Correcting Radiated EM Emission Data Measured in Nonideal Environments

The Federal Communications Commission (FCC) requires that all computing devices meet radiated electromagnetic (EM) emission limits before they are marketed in the United States. EM emission measurements must be made in an environment where the results can be correlated with the results of tests made in an open field. Although the FCC does not specify a method of correlation, it is not uncommon to add or subtract correction factors to the measured results. These correction factors are usually arrived at by comparing data taken in the nonideal environment with theoretical or open-field data. However, when correction factors are applied without regard to the characteristics of the EM source, the corrected value may be more in error than the uncorrected value.