Hi Dough
I am not sure that this increased current contributes to radiation, as it might be only a capacitive coupled local current that flows back from the cabling through the conductive table to EUT. By lifting the EUT that loop capacitance becomes smaller and so the current. It might even be so -and I suspect that to be true- that radiated emission reduce by placing the EUT on a conductive table. All that can't be evaluated correctly as long as the common mode impedance at the power supply and audio cabling is not defined...You might think of a CISPR16 set-up , or a set of CDN's or a lot of ferrite. In any way, not just put on the table. Regards, Ing. Gert Gremmen, BSc 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: d...@dsmith.org \ _ / ] \ _ / 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 <emc-p...@ieee.org> 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 <emcp...@radiusnorth.net> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher <j.bac...@ieee.org> David Heald <dhe...@gmail.com> - ---------------------------------------------------------------- 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 <emc-p...@ieee.org> 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 <emcp...@radiusnorth.net> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
