  We investigated 1234 fundamental mode RR Lyrae stars observed by the All Sky
Automated Survey (ASAS) to identify the Blazhko (BL) effect. A sample of 1547
BL stars from the literature was collected to compare the modulation-period
distribution with stars newly identified in our sample. A classical frequency
spectra analysis was performed using Period04 software. Data points from each
star from the ASAS database were analysed individually to avoid confusion with
artificial peaks and aliases. Statistical methods were used in the
investigation of the modulation-period distribution. Altogether we identified
87 BL stars (48 new detections), 7 candidate stars, and 22 stars showing
long-term period variations. The distribution of modulation periods of newly
identified BL stars corresponds well to the distribution of modulation periods
of stars located in the Galactic field, Galactic bulge, Large Magellanic Cloud,
and globular cluster M5 collected from the literature. As a very important
by-product of this comparison, we found that pulsation periods of BL stars
follow Gaussian distribution with the mean period of $0.54\pm0.07$ d, while the
modulation periods show log-normal distribution with centre at $\log(P_{\rm
m}~{\rm [d]})=1.78\pm0.30$ dex. This means that 99.7 % of all known modulated
stars have BL periods between 7.6 and 478 days. We discuss the identification
of long modulation periods and show, that a significant percentage of stars
showing long-term period variations could be classified as BL stars.
