The iterative complex demodulation applied on short and long Schumann resonance measured sequences

Abstract

The precise determination of instantaneous frequency of Schumann resonance
(SR) modes, with the possibility of application to relatively short signal sequences, seems
to be important for detailed analysis of SR modal frequency variations. Contrary to commonly
used method of obtaining modal frequencies by the Lorentz function fitting of DFT
spectra, we employ the complex demodulation (CD) method in iterated form. Results of
iterated CD method applied on short and long measured sequences are compared. Results
for SR signals as well as the comparison with Lorentz function fitting are presented.
Decrease of frequencies of all first four SR modes from the solar cycle maximum to solar
cycle minimum has been found using also the CD method.