Hi, I work at a company where they have a lot of difficulty getting network equipment to pass class A emissions. We have verified that the problem with the current board is coming from the ethernet cable - when we put on a shielded ethernet cable the emissions go way down. The violations occur in the range of 20Mhz to 150Mhz and they are very broad peaks with multple peak frequencies throughout the range. None of the frequencies are recognizeable - it's very "messy". The ethernet grounding method used here has always bothered me. They do not use a seperate chassis ground for the signals/connector on the connector side of the RJ45. The power planes are held back but the digital ground plane is common to the connector side of the magnetics. The connector side transformer center tap is connected to the common digital logic ground as is the shielded RJ45 case. The ethernet transformer is a Pulse H2017 with integrated common mode chokes. In my experience, there is always a seperate chassis ground on the connector side of the transformer which is ultimately connected to the digital logic ground via the chassis only. I also have an app note somewhere that states that the integrated common mode chokes don't work well with a common ground. In my experience it's sort of a no-brainer to have a seperate chassis ground. My question is would you expect that the problems we are having could be caused by the common ground implementation? Thanks, Alex - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/
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