[RFI] RFI Digest, Vol 71, Issue 8

aa8ia at aa8ia.org aa8ia at aa8ia.org
Sun Nov 16 13:49:47 EST 2008

> From: "Martin Ewing" <martin.s.ewing at gmail.com>
> Subject: Re: [RFI] ethernet EMI revisited - questions for the pros
> This is an interesting discussion.  I would add a few points/questions:
> -Does anyone know of published "typical" spectra of 1000baseT vs 100 vs 10?
> I agree that 10bT is much quieter on HF than 100bT, but it is possible that
> 1000bT pushes the spectrum up enough to be quieter on HF. I did some work on
> this some years back: http://aa6e.net/rfi/ether_details.html .

After hearing what Roger had to say regarding his all-gigabit network,  
I was wondering the same thing.  I'll check out your link.

> -Do you know if your RFI is coming in through your antenna?  It may be
> coupling in to your feedlines locally in the shack.  If this is so, you need
> to look into balancing your antenna system.  In-shack RFI sources should not
> matter very much if you're only listening to what's coming from your
> (distant?) antenna.

I probably should have mentioned that my antenna is only up about 20  
feet right now - It is outside and the closest point is about 10 feet  
from the house.   The RFI can be heard, but to a lesser extent, from  
inside the house using a portable antenna.   When I hook up my  
receivers to the antenna outside, via the feedline running next to the  
routers, the signals are definitely stronger.   My feedline is LMR400  
and runs into the basement to within a foot of the DSL router.   I  
wouldn't have expected the intereference to be picked up by the  
LMR400, but I'm guessing that is a possibilty?  If I hook the receiver  
up to the antenna outside, bypassing the feedline that runs into the  
basement here, the signal levels of the interference are much less.   
So yes it does sound like it is getting in through the feedline.

> -I have found that much of the Ether RFI is generated by switches/routers
> and passed on CAT 5 as common mode signals.

I think that is my experience as well - specifically from the ethernet  
transceivers.   If I have nothing plugged into the ethernet of either  
router, there is no interference from those devices.

> -The "right" solution for wiring around the house is WiFi in my case.
> Security is a minor issue in my situation, and all the high-speed traffic is
> between my systems in the shack.  Long runs of any copper cabling are an
> invitation to HF troubles, esp. if you're QRO.

I agree with you, as long as you don't have a need such as Rogers' for  
high speed backup.  The wireless adapters I currently have in use are  
running at 54 mbit and are "quiet."   I'm going to get another USB  
wireless adapter and a PCI wireless card (for an older machine) and do  
away with ethernet for normal operation.  But there will always be  
times when I have to plug some ethernet device in for a day or two in  
order to work on it, and so I want to clean things up.


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