Shielded CAT6 cable - worth the hassle?

Doug Hall

I've been perusing various sources of wisdom on mitigating noise in my HF station. I'm fortunate that I have a fairly quiet station, even living in a city environment. Given that most of the noise I do have seems to come from Ethernet I found the paper by K9YC particularly interesting. I am in the process of replacing the Ethernet cable and switches in my house in anticipation of gigabit internet service (they just buried fiber in our neighborhood), and one question that hasn't been answered definitively is whether to go with shielded (STP) or unshielded (UTP) Ethernet cables. You'd think it would be a no-brainer, and maybe it is, but it's not clear to me whether it helps or hurts in the case of radiated noise. I currently use CAT5 UTP and have no RFI issues here from a TX point of view even at 1300 watts (which is about all the old L7 will do.) But on receive I get some interference in various places.

I'd appreciate hearing from those of you who have personal experience with the issue of shielded vs. unshielded Ethernet cable as it relates to radiated noise mitigation. If you have a brand of gigabit switch that has proven to be quiet I would like to hear about that as well.

73,
Doug K4DSP

George KF2T

Hi Doug,

I think the FRS recommendation was to NOT use shielded CAT cable to avoid potential ground loops. That said, I have found that in some situations, the shielded cable does help with devices that might be elsewhere in the home (DirecTV box to router connection, for example). Try both ways to see. A good ferrite toroid core on the unshielded CAT works well too, in some situations. More towards alleviating RF ingress to the computer, I've noticed.

Tim - W4TME

Doug - the issue is ground loops with STP.  If you cut off one end of the STP cable and install a plastic RJ-45 and connect the shielded end to a properly grounded switch (assuming it is RF grounded) which does not emit RF (the only switches I have used that conform are NEBS L3 complaint), that may provide some additional RFI immunity.

Try CAT6 UTP cable.  It should work fine.

If you are getting new Ethernet switches and want them to be RF quiet, you want to look at business class devices with a metal chassis.  I have been using Cisco SG 200-08 switches in my shack and they are very quiet.  Just turn off the darn Green Ethernet feature.

Mike va3mw

I found this very helpful as it deals with common mode currents and household noises.

http://www.ea1ddo.es/docu/Chokes_W1HIS.pdf

Mike va3mw

Jay Nation

Ethernet UTP uses balanced pairs to eliminate the induced RFI, just like a balanced microphone cable. the paired conductors are twisted together inside the cable in such a way that the RFI cancels out. 

73, Jay - NO5J

Doug Hall

Yes, thanks Mike, very good info.

Doug Hall

Agreed, Jay, but in K9YC's paper he says:
"CAT5/6 cables carrying Ethernet data do radiate RF trash, but most of that radiation is common mode – that is, longitudinally along the cable – because the line drivers on either (or both) ends of the cable have poor common mode isolation."

My thinking was that shielded cable might cut down on that radiation, but based on info I have so far I think I'll attack the problem with non-shielded Ethernet cables and a bunch of ferrites.
73,
Doug K4DSP

Stan VA7NF

Cat 6 UTP is better that CAT5 UTP due to the wire size and tighter twist, but

STP or SSTP stock cables are good PROVIDED the shield is interrupted by the method Tim mentioned (cut off and add a non-shielded connector OR, my preference, purchase some plastic female-female couplers and 3 inch UTP jumpers.

This will break the shield ground loop.

Run the shielded portions out from one grounded switch and place the couplers near the far device.  I use CAT 6 SSTP and double female couplers throughout.

I had significant common mode noise generated by LinkSys / Cisco switches and converted my backbone and remote switches all to NetGear prosafe series.