The book contains an exposition of the theory of radiotechnical circuits and signals. Radio signals and the main radio engineering systems are considered - linear, nonlinear and parametric, as well as the transformations and processes occurring in them. Basic information on statistical phenomena in radio electronic devices - linear (amplifiers and auto-generators. In brief, the problem of synthesizing a circuit optimal for isolating a given signal on a white noise foyer is considered. The book is intended for students of radio engineering faculties and universities. It can also be useful for a wide range of specialists working in the field of radio engineering and related fields of science and technology.