Nokta FoRs Gold - Possible EMI Issue - Video

[DizzyDigger]

Took the FoRs Gold out again yesterday for some coin shooting at
our city park, and again blamed the constant chattering (EMI) on the
local power lines that were about 50 yds. away. Still, it's getting annoying.

This afternoon I drove a few miles back in the hills just to check if the
unit was chattering there too. It was, and there was not a source for EMI
within miles from the location.

Maybe I'm just nuts, and this is how the unit is supposed to sound, but
I do have my doubts. Spent many years in the world of EMC (Electro-magnetic
Compatibility) and know quite well what EMI sounds like.

Needed to have someone else with some knowledge of detectors take
a listen to it, just to make sure I'm not off-base. Made a quick video,
and while the video portion isn't great, the audio is what it's all about.

Do me a favor, if ya would, and listen to the machine. Is this typical
of a FoRs Gold?



Should add here that EMI does not always come from an external source,
although that is common. Other common sources for EMI are internal, relating
to circuit board design, or conducted, meaning the EMI follows a cable or loose
wire in the control box (acting as an antenna), and carrying the interference
into the electronics.

 

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[QNCrazy]

Just a little FYI but I didn't realize there was a Nokta specific subgroup in the metal detecting forum. might be worth checking out.

 

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[Treasure_Hunter]

Oops looks like I was typing same time as you, went to get something to drink then finished and hit enter and see you already posted..

 

[QNCrazy]

Already checked it out. Some good stories and advice. Nokta even has thier own profile. Learn more from this forum every day. Love it!!!!!!

 

[NeoTokyo]

For EMI I do get chatter like in your video inside my house, I can find quiet spots but still its mostly filled with EMI.

Power lines make mine chatter a little bit for a couple hundred feet.

Otherwise when I am out in the brush with nothing on I don't have any problems.
I recorded several video's with my GoPro before it went down stream and didn't notice any extra chatter from the Nokta.
I usually carry my pinpointer, my keys, my pick and a knife with me and it doesn't cause chatter either.

Contacting Dilek is one of your best bets right now, she might know exactly what to do without having to send it back.


dilek@noktadetectors . com

 

[californiagold]

Reminder: dilek is in turkey and they are 10 hrs ahead of us pdt. So they are probably gone till monday. So it might be till then before you hear anything

 

[DizzyDigger]

Posted a video in the Nokta forum late last night, and so far no responses.
Could well be they are out for the weekend.

A cell phone can cause EMI, that is true, but cell phones generally operate at
2.4 Ghz, so even a distant sub-harmonic of that should not cause an issue.
Also, I do not carry my cell phone when detecting..can't hear the damn thing
anyway. The Nikon D90 is well shielded, and does not transmit any RF at all.

As ya all know I'm a late sleeper, and just getting my wheels under me for
the day/night. Still, it's just past 3 so I have plenty of time to run up into
the hills and see how it does there.

Should clarify...aside from the chattering I am very pleased with the performance
of the machine. Even with the 5" Double-D, I've dug zincoln's down to more than
6". Haven't had the larger elliptical coil out in the field yet, but will take it with
me this afternoon.

It is possible that the Sensitivity function was not calibrated correctly, but that
would be a rare case as I'm sure each machine goes through a number of QC
checks before it get's it's final stamp of approval.

Back in a couple hours with the results.

 

[Treasure_Hunter]

Dizzy, just FYI, I wasn't trying to blame your cell phone, just throw out possibilities of causes.... If you want to send it to Kellyco go ahead.. I do know they are out of stock and waiting for the next shipment of new units but the Kellyco repair center did have spare coils, joysticks and end caps the last time I was there if that is the issue.

 

[DizzyDigger]

Dizzy, just FYI, I wasn't trying to blame your cell phone, just throw out possibilities of causes....

No worries at all TH; in fact I appreciated the input. Tracking down
an EMI issue is often like trying to toss a net over a ghost. First,
there's figuring out what is radiating the EMI/RFI, and second is
tracking down where it is getting into the circuitry of the effected
device.

Yesterdays trip into the hills plus reading a few technical papers
last night gave me a pretty decent idea of what the issue is,
and I don't believe it'll be a serious concern.

Here's a short video showing the area I drove up to.



Headed quite a ways further up the road to a spot I had picked
out in my mind in advance, and was surprised at what I found when
I arrived there:



So, I took a logging road that went up about 1000' in elevation
from where I was, but this time I wasn't so surprised:



Decided that was the spot to fire up the detector:



Did some research into power line EMI on the web last night, and
one thing I learned was that emission levels, or the distance from
which they affect a device can vary greatly depending on atmospheric
conditions.

If the Nokta FoRs Gold has any problem at all, it's a susceptibility
issue with radiated EMI from power lines, but based on my observations
it's not something likely to, for the most part, cause any performance issue.

There is some testing that Nokta could do (or may already have) that
might provide a solution, but it is time consuming testing (ie: expensive),
and it may not provide any performance boost at all.

I think of the Nokta FoRs Gold as a high-performance VLF detector, and like anything
else that is "high-performance", it runs the best when it is pushing the edge of
it's abilities, but not exceeding that limit. With that high level of sensitivity, it
doesn't seem unusual at all that the detector may be susceptible to power line
interference under certain weather conditions.

We've had very dry weather up until last night when a storm came
in, and when I got home last night I fired up the detector right in
the driveway...where I had the worst EMI chattering so far. Last night
there's was very little EMI or chattering, if any..weather had changed
and that knocked the EMI way down.

Everyone likes a good mystery, and for me this one is satisfactorily solved.

I've asked that the thread I posted for Dilek be removed, as I see no
reason to bother Nokta over an intermittent, common issue.

So, to sum it all up: I'm thrilled with the overall performance of the Nokta
FoRs Gold. Yes, it is sensitive to power line interference under certain
conditions, but most high-performance detectors suffer the same problem.

Now, I just need to get out there and find me some GOLD!

 

[californiagold]

Dizzy
I had a spot last winter where I was using fors with the 11x7 coil right under and off to the side of 3 powerlines. I did have a little trouble right under them but minimal off to the side. I run my sens at 80-85 always. Usually the only issue I have is chirpy hot ground. But it is very minimal. You definately hear the metal signals. Even tiny ones over the chirpy soil. Do you have the emi problem while the coil is sitting still on the ground? You might still have a defective detector. Dont be affraid to still contact dilek. They want things to be right for their customers. Besides you paid good money . It needs to work properly.
Good luck

 

[DizzyDigger]

Dizzy
I had a spot last winter where I was using fors with the 11x7 coil right under and off to the side of 3 powerlines. I did have a little trouble right under them but minimal off to the side. I run my sens at 80-85 always. Usually the only issue I have is chirpy hot ground. But it is very minimal. You definitely hear the metal signals. Even tiny ones over the chirpy soil. Do you have the emi problem while the coil is sitting still on the ground? You might still have a defective detector. Don't be afraid to still contact dilek. They want things to be right for their customers. Besides you paid good money . It needs to work properly.
Good luck

You've been a huge help, I very much appreciate your input.

I do have power lines on my property, both overhead and underground.
A bad ground somewhere could cause a load of EMI under certain conditions,
and from what I've been able to discern, the issue completely goes away
under higher humidity. Took the detector out in the front yard again today,
and again it ran very quiet...BUT, I did begin to pick up the EMI once again
when I got closer to the power pole. Further I moved away from it, the
less it was an issue, and after about 100' the detector was running very
quiet with no hint of EMI.

After all the testing and cogitating over the EMI issue, I do
believe the detector is working as designed.

Still going to send Dilek an email with the thread link and
videos, and maybe one of their engineers will check it out
and share their thoughts.

(Now, if I can just figure out how to read the depth during pinpointing!)

 

[californiagold]

Im sure you seen that the depth reading when pinpointing is in centimeters. Not inches.

 

[QNCrazy]

10 cm = 4 in approximately if that helps.

 

[DizzyDigger]

I'm sure you seen that the depth reading when pinpointing is in centimeters. Not inches.

Actually...no..hadn't seen that, but had suspected.

Just re-checked the manual, and they don't specify what unit of measurement
is used for depth indication. My brain still thinks in "old American", so guess
I'll need to get used to translating CM to IN. No biggie.

 

[californiagold]

Well for simple starters. 30cm is a foot. 15cm 6". Fun huh

 

[DizzyDigger]

Well for simple starters. 30cm is a foot. 15cm 6". Fun huh

It's not a problem at all..just divide by 2 and you're close enough.
I usually go off the signal strength and sound, but my ear does
play tricks on me from time to time.

No problem...truth is, if I like the signal, I'm diggin' till I find it...

 

[DizzyDigger]

Regarding the EMI issue..

Today I received a superb response from Nokta, and I'd like to
share a couple of paragraphs. This seems to be excellent information
that could apply to many sources of EMI:

"
Additionally, noise has a casual nature even if the source is specific such
as power lines etc. External noise sources may interfere [with] the device
depending its own design. Different brands/models of metal detectors may
have different behaviours in same case. This is because all detectors are
not doing things exactly same way, or it may have a weakness relative
to the others in specific conditions. One detector may behaving good,
noiseless at some place relative to the other may interfere more with some
noise source somewhere else.

Urban areas are full of noise sources because of electricity an
technological environment, but high-voltage transmission lines found almost
everywhere and are significant noise sources because high voltage and high
current has a great radiation capability and also the frequency is low (50
or 60 Hz). This frequencies are more near to VLF and have more influence
rather than they do to high frequency communication equipment (such as FM
radios, mobile phones etc.).

Typically ISM and GSM band noises (cellular phones etc.) do not affect VLF
metal detectors because the sub 1GHz to 15 GHz frequencies are filtered
strongly by metal detectors in natural way, additionally even lower
frequencies (HF, VHF) are also highly blocked by the filters inside the
detector.

Regarding the ground balance; in case there is a high noise reception of the
detector, the ground balance may not be adjusted accurately by auto-gb
feature, that a user can better do it manually. But, the noise in the video
does not seem to be of incorrect ground balance. The device will be produce
a noticeably increasing noise only when the coil is swept on the ground (as
experienced detectorists will know it) if the ground balance is incorrectly
adjusted.

If there is a noise problem from external sources the best way will be
reducing its gain and/or trying different modes of the device. Modes have
different characteristics (gain base, differentiation delays, etc.) and also
a frequency shift is also worth trying (Fors Core does have this function,
selectable from the menu).


I am now more than satisfied that the detector is operating just as it should,
and that my initial assessment of powerline interference was correct.

My thanks to Dilek and Nokta, as that's above and beyond the level of
service most any other company would provide.

 

[californiagold]

I was going to ask you if your core has a frequency change like fors gold. But I guess it dont. Ive never have used mine, but it might help with certain emi. Good luck with your core.

 

[DizzyDigger]

I was going to ask you if your core has a frequency change like
fors gold. But I guess it dont. Ive never have used mine, but it might help with certain emi. Good
luck with your core.

I don't have the Core, I have the FoRs Gold (Pro Pack), but I am sure he
was referring to the FoRs Core circuitry which is also used in the FoRs Gold.

Thought about changing frequencies, but the manual also suggested
that optimal performance may not be available when changed from
the preset (#3) Freq.

If you watched the last video I posted, it shows the detector operating
perfectly when away from the power lines, and even here at home (where
I had the initial problem) I am no longer getting that EMI due to the
change in the weather.

The detector is operating perfectly, and while it did pick up that power line
EMI, any detector probably would have. Case closed as far as I'm concerned.

Wanna find a nugget so bad I can dang near taste it!

 

[GoldminingWookie]

I just just recieved my fors gold pro pack yesterday and noticed the same issue. I really appreciate reading all of you guys comments about it. It's reassuring to know it's not a defect. Took it out for a few hours aand found a fair amount of scrap but alas no GOLD. I'm new to treasurenet and will update my finds.

 

[IMPDLN]

EMI is a weird beast for sure. Radio waves of different types travel through the air in different ways. I have a spot I hunt that is miles from any power lines or any obvious sources of EMI, yet no matter what machine is used in there the EMI can't be tuned out. Go around the corner into a different wash and don't have the problem. Been tested with 4 different Minelabs and 2 different Gold Bugs. My explanation for the problem and most reasonable cause would be the cell phone tower 7-8 miles away that likely has an antenna pointed in that direction. Also this seems to be more erratic during our monsoon season at this particular area.

On a similar note.....If I have my cell phone on when detecting, I can hear incoming calls and messages on my Minelabs before they reach the phone, lol. So to airplane mode it goes before I turn on my detectors. Dennis