Abstract: A spectral analysis carried out on the beat signals obtained by the mixing of a transmission signal, the frequency of which is modulated in the form of recurrent sawteeth, with this same signal after it has been transmitted, reflected and then received. The spectral analysis is based on the computation of self-correlation coefficients enabling the definition of the spectral components. For this purpose, the coefficients are computed at each sawtooth and are combined with the coefficients determined with the most recent previous sawteeth to give so-called global coefficients, from which the spectral components sought are restituted in a conventional way. Application especially to altimeters for the measurement of small heights.