[RFI] ethernet EMI revisited - questions for the pros

aa8ia at aa8ia.org aa8ia at aa8ia.org
Sat Nov 15 20:46:02 EST 2008

Hi Folks,

I've been subscribed to this list for about a year.  I've read through  
much of the archives in the past.   I'll admit the answers to the  
question[s] I pose are probably found somewhere in the archives.   
Forgive me for asking them again.

I've got a Zoom X5 DSL router, wired via cat5 of questionable origin  
to a 4-port Linksys WRT54G wireless router.   I've got three computers  
cabled via cat5 to the linksys as well as a couple of computers  
connected over the wireless.

I have noticed significant interference across HF and up to at least  
50 Mhz that I have tracked down specifically to the 100 mbit ethernet  
connections I have spread throughout my office.   I know this because  
when I unplug all of these, the specific interference goes away.   
Looking to put as little effort into this as possible, the first thing  
I did was decrease the ethernet speeds of the hardwired computers to  
10 mbit/FD.   This has signfiicantly lessened the interference but  
obviously has some undesired consequences.   We all know faster is  

Unfortunately, I'm now at the point that the ethernet link between my  
DSL router and my Linksys wireless router is autonegotiated with no  
way on either device, via web config or command line configuration, to  
actually set the speed specifically to 10 mbit / FD in order to lessen  
the interference there.

So now I'm moving on to doing things over.   I'll still have a  
combination of wired and wireless devices and will still have to have  
the cat5 cabling between the two routers.   I want to be able to run  
100 mbit across the board on the cat5 without the interference issues  
to my HF receivers and low band VHF.

I want to incorporate ferrites into the mix from the beginning.   My  
understanding is that I could buy premade cables and trust that they  
are wired using the recommended T568B standard.   I could then get  
some torroidal ferrites to wind the cat5 around.   I'm guessing it  
would be preferable to buy the cable, connectors, installation tool to  
put the connectors on, and then do the needed winding before I install  
the connectors (allowing possible more turns on a torroidal ferrite  
than I might get if I have to deal with the connectors).

I don't know what type/size of torroid is recommended for my specific  
application and would like some recommendations.   I only want to do  
this once, and thus I want to do it right the first time.

While I'm at it, does it make a difference if I'm buying cat5 or cat6?  
   I won't have any gigabit ethernet adaptors in play.

Thanks for your assistance.



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