How does the length of EPS cable affect radiation testing?

EPS cable length has a significant impact on its radiated emission (RE) test results. Cables, especially those that are not properly shielded or whose shielding is not properly grounded, are highly efficient radiating antennas. Their radiation intensity is related to the effective antenna length, typically reaching its highest efficiency when the cable length is 1/4 or 1/2 of the wavelength of the radiated noise frequency. Therefore, longer cables may generate efficient radiation at more frequencies (including lower frequencies), leading to worse RE test results, particularly in the 30MHz-200MHz band. In EMC testing, standards usually specify the use of cables of typical length (e.g., 1 meter). When rectifying issues, if exceeding limits at specific frequencies is found to be related to cable length resonance, methods such as shortening the cable length, improving shielding grounding, using ferrite cores on the cable, or adding common-mode chokes can be attempted to reduce the cable's radiation efficiency.