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It's fairly common now to see desktop computers in cases with large windows cut in the sides. I've always been under the impression that if unshielded, computer equipment will produce a lot of radio frequency interference. Given the ubiquity of cell phones/wireless routers, etc, I can only assume it's not radiating all that much. What I'm interested in is how much power, over the whole RF spectrum, a shielded and unshielded computer system could produce. My desktop has a 900 Watt power supply. If it radiated even 1% of that power, there'd be a huge amount of radio interference in my apartment, wouldn't there?

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  • \$\begingroup\$ Dunno how much actual radiation gets emitted, but I did some calculations a while back for shielding effectiveness and even 0.01" of stainless steel has >100dB attenuation (1Hz-1MHz, increasing attenuation with frequency). Assuming that all 900W is emitted as EMI in this frequency range, there's 90nW of EMI leaving a well shielded case. Of course PC's run at much higher frequency, where hole sizes will decrease the effectiveness of the shielding because the holes will start looking like holes to the EMI. \$\endgroup\$ – helloworld922 Nov 14 '14 at 5:39
  • \$\begingroup\$ Given that everything shipped in the EU has to meet strict RF emissions limits, I'm fairly sure that it doesn't emit a lot. \$\endgroup\$ – pjc50 Nov 14 '14 at 10:39
  • \$\begingroup\$ @helloworld922 Can you walk me through those calculations? \$\endgroup\$ – Joel Nov 14 '14 at 12:17
  • \$\begingroup\$ Any RF emissions that are emitted (which have to be very low, or the PC's wouldn't have passed FCC/CE testing) have little to do with how big your power supply is. The emissions are coming from the CPU chip and other chips which are switching very fast. \$\endgroup\$ – tcrosley Oct 18 '15 at 2:57
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Well I don't really know. But two ideas to measure (or compare) it. First if you have a 'scope then clip a bit of bus wire on the end of your x10 scope probe and move it around... take off the case, put it near the over head fluorescent lights. If you don't have a 'scope then you can do some with an AM radio. Tune to a blank spot and try and hear the noise as you move it around. (The radio idea comes from here.)

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If you look on the chassis you should see the compliance rating class. Class a or b for instance. This will lead you in the right direction to see what the maximum allowed emissions would be for that device class. Most reputable manufacturers do not publish exactly how close to the class limit the product is as that would give the competition too much info.

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