Q: What are the differences between radiated and conducted emissions testing and how to prepare for each?
Answer
Radiated vs conducted emissions: Conducted emissions (150 kHz-30 MHz): measured on power lines using LISN (Line Impedance Stabilization Network). Source: switching noise that couples to power cables. Fix: EMI filter (X-cap Y-cap CM choke) on power input. Radiated emissions (30 MHz-1 GHz): measured in anechoic chamber or OATS using antenna at 3m or 10m distance. Source: cables acting as antennas and PCB traces. Fix: PCB shielding cable shielding ferrite clamps. Test preparation: (1) Operate the EUT at representative worst-case configuration. (2) Ensure EUT is in normal operating mode. (3) Provide representative load if applicable. (4) Have all cables present as in the final product. (5) Calibrate LISN and antennas. (6) Pre-scan with near-field probes (cost-effective but not official). (7) For automotive (CISPR 25): conducted on supply lines using current probe; radiated in absorber-lined shielded room (ALSE). Typical pass criteria: Class B (residential): <40 dBuV/m at 3m for radiated.
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