On 12/16/2013 12:54 PM, Jeff Liebermann wrote:
On Mon, 16 Dec 2013 07:46:16 -0500, Jerry Stuckle
wrote:

Then he has a problem in his ethernet. Properly installed, ethernet
creates virtually no interference.

Yes, that's the theory. If the cable isn't perfectly balanced, it
will become an antenna. Shielded ethernet adds additional
opportunities to radiate. Most of the RFI originates from ethernet
switches and routers.


It's more than just theory. Over the years, we've installed hundreds of
ethernet systems, with little or no interference.

Shielded Category cable is much better - but you need to be careful. It
needs to be grounded at one end only (to prevent ground loops), and the
shield must carry through to the devices at the far end. The devices
must be shielded also, preferably in metal cases. Unfortunately, most
consumer-grade devices have plastic cases with little or no shielding
and do not connect to the shield. In cases like this, yes, the shield
can become a radiator. Commercial devices are better at this (but are a
lot more expensive).

One oddity are ethernet hubs. What goes in one port, goes out all the
other ports. With a switch, only data destined for a specific MAC
address on another port is passed. The problem is many older hubs
will send data to a port if a cable is inserted but not terminated.
They're not suppose to do that, but I've found a few old hubs that do
that. If you have an ethernet RFI problem, look into replacing hubs
with switches.


Again, that's the case with consumer-grade goods. Commercial grade are
much better at this.

"Understanding and Eliminating RF Interference" by Jim Brown K9YC
http://www.audiosystemsgroup.com/RFIHamNCCC.pdf
Start reading at Page 20 for the ethernet radiation section.
Mo
http://www.audiosystemsgroup.com/publish.htm


I think our expertise of doing this as a business for years in both
residential and commercial establishments qualifies us.

This thread may also be of interest:
http://lists.contesting.com/_rfi/2008-11/msg00025.html

Note that 100baseT is quieter than 10baseT. With 100baseT, the data
is first 4B5B encoded at 125Mbits/sec. To reduce crosstalk, it is
then scrambled and MLT-3 encoded. The result is a 31.2MHz carrier and
a mess of sidebands. The necessary scrambling has the side effect of
reducing high power peaks, and evening out the power spectrum over a
wider frequency range, thus reducing the RFI power at any given
frequency. It's much the same idea as the "spread spectrum"
modulation of computer clocks, to spread the power over a wider
frequency range, to meet FCC Part 15 requirements. So, instead of a
carrier or birdie, you'll hear broadband noise, which I guess is more
tolerable.


Again, it depends on the installation and equipment being used. But
10baseT is also old technology. 100baseT is more recent and solves a
lot of problems - both in radiation and susceptibility to interference
from external radiation.

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