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<TITLE>RE: Computer Shelves (RF EMI/EMC issue)</TITLE>
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<P><FONT SIZE=2>During college, I lived in a trailer, and had my CPU next to the water heater. Some times it would turn on, others not. Eventually found out that when the water heater turned on, the EMR would not let the computer work. That was really confusing until I figured it out. Also, the radio, when plugged into the wall would howl like Robert said. </FONT></P>
<P><FONT SIZE=2>So be careful of putting CPUs next to other equipment, including circuit breakers. They could disrupt the machines.</FONT>
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<P><FONT SIZE=2>Richard Schilling</FONT>
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<P><FONT SIZE=2>> -----Original Message-----</FONT>
<BR><FONT SIZE=2>> From: Robert G. Brown [<A HREF="mailto:rgb@phy.duke.edu">mailto:rgb@phy.duke.edu</A>]</FONT>
<BR><FONT SIZE=2>> Sent: Tuesday, February 20, 2001 11:30 AM</FONT>
<BR><FONT SIZE=2>> To: Jim Lux</FONT>
<BR><FONT SIZE=2>> Cc: Leonardo Magallon; Peter Eriksson; beowulf@beowulf.org</FONT>
<BR><FONT SIZE=2>> Subject: Re: Computer Shelves (RF EMI/EMC issue)</FONT>
<BR><FONT SIZE=2>> </FONT>
<BR><FONT SIZE=2>> </FONT>
<BR><FONT SIZE=2>> On Tue, 20 Feb 2001, Jim Lux wrote:</FONT>
<BR><FONT SIZE=2>> </FONT>
<BR><FONT SIZE=2>> > I doubt that metal shelving would have any beneficial EM </FONT>
<BR><FONT SIZE=2>> properties, and, in</FONT>
<BR><FONT SIZE=2>> > fact, might actually make things worse by being a </FONT>
<BR><FONT SIZE=2>> capacitively coupled</FONT>
<BR><FONT SIZE=2>> > radiator. Trust in your FCC Class B cases...</FONT>
<BR><FONT SIZE=2>> ></FONT>
<BR><FONT SIZE=2>> > Actually, does anyone have any evidence of Electromagnetic </FONT>
<BR><FONT SIZE=2>> Compatibility</FONT>
<BR><FONT SIZE=2>> > problems in a cluster? Lots and lots of computers, all </FONT>
<BR><FONT SIZE=2>> with switching power</FONT>
<BR><FONT SIZE=2>> > supplies, running off fairly long extension cords all </FONT>
<BR><FONT SIZE=2>> strewn about (neatly,</FONT>
<BR><FONT SIZE=2>> > of course), and the conditions are certainly ripe for </FONT>
<BR><FONT SIZE=2>> EMC/EMI problems.</FONT>
<BR><FONT SIZE=2>> > Fortunately, the computers themselves are probably fairly </FONT>
<BR><FONT SIZE=2>> immune, but what</FONT>
<BR><FONT SIZE=2>> > about other devices (i.e. does your cell phone still work </FONT>
<BR><FONT SIZE=2>> standing next to</FONT>
<BR><FONT SIZE=2>> > your cluster?).</FONT>
<BR><FONT SIZE=2>> </FONT>
<BR><FONT SIZE=2>> Back in oh, 1983 or 1984 my 4.77 MHz IBM PC would radiate </FONT>
<BR><FONT SIZE=2>> like all hell</FONT>
<BR><FONT SIZE=2>> on FM 100 or thereabouts. I could even hear it "work" in the static.</FONT>
<BR><FONT SIZE=2>> I'm sure that any good phreaker could have told you character by</FONT>
<BR><FONT SIZE=2>> character what I was typing from fifty feet away. Messed up </FONT>
<BR><FONT SIZE=2>> my ability</FONT>
<BR><FONT SIZE=2>> to listen to music and work.</FONT>
<BR><FONT SIZE=2>> </FONT>
<BR><FONT SIZE=2>> Shortly thereafter, those Class B cases started to be required and</FONT>
<BR><FONT SIZE=2>> motherboard designs improved (probably fewer sharp turns and more</FONT>
<BR><FONT SIZE=2>> attention paid to conductive path shapes and lengths) -- </FONT>
<BR><FONT SIZE=2>> haven't heard a</FONT>
<BR><FONT SIZE=2>> peep for well more than a decade out of anything except the sound card</FONT>
<BR><FONT SIZE=2>> of the system itself, which DOES sometimes register a bit of system</FONT>
<BR><FONT SIZE=2>> state-dependent noice. Given that this is an amplifier with all sorts</FONT>
<BR><FONT SIZE=2>> of resonant loops sitting INSIDE the box I'd have to say this </FONT>
<BR><FONT SIZE=2>> is pretty</FONT>
<BR><FONT SIZE=2>> darn good.</FONT>
<BR><FONT SIZE=2>> </FONT>
<BR><FONT SIZE=2>> I honestly don't think that metal shelves or the lack thereof make any</FONT>
<BR><FONT SIZE=2>> real difference to cluster stability or performance these days.</FONT>
<BR><FONT SIZE=2>> </FONT>
<BR><FONT SIZE=2>> rgb</FONT>
<BR><FONT SIZE=2>> </FONT>
<BR><FONT SIZE=2>> -- </FONT>
<BR><FONT SIZE=2>> Robert G. Brown </FONT>
<BR><FONT SIZE=2><A HREF="http://www.phy.duke.edu/~rgb/" TARGET="_blank">http://www.phy.duke.edu/~rgb/</A></FONT>
<BR><FONT SIZE=2>Duke University Dept. of Physics, Box 90305</FONT>
<BR><FONT SIZE=2>Durham, N.C. 27708-0305</FONT>
<BR><FONT SIZE=2>Phone: 1-919-660-2567 Fax: 919-660-2525 email:rgb@phy.duke.edu</FONT>
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