I am currently developing my first product which needs to fulfill EU EMC requirements.
Below you can see the first result out of the EMC lab (radiated emission test):
One can clearly see the 16 MHz clock frequency and the radiation out of the product seem to go over the power lines through multiple connectors from the main PCB.
This assumption also comes from the following results of a measurement without having the connectors attached:
So, now I am designing an update and beside optimizing the layout regarding the crystal, uC decoupling, trace length reductions, and provisions for ferrite beads on the signal lines, but I am not really sure about one countermeasure - an LC filter.
Here I would be very thankful to get some help.
I want to add an LC filter on every power line right before the connector. But here I have the first issue - which cut-off frequency needs to be used? Is it the frequency of the first peak (32 MHz) or, as I read a lot, 1/10th of the first peak (3.2 MHz)?
Filter: I have a connector which has 1 x 12 V power and 3x switched low-side power (PWM/MOSFET). Does it make any sense to add filters to these lines, or is it just the power line which makes sense to filter?