A moving-window discrete Fourier transform (MWDFT) based frequency locked loop (FLL) is proposed for retrieving the message signal from sinusoidal frequency modulated signals. The spectra of MWDFT exhibits almost flat amplitude and phase responses when it is placed in a closed-loop with fixed sampling frequency. These flat characteristics for variation in input frequency is utilized for tracking frequency modulated carrier. The small leakage observed in terms of magnitude and phase errors of MWDFT is further corrected by adaptive sampling frequency control. The simulation and experimental investigations demonstrate the capability of proposed FLL in sinusoidal message signal retrieval with good metrics.