About the errors related to the application of time to frequency domain transforms to nonstationary signals

Several measurement processes are based on digital signal spectral analysis. Physic signals are usually nonstationary and can be considered stationary only in limited time intervals. Moreover, spectral analysis techniques report accurate results only if applied to signals with constant harmonic content. In common industrial and research applications the stationariety is usually a hypothesis without any proof verification. This can often produce errors on the spectra and then on the measurements. In this paper we propose an experimental approach to the problem of nonstationary signals spectral analysis with the aim to show the possible errors that this condition may cause. Different kinds of algorithms are considered and some practical application and verification of the carried out conclusions are reported.