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#61
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In comp.sys.ibm.pc.hardware.chips KR Williams wrote:
Please, "LC filters" aren't used for EMI reduction *AT ALL* in this application. Al LC filter simply rings at its resonant frequency, it doesn't attenuate anything. If you're thinking of ferrite beads, they're not an 'L' at all. They're 'R's at the frequency of interest. It takes an 'R' to dissipate power. That's my point. There aren't LC circuits used to attenuate anything, unless they're *REAL* morons. Perhap;s they can't pick the right ferrite, but that's another issue (if they cannot even follow the reference design...). Well, maybe my terminology is off. I see three sets of "L" components and "C" components on vidcards near the VGA connector. They are most probably connected to the RGB analog output lines and reduce the sharp corners, overshoot and high rise rate of digital signals for analog transmission. I don't buy it. The ferrite on the I/O won't help one iota if the card is radiating elsewhere. Sure there are crappy designs, but I'm not buying your LC filter theory. ...at least as stated. Ah, but if the card is otherwise good, or nearly so, then won't L & C omponents on the output stages help reduce EMI from the monitor cable (aka antenna)? -- Robert |
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