An analysis of peculiarities of autodyne and noise characteristics' formation in autodyne oscillator at the influence of own electromagnetic radiation reflected from the object under study is carried out. The expressions for calculation of conversion factors, measurement error and the dynamic range of autodyne instrument for vibrations and small displacement parameters measurement are derived. The calculations of measurement errors and of dynamic range of autodyne measuring instrument. The recommendations on correct choice of an operating point of autodyne vibrations and small displacements measuring instruments were developed.