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Suppose a commercial product uses a FCC pre-certified WiFi module. If the quality is not consistent throughout the batch, I'd guess some pre-certified modules may produce unacceptable emissions. In that case, could these emissions fail the unintentional emission test for the final product? Or is it that pre-certified modules are somehow isolated during the test such that the emissions produced by the pre-certified modules will not affect the unintentional emission test outcomes?

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  • \$\begingroup\$ There are a lot of "Ifs", "guesses" and "coulds" in your question - individual modules may well be certified but by creating a new product you also create new opportunities for unwanted emissions (e.g. power lines/tracks acting as aerials). The only way to know is to test the final product. \$\endgroup\$ – JIm Dearden Mar 4 '17 at 12:24
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Well possible that an unit that has approved building blocks fails as one new system. The cumulated total emission can be too much due a simple summing or due increased individual emissions caused by new interactions. Do not rely only on "all my parts already have the certificate".

Do not believe? What interactions????

Think about a radio device and a too high voltage power supply for it. The higher voltage can easily raise the spurious outputs too high or the output at the legitimate frequency can have too high power.

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