Yes, this is cross posted. Dave Sharples (and anyone with an answer) I am currently working a job that the frequency is only in the Mhz. Before I get to far into this job and others I am attempting to research the subject, make a table that show the correlation between Frequency, fall time, spacing and ground shielding. Initially, does anyone have any data or a good rule of thumb for parallel distance per frequency and fall time? When using shielding, the book "High speed digital design" suggests grounding the shielding line every so many inches/mils to the plane. Does anyone have additional information with this? I do know the increase of Frequency and fall time inversely affects the distance for the grounding. I just don't have a good rule of thumb or data to go by. Does anyone use something that works well? When this is complete you can count that it will be added to the Resource file. Chris Robertson CAD/CAM Engineer Lockheed - Martin Services, Inc. 4912 Research Dr. Huntsville, AL 35805 [log in to unmask] Ph/Fax (256) 722-2626 ICQ# 13541566