  The aim of this article is to establish asymptotic distributions and
consistency of subsampling for spectral density and for magnitude of coherence
for non-stationary, almost periodically correlated time series. We show the
asymptotic normality of the spectral density estimator and the limiting
distribution of a magnitude of coherence statistic for all points from the
bifrequency square. The theoretical results hold under $\alpha$-mixing and
moment conditions.
