[TowerTalk] 3M™ External PIM Absorber 1000 | 3M United States

[Jim Lux]

I was using 31 mix more as an example.  The data sheet for the tape or sheet gives curves for R and X. The big issue is, for HF, you don’t want the stuff for microwaves (which is what most of them are).

I’ll see if I can find what we used - we were in the 100kHz -23 MHz range.  We got rolls of stuff that we could wrap our cables with, or put around holes in the chassis where the wires came through.

I should point out that this is a “fix” - people should really design things that don’t radiate on their wires (other than antennas!) or are susceptible to signals, or that have nonlinear characteristics.

And it’s not like you could afford to wrap a 50 foot length of chain link fence with the stuff.
 


On Sat, 18 Nov 2023 17:43:10 -0800, Jim Brown <jim at audiosystemsgroup.com> wrote:

On 11/18/2023 1:40 PM, Jim Lux wrote:
> I’ve used similar products at lower frequencies (<30 MHz) to good
> avail for knocking down RFI carried on power and data cables. It’s
> basically a ferrite/powdered metal in a elastomeric binder, or you can
> get it as an adhesive tape. So the mix of the ferrite is important -
> something like a 31 mix would be better than a mix tailored for higher
> frequencies.
> I think the stuff I’ve used most recently came from Laird.

Thanks for the info, Jim. FWIW, Fair-Rite #31 doesn't do its good stuff
without winding turns, but there certainly are other mixes that are
useful at HF, like the #73 mix that W2DU found for his "string of beads"
chokes. His initial work was with 50, 100, and 200 of them. I don't know
if he was always working with that small size, but the only bead that
survives in the Fair-Rite catalog just fits on RG142 coax.

Unfortunately, the only commercial products using that design use the
smallest number of beads, which limits their effectiveness and leads to
destructive failures with badly unbalanced antennas.

73, Jim K9YC
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