Does EMI noise reduction even do anything?

Cherry Picker · Sep 18, 2022

Thanks Carl.

What made detectors so much more stable 30+ years ago? I don't remember dealing with all this snap, crackle, & pop back then. Was is that detectors were far less sensitive, or less interference to deal with like wireless, etc.?

First detector I remember having EMI issues with was the Fisher F75 LTD. I sold it because the noise was just too much for me after years of no interference.

Diga · Sep 18, 2022

Thank you for the explanation Carl. I have 2 questions that I hope you can answer:

1) At any given frequency, is the harmonic static, or can it vary?

2) When it comes to our hobby and EMI (MI

), what do you see happening in the future?

goodmore · Sep 18, 2022

Detector said:
Thanks Carl.

What made detectors so much more stable 30+ years ago? I don't remember dealing with all this snap, crackle, & pop back then. Was is that detectors were far less sensitive, or less interference to deal with like wireless, etc.?

First detector I remember having EMI issues with was the Fisher F75 LTD. I sold it because the noise was just too much for me after years of no interference.

EMI or the sprawl of electric gadgets got worse.

longbow62 · Sep 18, 2022

There are non metallic EMI shielding materials. Shielding the top of the coil might reduce EMI enough to make it's affects negligible. I've kinda been researching the possibilities.

Cherry Picker · Sep 18, 2022

longbow62 said:
There are non metallic EMI shielding materials. Shielding the top of the coil might reduce EMI enough to make it's affects negligible. I've kinda been researching the possibilities.

I was thinking some kind of lightweight shield.

I've noticed the EMI, at least in dodge, gets a lot worse during the day. If I go out hunting before the sun comes up my detector is actually pretty quiet. Around 7:00 AM it starts going crazy.

Carl-NC · Sep 18, 2022

Detector said:
What made detectors so much more stable 30+ years ago? I don't remember dealing with all this snap, crackle, & pop back then. Was is that detectors were far less sensitive, or less interference to deal with like wireless, etc.?

Both, I'm sure. You can still take out an old TR/VLF and it'll run quietly. Also coils are bigger, also internal filters and audio have been design to be much faster for target separation. Nullum gratuitum grandium.

Digalicious said:
Thank you for the explanation Carl. I have 2 questions that I hope you can answer:

1) At any given frequency, is the harmonic static, or can it vary?

2) When it comes to our hobby and EMI (MI), what do you see happening in the future?

If the detector runs at a rock-steady frequency then the Nyquist frequencies (often called the harmonics) will also be rock steady.

I would expect more coil designs that are differential and cancel far-field EMI.

longbow62 said:
There are non metallic EMI shielding materials. Shielding the top of the coil might reduce EMI enough to make it's affects negligible. I've kinda been researching the possibilities.

Electric field shielding is cheap and lightweight. Magnetic field shielding is expensive and heavy. Yes, you might be able to shield just the top of the coil and block some EMI. You could also use a Halbach coil design which is sensitive in one direction. They are heavy and difficult to make. Or use a differential coil like is used on the GPZ. That would be my vote.

itsaring! · Sep 18, 2022

longbow62 said:
There are non metallic EMI shielding materials. Shielding the top of the coil might reduce EMI enough to make it's affects negligible. I've kinda been researching the possibilities.

Shielding inside a couple Bigfoot coil tops.

longbow62 · Sep 18, 2022

itsaring! said:
Shielding inside a couple Bigfoot coil tops.

I was thinking the same, but with multiple coatings with foam/air gaps between.

Does EMI noise reduction even do anything?

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