Don't discount the fact that when you split the ground plane you have two pieces
of copper at different RF Potentials, this in effect creates a whip/dipole
antenna.  And that is exactly what you are trying to eliminate.

=============================================================
Clint Cote                      GE Fanuc Automation
PCB Designer                    PO Box 8106, Mail stop D-40
Phone:  (804) 978-5946          Charlottesville, VA 22906
e-mail: [log in to unmask]


>
> The biggest problem is when high speed lines cross the split in the planes.
>  The return currents follow directly under the traces, and if there is a
> split in the plane, the currents have to flow around the split causing
> emissions problems.  There is no real problem splitting the plane if high
> speed lines do not cross that barrier.
>
> Dave.
>
> At 10:13 AM 7/21/98 -0700, you wrote:
> >At the expense of sounding ignorant, what are the problems caused by
> >splitting gnd planes?  I have to do this constantly, mainly under
> >opto-isolators, to separate the part of the board that is our product from
> >the outside world.  I hope you can get some online answers so that everyone
> >has a chance to check the data.  Thanks.
> >Richard

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