EMI shield

[Altair]

In my experience, I have got good result with mylar conductive taken from some shielded cables, e.g. video cables, used like in the attached photo.
My primarily purpose is to shield from electrostatic field in order to avoid external capacitive influences.

[Ferric Toes]

I also use this tape for shielding. I have applied it overlapped, as Eric has described, and non-overlapped with about 2mm (actually varies from ~2mm to ~4mm) spacing. Both seem to perform equally. I have also used it for shielding my probes. Note however, do not overlap when shielding probes... you will not like the result!

Yes, indeed! I used to shield ferrite cored probes with a gapped helical wound tape, or latterly with a tape that is wide enough to go round and leave a longitudinal gap. However, I have since thought these are not the right approach. Screening along the length of the rod will stop hand capacity and down hole effects, but probable does nothing for EMI. For that we also need to screen the ends of the rod. Another point is that most of the rods I use are conductive with a 70mm x 12mm diameter rod measuring 5k from end to end. I now run a 0.2mm drain wire along the rod and wind the coil on top of it; the drain wire being connected to the ground side of the coil. This appears to stop capacitive effects, but I doubt EMI. What do you think?

Eric.

[KingJL]

Yes, indeed! I used to shield ferrite cored probes with a gapped helical wound tape, or latterly with a tape that is wide enough to go round and leave a longitudinal gap. However, I have since thought these are not the right approach. Screening along the length of the rod will stop hand capacity and down hole effects, but probable does nothing for EMI. For that we also need to screen the ends of the rod. Another point is that most of the rods I use are conductive with a 70mm x 12mm diameter rod measuring 5k from end to end. I now run a 0.2mm drain wire along the rod and wind the coil on top of it; the drain wire being connected to the ground side of the coil. This appears to stop capacitive effects, but I doubt EMI. What do you think?

Eric.

For my probes, I never even worried about EMI. I always figured that if I was getting severe EMI with my probe, I really ought to be more concerned with getting into some rubber gloves! Seriously though, even in my living room where EMI does impact my search coils, my probes are not really impacted.

[green]

Been reading the EMI-free test chamber? thread. Reminded me of some testing I did Sunday. 20cm diameter coil. Turned FFT on with my scope. Saw a peaks near 500kHz and 1MHz. Turned the AM radio on. 550kHz and 990kHz wear the only two stations I could hear, 990kHz was strong. Tried again today. Some observations. Shielding the mono coil removed the radio stations and reduced peak noise. Don't see radio stations with the figure eight coil. Shielding the figure eight coil didn't help. Shielded mono and figure eight similar noise level. Maybe shielding helps for noise signals at a great distance, not for close(noise from scope)?

[sinclairuser]

on the pi coils I have made I used electrical tape sealed with a coat of resin, then a simple fine single wire wrapped around spaced about 1/2 an inch apart, then I coated it with this paint,

292_appl.pdf
the shield braid of the audio coax is connected to the wire wrap which is also connected to the paint.
its worked well for me.
aly.

[green]

on the pi coils I have made I used electrical tape sealed with a coat of resin, then a simple fine single wire wrapped around spaced about 1/2 an inch apart, then I coated it with this paint,

[ATTACH]45755[/ATTACH]
the shield braid of the audio coax is connected to the wire wrap which is also connected to the paint.
its worked well for me.
aly.

Have you tried a scope picture before and after shielding to see how much noise reduction?

[Koala]

no idea if you can buy it
no idea how much it costs if you could buy it
but looks cool

https://www.youtube.com/watch?v=iaSvT8U7an0

[Koala]

https://www.youtube.com/watch?v=zyGX-VyXXTQ

a recipe

[Ferric Toes]

Been reading the EMI-free test chamber? thread. Reminded me of some testing I did Sunday. 20cm diameter coil. Turned FFT on with my scope. Saw a peaks near 500kHz and 1MHz. Turned the AM radio on. 550kHz and 990kHz wear the only two stations I could hear, 990kHz was strong. Tried again today. Some observations. Shielding the mono coil removed the radio stations and reduced peak noise. Don't see radio stations with the figure eight coil. Shielding the figure eight coil didn't help. Shielded mono and figure eight similar noise level. Maybe shielding helps for noise signals at a great distance, not for close(noise from scope)?

One way to see how effective coil shielding is, is to use the coil as an antenna on a radio and hear what you can pick up. I have a communications receiver on which I use a detector coil from a down under manufacturer as a direction finding antenna. Attenuation from the graphite shielding starts at 7MHz. I listen to stations in the broadcast band 1.5MHz to 0.6MHz quite clearly. In my EMI foggy workshop the general noise and hash is much very much lower with a frame type antenna anyway, than with a wire.

Eric.

[pustareka]

My 5 kopeek

[kt315]

i have for release two types of soviet made coax cable. one is more hard. not chinese quality and fake copper. REAL COPPER SHIELD.
i will send 1.80-2.0m to whom want to probe it for 8euro.

[sinclairuser]

Have you tried a scope picture before and after shielding to see how much noise reduction?

to be honest the scope does not do the shield justice, obviously it cleans it up removing the random spikes, its the real world test where its best results are seen.
totally removing detection of the hand, and i was getting falsing at the end of swing(sometimes) now gone, also the cable does not cause chattering anymore.
it turned the minipulse i built from an interesting toy into a great detector that is really usable, as for interference it does help my shack is very noisy with radios scanners and test equipment not to mention a computer buzzing away in the background.
i used to test pi's out in the garden but can do it indoors now with a few considerations, as for the coating i use its nothing special you can get it as a paint in small tins, or as a powder in sacks that can be mixed with water or solvent, water based takes longer to dry, its just good old graphite dope used for shielding CRT's, guitar pickups etc, iv'e still got loads of the powdered type from philips from years ago, i put the pdf in the last post as it was the type you get cheap on ebay in small tins, which is better for those who want to try it.


aly.