Dear Group, We're working on a next Rev of board on our system and we're having a problem with a 66MHz oscillator during radiated emissions testing. The board slides vertically into a shelf(aka the card cage). The solder side of the board is approx 1/4" from a plated steel vertical which is one of the shelf ends. Our problem is that when the card is inserted in slot 1 a harmonic of the 66MHz is leaving the card cage from the small gap between card and the shelf end. Covering the small gap with CU tape cures the emission problem. Various experiments with foil and CU tape have established that shielding the solder side directly underneath the oscillator yields considerable improvement.
Moving the card away from the shelf end into higher slot numbers reduces emissions considerably. Before I rush off back to development, I wondered if anyone in the group had any advice about implementing small areas of ground plane directly underneath oscillators ? I'm going to request upper and lower ground planes with via stitching between them and our internal groundplane. The oscillator is a 4pin plastic packaged device. Is there anything else or experience that anyone else in the group can pass on this subject. Many thanks Carl Carl Richards, Regulatory Compliance Manager, Aspect Communications E-mail carl.richa...@aspect.com Tel +44 (0)208 589 1461 Fax +44 (0)870 460 1950 This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to emc-p...@ieee.org Instructions: http://listserv.ieee.org/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Scott Douglas emcp...@ptcnh.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
