# The 3dB EMC Margin — Why a 'Pass' 2dB Under the Limit Is Risky

Your product measured 2 decibels below the CE or FCC emission limit in the
test chamber. The engineer marks it a pass. You should be worried. This short
explains measurement uncertainty, production variation, and why 6dB of margin
is the real target.


## Transcript

### Why a marginal pass isn't safe

Your product just measured 2 decibels below the FCC or CE emission limit in the test chamber. The engineer calls it a pass. You should be worried. Here is why that 2dB gap is nowhere near enough.

### Sources of measurement variation

Every EMC measurement carries built-in uncertainty. A chamber alone can be off by three to six decibels — enough to turn a marginal pass into a fail elsewhere. Production units add more spread. Surveillance tests your worst case.

### The real target: 6dB of margin

Industry guidance targets at least 6dB of margin — treat any spike within that range as a problem before formal testing. Common fixes: a bypass capacitor, a ferrite bead, tighter ground stitching, or spread-spectrum clocking. Early fixes cost hundreds; the lab costs thousands.

Tags: EMC, EMC testing, pre-compliance, CE marking, FCC