In this paper, applying Vondrák band filter to both series of (l.o.d.) and sunspot relative number (R), we obtain variations of amplitude of 11 yr term during 1800 1985. The results show that solar cyclic signal in (l.o.d.) series is weak and unstable. The amplitude of 11 yr term in R series has long-periodic variation. The paper has briefly discussed some results about effects of solar activity on the Earth's rotation through the atmospheric motion. From the variation of (l.o.d.) obtained by band filter, we find that maxima of amplitude of annual term in (l.o.d.) occur at the same time with those of sunspot number. It implies that the angular momentum imbalance between the circulations in Southern Hemisphere and Northern Hemisphere is controlled in some way by solar activity.