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 spectrum".
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.
Not surprising, since the class-A spec is 10dB below class-B. If they passed class-B as an indivicual board (with the 6dB allowance for the case), they'll pass class-A without a case with at least a 4dB margin.
Computers (before PCs) once did use a lot of linear supplies and T-R packs.
They were in every building I worked in. They were up and down the halls, even. Cleaning crews were instructed to use them exclusively.
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 our specs.
I can categorically deny that as being even remotely possible, having been in the computer manufacturung business for 5 years, and having had numerous designs tested for FCC and DOT compliance. A full foil lining on the wood case, at a very minimum, would be required to pass.
I didn't say PC. I said computer. I've got several linear computer power supplies stashed away in the "way back" box., as well as 2 operating 6809 boxes with linear power supplies.
"Required" and "have" are at least 3 different things it appears. A very LARGE percentage of low end PC power supplies have NO EMI filtering on the line input. Noise in the power cord WILL end up on the ground, to one extent or another - and an IG keeps it more or less localized to that circuit.
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, component wise.
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.
I started in the computer biz in 1966
Yes, and my stint in the computer manufacturing business goes WAY back too. Not quite as far as you though!!!! I got out of the manufacturing business many years ago - just before the manufacturer went "T.U."
QRZ, I suppose, too.
You're *clearly* wrong. Computer components must pass *without* a case (with a 6dB exemption). A component designed for class-B will *easily* pass class-A limits without a problem.
No, they're required to pass the test. That's made a lot easier with the line filter, but the filter is not a requirement.
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.
That's somehow supposed to be surprising?
Like I said, this was in the lab buildings.
replying to Mortimer Schnerd, bremar wrote: dear Mortimer, The red outlets are always hot ( always powered ). Use the red outlets anytime, during regular power corp supply or power outage (hospital backup UPS). Although, your hospital may have a different electrical control scheme.
Dedicated power and ground for sensitive equipment
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