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533.908The signals of radio-wave backscattering from small-scale irregularities located at the altitudes from 200 to 400 km were first recorded by the "Sura" facility radar in 2006. The experiments with the "Sura" facility were repeated in the summer of 2009. Radar signals scattered in the altitude range 300-500 km were observed in 10% of the cases. Pronounced variation in the radar-signal intensity was observed during modification of the ionosphere by high-power radio waves. We discuss the possibility of an experimental study of the spectrum of small-scale turbulence in the upper ionosphere by the modified method of backscattering of HF waves. EXPERIMENTAL TECHNIQUES AND RESULTSA radar with unique energy potential was developed on the basis of the "Sura" facility in 2005 to study the troposphere and the mesosphere. The radar operated at a frequency of about 9 MHz [1]. As a result of experiments, backscattering of radio waves from small-scale irregularities located in the altitude range from 200 to 400 km was observed in the summer of 2006 [2]. The measurements of the backscattering cross section of radio waves in the upper ionosphere are of interest for studying the processes of excitation, relaxation, and transfer of natural and artificial ionospheric turbulence.The second series of the radar experiments was performed in the summer of 2009 to study natural and artificial turbulence in the ionospheric F layer. As in 2006, one of the three radio transmitters of the "Sura" facility connected to an antenna section of the facility was used for ionospheric sounding. The radio transmitter operated in the pulsed regime with a peak power of about 200 kW. Another antenna section received the scattered signals. Each antenna section contained 48 crossed wideband dipoles mounted on a 300 × 100 m area. The crossed dipoles form circular polarization of the emitted radio waves. Ionosphere was sounded using the ordinary mode. The in-phase feeding of dipoles created the vertical beam of radio waves with the angular dimensions 6 • × 18 • . The receiving-antenna signal arrived at the input of a radio receiver with the passband 30 kHz. The signal at the radio-receiver input had the frequency 127.8 kHz. The signal was digitized with a rate of 56800 readouts per second, which ensured the signal transformation to the frequency 14.2 kHz. The transmitter frequency and the frequency of local oscillators of the receiving and recording equipment are synchronized by the general frequency standard, which allowed us to record both the scattered-signal amplitude and phase.As a rule, sounding was performed by pulses with duration τ = 200 μs and clock period T = 15 ms. Maximum sounding range was 2250 km with a resolution of 30 km. The radar operated at one of the following four frequencies: 9310, 8900, 7815, and 5828 kHz. The critical frequency of the ionosphere was always lower than the above values. In individual sessions, the carrier frequency of the radar and the tuning frequency of the radio receiver were switched over within the period 0.5...

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