[RFI] RFI suppression cores for 147 MHz
cbrown at woods.net
Wed Feb 27 16:07:48 EST 2013
Fair-rite 0431164281 is a good fit for that size cable.
Where I was getting common mode inband on 2M I added 3 to each end of
the cable. These are large enough they will slide around on cable, need
to be restrained, I used velcro "table" as commonly available for cable
When 3 per end not enough I added a second set of 3 ~ 19" from each.
Mouser has them for < $2 each in lots of 10. I picked up 100 last year,
for about $130 IIRC.
I do similar on all of my VHF and up LMR400 runs with the solid
2631102002. Slip a batch of them on when making the cable and
group/space approp to the use.
On 2/27/13 8:22 AM, Jim Brown wrote:
> On 2/27/2013 8:42 AM, N1BUG wrote:
>> I could use a little guidance. I have a case involving radiation from
>> ethernet cables at 147 MHz. The common clamp-on cores seem to offer
>> about 250-300 ohms ESR. It looks like I probably need a lot of them to
>> clean this up, and there are several cables involved. Is there any
>> core which would give more suppression with 2 or 3 turns of the cable
>> through it? Thanks for any info or suggestions.
> Hi Paul,
> I had that issue in Chicago, and never found a solution.
> Suppression works by inserting the resistance of the choke at resonance
> into the common mode circuit. The natural resonance of materials like
> #31 and #43 is around 150 MHz. To use them on the HF bands, we move that
> resonance down by winding turns, which also multiplies the impedance by
> the square of the number of turns. But when the resonance is already in
> the right place, our only solution is more cores. The good news is that
> #43 cores small enough to fit over Ethernet cables cost a lot less than
> the big ones we need for HF. #43 material is less expensive than #31,
> and is slightly better than #31 at VHF.
> One thing you might try is using shielded CAT5/6/7 cable. One thing I
> tried that did not help at all was to use Belden's premium Mediatwist
> cable. It's excellent cable, and it did improve error rates on my
> network, but not RFI.
> Another approach, of course, is to use WiFi for as much as practical of
> the network.
> 73, Jim K9YC
> RFI mailing list
> RFI at contesting.com
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