Computer Shelves (RF EMI/EMC issue)

[Robert G. Brown]

On Tue, 20 Feb 2001, Jim Lux wrote:

> I doubt that metal shelving would have any beneficial EM properties, and, in
> fact, might actually make things worse by being a capacitively coupled
> radiator.  Trust in your FCC Class B cases...
>
> Actually, does anyone have any evidence of Electromagnetic Compatibility
> problems in a cluster?  Lots and lots of computers, all with switching power
> supplies, running off fairly long extension cords all strewn about (neatly,
> of course), and the conditions are certainly ripe for EMC/EMI problems.
> Fortunately, the computers themselves are probably fairly immune, but what
> about other devices (i.e. does your cell phone still work standing next to
> your cluster?).

Back in oh, 1983 or 1984 my 4.77 MHz IBM PC would radiate like all hell
on FM 100 or thereabouts.  I could even hear it "work" in the static.
I'm sure that any good phreaker could have told you character by
character what I was typing from fifty feet away.  Messed up my ability
to listen to music and work.

Shortly thereafter, those Class B cases started to be required and
motherboard designs improved (probably fewer sharp turns and more
attention paid to conductive path shapes and lengths) -- haven't heard a
peep for well more than a decade out of anything except the sound card
of the system itself, which DOES sometimes register a bit of system
state-dependent noice.  Given that this is an amplifier with all sorts
of resonant loops sitting INSIDE the box I'd have to say this is pretty
darn good.

I honestly don't think that metal shelves or the lack thereof make any
real difference to cluster stability or performance these days.

   rgb

-- 
Robert G. Brown	                       http://www.phy.duke.edu/~rgb/
Duke University Dept. of Physics, Box 90305
Durham, N.C. 27708-0305
Phone: 1-919-660-2567  Fax: 919-660-2525     email:rgb at phy.duke.edu