What is the acceptable margin for radiated emission on an European CE device

Question

One of our prototype (IOT gateway) has completed the emission test (EMC) but we have a margin on two particular frequencies, just wondering what is the acceptable margin for CE device in Europe ? I have been through various sites but still not able to figure out this the Margin acceptable. This will be installed at private sites (with public access).

For 160 MHz - Limit=40dBµV/m QuasiPeak=37.20 Margin=-2.80
For 550 MHz - Limit=47dBµV/m QuasiPeak=43.01 Margin=-3.99

Any suggestion would be greatly appreciated !!

Answer 1

It's a limit, defined in CISPR 11 and other places. So anything below the limit is fine. If you're at the limit exactly it's a bit fuzzy situation, I can't remember off hand if the limit is up to and including the cut-off value.

In any case, 4dB is a healthy margin, 2.8dB isn't anything to lose sleep over. If the margin is very small e.g. <1dB you might fail at another time and different test lab, just because of how the cables are arranged, equipment calibration and so on. In most situations, if you're -0.1dB, they stamp the certificate and off you go.

If you supply parts for a larger assembly, this attitude can come back to bite you when the client retests the entire setup.

From your test limits, it seems you're testing Class B "normal" commercial or domestic environment device at 3 meter antenna position.

Answer 2

There is no margin. You have to ensure your production units are below the limit, even if only by 0.1dB.