and get a fairly convincing audio report