  The classic problem of detection of periodic signals in the presence of noise
becomes much more challenging if the observation times are themselves periodic,
contain large gaps, or consist of data from several different instruments. For
RR Lyrae light curves the additional attribute of highly non-sinusoidal
variation adds another dimension. This memo discusses and contrasts Discrete
Fourier, Periodogram, and Phase Dispersion Minimization (PDM) analysis
techniques. A new version of the PDM technique is described with tests and
applications.
