Offline 20W Flyback SMPS failing QP radiated emissions at peaks 57MHz to 184MHz

[treez]

Hi,
Its an offline 20w flyback SMPS in an earthed metal enclosure with its output coming out of the enclosure on a 2 metre cable...(going to a DCDC buck onverter)
What is the likely culprit of these frequencies?

--- Updated Feb 18, 2021 ---

Please also confirm that cable ferrites are no use for these frequencies?

 

[Easy peasy]

no snubber on the o/p diode the most likely cause ...

 

[treez]

Thankyou. I placed RC snubbers on Aux and Sec of 220pF,47R (all i had in the lab) and it didnt improve the "el cheapo" radiated emissions scan that i did after fitting these RC snubbers.
(This el cheapo scan simply involved torroid wrapping the cable from the flyback through a near field probe loop (18 turns), and then looking at the probe output with a spctrum analyser (SA1002A)

 

[Velkarn]

try to look at output diode and power MOSFET source-drain and measure the freq of oscillations at this points, is any correlations with peaks

 

[treez]

try to look at output diode and power MOSFET source-drain and measure the freq of oscillations at this points, is any correlations with peaks

Thankyou yes i was doing this, but the frequency of the oscillations there was nowhere near like the failure frequencies....mind you, i only had a 100MHz scope to look there. But then again, maybe the scope capacitance was making it seem lower in frequency than it really is.