  We found a possible relationship between the modulation period and the
amplitude of the Blazhko RR Lyrae stars: long modulation period generally
implies high modulation amplitude while the short modulation period results in
small amplitude. Although this effect is much more a tendency than a strict
rule, it can be detected easily in the space-born time series data produced by
Kepler and CoRoT. Good quality ground-based data show this relation, too. This
phenomenon could give us constraints for the physics of the Blazhko effect.
