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Is Emi From Telecomm Equipment The Beast That Can't Be Slain?


SwiftSword

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All, 

I'm looking for some insight on my experience. This is totally anecdotal, I have done no scientific testing. 

I find that my Deus II is getting great depth in open spaces, where there are no obvious sources of EMI, or only a single source (like an overland transmission line). As soon as I get into suburban backyards, my depth in any mode is greatly reduced. Yesterday, I detected across the street from a fire station (with a big radio tower on the roof) and found the Deus could barely see a penny lying on the ground.  Even in single frequency mode I can't ever find a quiet one.  

It seems to me that communication equipment (radio / cell / wifi) specifically causes these problems. My understanding is that all these things transmit on a wide variety of frequencies. I know there are some folks here with an engineering background – do you see a possibility that manufacturers will overcome this problem in the near term, or are we screwed until the next technological revolution in MD?

 

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You need to choose smoother program and do frequency scan. Sensitivity should to be reduced also. That is only way. 

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5 hours ago, SwiftSword said:

...

I find that my Deus II is getting great depth in open spaces, where there are no obvious sources of EMI, or only a single source (like an overland transmission line). As soon as I get into suburban backyards, my depth in any mode is greatly reduced. Yesterday, I detected across the street from a fire station (with a big radio tower on the roof) and found the Deus could barely see a penny lying on the ground. ....

 

I noticed that my D2 is more sensitive to EMI than my D1 . My D2 becomes very chatty when I am very close and especially under powerlines , while the pb disappears as soon as I am 20 or 30 yards away from the powerlines .  

Long story short my D2 does not like powerlines . Hopefully I dont have any other EMI issues with it  , including in suburban areas ...

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When Dave Johnson speaks, people listen:

Common sources of electrical interference include:  overhead electric power lines, underground power lines, other metal detectors, telephone lines carrying electronic data, computer systems, electric fences, old CRT-based televisions, cell phones, thunderstorms,  fluorescent lights, metal vapor lamps, military aircraft with electronic warfare countermeasures turned on, electric motors, VLF military communications systems, and automobile ignition systems.   It will sometimes be the case at home, in the showroom, or in an urban environment that there are several different sources of electrical interference present simultaneously.

I count 16 sources he mentions and note he says 'include' so he's not covering all.  The proliferation of sources is the first problem.  Different standards around the world is another (e.g. 50 Hz vs. 60 Hz AC transmission frequency for electricity distribution).  Then there's the 'moving target' problem where new technologies and applications add more sources.

I predict that if you took a good detector engineer to a typical site he could (possibly only after hundreds of hours of R&D) build a detector that would deal with that local EMI and still work well.  Doing that for all possible sites??  This is the problem they are actually presented with.  (I did say 'typical'.  Your transmitter tower on top of the fire station -- that might not be solvable.)

You may want to read Dave's full article.  I just reread it.  13 years later it's unfortunately still relevant.  And he has an answer to your direct question which you won't like:

...The battle will never be won because metal detectors are by their nature designed to detect magnetic fields, and electric current always produces magnetic fields.

 

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On 11/5/2022 at 9:32 AM, SwiftSword said:

It seems to me that communication equipment (radio / cell / wifi) specifically causes these problems. My understanding is that all these things transmit on a wide variety of frequencies.

I have EMI from communications equipment. It bothers the Equinox and the D2 has no issues> So there is that! 

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I guess it depends on the source and type of the EMI as to how it affects the D2. Most times, I have no problems with EMI in parks, schools, neighborhoods, etc, but ocassionally I'll hit a spot that just lights up with chatter. It's usually a relatively small area and very localized, so I suspect it may be underground wires or junctions or possibly a wifi or cell repeater or something like that. But usually I can just walk a little past the noisy spot and the chatter goes away.

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I just detected a new permission today  that was nearly 5 acres with a large house and gardens.  About half of it was really annoying as the neighbor had one of those invisible dog fences right on the property line.  I tried different programs, lowering the sensitivity down to 80, and even single frequency (which seemed just slightly better), but nothing worked.  
Any ideas?

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On 11/12/2022 at 7:32 PM, NCtoad said:

I just detected a new permission today  that was nearly 5 acres with a large house and gardens.  About half of it was really annoying as the neighbor had one of those invisible dog fences right on the property line.  I tried different programs, lowering the sensitivity down to 80, and even single frequency (which seemed just slightly better), but nothing worked.  
Any ideas?

The dog fence is probably transmitting on a frequency very close to the D2's stock frequency.

You might try auto noise cancel or even manually changing the frequency shift numbers to see if you could quiet it down.

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On 11/12/2022 at 9:32 PM, NCtoad said:

I just detected a new permission today  that was nearly 5 acres with a large house and gardens.  About half of it was really annoying as the neighbor had one of those invisible dog fences right on the property line.  I tried different programs, lowering the sensitivity down to 80, and even single frequency (which seemed just slightly better), but nothing worked.  
Any ideas?

I've got some spots with underground power lines that make it impossible to detect on any program or single frequency. Also under overhead lines you may just have to deal with the chatter, targets will still come through.

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