The processes of useful signal formation in the short-range radar systems constructed on the heterodyne, homodyne and autodyne principles are considered. The mathematical fundamentals of the fulfilled analysis are described in brief. It is shown that the autodyne configuration is much more complicated for the examination compared to the heterodyne and homodyne configurations due to the necessity of taking into account its own re-reflected signal. To simplify the theoretical analysis, the examination of the autodyne effect is performed under an assumption of reflected signal smallness. The comparison results of the considered configurations, which show that the homodyne and autodyne signal processing in the usual Doppler short-range radar turns out similar, are given. However, the autodyne short-range radar configuration itself has its own specific peculiarities, which should be taken into consideration in practice. It is proved that in the autodyne configuration one can meet the accompanying frequency modulation of the probing oscillation. It appears even at the absence of the forced frequency modulation, which is widely used to improve the short-range radar noise immunity. It is found out that this accompanying frequency modulation at weak reflected signals does not affect noticeably on the autodyne converter operation. The main theoretical conclusions of this paper are in the good conformity with the published results.