I was trying to pass EMC tests for my 48V 5A BLDC driver and failed in 30-50 MHz range. I think I found the problem in my drive circuit, but I have a few questions that got me thinking, maybe someone can help me to answer.
If my PCB is not too large (15cm x 5cm) 30-50 MHz emissions are mainly radiated through power cables? If 30-50 MHz 1/4 wavelength is 2.5-1.5 m then I need to mainly look at cables with length around 2.5-1.5 m?
If I have 48V and GND which radiates and I want to decrease emissions. What is the difference if I place ferrite around 48V and GND together or I place two separate ferrites one for 48V and one for GND? If I place one ferrite it will only filter common mode emissions?
Will inductor chokes will work better then ferrites for 30-50 MHz range? Because there is no ferrite to work in such low frequencies.