Ian,
PCB layout is very critical; especially in the I/O area (around the RJ-45
connectors). Make sure that the Ethernet transformer you use has good
common-mode filtering built in. You might also try using "Bob Smith
termination" on the un-used pins of the I/O connector. If you've never heard
of "Bob Smith termination", do a google search and you can find info about it.
App notes from the manufacturer of the Ethernet Phy you're using usually are a
good place to start looking for recommendations related to layout. One thing I
have found is that if you do use shielded cables make sure you use a cable
that has 360 degree connection on the shield.
Hopefully some of this helps. I'm no expert but have struggled with these same
issues.
Bill Fleury
From: McBurney, Ian [Allen & Heath UK] [mailto:[email protected]]
Sent: Friday, June 17, 2005 6:17 AM
To: [email protected]
Subject: ethernet radiated emissions
Dear colleagues;
Can anyone advise me how to reduce the radiated emissions from a 100 base-T
Ethernet port with a UTP cable connected to below the EN55022 class B limit?
At the moment I am 20dB above the limit at 33MHz. Using STP only reduces the
emissions by 6dB.
Thanks in advance;
Ian McBurney.
Allen & Heath Limited.
email: [email protected]
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