Use of time domain methods for CISPR16 compliant EMI measurements

A common problem with EMI measurements using conventional time-saving procedures is that in most cases the total measurement time is still very long (e.g. in the order of hours). A significant reduction of the measurement time is possible when using time-domain methods that determine the interfering spectrum by means of the digital fast Fourier transform. But when performing measurements of an unknown combination of narrowband and broadband EMI signals with a broadband time-domain EMI (TDEMI) measurement system special problems has to be considered and measures to be taken to be in line with CISPR 16. The paper starts with a general description of the TDEMI system followed by an explanation of the major problems and how they are solved without missing any inferring signal or without losses in accuracy. An example introducing an EMI measuring system consisting of a compliant test receiver enhanced by fast Fourier transform (FFT) to reduce the measurement time by a factor of up to 590 concludes the presentation.