M. I. Ryabova

Propagation of broadband HF signals in a medium with nonlinear dispersion

Effect of nonlinear dispersion on distortions of broadband signals due to propagation in ionospheric channel is considered with allowance for matched processing in detector. Distortions of the shape of pulse response are studied versus nonlinearity parameter, and the effect of geophysical factors on the parameter is analyzed. The pulse response is used to estimate the group delay. It is demonstrated that the problem of propagation of broadband signals is reduced to the analysis of distortions of an equivalent signal with uniform in-phase spectrum in the ionospheric channel similar to the distortions of the pulse response of the channel. For the polynomial dispersion characteristic of the channel, the effect of nonlinearity on the pulse characteristics is described using incomplete Airy functions and the shape of the envelope of such a characteristic becomes asymmetric. Owing to uncertainty, the parameter of the group delay in the channel with the nonlinear dispersion cannot be accurately determined using the data on the pulse characteristic as distinct from the dispersion-free or linear-dispersion channel.

Software-defined radio technology in the problem concerning with the successive sounding of HF ionospheric communication channels

The problem concerning new software-defined radio technology is investigated as applied to the successive sounding of HF ionospheric communication radio channels. The algorithm for quadrature processing of chirp signals subjected to elementwise compression in the frequency domain is developed. It is established that a channel scattering function and a delay power profile are related to a compressed-signal spectrum and their basic parameters. Data on the key characteristic of HF communications modems are presented. The efficiencies of different modems are estimated using the experimental data on channel parameters. It is demonstrated that the aforementioned technology can be used to estimate not only HF communication channel parameters from the pass band of a radio line but also select the optimal one and, furthermore, makes it possible to combine communications and radio sounding systems in the single device.

Developing methods and software for research the effects of phase dispersion depending of the state of ionospher based on LabVIEW

Methods and software are developed for research the effects of phase dispersion, depending of the ionospher, based on LabVIEW. It is found that the leading edge increased with increasing of the third order parameter of impulse response, which leads to the case without the frequency dispersion, while trailing edge moving away from the peak, which leads to the case of linear frequency dispersion. Ionospheric radio channel with a bandwidth of 1 MHz is destroyed with the nonlinearity parameter equal to 267,4 ms/MHz2. Developed filtering methods ionograms oblique sounding ionosphere.

Research of dispersion distortion of signals in the ionospheric plasma and optical fiber

Technique of research the dispersion distortion of wideband chirp signal elements was proposed and theoretically justified. It is shown that in a first approximation, the difference frequency element signal assumes a linear frequency modulation. A formula that relates the rate of change of frequency characteristics of the signal and the dispersion properties of the medium was derived.

Optical fiber as a linear one-dimensional system with frequency dispersion

The paper presents the findings of the research into the effects of material dispersion in an optical fiber link. The general framework of normal and anomalous dispersion of the second and third orders were formulated by means of a principle of equivalence. The approach to the problem is based on a method of transforming a frequency response of an equivalent liner system into its impulse response with the use of a dispersion characteristic. This approach was used to thoroughly consider the effects of chirping, soliton (stable) propagation and collapse of solitons.

The comparative analysis of the intensity of the total electron content of the ionosphere variations above Yoshkar-Ola and Irkutsk cities

In the study there was carried out the analysis of the daily dynamics of the TEC, the intensity of variations changes and seasonally analysis of TEC variations for Yoshkar-Ola and Irkutsk, according to 2012.

Modeling and studying ionograms of oblique sounding of HF radio channels for radio links of various length using a digital ionosonde with USRP platform

The paper analyses the outcomes of numerical studies into the effect of phase dispersion on broadband elements of a FMCW signal with varying central spectrum frequencies corresponding to the central frequencies of radio channels. We used the International Reference Ionosphere (IRI) model as the background ionosphere, which takes into account the spatiotemporal variability of the radio channel. The data corresponding to the extreme values in the annual distribution of solar activity were selected for modeling ionograms. The effect of the second-order phase dispersion on power delay profile distortions was analyzed.

A compression of light pulse in an optical fiber

This paper focuses on the technology of compression of light pulse in an optical fiber. Investigated the effects of compression and decompression of the optical linear chirp pulse and define the parameters of optimal pulse. Simulated the rectangular chirp light pulse at different ratios between the parameters of the phase and frequency change.

Estimation of the effective recombination coefficient by variations in the maximum usable frequencies of one-hop high-frequency radio lines during the solar eclipses of March 29, 2006, and August 1, 2008

This paper presents the results of experimental investigations of variations in maximal usable frequencies (MUFs) during solar eclipses with the use of the method of panoramic tilt sounding by chirps in Eastern Europe and Western Siberia. The characteristics of perturbations of MUFs have been obtained experimentally. It has been established that the effective recombination coefficient increases by 24% in the ionospheric F region with an increase in the maximum eclipse phase from 0.49 to 1.0.