02-20U

Description of the general theory of two shifted signals at the FFT is given. Influence of the interference terms on the image formation is pointed. Espessial attension is tern to the case of two shifted signals modulated by plane waves with nonzero space frequencies. The FFT images from two rectangular impulses are calculated and dependance of the FFT image form parameter $p$ is presented. The FFT images from two shifted gausian signals modulated by the plane waves are obtained and results of numerical calculations are given. Domain of the maximal modulation for such signals is investigated in detail.