ETF Journal of Electrical Engineering

8

Authors: Žarko Zečević, Tomo Popović, Zdravko Uskoković, Božo Krstajić

In this paper, a new algorithm for synchrophasor and frequency estimation in power systems is proposed. The proposed approach is based on transformation of the measured signal into a complex sinusoid by using the Constant Modulus algorithm. The transformed signal and transformation coefficients are used for estimation of the parameters of interest. Simulation results show that the proposed algorithm exhibits better performances compared to the considered algorithms.

9

Authors: Vesna Rubežić, Luka Lazović, Marko Babić, Ana Jovanović

In this paper, the linear dynamic behavior of the helicopter in terms of characterization of the vibrations in a helicopter, is described. After analyzing in the time and frequency domain, vibrations are analyzed in geometrical and topological methods of chaos theory. Although the vibration in a helicopter are mainly periodic, the presence of chaotic dynamics using a systematic and detailed approach, is investigated. The aim of the research is to characterize the vibration mechanism based on a one set of measured data.

10

Authors: Stefan Vujović, Miloš Brajović, Vesna Popović-Bugarin, Nedeljko Latinović, Jelena Latinović, Milija Bajčeta

A web-based expert system for the grapevine monitoring and forecasting the appearance of downy mildew, which is a common disease of grapevine in Montenegro, is presented in the paper. The system is based on the 3 10 rule, customized for the south Montenegro region. The proposed web-based expert system is user-friendly, requiring minimal user-input data. In addition to several locations and weather stations which are initially embedded into the system, new locations can be easily added, and each location may use an arbitrary weather station. Moreover, the system is implemented with a multi-user structure, providing two types of predefined users: the administrator and the farmer. The priority levels and privileges depend on the active type of user. The purpose of the system is to predict the grapevine disease appearance based on the live data collected from weather stations in the field, combined with the expert knowledge implemented into the system. The proposed system provides the live monitoring of several relevant parameters, and alerts the user when a risk of infection is detected.

10

Authors: Jelena Šoškić, Budimir Lutovac, Dragan Filipović

This paper presents an analysis of the rectangular patch antenna. The analysis is based on the resonator model. Theoretical results are verified by using the software package MATLAB. Besides, some of the patch antenna parameters, which are very important for design and analysis of patch antennas, are presented in the same program package.

11

Authors: Zoran Veličković, Zoran Milivojević, Marko Veličković, Milojko Jovetić

Secure sharing of the digital video content over the Internet requires the use of modern techniques of protection. This paper describes the insertion of the encrypted watermark in the uncoded video content as a way of protecting copyrights. The impact of the prediction structure in the H.264 encoder to the survival of the inserted watermark is tested for two schemes. The watermark is encrypted with multistage Arnold transformation, and on the reception, an advanced algorithm for the realized by the SSIM index 0.71521 for an IBBBBBP scheme has been applied. The results obtained through the displayed example justify the application of multistage Arnold transformation for the video copy protection and raise security to a higher level.

16

Authors: Nataša Savić, Zoran Milivojević, Dejan Blagojević, Darko Brodić

First part of this paper describes Greville’s one-parametric interpolation kernel and provides its calculated spectral characteristics. Then it provides the calculation of optimal parametric values of Greville’s kernel a) by minimizing wiggles of spectral characteristics, b) by minimizing differences of the spectral characteristics in relation to kernel characteristics in the form sin(x)/x. Furthermore, this paper provides analytical form of the slope of spectral characteristics in boundary area. Second part of this paper describes an experiment in which the assessment of Greville’s algorithm efficiency in interpolation of audio signals (G tones played on piano) and speech signals (logatoms spoken in Serbian language) was performed. The results are presented in tables and graphs.