[SI-LIST] Re: Ethernet emissions.
- From: "Orin Laney" <olaney@xxxxxxxxx>
- To: <bryan@xxxxxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Fri, 5 Apr 2013 22:58:14 -0700
"Integral magnetics" might mean transformer only or it might also include a
common mode choke. Make sure you are using the latter. I think a lot of
transformer only parts are sold because designers don't know the difference
and go for lowest price. Sometimes they actually pass EMC that way, but a
lot of boards are fixed by spending the extra two bits for the proper part.
Orin Laney
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Bryan Ackerly
Sent: Friday, April 05, 2013 4:40 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Ethernet emissions.
I have a question regarding a (10/100) ethernet implementation that failed
radiated EMC. The phy is an SMSC LAN-8720. Due to space requirements a
connector with integral magnetics is used.
The main problem seems to be emissions at 375, 500 and 625MHz being radiated
from the UTP cable.
For an expeiment i added an LC lowpass filter on each line from the PHY
cutting off from 125MHz which seems to improve things a bit, especially at
the higher frequencies.
But i dont know what impact this will have on the ethernet signalling
itself.
Has anyone else done this to pass emissions? Is there a better way of doing
it?
Regards,
Bryan Ackerly
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