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Re: [RFI] RFI From Wireless Internet Radio

To: "RFI List" <rfi@contesting.com>
Subject: Re: [RFI] RFI From Wireless Internet Radio
From: "Jim Brown" <jim@audiosystemsgroup.com>
Date: Fri, 08 Jul 2005 09:30:24 -0500
List-post: <mailto:rfi@contesting.com>
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




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