RESEARCH OF THE AMPLITUDE-FREQUENCY CHARACTERISTICS OF THE REFERENCE LINES USING THE MICROCAP PROGRAM

ABSTRACT

In this paper, the results of modeling the amplitude frequency characteristics (AFCh) of the train radio guide line are analyzed using special MICROCAP software, since this product is the most reliable and convenient way to analyze the results obtained. The program independently compiles the circuit equations and performs an instant calculation. Any change in the scheme or parameters of the elements leads to automatic updating of the results. Modeling includes a whole set of different analyses: transients, DC transmission characteristics, low-signal frequency characteristics, DC sensitivities, nonlinear distortions, Monte Carlo method and many others.

АННОТАЦИЯ

В данной работе проанализированы результаты моделирования  амплитудно-частотных характеристик (АЧХ) направляющей линии поездной радиосвязи с помощью специального программного обеспечения MICROCAP , так как данный продукт является наиболее надёжным и удобным способом анализа полученных результатов. Программа самостоятельно составляет уравнения цепи и проводит моментальный расчёт. Любое изменение схемы или параметров элементов приводит к автоматическому обновлению результатов. Моделирование включает в себя целый набор различных анализов: переходных процессов, передаточных характеристик по постоянному току, малосигнальных частотных характеристик, чувствительностей по постоянному току, нелинейных искажений, метода Монте-Карло и многих других.

Keywords: reference line (RL), amplitude-frequency characteristic, dividing capacitor, adaptive circuit, reflectometer, correlation, train radio communication (TRC), MICROCAP, electromagnetic field.

Ключевые слова: направляющая линия (НЛ), амплитудно-частотная характеристика, разделительный конденсатор, согласующий контур, рефлектометр, корреляция, поездная радиосвязь (ПРС), MICROCAP, электромагнитное поле.

INTRODUCTION. To date, there are many software packages for studying electrical circuits that simplify the procedure for creating a mathematical model. Such packages include the MICROCAP schematic modeling program.

To design a computerized single-wire and two-wire test model for the analysis of guide lines on the Uzbek Railway, data were collected on the elements that form the reference line. Figures 1 and 2 show diagrams of the test sections of a single- and two-wire guide line, respectively.

Figure 1. Schematic of a single-wire test section of a reference line in MICROCAP

The length of the section is 18 km. Their amplitude-frequency characteristics were obtained using computer models of the guide line. The frequency response for a single-wire and two-wire test section is respectively shown in figures 3 and 4.

Figure 2. Schematic of a two-wire test section of a reference line in MICROCAP

METHODS. To simulate the current section of the route, a two-wire guide was chosen, located on the Angren-Pop section with a length of 23 km. The object in question was located in an area with a complex electromagnetic environment, which affected the location of high-voltage equipment along the entire REFERENCE LINE [3]. On fig. 5 shows the frequency response of the guide line at the Angren-Pop section. As a result, the real width of the cross section of the two-wire reference line waveguide was ~ 1 MHz at a level of 6 dB.

Figure 5. The amplitude-frequency characteristic of a two-wire reference line in the Angren-Pop section

The evaluation of the obtained amplitude-frequency characteristic showed that the real bandwidth of the REFERENCE LINE has a value of Δf ~ 1 MHz in the form of a two-wire wave, which is several times higher than the frequency range of the transmitted signals of the train radio communication (TRC) [5].

As a result of data analysis, the value of SNR = 14 dB was determined, at which damage to the REFERENCE LINE can be detected [1, 2]. After compiling several reflectograms with different perceptions of noise SNR = 14 dB, it was determined that the accuracy of determining the distance is about 50 m.

RESULTS. Comparing the SNR = 14dB value obtained in the reflectometer modeling with the actual signals and noise at the reflectometer input, SNR = -20dB shows that in real conditions it is not possible to determine the temporal state of each reflected pulse. and an increase in the energy of the useful signal is required. An increase in the control pulse can lead to interference from the TRC itself and other radio systems, so the accumulation of experimental reflexograms and the SNR parameter should be increased on average. In this case, using the assumption that the noise is not correlated during individual measurements and assuming that the reflection of the defined irregularities is stationary, the signal / noise ratio increases to  , where N is the mean number. Therefore, in order to increase the SNR to an acceptable value of ~ 15 dB, that is, an average of 3000 reflectograms must be added to 35 dB.

To automate the fault detection process, the reflectometer model was supplemented with a solvent, which could eliminate the uncertainty of decision-making in determining the location of the damage [4, 5].

If we look at the speed of propagation of electromagnetic waves along the RL, we can see that the accuracy of locating the lesion depends on it. An input called the contraction coefficient g is taken, which shows how many times the speed of light in a vacuum is greater than the speed of propagation of waves along the line: v =c/g,  , L- boundary inductance of the line, C is the boundary capacitance of the line. Although g=1.05 calculation values were used in the development of the RL model, the presence of additional reactivity in the line led to a change in the coefficient g in different parts of the line and therefore the wave propagation velocity o in these regions. led to a change [6]. Thus, in the modeled part of the RL, the coefficient g varied from 1.05 to 5.07, such a distribution in determining the location of the RL damage could lead to an error d = 0.02l, e.g..

Thus, the coefficient g depends on the number of additional elements of RL and takes different values between different elements. Using information about the exact distances to the operating RL elements, we can perform g measurements on all plots, enter the obtained values into a table of abbreviated coefficients for a given RL, and use them to identify faults.

CONCLUSIONS. Experimental data on measuring signal levels in real communication conditions made it possible to form the following main results of the work:

- with the help of computer simulation, the amplitude-frequency characteristics of single-wire and two-wire reference lines of the TRC are considered. The bandwidth of such lines is several times greater than the frequency range of the signals used for TRC, and is ~ 1 MHz, which allows you to select the frequency range of the controller signals and minimize the interaction of diagnostic systems and TRC.

- the accuracy of determining the distance to the damage site was evaluated using the tester signal in the form of a single video pulse. This analysis shows that in the absence of noise on the line under study, the accuracy, limited by the velocity dispersion, does not exceed 10 m; with the introduction of noise into the line, the signal-to-noise ratio of accuracy is reduced to 50 m at 14 dB.

References:

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