Charles: I haven't found the excerpt you provided from May of 2000 (repeated here for convenience)... > ... Because the slot created along the edge of any surface plane (or > fill) may be inadvertently excited to radiate, mounting provisions for > "resonance spoiler" capacitors should be placed along the slot. These > capacitor provisions allow "doctoring" of the structure if emission problems > are found and avoid another board spin. ...but, the above comment can apply to the slots created by moats around functional circuits located within the body of a PCB, and the slots created by the addition of chassis-ground rings around the periphery of a PCB. I suspect from your other comments that the latter case is of concern. With this interpretation in mind, I suggest you review the following in your design. Signal ground planes should extend AT LEAST three to five dielectric thicknesses (i.e., the distance between the power and signal ground planes) beyond the power plane edge. Propagations (i.e., noise from any source) on the power planes will then be strongly coupled/terminated to the adjacent ground planes, thereby minimizing radiation. With the above in place and at your option, picket fences of staggered-spacing vias (to minimize possible narrowband ladder resonances) between ground planes can enclose the noisy power planes, thereby forming an approximation to an on-board Faraday cage which helps confine leakage of emissions from the power plane edges. Assuming chassis ground rings around the board periphery, include "spoiler" chip capacitor mounting provisions (perhaps three per side/edge) that if installed would allow a capacitor bridge from the ground plane(s) edge to the chassis ring structure. Using a suitable near-field probe and a spectrum analyzer, check for high field strengths along the board edges ("high" is relative of course). If emission peaks are detected, selectively add one capacitor at a time in the vicinity of the maximum E-fields and recheck the emissions. Look for frequency shifts as well, as you may simply have changed the resonant point for the emissions. The primary intent of the capacitor provisions is to detune and lower the Q of any slot resonances that may arise, which in turn would lower the radiated emissions. Selection of a capacitor value that is self-resonant (when mounted) at the detected frequency of concern sometimes helps. As an elaboration to the above, if your near-field probe is a magnetic field detector, and strong fields are detected near the center of a board edge, you should add capacitors half way to the corners on each side of the detected point. I hope this commentary is of help. Mike Michael L. Conn Owner/Principal Consultant Mikon Consulting Cell: (408)821-9843 *** Serving Your Needs with Technical Excellence *** ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu