Joe, That's a pretty wide open question! Some things to look at are... Try to identify where it's coming from. If your tests are showing spikes in specific bandwidths, try to determine what is operating at (or it is a harmonic of) and concentrate your changes in that area of the board. Look for looping signal structures. The traces on the board act as radiating antennas. If you have a signal which loops around the board you have a loop antenna - highly directional in the plane of the board. Remember that you are looking at current paths and that the current path starts at the signal source goes to the receiving device AND then back to the ground source. Many times a structure won't look like an antenna until you consider the current path through the ground plane. Keep high freq signals short and away from the edges. Less signal length means less metal and less antenna. At the edge you lose the advantage the ground plane gives you and increases return current there. In the ground plane, look for bottlenecks and slots where return and shadow currents will intensify. A nice straight up and back current path may be forced to detour if the ground plane is too perforated. Especially watch for high freq lines crossing over a slot in the ground plane - the return and shadow currents can excite the edges of the slot just like a slot antenna. High freq lines (and/or lines with short rise times) may need to be terminated with a impedance matched load. If the prop delay becomes large relative to the wavefront rise time you can get pulse ringing. This oscillation can double crosstalk and emission levels. This is by no means all - some may apply to your situation. Let me know if I can help or if you just cannot make sense out of my ramblings :^). DonW... [log in to unmask] Don Walker Sr. CAD Designer Austron Inc. **************************************************************************** * The mail list is provided as a service by IPC using SmartList v3.05 * **************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * ****************************************************************************