In order to take effective measures to solve the interference problem of electronic devices, it is important to know the equivalent current distribution which is equivalent to the radiation source of unnecessary electromagnetic waves inside the electronic devices. Although many researches are focused on estimation of source location of the radiation source, most of the approaches are valid for the coherent radiation source, but invalid for incoherent radiation source. In this report, an approach is studied which is expected to be applied to construction of equivalent source for incoherent radiation such as modulated electromagnetic radiation. The proposed method includes a time domain near-field (TDNF) method to measure the modulated radiation in time domain, and an inverse matrix method for constructing of equivalent source from the correlation analysis of the measured near-field distribution. The method is introduced and described at first and the validity of this method is demonstrated by some examples using numerical simulation.