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Estimating for the frequency drift rates of type III solar bursts is crucial for characterizing their source development in solar corona. According to Melnik et al. (Solar Phys. 269, 335, 2011), the analysis of powerful decameter type III solar bursts, observed in July-August 2002, found a linear approximation for the drift rate versus frequency. The conclusion contradicts to reliable results of many other well-known solar observations. In this paper we report on the reanalysis of the solar data, using a more advanced method. Our study has shown that decameter type III solar bursts of July-August 2002, as standard type III ones, follow a power law in frequency drift rates. We explain possible reasons for this discrepancy., 10 pages, 4 figure, 3 tables

We report the history of the first recorded ground-based radio detection of Saturn’s lightning using the Ukrainian UTR-2 radiotelescope at frequencies from 20 to 25 MHz. The observations were performed between 29 January and 3 February 2006, during which lighting activity (E-storm) on Saturn was detected by the radio experiment onboard Cassini spacecraft. The minimum detectable flux density ( 1 σ -level) at UTR-2 reached 40 Jy ( 1 Jy = 10 - 26 W m - 2 Hz - 1 ) for narrowband observations ( Δ f = 10 kHz ) and 4 Jy for broadband observations ( Δ f = 1 MHz ), for an effective telescope area of ≈ 100 , 000 m 2 and integration time of 20 ms. Selection criteria including comparison of simultaneous ON/OFF-source observations were applied to distinguish detection of lightning-associated radio pulses from interference. This allowed us to identify about 70 events with signal-to-noise ratio more than 5. Measured flux densities (between 50 and 700 Jy) and burst durations (between 60 and 220 ms) are in good agreement with extrapolation of previous Cassini measurements to a ground-based observer. This first detection demonstrates the possibility of Solar System planetary lightning studies using large, present and future ground-based radio instruments. The developed methods of observations and identification criteria are also implemented on the UTR-2 radio telescope for the investigation of the next Saturn’s storms. Together with recently published UTR-2 measurements of activity measured after the 2006 storm reported here, the results have significant implications for detectable planetary radio emission in our Solar System and beyond.

The third part of the work dealt with the heliograph of the UTR-2 radio telescope description shows that every pixel from the signal received by the corresponding beam of the antenna pattern is the crosscorrelation dynamic spectrum (time-frequency-intensity) measured by the digital spectrum processor in real time. This new generation heliograph allows the solar corona images within 8÷33 MHz with the 4 kHz frequency resolution, time resolution to 1 ms, and for a 90 dB dynamic range. The illustrations of observations of solar corona and other radio sources made in summer of 2010 with the heliograph are demonstrated.

International audience; The properties of powerful (flux >10-19 W m-2 Hz-1) type III bursts observed in July - August 2002 by the radio telescope UTR-2 at frequencies 10 - 30 MHz are analyzed. Most bursts have been registered when the active regions associated to these bursts were located near the central meridian or at 40° - 60° to the East or West from it. All powerful type III bursts drift from high to low frequencies with frequency drift rates 1 - 2.5 MHz s-1. It is important to emphasize that according to our observations the drift rate is linearly increasing with frequency. The duration of the bursts changes mainly from 6 s at frequency 30 MHz up to 12 s at 10 MHz. The instantaneous frequency bandwidth does not depend on the day of observations, i.e. on the disk location of the source active region, and is increasing with frequency. The results of observational properties are discussed in the frame of the standard plasma model of type III bursts radio emission.

A detailed description of the wideband analog- digital heliograph based on the UTR-2 radio telescope has been suggested. This device operates in the parallel-serial scheme, when five uniformly spaced beams (formed simultaneously) of the antenna pattern scan a given radio source (e. g. solar corona). As a result, the obtained image represents a cadre consisting of 5×8 pixels with the spatial resolution 25′×25′. Every pixel is caused by a signal from the corresponding beam of the antenna pattern.

International audience; Solar S-bursts observed by the radio telescope UTR-2 in the period 2001 - 2002 are studied. The bursts chosen for a detailed analysis occurred in the periods 23 - 26 May 2001, 13 - 16 and 27 - 39 July 2002 during three solar radio storms. More than 800 S-bursts were registered in these days. Properties of S-bursts are studied in the frequency band 10 - 30 MHz. All bursts were always observed against a background of other solar radio activity such as type III and IIIb bursts, type III-like bursts, drift pairs and spikes. Moreover, S-bursts were observed during days when the active region was situated near the central meridian. Characteristic durations of S-bursts were about 0.35 and 0.4 - 0.6 s for the May and July storms, respectively. For the first time, we found that the instantaneous frequency width of S-bursts increased with frequency linearly. The dependence of drift rates on frequency followed the McConnell dependence derived for higher frequencies. We propose a model of S-bursts based on the assumption that these bursts are generated due to the confluence of Langmuir waves with fast magnetosonic waves, whose phase and group velocities are equal.

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The properties of powerful (larger than 10 -19 W/(m 2 ⋅Hz)) Type III bursts observed in July-August 2002 using the UTR-2 radio telescope at frequencies 10 ÷30 MHz are analyzed. The majority of these bursts were found to be observed on the days when an active region was located near the central meridian or at 40°÷60° eastwards or westwards from it. All these bursts drift from high frequencies to low ones, their frequency drift rates being within 1÷2.5 MHz/s in most cases. The frequency drift rate increases linearly with frequency for all days of observations. Duration of powerful Type III bursts varies within 6÷12 s with smaller values at high frequencies. Instantaneous frequency widths of these bursts do not depend on the day of observations and show a linear growth with frequency. The results of these observations are discussed in the frame of the plasma model for the Type III bursts generation.

International audience; Aims: Decameter radio observations of the solar corona reveal the presence of numerous faint frequency drifting emissions, similar to ``solar S bursts'' which are reported in the literature. We present a statistical analysis of the characteristics of these emissions and propose a mechanism to excite the Langmuir waves thought to be at the origin of these emissions. Methods: The observations were performed between 1998 and 2002 with the Digital Spectro Polarimeter (DSP) receivers operated at the UTR-2 and Nançay decameter radio telescopes in the frequency range 15-30 MHz. Our theoretical explanation is based on Vlasov-Ampère simulations. Results: Based on the frequency drift rate, three populations of structures can be identified. The largest population presents an average negative frequency drift of -0.9 MHz s-1 and a lifetime up to 11 s (median value of 2.72 s). A second population shows a very small frequency drift of -0.1 MHz s-1 and a short lifetime of about 1 s. The third population presents an average positive frequency drift of +0.95 MHz s-1 and a lifetime of up to 3 s. Also, the frequency drift as a function of frequency is consistent with the former results, which present results in higher frequency range. No specific relationship was found between the occurrence of these emissions and the solar cycle or presence of flares. Assuming that these emissions are produced by ``electron clouds'' propagating the solar corona, we deduce electron velocities of about 3-5 times the electron thermal velocity. As previously shown, a localized, time-dependent modulation of the electron distribution function (heating) leads to low velocity electron clouds (consistent with observations), which, in turn, can generate Langmuir waves and electromagnetic signals by nonlinear processes.

International audience; Here we report a radio burst in absorption at 9 30 MHz observed with the UTR-2 telescope. This event occurred on 19 August 2003 about 11:16 11:26 UT, against solar type IV/II emission background. It is the first event where absorption was observed below 30 MHz. The absorption region, comparable with the solar radius size, traveled a long distance into the upper corona from the Sun. We show that the burst minimum corresponds to the almost full absorption of the solar radio emission up to a background level of the quiescent Sun. This supports the interpretation of the phenomenon as an absorption. The result is examined independently with the Nançay Decameter Array measurements and the Wind WAVES instrument records.

We have performed a comparative analysis of the fine structure of two decametric type II bursts observed on July 17 and August 16, 2002, with the 1024-channel spectrograph of the UTR-2 radio telescope in the frequency range 18.5-29.5 MHz and with the IZMIRAN spectrograph in the frequency range 25-270 MHz. The August 16 burst was weak, ∼ 2-5 s.f.u., but exhibited an unusual fine structure in the form of broadband fibers (∆fe > 250-500 kHz) that drifted at a rate characteristic of type II bursts and consisted of regular narrow-band fibers (∆fe > 50-90 kHz at 24 MHz) resembling a fiber bundle. The July 17 burst was three orders of magnitude more intense (up to 4500 s.f.u. at 20 MHz) and included a similar fiber structure. The narrow fibers were irregular and shorter in duration. They differed from an ordinary fiber bundle by the absence of absorption from the low-frequency edge and by slow frequency drift (slower than that of a type II burst). Both type II bursts were also observed in interplanetary space in the WIND/WAVES RAD2 spectra, but without any direct continuation. Analysis of the corresponding coronal mass ejections (CMEs) based on SOHO/LASCO C2 data has shown that the radio source of the type II burst detected on August 16 with UTR-2 was located between the narrow CME and the shock front trailing behind that was catching up with the CME. The July 17 type II fiber burst also occurred at the time when the shock front was catching up with the CME. Under such conditions, it would be natural to assume that the emission from large fibers is related to the passage of the shock front through narrow inhomogeneities in the CME tail. Resonant transition radiation may be the main radio emission mechanism. Both events are characterized by the possible generation of whistlers between the leading CME edge and the shock front. The whistlers excited at shock fronts manifest themselves only against the background of enhanced emission from large fibers (similar to the continuum modulation in type IV bursts). The reduction in whistler group velocity inside inhomogeneities to 760 km s −1 may be responsible for the unusually low drift rate of the narrow fibers. The magnetic field inside inhomogeneities determined from fiber parameters at 24 MHz is ∼0.9 G, while the density should be increased by at least a factor of 2.

The results of observations of solar decametric drift pair bursts are presented. These observations were carried out during a Type III burst storm on July 11–21, 2002, with the decameter radio telescope UTR-2, equipped with new back-end facilities. High time and frequency resolution of the back-end allowed us to obtain new information about the structure and properties of these bursts. The statistical analysis of more than 700 bursts observed on 13–15 July was performed separately for “forward” and “reverse” drift pair bursts. Such an extensive amount of these kind of bursts has never been processed before. It should be pointed out that “forward” and “reverse” drift pair bursts have a set of similar parameters, such as time delay between the burst elements, duration of an element, and instant bandwidth of an element. Nevertheless some of their parameters are different. So, the absolute average value of frequency drift rate for “forward” bursts is 0.8 MHz s−1, while for “reverse” ones it is 2 MHz s−1. The obtained functional dependencies “drift rate vs. frequency” and “flux density vs. frequency” were found to be different from the current knowledge. We also report about the observation of unusual variants of drift pairs, in particular, of “hook” bursts and bursts with fine time and frequency structure. A possible mechanism of drift pairs generation is proposed, according to which this emission may originate from the interaction of Langmuir waves with the magnetosonic waves having equal phase and group velocities.

The paper describes the preamplification antenna system (PAS) ofthe decameter radio telescope UTR-2. The new PAS have the continuous frequency range 8 to 40 MHz. The dynamic range is: 54 dbm at low frequencies and 30 dbm at high frequencies. To extendthe dynamic range the signal spectrum is divided and summed up with the aid of frequency selective devices, each consisting oftwo identical antimetric bandpass filters of even order and twohybrid adders. Within each of the three bands, the signal is amplified in multistage amplifiers with a deep linear frequencyindependent negative feedback in each stage. Part One presents thegoals, underlying ideas and structure of the PAS. Part Twodescribes details of the design, specific parameters and some observational results.

We prove experimentally the possibility of direct observations of natural radio echoes on the Sun. The generally simple echo hypothesis on the origin of the time splitting in solar type IIId radio bursts sustained the crucial experimental test. These conclusions are based on both the new positional data and previous information obtained using the UTR-2 antenna system in different years since 1973. In summer 1992, we were able to register for the first time a large number of decameter type IIId bursts with pronounced echo-like components using a radioheliograph at frequencies of 20 and 25 MHz. Elementary (quasi-monochromatic) sources of the short-lived bimodal type IIId bursts were observed especially often on July 6. In this case, the time delay of the second peak, which depends on the heliolongitude of the active region, reached a maximum of about 7 s. All these double-peak bursts were localized in the central region of the solar corona, and, similar to the case of single-pulse “limb” type IIId bursts at a given radio frequency f, the observed elementary sources of these events appeared to be nonstationary. Such a dynamic pulsating source can radically change, at least once, its location in the celestial sphere in the field of view of a two-dimensional radio heliograph during the burst lifetime τΣ. While decaying, an echo-like burst formed rather slowly may abruptly jump from one location to another. As far as its short (3- to 4-s) steep-front precursor is concerned, its visible source behaved usually as an ephemeral sub- or ultrarelativistic object moving at a subluminal velocity over a global-scale trajectory. To all appearances, a twice-pulsing, narrow-band (Δ f/f∼ 0.01) radio burst with an intensity-time profile of type IIId is generally a rather long-term (τΣ ≈ 10-20 s) transient response of the solar atmosphere to the short-term flare of harmonic radio emission generated in the real (probably motionless and compact) source. This complex double-peak profile is due not only to the existence of a reflecting surface deep in the corona near the corresponding plasma level but also, to a considerable extent, to some opaque or semi-transparent structures located at heights of the middle corona. In particular, due to the strong influence of such structures, a coronal primary source of a bimodal burst can be seen on the Earth in some indirect rays before the solar radio echo and has the form of an additional delayed pulse.

The intensity-time profiles I(t) of narrow-band (δf/f≈10−2) radio bursts, which from the slanted dynamical spectrum (If,t) of type IIId emission, are strongly dependent on the heliolongitudes |l| of their coronal (quasi-monochromatic) sources. In the central sector (|l

We present for the first time a set of intensity-time records for one solar type IIId radio burst with an echo component obtained as a result of angular selection of the radiation observed using an UTR 2 antenna operating in the mode of a two-dimensional heliograph at f=25 MHz. It is found that in the case of such events, which occur only in the central sector of heliolongitudes |l|≤50°, the apparent pulsating source of narrow-band (∼0.1 MHz) radiation at the second harmonic (f≈2fp) can have a complex, constantly varying angular structure. The coronal source positions determined at the time of the main peak of a two-hump burst and 6.5 s later at the time of its second, relatively low, maximum did not coincide and their divergence was ≈12′ in hour angle and ≈0′ in declination. During the first pulse (having a steep front) the source did not remain immobile and travelled for 3 s, gradually decaying, predominantly to the west at an average velocity close to the velocity of light. The amazing fact of initial nonstationarity and other properties of the pulsing type IIId source show that a fast imaginary source occurred in the solar corona at the site of short-time (< 1 s) radio wave generation, i.e., well above the normal level of plasma frequency $$\bar f_p {\text{ = }}f$$ . The background of the source was obviously an extended opaque or translucent region of disturbed plasma. Operating as a passive retranslator of signals, at the plasma levels fp∼f/2 this strange coronal structure could prevent the radio waves, including those reflected specularly at the plasma level $$\bar f_p {\text{ = }}f$$ deep in the corona, from propagating freely. Most probably, this is exactly the reason why the decay of the echo component is slow and nonmonotonic in the case of type IIId bursts, many of which pulsate rhythmically 3 or 4 times.

The results of photometric, spectral and radio studies of the flare star EV Lac we obtained during the course of cooperative observations in 1994 and 1995 are presented. A quantitative analysis of the radiation emitted by two powerful flares using the colour-colour diagram confirms the previous conclusion on the essential heterogeneity of matter radiating in optical flares. From simultaneous observations of the star in UBVRI, K and H bands no significant brightness variations in IR were found in coincidence with observed small-amplitude optical flares, except a gradual decrease in the K-band following a 1.0 mag flare in the U-band. A differential spottedness of bright and dark hemispheres of EV Lac is estimated using observations in separate seasons and the total stellar spottedness is determined within the framework of the zonal spottedness model. Spectra of quiet and active states of the star in the blue-green region in 1994 and in the red region in 1995 are described: the characteristics of th...

By solar observations with an UTR 2 antenna, we detected a new variety of type IIId radiation in which the narrow-band spectral elements have an explicit quiasiperiodic structure and contain an additional component in the form of a triple echo. According to amplitude records at 25 MHz, the initial short radio burst looks like a weak precursor of a more powerful echo-like burst accompanied by a pair of final pulses which exceed slightly the background. Nine events of this kind were registered in August 19, 1992 during a type IIId noise storm related to the active region in the central heliolongitude sector. In each event, all the three time intervals between successive peaks of the complex amplitude-time profile were almost identical and were equal to 4.7, 5.1, and 5.7 s on the average. They were somewhat (by 1 or 2 s) shorter than the maximum delay in the known events with a two-hump amplitude profile and time-split narrow-band spectral elements in which the delay t2−t1 and relative intensity (I2/I1≲1) of echo-like bursts depend on the heliolongitude of the type IIId sources. The discovery of a new complex variety of decameter type IIId radiation confirms the hypothesis of multiple quiasiperiodic echoes after short radio bursts at the second harmonic of the local plasma frequency in the solar atmosphere.

We consider the approach to simultaneous (synchronous) solar observations of radio emission by using the STEREO-WAVES instruments (frequency range 0.125–16 MHz) and the largest ground-based low-frequency radio telescope. We illustrate it by the UTR-2 radio telescope implementation (10–30 MHz). The antenna system of the radio telescope is a T-shape-like array of broadband dipoles and is located near the village Grakovo in the Kharkiv region (Ukraine). The third observation point on the ground in addition to two space-based ones improves the space-mission performance capabilities for the determination of radio-emission source directivity. The observational results from the high sensitivity antenna UTR-2 are particularly useful for analysis of STEREO data in the condition of weak event appearances during solar activity minima. In order to improve the accuracy of flux density measurements, we also provide simultaneous observations with a large part of the UTR-2 radio telescope array and its single dipole close to the STEREO-WAVES antennas in sensitivity. This concept has been studied by comparing the STEREO data with ground-based records from 2007–2011 and shown to be effective. The capabilities will be useful in the implementation of new instruments (LOFAR, LWA, MWA, etc.) and during the future Solar Orbiter mission.

The many-parametric data on decametric type III bursts containing more than 1000 events were classified with use of cluster analysis, i.e., the pattern recognition procedure. For the classification such parameters have been used as intensity, duration and degree of circular polarization derived from burst time profiles. The automatic classification has resulted in division of daily samples of type III bursts into classes of bursts, more homogeneous statistically, which can be associated with different components of type III radiation distinguished by their physical origin. For the classes obtained, statistically reliable dependences of the mean intensity on source position can be found which allow one to conclude about the source structure and evolution, as well as about the characteristics defined by a burst generation mechanism and propagation effects.

We report on the observation of powerful (fluxes are larger than 10-19 W/m2Hz) solar type III bursts at frequencies of 10-30 MHz using the radio telescope UTR - 2. The properties of powerful type III bursts observed in July 2002 (163 bursts) and August 2002 (231 bursts) were analysed. It was determined that the majority of these bursts were observed on days when an active region was located near the central meridian or at longitudes of 400 - 600 to the east or west of the central meridian. All of these bursts drift from high frequency to low with frequency drift rates of 1-2.5 MHz/s in most cases. We note that the frequency drift rate of these bursts increases linearly with frequency for all days of observation. This indicates that the solar corona above active regions shows an exponential density decrease with distance. The typical duration of the powerful type III bursts changes from 6 to 12 s. The instantaneous frequency widths of these bursts do not depend on the day of observation. There is a linear dependence between the average frequency width and frequency. The implication of these observations are discussed in the frame of the plasma model for the type III bursts generation.

It is currently accepted that the dependences of frequency drift rate and instant duration of type III bursts on frequency follow a monotonic function. The observations carried out during summer months of 2002-2006 by the world largest decameter wavelength radio telescope UTR-2 in frequency band 10-30 MHz show that sometimes these dependences may have a jump at some frequency, when the steepness of the dependence changes step-wise. In this paper the results of observations of such unusual type III bursts are given. Since the dynamic spectrum of such bursts resembles a dog’s leg we call them “dog-leg” type III bursts. More than a hundred of these “dog-leg” bursts were observed during 5 years. The parameters of the 41 bursts observed in 2002 were defined and statistically analyzed. The fact that “dog-leg” type III bursts are observed on the background of standard type III bursts allows to exclude any instrumental component of the observed phenomena.

In this paper properties of decameter spikes observed in July - August, 2002 by radio telescope UTR-2 are discussed. These bursts have short duration (about 1s) and narrow frequency bandwidth (50 - 70 kHz). They are situated chaotically on the dynamic spectrum at the decameter wavelengths. These bursts are weak, their fluxes are not higher than 200 - 300 s.f.u. One of the interesting features of decameter spikes is linear dependence of frequency bandwidth on frequency. Such dependence can be explained in the frame of plasma mechanism of radio emission if to take into account that Langmuir waves are generated into the angle about 20 deg along the direction of electron beam propagation. In the paper the cause of small duration of spikes and generation of plasma waves in limited spatial regions are discussed.

We present an overview of the recent results in solar observations obtained at decameter radio waves using the radio telescope UTR-2. Due to up-to-date recording facilities some newly discovered phenomena in the frequency range 10 - 30 MHz are given: fast type III bursts, fine time structures in normal type III bursts, solar S-bursts, type IV bursts with zebra-like fine structures, third harmonic in type II bursts and bursts in absorption of different time scale. Newly discovered properties of well known bursts such as type III bursts, type IIIb bursts, type II bursts and drift pairs were obtained too.

The overview of last results obtained on decameter radio emission of the Sun with radio telescope UTR‐2 is presented. Due to modern registered facilities new phenomena at frequencies 10–30 MHz were observed. There are fast Type III bursts, fine time structure of usual Type III bursts, solar S‐bursts, Type IV bursts, their fine structure in the form of zebra structure, the third harmonics of Type II bursts, bursts in absorption of different time scales. New properties of well‐known bursts as Type III bursts, Type IIIb bursts, Type II bursts and drift pairs was obtained also.

The results of the first observations of solar U‐ and J‐ bursts with the radiotelescope UTR‐2 at the decameter wavelengths are reported. During 2003–2004 more than 50 J‐ bursts and only 7 U‐ bursts were registered. It is the first case of ground based observations of J‐ and U‐ bursts with turning frequencies below 25 MHz. For the first time the harmonic structure of J‐ bursts in the form of Jb‐J pairs was found. The mean harmonic ratio appeared to be 1.8. Also a group of J‐bursts with unusual Turning Frequency Drift (TFD) of −2 kHz/s was detected. Such TFD corresponds to the velocity of coronal loop elevation of about 60 km/s. Coronal loops with similar elevation velocities were also detected by SOHO‐LASCO coronagraph in white light. The dynamic spectra of unusual U‐ and J‐ bursts are shown. Simplified model of the coronal loop in the form of semicircle was created on the base of the U‐ burst dynamic spectrum and the Newkirk coronal density model. With this loop model the linear velocity of the source alo...

Recently decameter Type IV bursts were observed with the radio telescope UTR‐2. One of the prominent properties of decameter Type IV bursts is the existence of fine structure in the form of bursts in emission and absorption. These bursts have practically the same frequency drift rates and durations at decameter wavelengths as the standard Type III bursts, but there are a lot of cases, when the drift rates have an opposite (positive) sign of drift rates. The results of the statistical analysis of bursts in emission and absorption and a comparison of their properties with those of usual Type III bursts are presented in the report. The functional dependences of drift rates and durations via frequency are derived. The connection of properties of these bursts with the position of active regions on the solar disk is discussed.

This paper deals with Type IIIb bursts, which were observed in the frequency band from 18 to 30 MHz. These bursts have fine frequency structures contrary to usual Type III bursts. The main properties of Type IIIb bursts such as number of striae in a burst, their frequency drift rates, durations, frequency widths of stria, emission fluxes are presented. It is also shown that parameters of stria bursts depend on the position of active areas on the solar disk.

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Decameter wavelength radio emission is finely structured in solar bursts. For their research it is very important to use a sufficient sensitivity of antenna systems. In this paper we study an influence of the radiotelescope-antenna effective area on the results of decameter solar radio observations. For this purpose we compared the solar bursts received by the array of 720 ground-based dipoles and the single dipole of the radiotelescope UTR-2. It's shown that a larger effective area of the ground-based antenna allows us to measure a weaker solar emission and to distinguish a fine structure of strong solar events. This feature has been also verified by simultaneous ground- and space-based observations in the overlapping frequency range., Comment: 7 pages, 3 figures

The results are described of experimental investigations and the development of broadband amplifiers with transformer feedback, the theory of which has been given in Part 1. The amplifiers have a gain of 6 to 30 dB, a noise figure of 1.5 to 2, a bandpass of 1 to 250 MHz and a dynamic range of 85 to 104 dB, The consideration of cascading is presented, ensuring stability and other design features. Design principles are given for low-noise amplifiers with high gain and wide dynamic range.

Circuits are studied of matched broadband amplifiers that use lossless transformer feedback. The latter ensures high stability, linearity, constancy of gain and an extremely low noise figure. Actual parameters of transistors and transformers are accounted for. First, two basic circuits are studied in detail: one with transformer feedback and the other with autotransformer feedback. The latter has been shown to ensure higher linearity and a substantially broader bandpass. Subsequently, lossless current amplification was introduced in both circuits. Two circuits with positive and negative feedback are briefly discussed.

Starting from 1960s Type III-like bursts (Type III bursts with high drift rates) in a wide frequency range from 300 to 950MHz have been observed. These new bursts observed at certain frequency being compared to the usual Type III bursts at the same frequency show similar behaviour but feature frequency drift 2-6 times higher than the normal bursts. In this paper we report the first observations of Type III-like bursts in decameter range, carried out during summer campaigns 2002 - 2004 at UTR-2 radio telescope. The circular polarization of the bursts was measured by the radio telescope URAN-2 in 2004. The observed bursts are analyzed and compared with usual Type III bursts in the decameter range. From the analysis of over 1100 Type III-like bursts, their main parameters have been found. Characteristic feature of the observed bursts is similar to Type III-like bursts at other frequencies, i.e. measured drift rates (5-10 MHz/s) of this bursts are few times larger than that for usual Type III bursts, and their durations (1-2 s) are few times smaller than that for usual Type III bursts in this frequency band., Published in Proceedings of the 14th Young Scientists Conference on Astronomy and Space Physics, Kyiv, Ukraine, April 23-28, 2007

The first results of observations of solar sporadic radio emission with the UTR-2 radio telescope in 2001–2003 are reported in this paper. Using new back-end facilities, the digital spectro-polarimeter and 60-channel spectrometer allowed us to obtain data with a time resolution up to 2 ms and a frequency resolution of 12 kHz in a continuous frequency band of 12 MHz. The usual type III bursts, type IIIb bursts, U and J bursts, spikes and unusual bursts in the decametre wavelength band are discussed in this paper. Special attention is paid to the detection and analysis of type II bursts and their properties, the fine structure of type III bursts, the new observational features of drift pair bursts, ‘absorption’ bursts and the statistical analysis of solar radio bursts.

International audience; We present the results of radio telescope UTR-2 observations of solar Type II radio bursts in the 10-30 MHz frequency range. These events possess a fine structure consisting of fast drift sub-bursts similar to Type III bursts. The frequency drift rate of the Type II bursts at decameter wavelengths is smaller than 0.1 MHz s-1. One of these bursts with herringbone structure has a wave-like backbone that almost does not drift. The features of the observed bursts are discussed.

A set of broadband low noise interference-immune amplifier modules comprising matched broadband amplifiers and matched filters is described. In the frequency band 1-100 MHz these devices ensure a low noise figure, high dynamic range, matching in a wide frequency band, stability, identity of parameters, versatility, and high compatibility of stationary and mobile systems. Connection of modules makes it possible to implement a complicated amplifier system with the specified amplitude-frequency response and low level of amplitude and phase errors. The parameters and characteristics of modules, their design features and principles are given. The amplification system of the largest UTR-2 decameter band radiotelescope is described. >

Some properties of solar radio bursts observed at the Earth are mainly due to propagation effects in the corona. A radio echo of short-time narrow-band bursts is observed by a decameter radioheliograph on the basis of UTR-2 antenna. Propagation effects are manifested in the marked regular change of the burst intensity-time profile at 25 MHz during a half-rotation of the Sun. A displacement of limb diffuse bursts deep into the solar atmosphere of 1.5 ∼- 2R⊙ has been also found during the burst lifetime.

To locate two-dimensional positions of the solar decametric radio bursts a heliograph was developed on the basis of the UTR-2 radiotelescope (Khar'kov) operated in the range 10–26 MHz. The beamwidth of the heliograph rapid-scanning pencil-beam is 25 arc min at 25 MHz, and its field of view is about 3.5° (E-W) × 2.0° (N-S). The instrument yields rapidly forty records of the radio brightness of all (8 × 5) elementary parts (each 25 arc min in diameter) of the investigated sky area during every period of 1/4 s. Both coordinates of a burst center are measured with an accuracy 5 arc min. The bandwidth of the receiving system is 10 kHz. The heliograph operates in conjunction with a radiospectrograph connected to the output of a N-S arm of the UTR-2 array. The data observations with the UTR-2 correspond only to one linear polarized component.

The UTR-2 antenna has been used to measure angular sizes of sources of narrow-band short-lived solar stria-bursts at frequencies 24–26 MHz. The majority of these sources have apparent diameters between 20 and 40′. According to this parameter they do not differ noticeably from that of type III bursts at the same frequency. The short duration of the stria-bursts prevents explanation of the large diameter by scattering in the solar corona.

Echo-type solar radio bursts are associated with preceding short-lived bursts in double events. The peculiar and rather rare decameter echoes are observed with a UTR-2 antenna. The initial narrow-band burst is followed, some 5 to 10 s later, by an echo-like burst at the same frequency. The observational data obtained for decameter echo evens are, on the whole, consistent with the model of a pulsed source emitting radio signals at the plasma-frequency harmonic, which is placed in a non-uniform corona and rotates together with the Sun.

A decameter solar radio storm of type IIIb and III bursts has been analysed, using single frequency records at frequencies 12.5 and 25.0 MHz.

A two-dimensional brightness distribution of the old supernova remnant G 160.5+2.8 (HB-9) has been measured at a frequency of 25 MHz with the T-Shaped UTR-2 radio telescope, with the resolution 29′×27′. The source has a distinctly pronounced, almost spherical envelope. At the same time, individual features located near the internal boundary of the source are observable. Certain considerations are put forward to validate a suggestion that the brightest feature in the decameter range (maximum atα=4h55m.3 and δ=46°.37) might be of an extragalactic origin. From structure considerations, the velocity of the pulsar PSR 0459+47 projected on HB-9 is estimated. The estimate does not contradict the hypothesis of Damasheket al. (1978) concerning a possible genetic relation between HB-9 and PSR 0459+47.

This study of type IIIb-III evenmts strongly supports their interpretation as fundamental-harmonic burst pairs. Type IIIb chains and the related type III bursts drift from 12.5 to 6.25 MHz and from 25.0 to 12.5 MHz, respectively, during similar time intervals of 11.1 and 11.0 s, on the average. This harmonic similarity is emphasized by the fact that the drift times of type IIIb chains across the upper octave are significantly less than those of type III bursts in the lower octave, the values being around 6 and 19 s.

An analysis has been made of type III bursts recorded during a decametric solar storm observed from July 29 to August 16, 1975 with the UTR-2 antenna (Kharkov, IRE Acad. Sci. Ukr. SSR). The bursts were recorded with a dynamic spectrograph and radiometers at 25.0, 20.0, 16.7, and 12.5 MHz. Daily observations have yielded histograms of the type III burst distribution with respect to the frequency drift rate in three subbands between 25.0 and 12.5 MHz. During the middle stage of the storm the drift rate was about twice as high as at the onset and the final stage of the storm. Abrupt changes in the mean frequency drift rate were registered some two to three days after the active region McMath 13790 had come onto the limb and also before it disappeared behind the solar disk. Sudden changes in the drift rates of the type III bursts were accompanied by sudden changes of their mean duration. The rather long burst durations observed at 25.0 MHz at the beginning and the end of the radio storm coincided with such at the twice lower frequency, i.e. 12.5 MHz, during the period when an increased drift rate was observed.