Each signal which is available as a sampled time signal can be transformed, without any loss of information, to the (complex) frequency domain and back, where it is represented as a spectrum of magnitude and phase. The operation for transforming from time to frequency domain is the Fourier Transformation, in this case realised in the form of the Fast Fourier Transformation (FFT). Re-transformation from frequency to time domain is performed by an inverse Fourier Transformation, here the Inverse Fast Fourier Transformation (IFFT). These operations are the essential component of the measuring technique implemented here.