B.D. Zaitsev - Dr.Sc. (Phys.-Math.), Head of Laboratory, Kotelnikov IRE RAS (Saratov Branch) A.A. Teplykh - Ph.D. (Phys.-Math.), Senior Researcher, Kotelnikov IRE RAS (Saratov Branch) A.M. Shihabudinov - Ph.D. (Phys.-Math.), Researcher, Kotelnikov IRE RAS (Saratov Branch). E-mail: alex-sheih@ya.ru I.E. Kuznetsova - Dr.Sc. (Phys.-Math.), Leading Researcher, Kotelnikov IRE RAS