[SI-LIST] Re: Reference ground plane below ethernet differential pairs - good or bad?

That solution might help or might do almost nothing at all.  It will 
reduce the magnitude of line side energy coupling to the planes. That 
will reduce the imbalance and improve the common mode noise.  If that 
was your big offender, it could help a lot.  If your big common mode 
offender was someplace else, it won't do a lot for you.

The energy distribution in ENET twisted pair is almost all between 
the conductors in the pair and very little to an outside image plane.

Steve
At 12:54 AM 3/27/2007, Kbalasubramanian@xxxxxxxxxxxxxx wrote:

>Dear Experts,
>       EMI radiated emission is failing in our current ethernet product
>design .All the ethernet harmonics are appearing in the emission list. I am
>told that removing the reference plane below the ethernet differential pair
>signals (RX & TX) will solve this issue. For differential signals reference
>plane is not required since the return current flows through the other
>conductor. But will the presence of reference plane have negative effect?
>
>Sincerely
>
>K.Balasubramanian
>Project Leader - Hardware.
>
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