  Several VLBI EOP series were investigated with goal of determination of
parameters of the Free Core Nutation (FCN). Both the amplitude and period of
the FCN were studied using spectral and wavelet analysis. Our analysis reveals
a variability of both the amplitude (known also from other investigations) and
the period (or phase) of the FCN nutation. The FCN amplitude varies in the
range about 0.1--0.3 mas, and the FCN period -- in the range about 415--490
solar days. The latter may be also explained by changes in the FCN phase.
Comparison of time variations of the FCN period and amplitude obtained by
different authors and methods shows substantial discrepancies at the edges of
the period of observations.
