How to troubleshoot excessive radiated emissions (REs) from edge computing boxes in frequency bands?

Excessive radiated interference (RE) from edge boxes commonly falls into three frequency bands: 30-100MHz, mostly power module or clock harmonics; 100-200MHz, mostly common-mode radiation from interface cables; and 200-1000MHz, mostly high-speed signals such as DDR and USB 3.0. Troubleshooting involves using a near-field magnetic field probe in conjunction with a spectrum analyzer to scan each region. For peaks in the 30-100MHz range, the CMZ3225A-201T common-mode filter from Audiotech Electronics can be used. Its name is CM common-mode Z, impedance 3225, size 3.2×2.5mm, 201T impedance 200Ω. If the 100-200MHz frequency band is prominent, place it near the power input. Check the shielding of the network port or HDMI port. Connect a common-mode inductor CML3225A-510T in series on the differential line. Its name is CML common-mode inductor 3225, size 3.2×2.5mm. A 510T inductor with a capacity of 51μH can reduce common-mode radiation. For radiation above 200MHz, a ferrite bead PBZ1608E600Z0T needs to be added to the clock line, and the PCB stack-up needs to be optimized. High-frequency signals are referenced to a continuous ground plane. This positioning method can pinpoint the noise source within 30 minutes. After targeted rectification, the radiation margin is greater than 6dB.