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RE: hf noise from monitor



Hi Ray,

I'm confused...  My understanding of the FCC emissions classifications
is different that what you describe.  FCC-A is the worst; industrial
settings, not intended for home use.  FCC-B is for residential stuff,
and is generally RF-quiet.  I had a large problem with a surplus-store
PC chassis that came with what I now know was an FCC-A power supply. HF
receive had an S-5 noise level on a band that was S-0 otherwise.  A
new supply from CompUSA (FCC-B) fixed it.  And, I've never heard of
class-C.  Have things changed at the FCC?

Greg  KO6TH



>From: "Ray McKnight" <shortsheep@worldnet.att.net>
>To: <amsat-bb@AMSAT.ORG>
>Subject: RE: [amsat-bb] hf noise from monitor
>Date: Wed, 12 Feb 2003 15:38:25 -0800
>
>True, the most probable place you will pick up noise is from poorly or
>unshielded cables. But just buying a flat panel display won't guarantee
>a quiet receiver!  If you choose a digital flat panel, you might be in
>for a big surprise.  Also, most things nowadays come with switching
>power supplies, even when they look like a harmless wall wart.
>Switching supplies are notorious for being dirty.  And most computers
>you buy now only meet Class-C certification, or otherwise, no shielding.
>I have numerous SGI's and am amazed at how well they are shielded; they
>meet Class-A (even that doesn't guarantee zero emissions).  They're so
>good in fact I wouldn't doubt they could pass a military Tempest
>certification.  But you get what you pay for.  It's often impossible to
>peer into a cable to see how it's shielded.  Stay with known brands that
>have a reputation for quality, or roll your own with quality cables and
>shielded connectors.  For difficult problems, you can also try lead or
>copper tape for inside computer cases and such.
>
>73's
>Ray - WB3ABN
>Kingston, WA
>


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