A matrix-based stochastic method for the spectral correlation evaluation of memoryless digital modulation is presented. The method assumes that the symbol sequence is purely stationary. A new four-state aperiodic irreducible Markov chain for Offset QPSK (OQPSK) and MSK signal representation is introduced and, applying the proposed method, their spectral correlation evaluation and characterization is performed. Some computed and graphed results for the spectral correlation characterization of a few types of digital pulse-modulated and linearly digital-carrier modulated signals based on the proposed method are given as well.