[RFI] ethernet EMI revisited - questions for the pros

Martin Ewing martin.s.ewing at gmail.com
Sun Nov 16 08:22:24 EST 2008

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 .

-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 have found that much of the Ether RFI is generated by switches/routers
and passed on CAT 5 as common mode signals.  The appropriate ferrite core
stops it pretty well.  Shielded twisted pairs does not help so much,
particularly because the shield is connected at both ends - which is
probably not what you want.  There is a lot of variation between routers.  I
had a very bad Linksys, while my current NetGear is better.

-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.

-The very best solution would be fiber optic cabling, which still seems to
be excessively costly for general use.   Fiber (and wifi) also buys you
lightning/surge protection.

73 Martin AA6E

On Sun, Nov 16, 2008 at 1:48 AM, Roger (K8RI) <k8ri at rogerhalstead.com>wrote:

> aa8ia at aa8ia.org wrote:
> > 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.
> >
> Hi Mike,
> > 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.
> >
> >
> This kind of interference may be from the equipment rater than the
> connectors or cables as the equipment pretty much stops when nothing is
> hooked to it and although others will probably disagree, it's like voodoo.

Martin Ewing, AA6E
Branford, CT

More information about the RFI mailing list