[SI-LIST] Problem with emissions test standards - a class D amp example

From: Douglas Smith <doug@xxxxxxxxxx>
To: Si-List <si-list@xxxxxxxxxxxxx>
Date: Tue, 03 Jun 2014 21:47:49 -0700
 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
effectby measuring common mode current on its cables.

Link to the article: http://www.emcesd.com/tt2014/tt060114.htm[1]
Link to the whole site: http://www.emcesd.com/tt2014/tt060114.htm[2] (lots
ofnew stuff)

The class D amplifier I used to generate the data is a 20 Watt/channel
stereoamp 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 the
attendees in my July and January public courses in Boulder City.

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: doug@xxxxxxxxxx[3] \ _ / ] \ _ / Web:
http://www.dsmith.org[4]
-------------------------------------------------------------- 

--- Links ---
   1 http://www.emcesd.com/tt2014/tt060114.htm
   2 http://www.emcesd.com/tt2014/tt060114.htm
   3 mailto:doug@xxxxxxxxxx
   4 http://www.dsmith.org
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[SI-LIST] Problem with emissions test standards - a class D amp example

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