  Thanks to the space missions CoRoT and Kepler new oscillation frequencies
have been discovered in the Fourier spectra of Blazhko RR Lyrae stars. The
period doubling (PD) yields half-integer frequencies between the fundamental
mode and its harmonics. In many cases the first and/or second radial overtone
frequencies also appear temporally. Some stars show extra frequencies that were
identified as potential non-radial modes. We show here that all these
frequencies can be explained by pure radial pulsation as linear combinations of
the frequencies of radial fundamental and overtone modes.
