[SI-LIST] Re: Traces don't cause EMI - really?
- From: Alex Horvath <alexh1@xxxxxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Fri, 17 Oct 2003 11:31:55 -0700 (PDT)
Probably getting off topic here but my computer which is not a name brand, was
simply assembled from components and has none of the obvious EMI preventative
measures like gaskets, filters etc that you see on a name brand. Also, it was
never EMI tested as a unit. So is this unit legal from an FCC emissions
standpoint?
Lfresearch@xxxxxxx wrote:
In a message dated 10/17/2003 1:09:11 PM Central Daylight Time,
alexh1@xxxxxxxxxxxxx writes:
Assuming the EMI testing that's done for CISPRB and CE is done
with a base configuration (no added PCI cards, etc.), the inclosure could be
providing a great deal of the necessary shielding. The mother board itself
would then not need to be especially clean.
This has been an area I've looked at in great depth recently. I have been EMI
testing a great many PC Cards, and it took me a long while to find a PC that
would comply on it's own. I found only 2 motherboards, both made in the USA,
that could pass with no cover on.
The worst motherboard was close to 35 dB over spec when tested with the cover
off. It was made offshore. The reason this was a problem to the card makers, is
that noisy motherboards use plug in cards and their cables for an exit point.
So, the performance of the card is often disguised.
Back to my point :-).
The MB performance is often swamped by the plug in cards and interconnections
that take place to off the boards... So even if the MB is quiet, the rest of
the PC isn't. However, what leaves the case raely comes from here anyway, it
leaves fom the the leads that leave the case like the mouse and keyboard...
Cheerz,
Derek N. Walton
Owner, L F Research EMI Design and Test Facility
Poplar Grove,
IL 61065
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