[Reverberator in an active medium. Analytical results]

An approximate analytical method for calculating rotating spiral wave in an active medium is described. The method is based on the transition to the system of coordinates connected with the wave front. An equation for the spiral wave is derived. A method is developed for setting boundary conditions for the solution of this equation. As an illustration for the Rincell-Keller model, there were plotted estimations of the medium parameter functions of the reverberator frequency and the wave length and the spiral wave rotating around the aperture.