OBSERVATION CONTROL DEVICE FOR THE URAN-4 DECAMETER RADIO TELESCOPE

The URAN-4 radio telescope has been operating at the Odessa Radio Astronomy Observatory of the Radio Institute of the National Academy of Sciences of Ukraine since 1986. The telescope is an element of a decameter long-base interferometer – the radio telescopes which are located across the territory of Ukraine from west to east. The URAN-4 consists of antenna and upgraded radiometer. Antenna consists of 128–element with phased array with dimensions of 232.5 x 22.5 m. The telescope operates in the 10 – 30 MHz range. Its receiving equipment is capable of separating two polarization components of the received signal. The radiation pattern of the radio telescope is 2,7x22 degrees at 25 MHz. The resolution of 2 seconds is realized in the interferometer mode. The instrumental complex of the radio telescope includes the upgraded device for controlling its operation. This device is made in the form of a separate unit. The ATMEL AT90S8515 microcontroller with registers and a communication circuit between the unit and the computer are mounted in it. The discrete movement in space of the antenna's directional pattern and sets the required attenuation in the attenuator during calibration are carried out with the upgraded controlling device at a given time during the observation period. The controlling device also allows adjust the current time of the computer using GPS.

MODELING A DECAMETER RADIO LINK IN PREDICTING THE RELIABILITY OF COMMUNICATION

Представлено краткое описание последовательности расчета надежности связи в декаметровом диапазоне волн, включающее в себя ряд методик и моделей определения характеристик условий распространения радиоволн и технических параметров элементов радиолинии. Особенностью предлагаемой модели декаметровой радиолинии является системное построение методик и алгоритмов определения параметров радиолинии для единой задачи прогнозирования условий радиосвязи, имеющей целью создание адаптивной радиолинии нового типа - с учетом параметров изменений геомагнитной возмущенности. A brief description of the sequence of calculation of communication reliability in the decameter wave range is presented. It includes several methods and models for determining the characteristics of radio wave propagation conditions and technical parameters of radio link elements. A feature of the proposed decameter radio line model is the system construction of methods and algorithms for determining radio line parameters for a single problem of predicting radio communication conditions, which aims to create an adaptive radio line of a new type - taking into account the parameters of changes in a geomagnetic disturbance.

Numerical-analytical method for calculating the refraction of radio waves in a chaotic upper atmosphere

An operational method is proposed for calculating the refraction of decameter radio waves in a randomly-inhomogeneous upper atmosphere. The method is based on the numerical-analytical solution of stochastic equations of geometric optics. An integral expression is obtained for the dispersion of the refraction angle of a radio wave on the atmospheric path using the approximation of the perturbation method. For a quick calculation of the statistical moment of the refraction angle, the integral expression is reduced to an ordinary first-order differential equation. The joint numerical solution of the unperturbed ray equations and the equations for the statistical moment allows doing an operational estimate of beam width of radio waves arriving at the observation point. The results of numerical calculations of the standard deviations of the refraction angles of radio waves on paths of various lengths are presented.

THE FOUNDER OF THE DECAMETER RADIO ASTRONOMY IN UKRAINE ACADEMICIAN OF NAS OF UKRAINE SEMEN YAKOVYCH BRAUDE IS 110 YEARS OLD: HISTORY OF CREATION AND DEVELOPMENT OF THE NATIONAL EXPERIMENTAL BASE FOR THE LAST HALF CENTURY

Purpose: A historical review of the experimental baselopment of low-frequency radio astronomy in Ukraine, its foundation half a century ago by an outstanding scientist S.Ya. Braude to the current state. Design/methodology/approach: The constant progress of electronic, computer and digital technologies, information and telecommunication technologies, theory and practice of antenna and receiving systems design, which introduction enriched the hardware and methodological ideology of construction and usage of the UTR-2, URAN, and GURT radio telescopes, have been used. Findings: The worldwide most effective national experimental radio astronomy means, the UTR-2, URAN, and GURT decameter-meter wave radiotelescopes, have been created and improved. The best combination of the systems main parameters: sensitivity; frequency band; spatial, frequency and temporal resolutions; noise immunity; uniformity of amplitude-frequency and space-frequency characteristics and multifunctionality has been provided. Conclusions: For the half a century of radio astronomical scientific and technical at the Institute of Radio Astronomy of NAS of Ukraine, the high astrophysical informativeness of the low-frequency radio astronomy and the possibility of creating a highly efficient experimental base – giant radio telescopes of decameter-meter wavebands have been proved. Today, the Ukrainian radio telescopes are well known and recognized world-wide being indispensable and most in demand by the scientific community. The founder of the decameter radio astronomy in Ukraine, the eminent scientist Semen Yakovych Braude was not mistaken when he decided to start radio astronomical explorations. The memory of him will always remain in the minds and hearts of many generations. Key words: low-frequency radio astronomy; radio telescope; phase shifter; antenna amplifier; digital signal recorder; effective area; sensitivity; resolution; noise immunity

EXPLORATION OF THE SOLAR DECAMETER RADIO EMISSION WITH THE UTR-2 RADIO TELESCOPE

Purpose: The overview of the scientifi c papers devoted to the study of the solar decameter radio emission with the world’s largest UTR-2 radio telescope (Ukraine) published for the last 50 years. Design/methodology/approach: The study and analysis of the scientifi c papers on both sporadic and quiet (thermal) radiation of the Sun recorded with the UTR-2 radio telescope at the decameter wavelength range. Findings: The most signifi cant observational and theoretical results of the solar radio emission studies obtained at the Institute of Radio Astronomy of the National Academy of Sciences of Ukraine for the last 50 years are given. Conclusions: For the fi rst time, at frequencies below 30 MHz, the Type II bursts, Type IV bursts, S-bursts, drift pairs and spikes have been recorded. The dependences of these bursts parameters on frequency within the frequency band of 9 to 30 MHz were obtained. The models of their generation and propagation were suggested. Moreover, for the fi rst time the fi ne time-frequency structures of the Type III bursts, Type II bursts, Type IV bursts, U- and J-bursts, S-bursts, and drift pairs have been observed due to the high sensitivity and high time-frequency resolutions of the UTR-2 radio telescope. The super-fi ne structure of Type II bursts with a “herringbone” structure was identifi ed, which has never been observed before. New types of bursts were discovered: “caterpillar” bursts, “dog-leg” bursts, Type III bursts with decay, Type III bursts with changing drift rate sign, Type III-like bursts, Jb- and Ub-bursts, etc. An interpretation of the unusually high drift rates and drift rates with alternating signs of the Type III-like bursts was suggested. Based on the dependence of spike durations on frequency, the coronal plasma temperature profi le at the heliocentric heights of 1.5–3RS was determined. Usage of the heliographic and interferometric methods gave the possibility to start studies of the spatial characteristics – sizes and locations of the bursts emission sources. Thus, it was shown that at the decameter band, the Type III burst durations were defi ned by the emission source linear sizes, whereas the spike durations were governed by the collision times in the source plasma. It was experimentally proved that the effective brightness temperatures of the sources of solar sporadic radio emission at the decameter band may reach values of 1014–1015 K. In addition, it was found that the radii of the quiet Sun at frequencies 20 and 25 MHz are close to the distances from the Sun at which the local plasma frequency is equal to the corresponding observed frequency of radio emission in the Baumbach–Allen model. Key words: UTR-2; Sun; decameter radio emission; radio bursts; corona

Refined method for determining the spatial correlation interval of the fading in a single-beam decameter radio link.

In this articlea a refined method have been developed for determining the spatial correlation interval for fading in a decameter radio link with one discrete beam (mode), which are caused by wave diffraction on small-scale ionospheric irregularities. A refined dependence of the spatial correlation interval of fading in a single-beam decameter radio line on the parameters of small-scale ionospheric irregularities, the equivalent length of the radio line and the choice of the operating signal frequency through the value of the root-mean-square deviation of fluctuations of the wave phase front at the output of the inhomogeneous ionosphere is obtained. It is shown that under conditions of disturbances (diffuseness) of the ionosphere, as well as the approach of the operating frequency of the radio line to the maximum applicable frequency, when fluctuations of the phase front of the wave at the output of the ionosphere exceed 1.25 radians, the well-known simplified expression for estimating the interval of spatial correlation of fading can be used in a single-beam decameter radio links with an error of no more than 5%.

NCREASING IMMUNITY OF DECAMETER RADIO CHANNEL TRANSMISSIONS UNDER UNINTENDED INTERFERENCE

The transmission of messages is a complex process, which is largely determined by the properties of the radio channel used. Decameter radio channels are the most difficult for organizing communication, since the ionospheric propagation of radio waves is associated with their significant attenuation, due to the significant length of the paths, as well as the presence of Rayleigh fading in the channel. However, the possibility of transmitting information over long distances without serious resource costs stimulates further research to improve the reliability of decameter radio communication. In this paper, we investigate the possibility of increasing the noise immunity of frequency-shift keying transmissions of decameter radio channels in conditions of unintentional interference due to the use of broadband signals. An analytical expression of the dependence of the probability of a bit error on the level of the ratio of the peak signal power to the peak interference power is considered; a graph of this dependence is presented. It is shown that the plot is consistent with the overall noise immunity estimate for Rayleigh fading channels using double FSK signals. The rationality of methods for obtaining the required reception quality in decameter radio channels is analyzed. It is shown that the most rational direction for increasing the noise immunity of FM-2 transmissions in decameter radio channels with Rayleigh fading in conditions of unintended interference is the use of broadband signals. In this case, for expansion, it is advisable to choose a value kf = 7, which makes it possible to increase the noise immunity by 9 dB. The conclusions are illustrated by graphs.