Doug, While this may be the case, the use of a non-conductive table provides a repeatable test setup from one lab to the next. Standardization of test methods is every bit as important. Besides, the problem the standards (FCC and CISPR) were designed to address was fixed a generation ago. While not perfect, the limits and methods of measurement have accomplished the goal that was set forth in the 1970s - solve a large interference problem.
Ghery S. Pettit From: Douglas Smith [mailto:[email protected]] Sent: Tuesday, June 03, 2014 9:51 PM To: [email protected] Subject: [PSES] radiated emissions testing may understate actual emissions, an example using a class D stereo amp Hi Everyone, I just posted my latest Technical Tidbit a few hours ago using a class D stereo amplifier to illustrate a potential problem whereby emission test standards may understate the emissions from a digital device. Here goes: Abstract: Radiated emissions measurements of table top equipment are usually made with the equipment placed on a non-conductive table. But such equipment is often used on conductive surfaces, like a metal desk, and can couple to the conductive surface to enhance emissions, essentially turning the conductive surface into part of an antenna structure. When this happens, standard testing of emissions can understate actual emissions. A Class D (actually labeled Class Z) stereo amplifier is used to illustrate this effect by measuring common mode current on its cables. Link to the article: http://www.emcesd.com/tt2014/tt060114.htm Link to the whole site: http://www.emcesd.com (lots of new stuff) The class D amplifier I used to generate the data is a 20 Watt/channel stereo amp with preamp built-in, a Lepai LP-2020A+. It is a great little amp, if not a little noisy EMC wise, and makes a great EMC demo for those of you who run courses. I tried one at home and cannot tell the difference between it and a much larger amplifier. I plan to give one of these to all attendees in my public seminars. Doug -- University of Oxford Tutor Department for Continuing Education Oxford, Oxfordshire, United Kingdom -------------------------------------------------------------- ___ _ Doug Smith \ / ) P.O. Box 60941 ========= Boulder City, NV 89006-0941 _ / \ / \ _ TEL/FAX: 702-570-6108/570-6013 / /\ \ ] / /\ \ Mobile: 408-858-4528 | q-----( ) | o | Email: [email protected]<mailto:[email protected]> \ _ / ] \ _ / Web: http://www.dsmith.org -------------------------------------------------------------- - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]<mailto:[email protected]>> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe)<http://www.ieee-pses.org/list.html> List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]<mailto:[email protected]>> Mike Cantwell <[email protected]<mailto:[email protected]>> For policy questions, send mail to: Jim Bacher <[email protected]<mailto:[email protected]>> David Heald <[email protected]<mailto:[email protected]>> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
