[RFI] ethernet EMI revisited - questions for the pros

Roger (K8RI) k8ri at rogerhalstead.com
Sun Nov 16 01:48:53 EST 2008

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.
I have two computers here in the den with the VHF duobander control head 
between and almost touching the monitors.  The cable to the RF deck runs 
with the CAT5e from the computers to the gigabit switch which sets about 
3" to the South of the RF deck.  To the right of that is the 756Pro, 
Alpha 76, and MFJ989c tuner. The USB printer cable also runs with that 
CAT5e. The printer is about 2" from the cable modem which sets between 
the printer and switch.  From here the cables ALL run together to the 
basement. That's 3 runs of CAT5e, remote antenna switches, rotator 
cable, and coax. Two runs of CAT5e 132' long make the trip to the shop 
about half of that distance is parallel to and a couple feet away from 
the underground conduit to the tower.  At the shop the conduit from the 
house enters about 3' from the patch panel that connects to conduit 
running to the tower with 3 runs of LMR-600, 4 control cables, and a 
rotator cable.  The two computers are currently just to the left of the 
station and directly next to the Astron  50 amp PS which has the 
satellite receiver sitting on top. On top of the satellite receiver is 
the 144/440 duobander. Next to that is currently a 756 Pro and Tokeyo 
Hy-power HL1.5Kfx.
Although the installation is not complete both stations are connected to 
antennas on the tower, the satellite system, and the computers through 
the serial and/or audio ports.   I have absolutely no sign of the 
computers or network at either station nor do any of the stations bother 
the gigabit network which gets very heavy traffic.

I used to run DSL, but here cable is both faster and cheaper so I now 
have a cable Linksys cable modem, Liknsys router and D-Link switch 
running at gigabit speeds. The connections (and cables) are a mix of 
store bought shorter cables (3' to 25') and home made with no RF 
suppression.  Strictly RJ45s either crimped on by me or commercial cable.

I run Gigabit as 100baseT is far too slow for the system backups across 
the network.  My router has wireless capability but it is normally 
disabled for security.

> 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 would suspect one of the pieces of equipment and not the connections. 
As you remove connections, the traffic on the network drops until at the 
final connection it stops entirely.  There is only the equipment waiting 
to hear a packet and maybe a tiny bit of interrogation between the DSL 
modem and router.

If all of the computers are disconnected but the cables connected to the 
>   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  
> better.
and the newer equipment is probably quieter.
> Unfortunately, I'm now at the point that the ethernet link between my  
> DSL router and my Linksys wireless router is autonegotiated with no
Why run two routers?  Why not run one multipurpose with the CAT5e 
through a switch? IOW I have one port from the router running to a 
switch. There the computers can talk via CAT5e without any wireless 
activity or even bothering the router unless connecting to the Internet.

If I want I can turn the wireless on or off.  I have two problems with 
wireless. It's still way too slow and can't reach far enough (my shop is 
completely lined with steel - painted barn metal interior). Actually a 
third as I don't trust the security. When the next generation comes 
around I may consider it but getting into the shop even with a repeater 
is a challenge.
> 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  
My guess is the RF is related to one or both of the routers, possibly 
talking to each other.
Have you tried running just one router as a test?  If not, completely 
disconnect one including the power and all connections. Operate what you 
can on the other and check for interference. Then do the same with the 
other router.
> 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).
Typically I see the clamp on ferrites used although I used none.
> 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.
Only in expense or you want longer runs. Both are groups of unshielded, 
twisted pair. OTOH shielded is available.
One of my longer runs is CAT6

73 and Good Luck,

Roger (K8RI)
> Thanks for your assistance.
> Respectfully,
> Mike
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