[RFI] Ethernet Extenders

Mon Jun 25 18:49:24 EDT 2007

Dave,

You bring up an interesting problem and there have been a lot of very good 
reply comments.  I would like to add on one more to the pile.

I had the chance to evaluate Ethernet interfaces for RF emissions and 
susceptibility a few years ago in conjunction with my present work.  I can 
tell you that aerospace susceptibility standards require robust interfaces 
that are not "glitched" by the presence of relatively strong RF fields. 
The RF fields that are generated for doing the tests may be straight 
unmodulated CW, full carrier with 90% amplitude  modulation by a 1 kHz 
signal, or pulsed.  The carrier with 90% AM is a brutal test, and many 
interfaces fail that one unless properly designed.

I can also tell you that 10 Base-T is much more robust than 100 Base-T 
Ethernet.  The fact that you ran shielded CAT-5e helps, but as was noted 
in another reply comment, that only works if the shield is taken directly 
to the point of termination at the RJ-45 connector.  I might add that 
RJ-45 connectors do not pass aerospace RF emission or susceptibility 
testing, although they do pass FCC emission test requirements.  To pass 
the RF susceptibility requirements, much testing work showed that very low 
impedance terminations of the cable shield are required.  Sadly, RJ-45s 
don't provide a very good way to terminate shields with short, low 
impedance connections.  (Definition of short, low impedance = 
shield-to-chassis distance of less than 0.25 inch and net Z less than 10 
milli-ohms.) 

My guess is that SSB has such an overall short duration to the voice 
peaks, which occur at a variety of frequencies, that the interface works 
well because I don't think you are really "stepping on" any data to the 
point that errors occur.  However, CW (or AM) provides milliseconds to 
seconds of RF at a steady frequency and you may be running into problems 
with internal clocking rates that are part of the Ethernet protocol.  I 
learned that to be one of the reasons that 100 Base-T interfaces are so 
much more susceptible to RF than the 10 Base-T interfaces.

The fact that operation into a dummy load at only 5 watts causes problems 
is a clue, I think, to some fundamental weak spot in your system.  One has 
to wonder if, in fact, the radio itself might not have some RF "sneak 
paths" within it that are upsetting the Ethernet interface.  Since you 
operated for years with a slow dial-up interface, the problem only now 
surfaces.  I am assuming, of course, that the dummy load is fully shielded 
(complete metal housing) and the cable from rig to load was not run near 
the CAT-5e line.

Please keep the reflector posted on your work.  Best wishes.

73, Dale
WA9ENA

"David Jordan" <wa3gin at comcast.net> 
Sent by: rfi-bounces at contesting.com
06/25/2007 11:50 AM

To
"'Jim Brown'" <jim at audiosystemsgroup.com>, "'RFI List'" 
<rfi at contesting.com>
cc

Subject
Re: [RFI] Ethernet Extenders

Tests were done with 5 watts into a dummy load.  There is no problem in 
SSB
even at 1500 watts to 1/2 wave antenna. 

The problem appears to be something flaky in the actual command data 
stream.
Since I'm using encrypted tunneling I can't really sniff the data
transmissions but I'm working on removing the encryption. I have installed
Telco Grade line filters (K-COM, 2 in series) on the CAT 5 lead to the
Ethernet boxes. The power supply line(s) is also configured as described
below, with toroidal filters (multiple) at both ends of the connection. 

The CAT is buried and it is shielded like heliax. The shield is grounded 
at
both ends. The barn has a ten point UFER ground (8ft ground rods), the 
house
has two 8ft ground rods. 

I think more and more that this is an RFI problem but wanted to here from
folks on this reflector. 

Seems if I had any RFI the little Ethernet boxes would jump up and down 
when
I run 1500 SSB.  The connection lock-ups only occurs when a specific 
command
string is send from the remote PC to the host PC.  That Kenwood command
string, inside the encrypted pipe simple tells the TS-480 to go into 
"send"
mode. The failure only occurs while the radio is in CW or AM mode. 

This weekend I'll attempt to remove the encryption and try to sniff the 
data
stream. 

I really appreciate all the thoughtful suggestions.

Dave
Wa3gin 

-----Original Message-----
From: rfi-bounces at contesting.com [mailto:rfi-bounces at contesting.com] On
Behalf Of Jim Brown
Sent: Monday, June 25, 2007 12:17 PM
To: RFI List
Subject: Re: [RFI] Ethernet Extenders

On Mon, 25 Jun 2007 11:03:48 -0400, Martin AA6E wrote:

>However, you might want to seriously look at 
>your system grounding. 

The problem is only on 40M and 30M. 

This tells us that it is NOT a grounding problem, nor is it 
related to noise or the grounding between buildings. The most 
likely cause is that some wiring is acting as antenna and picking 
up HIS transmitter. The obvious culprits are the 1,000 ft wire and 
the power supply at either end. I also wouldnt rule out the 
cables connecting the extender to his rig, other networking box, 
etc. 

The first thing I would try is 7-9 turns of that cable at the ham 
shack end around a #43 or #31 2.4 inch toroid (FT-240). If that 
doesnt fix it, add one around the power supply on the ham shack 
end. If you still have problems, add chokes to those other cables 
in the shack, and finally at the house. 

These chokes will also suppress any common mode noise radiated by 
these cables that you may be hearing on the HF bands. Ordinary 
10BaseT Ethernet traffic, usually produces birdies on 30M, 20M, 
15M, 10M, and 6M. 100MB Ethernet equipment is multi-mode -- that 
is, it carries both 10MB and 100MB traffic, and most modems work 
at 10MB on their Ethernet port. 

For more detailed advice, see

http://audiosystemsgroup.com/RFI-Ham.pdf

73,

Jim Brown K9YC

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