Emi Revisit

[GB_Amateur]

2 hours ago, kac said:

They make a silver paint too but it is really pricey, bottle might cost as much as an average coil.

That sounds like a colassal waste of $.  Graphite paint has already been mentioned, and except possibly for durability it seems from a practical standpoint it ought to be as good.

I'm a bit skeptical that trying to shield the coil will have much impact on EMI, but I do like the experimentation you guys are doing.  Just make sure it's reversible.  The cable is coaxial (braided outer shield conductor) which is killer shielding.  The control box isn't as easy but Simon has shown it can be done and that the manufacturers already do a good job at least in some cases.  But the coil itself is meant to receive RF -- that's how/why it works!

BTW, you can buy metallic copper tape with conductive adhesive (make sure to get the conductive adhesive since they make versions with non-conductive adhesive) which might be worth playing around with.  However, it might not be practical to take into the field for hours as it will increase the weight of the coil much more than aluminum foil, for example.

I wish Carl would see this thread and respond.  He could probably short circuit some of these ideas, but then he'd take away the fun you're having.  😁

[kac]

Not sure if graphite paint would work, it is conductive in the sense it can carry electricity but it isn't metal.

A big sheet of emi tape on a coil will smother it. I used a foil that is the same used in hot foil stamping and is less than .0005" of an inch thick. on it's own it is barely detectable. My thoughts a thin copper wire may do the same. I think it just might interrupt  the emi on top but not enough to be significant in the coils response to targets below.

So technically it probably isn't an emi shield.

[midalake]

10 hours ago, phrunt said:

For graphite paint to work well it needs attached to the ground wire to make the entire ground circuit a floating ground.

If one were to paint the top side of the coil???

[kac]

Paint can chip off and the solvents may harm the plastic so I wouldn't paint mine.

Note that don't cover any areas where the Tx and Rx cross over on a dd coil as it may just mask the detection area.

What I didn't do on my initial tests was only put a wire on the Tx side top to see if it was just as effective as both Tx and Rx.

I only tested on a silver dime so what I don't know is does this disrupt the emi on the top of the coil or does it actually shift the frequency of the coil and act similar to frequency shift option on the machine.

The foil I used is nearly undetectable to the coil so I am thinking if the machine can really sense it then it maybe too much.

What I found curious is the larger coil I just bought does much better in emi areas than the stock, counter to what normally happens as larger coils are more prone to emi which happens on my other machines. I think the newer coil has extra shielding than the stock and maybe the reason, just a guess.

[kac]

Wonder if it is just heavier or extra emi tape on the coil windings?