How to locate the radiated noise source of the intelligent low-voltage monitoring unit?

Near-field scanning and spectrum analysis were used to locate the radiated noise source.

Tools: Near-field probe, spectrum analyzer.

Steps:

         1. Measure the radiated spectrum to identify the frequency points exceeding the limit;

         2. Scan the PCB with the near-field probe to find strong radiating areas at the same frequency points;

         3. Focus on checking the clock circuit, switching power supply, and high-speed digital lines.

Rectification after location: Add a shielding cover to the clock circuit; optimize the layout of the switching power supply; add grounding to the high-speed lines. Through location and rectification, the radiated emissions were below the limit.