In this paper we discuss the spectral analysis of gapped time series, set up therecurrence formulae and test the method with modelling signals. We have thusconfirmed the reliability of the method. It has been applied to the analyses of theshort period oscillations in ctalysmic variable V795 Her and pre-cataclysmic variableHW Vir. The oscillations with periods of 265.91s and 116.70s have been found inV795 Her.