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Weather Station Hardware => Blitzortung => Topic started by: SaintGimp on September 21, 2014, 03:13:43 PM

Title: Shielding tips?
Post by: SaintGimp on September 21, 2014, 03:13:43 PM
Got any tips for shielding my H-field ferrites?  I thought I read somewhere that one of the devs recommended not making the diameter of the shielding tube too small, but I can't find it again.  Should the shield cover the whole length of the rod, or more than the length?  I happen to have some extra 1" copper pipe lying around, would it be a good idea to cut a slit in it lengthwise and use it for shielding, or would that be too small/thick/whatever for correct shielding?
Title: Re: Shielding tips?
Post by: miraculon on September 21, 2014, 04:40:02 PM
Early on, I do remember seeing where someone made a shielded loop antenna using copper pipe. In that case, it was easy to make a break to avoid the shorted turn effect.

Cutting a slit into copper pipe sounds like a challenge. You would need to be really careful that there were no burrs on the inside of the cut that could pierce the shrink tubing and cause a short.

I used PVC pipe for my ferrite rods. The ferrite centered nicely inside the PVC, and the wall thickness kept the wire coil from getting "too close" whatever that is. I made the slit by judicious application of the tape, so I didn't need to make a cut to form the gap.

It seems that the ferrite rod would tend to lay to one side of the copper pipe, unless you could come up with some insulating spacer possibly at each end.

That "too close" might be capacitance between the windings and the shield. (a function of area and distance, as well as other constants)

Greg H.
Title: Re: Shielding tips?
Post by: SaintGimp on September 21, 2014, 06:20:15 PM
Yeah, I've already got the ferrites in a weather-proof 1/2" PVC housing so they're snug and safe.  If I use the copper pipe I'll put insulating spacers between the copper and the PVC to keep everything centered.
Title: Re: Shielding tips?
Post by: Cutty Sark Sailor on September 21, 2014, 06:47:41 PM
Ferrite Cores. Wrap a tube of 24wt printer paper around the antenna itself. Flush the PVC tubes. Secure with Scotch tape. Apply a layer of copper foil tape, available on Amazon, which you can solder to... or aluminum tape, from Lowes, which you can't. Leave a tiny gap length ways. Don't cover the ends. Ground alum tape with an 'S' bend of wire, secured with a patch of the same alum tape. Ground it to the amp antenna ground. Shielding ain't gonna work with Navy transmitters. or other M signals, if they're that close.
Ya can't shield E field Probe.
If it don't work, you can simply tear off the printer paper tube, flush it, and the 'shielding' and find other mediation.  And you won't screw over your pretty ferrites.
Been There.  Done That. Designed the Tee Shirt, which are available on a PM request.
Title: Re: Shielding tips?
Post by: StElmo on September 22, 2014, 12:00:49 PM
My gear is inside the house, so I didn't waterproof anything. I used 1/2" copper pipe foam insulation and some 2" wide copper foil tape from eBay. It took 2 1/2 strips of foil to surround, overlapping the strips. The adhesive is conductive and I was getting <1 ohm resistance across 2 overlaps. It's easy to leave a gap. The foil solders very easily.

Paul