[RFI] Wired vs Wireless Routers for RFI
jim at audiosystemsgroup.com
Sat Jan 12 11:09:41 EST 2008
On Fri, 11 Jan 2008 10:55:40 -0500, Paul Christensen wrote:
>I just purchased a box of 0.750"
>Fair-Rite #31 core material and the result is that router birdies are
>somewhat reduced, but still very annoying. Half the battle with CAT-5
>is in getting enough windings on the core without running out of room.
>Adding cores on the PC end seems to offer little befit, so it would appear
>that the majority of the RFI source is coming right out of the router.
>Any suggestions from here?
First, you MUST use enough turns before you begin seeing much benefit from
these chokes. The particular cores you purchased may be too small for this
use. I recommend the 2.4-inch o.d. 1.4-inch i.d. x 1/2-inch toroids (renamed
FT-240 by vendors who mark them up by 5X to hams) and the "big clamp-on"
listed in my tutorial (1-inch i.d. by a bit more than 1 inch long). These
parts allow enough turns for good choking action at 10 MHz -30 MHz both with
coax and with Ethernet cables.
Second, with the cores you have on hand, try using two or three cores
combined for a single multi-turn choke. The objective is to lower the
resonant frequency of the choke to the range of birdies you're trying to
suppress. See the guidelines in the tutorial for estimating the reduction in
resonant frequency for 2-4 turns based on the Fair-Rite data for a single
Third, don't forget what I call "threshold effect." (see the tutorial).
Fourth, once you've killed radiation from the cables, there may still be
radiation from the router itself.
Fifth, once you've killed radiation from the router end, you may start
hearing the lower level trash from the other end.
Sixth, once you've killed your own stuff, you may hear your neighbors.
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