[RFI] Computer birdies
jim at audiosystemsgroup.com
Tue Jun 26 12:45:20 PDT 2012
On 6/26/2012 11:49 AM, charlie at thegallos.com wrote:
> I personally found, with my router and computers that the computer was the really bad end, but putting cores on both ends helped too, as there was some low level stuff coming from the router
Yes. Each end of a cable connected to ANY digital electronics should be
viewed as a potential noise source, but as several have noted, some
products are much noisier than others.
Steve -- many thanks for posting your careful experimental work. I did
the same many years ago when I first diagnosed the problem and learned
enough about ferrite chokes to realize that they might be a solution.
Another point. These Ethernet birdies (most typically around 14030,
21052, and on the bottom end of 10M CW) are produced by by free-running
clocks that are synchronized to another clock in the system, which is
also free-running. The birdies will be CLOSE to 14030, 21052, etc., but
the precise frequencies will vary from one Ethernet system to another.
Once you've gotten your own system quiet you'll start hearing your
neighbors' systems, each a few hundred Hz from you and each other. You
can identify which is yours by killing power to your router or Ethernet
And yet another point. SOME of this noise may be radiated by wiring
(and circuit traces) internal to the box due to poor design. Nothing
you do to choke the cables will reduce that part of the noise. You CAN,
however, further reduce the cable part of the noise by adding a second
choke in series. A second choke having the same choking Z should help by
about 6 dB -- but ONLY on the part of the noise carried on that cable.
73, Jim K9YC
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