V.Ya. Shanygin - Senior Engineer, Saratov branch of Kotelnikov IRE RAS. E-mail: vitairerun@mail.ru R.K. Yafarov - Dr.Sc. (Eng.), Head of Laboratory, Saratov branch of Kotelnikov IRE RAS S.Yu. Suzdaltsev - Ph.D. (Eng.), Senior Research Scientist, Saratov branch of Kotelnikov IRE RAS D.V. Nefedov - Ph.D. (Eng.), Research Scientist, Saratov branch of Kotelnikov IRE RAS