Comparison of Distance Conversion Factors for H-field Emissions Limits

Radiated electromagnetic emissions requirements are defined as field strength levels that must not be exceeded when measured at a standard reference distance from the equipment under test. However, when such emissions are measured by placing the antenna at a distance different from the reference one, conversion factors are employed to adjust the emissions limits accordingly. This paper compares five alternative proposals of distance conversion factors for magnetic field emissions limits in the frequency range from 150 kHz to 30 MHz. This analysis intends to identify commonalities and differences between independent proposals presented in research articles, technical reports, and standards. The results suggest the different proposals could be merged into a single set of H-field conversion factors. Moreover, throughout the application of conversion factors in real cases, it is confirmed that, for in situ testing, H-field limits defined for distances greater than 10 m are likely to be surpassed by the ambient levels specially for frequencies higher than 4 MHz.