On 9/23/2010 8:34 PM, email@example.com wrote:
The problem with switchers is what happens when you have a lot of them
on a power system. Building transformers, especially those for office
buildings have been redesigned over the years to cope with the
asymmetrical loads from switching power supplies. Heck, these days
noise tolerance is designed into the darned integrated circuits
On Sep 23, 8:34 pm, firstname.lastname@example.org wrote:
Not necessarily. Boards today aren't as ugly RF wise as they once
were. Boards sold to the public (outside systems) must pass an FCC
compliance test that only allows 6dB for the case. Even at the worst
case, 6dB above the limits, it's hardly "radiating RF all across the
T-R packs, yes. Linear supplies, not as much.
Poorly designed ones, yes. Ones that haven't passed conducted
emissions tests, perhaps. There are specs for these things too.
Specs yes, but virtually no compliance enforcement.
Loads and loads of noncompliant crap come into the country every day -
with compliance stickers prominently displayed.
Like I said - I spent 5 years in the computer manufacturing business,
and what DID NOT comply was a whole lot more common than what did,
To make a SYSTEM compliant with non-compliand components is possible,
but quite difficult.
We used 4 layer boards even back then - with built-in ground planes in
the critical areas - and often the difference between a system that
passed and one that didn't was as simple as different PLASTIC on the
case front - or changing suppliers of the video card - which had the
same part number, and supposedly the same design.
One plastic has RFI coating on the inside, while the other didn't. One
vieo card supplier had left off the "non-critical" despiking capacitor
or other EMR suppression device - and "might" pass with a well
sheilded and ferrited cord to the monitor, while the other, slightly
more costly, fully populated board would pass, hands down.
When the accountants started running the company instead of the
engineers, all hell broke loose when it came to certifying new models.
On Fri, 24 Sep 2010 13:22:09 -0400, email@example.com wrote:
Not unless someone complains (usually a competitor).
Sure, but irrelevant.
I've spent >35 years, most of which was spent designing this stuff.
Wrong! You clearly don't know what you're talking about. PCs have special
dispensation. As long as the components are listed (at the 6dB tightened
spec) the computer doesn't even need to be tested. Many DO NOT have any
shielding at all; all perfectly legal.
It *very* few exceptions, ground planes go EVERYWHERE, not just in "critical
areas". Power planes, too. Eight layers (4S4P) was our standard card 35
years ago, motherboards had even more signal layers.
Sure, the PS/2s had a conductive coating on the inside (for ESD as much as for
RFI). There is no need for much of that anymore.
Old legends die hard. I was an Installation Planning Rep in the 90s
and I still ran into people who swore IG was necessary but they were
not in the IBM Physical Planning community and it certainly was not in
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