On Tue, 2 Dec 2003 11:25:22 -0600, Barry Merrill wrote:
> five snap-on ferrites on the LAN
>cable at the Thinkpad eliminated the rfi.
Five snap-on ferrites is the equivalent of several turns around a
typical toroid of the same material. What works will depend on how
severe the interference is, what frequency you're trying to eliminate,
and what parts you happen to have available. With a multiple turns on a
toroid, the inductance increases with the SQUARE of the turns, but as
the number of turns increases, the peak attenuation shifts down in
frequency. With a bead around the cable the inductance increases with
the length of the ferrite. Remember that square law is at play here.
Fair-Rite, the mfr of the materials cited in your link, has a pdf
catalog on their website with EXCELLENT tech data and applications
notes on the use of their products in many applications.
BTW, I'm running Writelog on a Thinkpad T22. The rigs are a K2/100 and
an Omni V.9 (I use one or the other, but not both. My weapon of choice
is currently the K2/100, both because of the excellent receiver and the
dual-output antenna tuner with memories for each antenna and band
combination.
One of my antennas is a 20 ft vertical with the base less than 3 m from
the operating position. I have NO RFI at all, and have taken NO
measures to eliminate it. For both rigs, keying is DTR with a single
transistor inverter. The receive audio goes straight into my sound card
to drive the CW decoder. I mostly operate CW, so I have not gotten
around to the interface to play back audio from the hard drive. That
interconnect may be more problematic.
Thanks for the link. It's hard to find good sources for ferrites!
Jim K9YC
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