On Fri, 8 Jul 2005 06:56:55 -0700, Dana Roode wrote:
>I will need to pull the radio down closer to where I can access
it,
>and will try some of your suggestions.
Your description reinforces my suspicions that common mode
radiation from the Ethernet cable is likely a major component of
the problem. The trash is generated at both ends of the cable.
Thus, the most likely solution is one or more ferrite chokes as
close as you can get them to BOTH ends of the cable. The chokes
should have the highest possible RESISTIVE impedance at the
frequency of the interference, and multiple chokes in series are a
good thing.
I strongly suggest that you study the Ferrite applications notes
on my website. For example, the data in Fig 15 of "Understanding
How Ferrites . . . " shows that 4-5 turns around the very common
2.4" o.d. x 1.4" i.d. x 1/2" #43 toroid (often sold as FT-240-43),
will give you about 1,000 ohms at 50 MHz. My experience is that it
takes R on the order of 1K ohms to make a dent in this
interference, and more is better.
A few more turns will give you more resistance at HF, without
hurting you at 50 MHz, but more turns than that will move the
resonance to too low a frequency to be useful on 6m. If I were
you, I would buy at least a half dozen of these toroids before my
next trip to your site. You'll want to put at least two of them on
each end of the cable, and on the power supply cable local end.
Other ferrite parts will work, but these parts are commonly
available, and will work better than most for your problem.
http://audiosystemsgroup.com/publish.htm
BTW -- the measured data in "Understanding" is much better and
newer than that in the ppt. Thanks to W4EF, who did those much
better measurements.
Jim Brown K9YC
_______________________________________________
RFI mailing list
RFI@contesting.com
http://lists.contesting.com/mailman/listinfo/rfi
|