Weighted multi-point interpolated DFTF to improve amplitude estimation of multi-frequency signal

The error reductions of frequency and amplitude estimations of periodic signals with multi-point interpolated discrete Fourier transform (DFT) are described. The properties of interpolations are studied for the rectangular and Hanning windows with respect to their ability for correction systematic effects of used windows and their noise sensitivity. The correction is improved with increasing the interpolation points of DFT. The use of a suitable interpolation algorithm depends on effective bits of A/D conversion, on the position of the frequency component of signal and on mutual components interspacing along the frequency axis. Using different algorithms, we change adaptively the apparent window shape for the particular component.