Dealing with EMI

Dont you love it when you are having a great day out there in the bush then rain clouds come over and the wind picks up, and then your detector starts speaking to you through squarking and electronic interference. We can describe what we say in wonderful terms.

So what do we do?- Put on a smaller coil, and just give up for a while.

On other topic I was was told that putting on a DD coil deals with EMI a lot better.

Whats your experience?

Jeff

believe it or not but I have been able to cut back a fair bit of all squabble within my 3500 as the day goes on...I used to have problems with keeping it stable once it got to around lunchtime, especially during the hot days and like most others when weather changes are around...I have simply installed a piece of anti RF cloth between the 2 main circuit panels in the unit...the stability has improved heaps and the unit runs a lot smoother,...since then, several mates have done the same and reported great improvements with extended detecting time on those days when you would normally pack up .....its cheap and might be worth a try for others who experience the same problems
cheers SS

please explain ...... with pics would be GR8 too

byronbinalong wrote:please explain ...... with pics would be GR8 too

I haven't got any pics available yet as I would have to take the back panel off the machine, I'll try to get something done tonight...
it is straight forward...I was a bit optimistic about it when one of my mates used this method..but soon changed my mind when I got a piece from him and tried it.....you might be able to get a piece of this type of cloth in electronics places such as Jaycar electronics, I would have to check....you can buy all sorts of RF and other shielding cloths on the net but most likely have to buy a meter of it...depending on what frequencies you want to shield against you also have a choice.......it might pay to find out if anyone else would like a piece and in that case the buyer could sell it on to others...you will only need a piece about 4 by 6 inch( or the size of your mainboards), ...there is not much room within the detector so just enough to slide between the 2 electronic panels will do the trick...it is easier to put in if you remove both ends on the unit as you can slide it in easier....that's all that's to it...even though the panels are all coated be sure not to use anything metallic such as tweezers as you don't want to risk a short within the system on the boards.....
I'm not familiar with internal circuit boards on other units but I think this could be applied to any with multiple boards as it simply shields opposite components from unwanted frequencies....I think most times manufacturers will pay great attentions on actual layout of components to eliminate interferences but obviously there is limited space on the boards.....

PS..I realise this post was posted by Jeff about EMI and I relpy mainly about RF interference but I would like to point out that it has reduced my EMI problems dramatically..

What is EMI and what can be done about it? My personal thoughts are that it has nothing to do from anything outside the detector but is internally generated. If that is the case it isn't actually Electromagnetic Interference but simply the detector circutry overloading and creating some sort of feedback. When I get it, and I don't often do, I simply switch the machine off, count to ten, and switch back on and away I go.

My worst problems happen in WA when the air gets very dry. The coil seems to become static charged and the discharges through anything it comes in contact with. This produces an annoying squeal, sometimes two or three times a minute. Vey annoying but doesn't stop me detecting.

Cheers, Jim

granite2 wrote:What is EMI and what can be done about it? My personal thoughts are that it has nothing to do from anything outside the detector but is internally generated. If that is the case it isn't actually Electromagnetic Interference but simply the detector circutry overloading and creating some sort of feedback. When I get it, and I don't often do, I simply switch the machine off, count to ten, and switch back on and away I go.

My worst problems happen in WA when the air gets very dry. The coil seems to become static charged and the discharges through anything it comes in contact with. This produces an annoying squeal, sometimes two or three times a minute. Vey annoying but doesn't stop me detecting.

Cheers, Jim

Yes Jim....I go along with that and think most of it is internal interference, hence I used the cloth for shielding, I also used to get instability mainly as the day gets hotter, it must run the internals pretty hot then which will affect the performance, but we do also encounter EMI from outside depending on the day, maybe better internal shielding with assist in reducing this...
cheers SS

granite2 wrote:What is EMI and what can be done about it? My personal thoughts are that it has nothing to do from anything outside the detector but is internally generated. If that is the case it isn't actually Electromagnetic Interference but simply the detector circutry overloading and creating some sort of feedback. When I get it, and I don't often do, I simply switch the machine off, count to ten, and switch back on and away I go.

My worst problems happen in WA when the air gets very dry. The coil seems to become static charged and the discharges through anything it comes in contact with. This produces an annoying squeal, sometimes two or three times a minute. Vey annoying but doesn't stop me detecting.

Cheers, Jim

While I agree that there is the possibility that in some circumstances internal feedback can happen, I also have no doubt that EMI is a very real issue, if there was not such a thing then how could you account for a machine running erratically when there is a thunderstorm approaching?, or a machine picking up the pulses of another detector operating nearby, all these are externally generated and its the coil (antenna) that is picking it up, as you say Jim on hot dry days you get static generated externally from grasses, trees, wire fencing etc etc, or simply the coil being scrubbed on the ground, so these are all external influences and all of these could be catorgorised under the label of EMI for the want of a better description.

The issue of internally generated electronic feedback is another story all together, and like I said I find it is plausible that in some circumstances it could in fact happen, and when you look at the way he gpx 4500 and also the gpx 5000 go haywire sometimes, even worse than previous models, then you would also have to consider that if there has been a change in the circuitry or components then there is also the possibility of there being internal flaws to the electronics that have not been ironed out as yet, but I think that if this were the case then the issue would be present all the time and not intermittent and that simply switching off the machine would not correct it.

cheers

stayyerAU

Actually the static is generated by the coil moving back and forth in dry air. The Discharge and resultant ping happens when the coil Discharges the electrical build up upon grounding.
As for thunderstorms - I have heard people saying your detector can pick up thunderstorms 100's and even 1000's of klm away. My experience has been that they must be fairly close to cause much problem. We were once detecting near Ararat in late summer when 3 seperate thunderstorms approached. There was thunder and lots of visible lightning but it wasn't until the got closer that they caused enough interference to make detecting difficult.

I don't know much about emi but we have never had the problems that many people seem to have and we have owned every model detector ever built by Minelab.

One thing I can say for sure about internally generated intereference is that it does happen. There simply is no other answer for this happening when you are hundreds of klm away from any generated emi such as microwave towers etc

Cheers, Jim

We dont seem to have the problems as much as others talk about either.

When a detector (or coil) is new our first reaction is 'isn't this really quiet' but
over time all the little noises sneak back but you get used to them.

I wonder if taller people have less of a problem? Coil being further away from all metal and body.
Sometimes you can wave your hand over a coil without any thing in it and get a small response.

When our Ground Hogs got noisy we got into giving them a CRC bath. Inside and out, connections too.
Made them very quiet after that. Did stop doing that when told how bad it was for electronic equipment.

Maybe cleaning the connections more regularly might help.
Probably not really EMI related, more noise in general.

Alan

Thunderstorms must surely cause a fair bit of interference..some of you might even have found this back in the VLF days....I recall heading up to Wedderburn from Geelong with my trusty Whites 5000D...I left at 2.30 am and once on the highway I noticed massive lightning up ahead in the direction of Ballarat, by the time I got there the sky was still clear and it looked like the lightning was somewhere around Maryborough, I kept driving till I arrived just on dawn in Wedderburn, still lightning ahead somewhere up towards the Murray, ...as it was clear all night and all day I figured it was just electrical discharge , not thunder storms, but....all day none of us could use our detectors, they just went haywire and would not keep stable....

Hi Guys,

Generally internal noise can be associated with a slight warble on your threshold. Generally this is due to the noise floor of your detector. However if there was a bad solder joint this could cause the detector to act up and it would be a hell of a lot worse than the slight warble of the threshold. If bumping your control box causes a response from your detector and it can be confirmed that it is not the coil plug wriggling a bit, that would be a fair indicator that there is an internal problem. Also dirty coil connectors can cause noise so it is a good idea to keep them clean and dirt free. Another source could be from a broken coil cable, especially where the cable enters the coil housing through the strain relief. I leave my strain relief fairly loose to prevent the coil lead from going bad there.

Then there is the emi! I find that aircraft flying over head can cause real problems. I normally have to stop detecting and wait for the plane to pass and then go on my merry way again. There are also a whole range of other things that interfere like AM radio broadcast, microwave towers, lightning, powerlines and solar radiation from the sun, oh almost forgot, Garret pinpointers! But we can do something about that one!

As for the coil discharging spikes, I have experienced this but have not for quite some time. On my SD2000 I think it was my front endcap and the coil plug not grounding to the detector case because of the paint insulating them. Everything is nicely grounded to the detector case now and it does not seem to do it anymore. Also the theory of the coil discharging static into the ground seems plausible too, especially in low humidity.

If your coil picks up your hand(PI detector) you have a coil shielding problem.

Cheers Mick

G'day Jeff.You was told correct. EMI is both internally(through the machines electronics) and externally generated via charged particles in the atmosphere.It is certainly generated and received through the coil,more so on larger monos than small.By using a dd coil in the place of a mono you'll find EMI will be reduced dramatically.Pulse detectors are designed not only to transmit pulses into the ground and into the surrounding atmosphere through a coils windings, but also to receive pulses from other external forms of power sources such as that of electro magnetic activity eg,thunderstorms overhead or underground power lines,large aircraft etc,etc.Hence small or large coils act like small or large antennas.The larger the coil,the larger the transmit and receive signal will be. By winding coils in a particular pattern and having the coil wire shielded appropriately,helps reduce EMI(such as that of the DD or figure 8 configuration).Coils can be manufactured to operate a lot quieter than what they currently are now,but at the same time,trying to maintain coil sensitivity will be the issue.

Cheers kon61.

hi jeff
back when i had my 4000 it had a sticker on the bottom that read...this machine has been built to accept external sources of interferance as
required by us law 401...or something like that...maybe some one has a 4000 with that sticker and could quote it excatly..

i figured minelab had to do that so the goverment or who ever could protect sensitive areas with jammers of some sort

if somebody knows the proper reason behind this law or more about it i would love to know what it was about

cheers