[Premium-Rx] Racal RA6830 digital noise

[Carcia, Francis A HS]

Hi All,
Last night I was looking at a 6830 motherboard and noticed it has a slot in
the ground plane between A11 and A12 on both sides of the board. My fix for
digital noise was to slide an insulator between A11 and A12. It seems to me
there are power supply return currents flowing through the shields when they
contact because the slots force currents to flow through the chassis. The
shields provide a lower Z path back to the power supply but these return
currents contain digital noise that can be picked up by the first IF
amplifier.
I'm thinking it might be better to put jumpers across the slots providing a
better return path back to the power supply keeping the noise out of the
chassis and modules. Maybe just do the slot on the bottom side of the
motherboard. 
I guess I have to ask why would you put a slot in a ground plane. There is
no RF flowing through the plane only power, bite and control signals. We
have issues like this at work so I'm trying to understand the motivation for
breaking up a ground plane. Some smart guy please set me straight on this.
frank