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Edit: Fixed the drawing, looks very weird in the message but proper when posted
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Thanksklankymen wrote:try to put your drawing intotags...Code: Select all
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It's not there. I am asking about how the shield can be constructed rather than the shielded object. Am I explaining it good enought?jaganath wrote:Where is the thing you are trying to shield in this diagram?
The spectrum of RFI from computers and other digital equipment is a mixture of narrow and broadband emissions with the narrowband spikes being spaced at intervals from kilohertz to many megahertz. There is usually some periodicity to the narrowband frequencies, but there will also be a jumble of spikes that don’t fit any well-defined pattern. A common preconception is that computers radiate primarily at their CPU clock frequency, but the intensityat this frequency is often no higher than at a lot of other frequencies in the spectrum. Most digital RFI is strongest below a few hundred megahertz, but strong digital noise can be seen to several gigahertz and above.
Heh how long is a computer wavelength in the metric system?jaganath wrote:AFAIUI the shield should have no holes in it larger than the wavelength of the radiation it is trying to contain/protect against.
http://www.cv.nrao.edu/~rfisher/Papers/rfi_sumschool.ps
The spectrum of RFI from computers and other digital equipment is a mixture of narrow and broadband emissions with the narrowband spikes being spaced at intervals from kilohertz to many megahertz. There is usually some periodicity to the narrowband frequencies, but there will also be a jumble of spikes that don’t fit any well-defined pattern. A common preconception is that computers radiate primarily at their CPU clock frequency, but the intensityat this frequency is often no higher than at a lot of other frequencies in the spectrum. Most digital RFI is strongest below a few hundred megahertz, but strong digital noise can be seen to several gigahertz and above.
That far? I assumed it was nano-size. Anyone know specificly about the length a compter is putting out and how much that's in "normal" length?floffe wrote:The wavelength of EM radiation at 2GHz is 15cm (6"), and 1MHz gives 300 metres, but I'm not sure how much smaller it has to be (wikipedia says "significantly smaller")
The typical peak EMI from a modern computer system is in the 300 MHz to 1 GHz range. This is usually suppressed by careful routing of signal traces on the motherboard, and coupling to ground planes within the motherboard. In PCs, the goal is to have essentially no EMI even with no case, since so many consumers compromise the case shielding for various reasons.McBanjo wrote:That far? I assumed it was nano-size. Anyone know specificly about the length a compter is putting out and how much that's in "normal" length?floffe wrote:The wavelength of EM radiation at 2GHz is 15cm (6"), and 1MHz gives 300 metres, but I'm not sure how much smaller it has to be (wikipedia says "significantly smaller")
I've been looking at net but it was rather expensive (~10-20USD for 1m). Atleast what I've found.Reachable wrote:How about using window screening -- insect screening -- a couple of layers perhaps? That would create smaller holes than in grids I've seen that would block approximately gigahertz or cellphone frequencies.
I don't speak with any authority on this -- just throwing out an idea. The quote was "Most digital RFI is strongest below a few hundred megahertz, but strong digital noise can be seen to several gigahertz and above." How important is this several gigahertz noise -- excluding the noise from the processor -- and what would it interfere with?
Great, then I simply ignore the imaginary need of shielding.cmthomson wrote:The typical peak EMI from a modern computer system is in the 300 MHz to 1 GHz range. This is usually suppressed by careful routing of signal traces on the motherboard, and coupling to ground planes within the motherboard. In PCs, the goal is to have essentially no EMI even with no case, since so many consumers compromise the case shielding for various reasons.