EMI-debugging of complex systems using different time, modulation, STFFT and frequency domain signal analysis techniques

One faces a difficult situation in EMI debugging if multiple sources radiate at the same frequency, especially, if little details on the EUT are provided. In this paper, we apply and compare a set of signal analysis techniques for identifying radiated emission sources. First, theoretical background of joint time-frequency analysis (JTFA) is given and an algorithm using short-term fast Fourier transform (STFFT) approach is applied for the data analysis. STFFT analysis provides an exclusive insight into time-dependent emission processes. Also, narrow span and zero span spectrum analysis are discussed. Special emphasis is given on signals sideband characteristics