Based on the differential equations for a single-circuit self-oscillating system subjected to its own delayed reflected radiation, expressions for analytical investigation of autodynes using phase-plane portraits and amplitudefrequency characteristics are obtained. Computation and graphical plotting of the latter characteristics are performed for the case of a moving reflecting target using different values of autodyne signal distortion. It is shown that an adequate description of the autodyne effect in microwave and millimeter-wave oscillators requires that a "phase" approach be used, which ensures a wide variation in the reflected radiation parameters, including those determining experimentally observed nonharmonic autodyne signals.