The effect of cable geometry on the reproducibility of EMC measurements

With respect to the reproducibility of EMC measurements and measurement uncertainty, an analysis of the deviation of cable transfer characteristics has been carried out. This paper shows some examples of the deviations by varying the length, height and manner of meandering of mains cables, which is far beyond the tolerance of 3.5 dB given for the measurement uncertainty limit for conducted emission measurements by IEC CISPR/A. For up to 30 MHz, the deviation varies between 0 and 10 dB, depending on the EUT's impedance. For cables meandered to a bundle or bifilair meandered on a board, notches down to -30 dB occur. Large variations in measurement results due to set-up geometries are also described.