Spectrum analysis and EMI measurements based on time-domain methods

Measurements of electromagnetic interference in time-domain allow to reduce the scan time by several orders of magnitude, in comparison to automated scans performed by the tuned selective voltmeters, which are known as EMI receivers. Spectrum analyzer are used for frequency selective measurements of signals. Such analyzers can perform fast sweeps or scans over large bands. A drawback of spectrum analyzers is the long sweep time, when a high frequency resolution is required. In this paper an overview of methods and systems is shown which perform the measurement in time-domain and use the short-time fast Fourier transform for the calculation of the spectrum rather than a sequential measurement. Baseband systems allow to speed up scans by several orders of magnitude. Systems with a broadband downconversion and a broadband analog-to-digital converter system allow to extend the frequency range beyond the Nyquist frequency of todays available ADCs. Powerful Short-time fast Fourier transform processors allow to process several frequencies at the same time. A gapless processing allows to analyze unstationary signals as well as small narrowband signals.