April 1999, Volume 8, Number 1

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T. Dostal [full-text]
ARC Filters Using Only Followers

Several structures of the active RC filters using non-inverting voltage unity-gain followers and dual current positive followers are given in this paper. These structures can be suitable implemented by the positive second generation current conveyors or by the transimpedance operational amplifiers. A symbolical analysis using SNAP and a simulation by PSpice have been made to confirm the given theoretical approach.

J. Pospisil, J. Brzobohaty, Z. Kolka [full-text]
Generalized Canonical State Models of Third-Order Piecewise-Linear Dynamical Systems And Their Applications

The elementary canonical state models of the third-order autonomous dynamical systems, topologically conjugate to Chua's circuit family, are generalized for any continuous and odd symmetrical piecewise-linear (PWL) feedback function. Their state equations are in accordance with the basic form of the Lur'e systems and the corresponding circuit model contains the multiple PWL feedback. The general results are applied for the simplest three-region case defined by three sets of the equivalent eigenvalue parameters. The application of these results is demonstrated on the double-scroll chaotic attractor with global attracting properties. As an example its utilization in synchronized chaos is shown.

J. Kolouch [full-text]
Synchronous Counters Implemented in the PLD Devices

The implementability of synchronous counters in the Programmable Logic Devices (PLD) is discussed in this paper. The most commonly used counters are analysed from this point of view. The expressions for their individual bits are given and the number of product terms is derived to allow to estimate the size of the particular counter which can be implemented in the chosen PLD.

M. Kasal, J. Sebesta [full-text]
Experimental Satellite Phase 3D before Launch

To build a satellite can be a dream for many engineers. We are happy that we can participate in the AMSAT PHASE 3D project. Our responsibility is very high because one of our on-board receivers is the main one of the command link and will never be switched off. The project is also a very good opportunity for our students to meet satellite technology.

Z. Kolka [full-text]
SNAP - Program for Symbolic Analysis

The paper deals with a program SNAP for symbolic analysis of linear circuits in frequency domain. The program is suitable for analysis of circuits with ideal network elements to explore basic principles of their operation. Besides graphical presentation the analysis results can be exported to popular mathematical programs for further processing. Currently, an algorithm for exact symbolic analysis is implemented. Therefore the program is suitable for relatively small circuits.

M. Pistek, V. Ricny [full-text]
Computer Simulation of the Transmission Channel Influence in the Video Signal

This article contains the time-spatial and spectral description of video signals. There are described methods for computer simulations of real transmission channels and for determination of their influence upon the video signal and the quality corresponding picture.

J. Cernocky [full-text]
Automatically Derived Units in the Speech Processing

Current systems for recognition, synthesis, very low bit-rate (VLBR) coding and text-independent speaker verification rely on sub-word units determined using phonetic knowledge. This paper presents an alternative to this approach - determination of speech units using AUSP (Automatic Language Independent Speech Processing) tools. Experimental results for speaker-dependent VLBR coding are reported on two databases: average rate of 120 bps for unit encoding was achieved. In verification, this approach was tested during 1998's NIST-NSA evaluation campaign with a MLP-based scoring system.

M. Brejl, V. Sebesta [full-text]
High Frequency Components Recovery in Music Signals

A new technique is presented which improves the subjective quality of band-limited music by recovery of high frequency components. Sequences of harmonics are found in the band-limited signal and these sequences are expanded to the high frequency band to estimate the lost part of spectrum. High frequency signal is generated to match this estimation and is added to the band-limited signal.

Z. Raida [full-text]
Exploration of Neural Networks in the Design of Microwave Structures

Artificial neural networks can be used for modeling microwave structures in order to obtain computationally efficient models of investigated systems. In conjunction with proper optimization techniques, these neural models can be explored for an efficient full-wave design of microwave structures. Moreover, neural networks can serve as a direct design tool of microwave systems.
In this paper, an overview of the so-far published applications of neural networks in microwaves is presented and their exploration in the full-wave design is discussed. Described neural modeling and design is illustrated by modeling and design of frequency-selective surfaces.

O. Wilfert, V. Biolkova [full-text]
Network Communication by Optical Directional Link

In this article, infrared point-to-point technologies (optical directional links) are discussed which are designed for digital transmissions. Optical directional links (ODLs) are transparent for the SDH/ATM, FDDI-II, Ethernet, and Token Ring protocols. Depending on type, ODL ranges are 300 m, 500 m, 1000 m and 2000 m. Steady and statistical models of ODL are presented as well as the measuring ODL arrangement and the graphs concerning the fluctuations of the received signal.