[RFI] ethernet EMI revisited - questions for the pros

Roger (K8RI) k8ri at rogerhalstead.com
Sat Nov 22 04:23:16 EST 2008

Christopher E. Brown wrote:
> I just got done taking care of my in home ethernet, a number of runs at 
> 10, 100 and 1000 made for alot of noise.
> Some of the noise can be from poorly made cables.  Many cheap jumpers that 
> come with gear are not correctly wired.  They work ok for data, but the 
> pair splits make things worse.
> I reduced my ethernet signals by 3 - 6 db on 20M by replacing all of the 
> cables with correctly wired CAT5  (some of the "came with the cear" 
> jumpers were flat (not twisted), or while wiremapping correctly had pair 
> splits).
> Further testing (disconnect all and reconnect one at a time) showed a 
> large difference in signal level between devices even with the same cable 
> length.  Some of the higher end gear had simple pow less common mode RF on 
> the wire.  All of the cheaper gear was very noisy, only the higher end PoE 
> (802.1af Power over Ethernet) gear was fairly decent (I assume the power 
> splitter hardware provides more RF isolation).
> I made all new jumpers using stranded CAT5 with a fairly thin jacket. 
> This allowed 3 turns through a 1.5 inch long .4 ID FairRite type 31 snap 
> on.  About half the gear is < 5 foot jumpers, the longer runs have 2 
> snap-ons  (gear - jumper - in wall run - jumper - gear), one on each 
> jumper.
> My 20M birdies went from S7 - S9 to no meter reading, only detectable when 
> 20M is quiet and only if I tune to exactly the right spot.
> 40M is slightly louder, but still low enough to miss.
> I need to order some FT-240 size type 31 toroids though.  I have 2 long 
> runs that still radiate on 80M.  I think about 12 turns through a FT-240 
> core on all 4 jumpers should do it.
> My antenna is a 35ft vertical up the back side af a tree about 40 feet 
> from the house.
> On Sat, 15 Nov 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.
>> 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
>> better.
>> 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 realize you asked part of this before, but with more information now...
If you are going to redo things what about first starting with upgraded 
routers and switches?  Good, routers will run less than $200 be they 
wired or wireless.  You can get up to about 300 Mbs wireless now days 
and gigabit on CAT5e is "old hat" so to speak.

My long runs are home made and I can guarantee it's important to have 
the correct pin out.  However I just use the plain old clear, cheap 
plastic connectors with gold plated pins and a Radio Shack crimping 
tool  The shorter runs are the color coded pre-packaged of the mid price 
range which vary from (IIRC) 6 to 25'. I have short runs from the modem 
to router and from the router to switch of 2 - 3' (home made) Old 
systems used a crossover between the modem and router, or was it between 
the router and switch. at-any-rate, the new stuff is all direct with no 
cross overs.

The proper pin-outs following the color code are readily available from 
the industry on the net.

As I mentioned before, using up-to-date equipment I've not had to resort 
to using any RF suppression to keep the signals in or out of the CAT5e. 
I will admit that learning to make good connections may use a few extra 
connectors<:-)) and you do have to make sure the wire is fully seated in 
the connector BEFORE trying to crimp it.  I use standard industrial 
grade CAT5e from the boxed 1000' spools. it's not exterior grade so it 
runs in conduit  for protection.
>> 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.
As the signal levels are very low even at S9, the clamp on units might 
be sufficient and it's easy to add or subtract them. These are pretty 
much the same ones used on audio, ham equipment, and computers. The 
control cables from the computers to my 897D and 756 Pro have them.  
OTOH I've used temporary patch cables without chokes in place of these 
with no problems.  I'd have to go look but I believe they also use them 
on the keying lines to the amps and alc lines.
>> 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.
No it won't except for price and possibly distance you can run. I 
wouldn't think there would be anything to gain unless you are running 
long gigabit lines or have lots of sharp bends in the runs.  Unless you 
need the extra distance I see no advantage of going to CAT6
 You might want to consider the 10/100/1000 Mbs equipment though,  
whether you need the capacity/band width or not as it's been my 
experience "in general" it tends to be much quieter than the older 
equipment. You can find the D-Link and LinkSys equipment at local stores 
such as Best Buy for reasonable prices.

One word of caution though, the new routers are _far_less_forgiving_ of 
non standard protocols than the older ones. The ones with built in 
firewalls can be fun to troubleshoot if you slip up programming them.  
JNOS is one system that has been haphazardly programmed at sites.  There 
are a number of site in this area and to the South that are not 
following the latest protocols and they can not get through these 
routers.  As time goes on and these routers become far more common those 
with these sites are basically going to have to update their programming 
which would take them all of about 5 minutes. Unfortunately some have 
just refused to change. I doubt you are going to be worried about this.

As I mentioned you can get shielded CAT5 and 6, but that brings with it 
a whole new bunch of *possible* headaches. No, it doesn't normally have 
to be grounded only on one end as ground loops are *usually* NOT a 
problem.  OTOH I'd never omit it as a possibility. <:-))

As I also mentioned I have a bunch of CAT5e, control cables, and LMR-400 
in a rather tight bundle from the Modem/router/switch and rigs from the 
equipment, through the floor and close to where the coax and control 
cables exit the basement into underground conduit.  About 2' from the 
conduit two network cables branch off but join the telephone and two 
RG-6 cables to the shop which is about a 130 foot run. In the basement 
they parallel the underground conduit for about 20 feet, then go through 
the end plate, up the South garage wall, about 25 North across the 
garage ceiling, down the North wall, through the wall at the base and 
then through underground PVC conduit for roughly 30 feet where it again 
go through a sweep L and into a box on the outside wall of the garage, 
through the wall and into a box on the inside wall. All cables in the 
shop are in grounded metal conduit with the exception of relatively 
short pigtails to the patch panels where they enter or leave the 
conduit.  The ground system between the shop, house, and tower are 
common and relatively elaborate.

Good luck,

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