[RFI] Ethernet RFI

Jim Brown jim at audiosystemsgroup.com
Sat Jan 22 22:40:59 EST 2005

On Sat, 22 Jan 2005 21:28:10 -0600, Ford Peterson wrote:

>I'm willing to bet my next paycheck that the noise will be gone 
>if they are properly shielded by retaining the 'pairs' in the
>proper sequence. 

You'd better go for a paycheck loan, Ford. :) You (and the tutorial) 
are absolutely correct that a twisted pair helps TREMENDOUSLY in 
killing DIFFERENTIAL mode coupling to/from the cable. And we have a 
lot of experience with loudspeaker cables that says that twisted 
pair is FAR superior to parallel wire (zip cord) in minimizing RFI. 

But twisting helps NOT AT ALL when the cable is excited COMMON MODE 
and radiates as a long wire antenna. That's what the chokes can 
reduce (a LOT). 

My experience with HF trash from Ethernet cable is that it is all 
COMMON MODE radiation from the cable, added (sometimes) to direct 
radiation from the box itself. 

Jim Brown  K9YC

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