Amplitude Characteristics Of Signals Research Articles

HF radio channel modeling by a waveguide approach

We present a modified method of HF radio channel modeling based on a waveguide approach. The waveguide approach represents the electromagnetic field of radiation inside the Earth—ionosphere waveguide as an eigenfunction series of a radial boundary problem with impedance conditions on the Earth surface and radiation conditions at infinity. The transfer function of the radio channel is represented as a series of products of angular-operator Green functions, excitation coefficients, and coefficients for receiving individual normal modes. We have obtained a solution of the boundary value problem of determining the eigenfunctions and eigenvalues of the radial operator. The solution can be applied to the frequency range below the ionospheric F-layer critical frequency. We examine algorithms for calculating distance-frequency, frequency-angular, and amplitude characteristics of signals by analyzing and numerically summarizing the series in terms of strongly damped normal modes.

Моделирование КВ-радиоканала на основе волноводного подхода

We present a modified method of HF radio channel modeling based on a waveguide approach. The waveguide approach represents the electromagnetic field of radiation inside the Earth—ionosphere waveguide as an eigenfunction series of a radial boundary problem with impedance conditions on the Earth surface and radiation conditions at infinity. The transfer function of the radio channel is represented as a series of products of angular-operator Green functions, excitation coefficients, and coefficients for receiving individual normal modes. We have obtained a solution of the boundary value problem of determining the eigenfunctions and eigenvalues of the radial operator. The solution can be applied to the frequency range below the ionospheric F-layer critical frequency. We examine algorithms for calculating distance-frequency, frequency-angular, and amplitude characteristics of signals by analyzing and numerically summarizing the series in terms of strongly damped normal modes.

Методика расчета параметров антиалайсинговых фильтров для коррекции спектральных характеристик в зависимости от используемых структур дискретизации массива светофильтров

When developing algorithms and methods for generating and processing image signals (IS) used in devices based on single-matrix light-to-signal converters (LSC), the effects of not only the elements of the system included in the optical pathway (OP) located directly between the exposed image and device sensor, but also the specifics of the structure of color filter arrays (CFA) used in such cameras, applied to the surface of the matrix. In this article analyzed the most popular SSF subsampling structures and their impact on the spatial characteristics of the generated images. Based on the model for constructing these characteristics, a method is given for calculating the optimal parameters of anti-aliasing filters that match the properties of the OP and the sensor for a given characteristic of the optical system. Specific examples of calculating and optimizing such filters and evaluating their impact on the amplitude characteristics of signals are given. Based on the results of applying the developed method, formulated recommendations for the design of the CFA.

SIGNAL FORMATION AND PROCESSING FEATURES FROM AUTODYNE RADAR WITH A WIDE FREQUENCY MODULATION BAND. (РART 1)

Subject and Purpose. In Part 1 of the paper, a mathematical model of an autodyne self-oscillator with frequency tuning by varactor capacitance varying is built and thoroughly analyzed for the features of signal formation in autodyne radar with a wide frequency-modulation bandwidth and a nonlinearity in the modulation characteristic. The aim of the study is to appreciate the action that the nonlinearity of the oscillator modulation characteristic exerts on the spectral characteristics of signals from frequency-modulation autodyne radar. Methods and Methodology. The research method is a mathematical analysis of the operation of an autodyne oscillator with electronic frequency tuning. To examine formation processes of emitted autodyne signals, the spectral, frequency and amplitude characteristics of signals from frequency-modulation autodyne radar are constructed with the use of numerical modeling techniques. Results. Numerical modeling of autodyne response signal spectra has been performed for various distances to the reflecting object and different modulating voltages across the varactor. It has been shown that a nonlinear dependence of the generator frequency on the varactor voltage makes for the broadening of the autodyne response signal spectrum. It has been found that as the object distance increases, the frequency of the autodyne response signal moves towards the higher frequencies, while the nonlinearity makes the spectrum broaden. The obtained calculation results refer to an 8-mm Gunn diode autodyne. Conclusion. The performed research of the spectral characteristics and into the features of signal formation in autodyne transceiver devices with a wide frequency tuning has shown that in order to achieve high resolution figures from autodyne radar, certain methods are needed to be developed for adjusting the laws of frequency modulation and for the processing of response signals from reflecting objects. Such a method and ways to solve these problems will be presented in Part 2 of the work.

Gravitational Wave Track in the Electromagnetic Field of the Earth in the Infra-Low Frequency Range

Signals in the infra-low frequency range in the electric and geomagnetic fields of the Earth have been detected, corresponding to frequencies of gravitational waves (GWs) emitted by a series of binary star systems (BSS). The coherence of the detected signals has been investigated. The amplitude characteristics of signals in the electric and geomagnetic fields at GW frequencies of BSS are estimated. The estimates of the amplitudes of the detected signals are in line with model estimates.