Successfully troubleshooting EMI/EMC problems isn't easy. You need time, you need a strategy, and you need to remain calm. Sometimes, you need a special "sixth sense" that only comes from experience because in some cases, your problems aren't even related with the EUT (equipment under test).
Article by instructor Arturo Mediano about near-field scanners.
I love near field probes because they let me "see" magnetic and electric fields with an oscilloscope or with a spectrum analyzer. They let locate sources of emissions in board, cables, and systems. Near-field scanners also let you see emissions, particularly all over a board. That's hard to do with a single probe.
Arturo Mediano teaches courses on EMC/EMI and Signal Integrity for Besser Associates. He is a frequent contributor to industry magazines and journals on these topics. This article appears in the "Practical Tips" section of InCompliance magazine.
Ferrites for EMI suppression are usually chosen looking for high (resistive) impedance at the frequency of interest; but, sometimes, that ferrite is not working as expected. Perhaps you have saturation effects?
Instructor Arturo Mediano has written an article for In Compliance magazine:
Digital and power electronic systems can reduce the radiated and conducted emissions profile using spread spectrum techniques. Typically, no more than 10-12dB can be obtained with those techniques but the result can be useful to comply with regulations...
Instructor Arturo Mediano has published an article with In Compliance magazine on reducing VHF EMI from a flyback power supply.
Usually, EMC design guidelines in flyback literature are related with the switching effects of the output transistor to minimize emissions for conducted tests in the 9 kHz to 30 MHz range. But failure in radiated emissions in the VHF range is typical when testing the product for EMC compliance.
Until now, the focus in developing wireless communications formats has been almost exclusively on using novel techniques to overcome specific channel impairments (i.e. multipath, selective fading, etc). What has been missing is an assessment of the overall energy efficiency of the final hardware that is to be deployed. This paper introduces this type of analysis.