[RFI] Linksys Routers, EMC, and Ferrite Chokes

[dj2001 at mn.rr.com]

Your post was timed perfect Jim.

This weekend I tracked down what I thought was a dimmer lamp or 
switch here in the area.  It turned out to not be the case.  I found 
my eithernet hookup for a laser printer in the basement to be the 
culprit.  The noise was only about a s-1 on the low end of 75 meter 
phone band, but irritating and occurring every 20 khz or so.  I 
disconnected the cat5 cable from my Asante router and the noise went 
away.  I'll try some cores as you suggested and if that don't work 
then I'll just leave the cable disconnected until needed.

73
Dale, K9VUJ




>On Fri, 28 May 2004 12:01:36 -0400, Martin Ewing wrote:
>
>>Fraser Robertson, G4BJM, kindly supplied some real Ethernet spectrum
>>measurements which I've posted at my  RFI web page --
>>www.aa6e.net/aa6e/rfi .
>
>I've been doing some research here in my office/ham shack and have learned
>some interesting things.  I have two Linksys beasts in my office -- one of
>the BEFR wireless routers that is cited in the class action lawsuit, and one
>of their eight port switches. Both radiate lots of trash in the HF spectrum,
>and I have identified them as the cause of strong carriers at 3511.25 kHz,
>10106 kHz, 10122.56 kHz, 14031.27 kHz, and 21052 kHz.
>
>The HF radiation from these boxes has a very strong common mode component. I
>say this because I am able to reduce their strength quite significantly (2-4
>S-units) by winding 6-8 turns of the offending Ethernet cable around ferrite
>toroids. The toroids I'm using are mostly Fair-Rite #61, but I've also used
>some #43 cores.
>
>I've also learned something quite important about toroids that was clearly
>noted in Fair Rite applications notes but not quantified. In general, the
>peak attenuation frequencies of ferrites are moved down in frequency a LOT by
>taking multiple turns around the ferrite. Thus, a #43 and a #61 material,
>although generally considered to be effective only VHF and low UHF for
>suppression, can be quite effective in the HF spectrum if you put enough
>turns around them. A #43 core can provide a lot of impedance at 160 m, and a
>#78 core will get you to the low end of the AM broadcast band!
>
>I'm off to the computer store now to look for an alternative to these Linksys
>dogs. The cores to suppress the RF trash cost more than the boxes that
>generate the trash!
>
>Jim Brown  K9YC
>
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