Dragi M. Dujkovic

High-quality OCXO for digital TV

The realization of high-quality 10 MHz crystal oscillators is under consideration. Some methods for improving the stability and phase noise in OCXO (oven controlled crystal oscillator) are described. High-quality 10 MHz oscillators may take a place in professional devices such as GPS and used for synchronization in digital TV.

Region-based phonocardiogram event segmentation in spectrogram image

Assisting physicians in the auscultation of the patients by providing cost effective, automatic and accurate signal processing module for the heart event detection and recognition is of importance. We suggest that the segmentation of time-frequency representation image of one-dimensional phonocardiogram signals (PCGs) could be effective for observing possible abnormal heart events. The fact that frequency bands of cardiac events overlap and that different heart dysfunctions can occur simultaneously make image event segmentation a difficult task. Ambient noise and artifact burden make the segmentation problem even more difficult. A method of “splitting and merging” algorithm involving region-growing based on seeds is presented. We demonstrate that this method contributes to design of patterns required for cardiac event recognition and identification on several examples presented here.

Crystal filter 50 MHz for applications in specific environmental conditions

High quality crystal filter which operates at 50 MHz has been realized. The filter with bandwidth of 15 kHz, and special requirements regarding the electrical and environmental characteristics, is designed by using the transformation techniques applied on the cascade of lattice sections. Filter realization was performed at the Institute Mihailo Pupin, Belgrade, in cooperation with the Faculty of Electrical Engineering, University of Belgrade.

Edge preserved low-pass filtering controlled by local dimension

Low-pass image filtering, especially averaging, causes edge blurring. To prevent this effect we propose in this paper controlled low-pass filtering. Local dimension is used as a control parameter, favoring only non-edge-like regions for filtering. Multifractal capacities used in that aim are maximum and minimum multifractal capacities, since of their sensitivity on edges. Obtained results are evaluated using average gradient measure.

Joint time-frequency analysis of phonocardiograms

Joint time-frequency representations of phonocardiograms enable fundamental characteristics of heart sounds and other physiological changes important for diagnostics to be more visible compared to time and frequency domain, separately. This paper discuss possibilities for relevant component extraction in such representations. Due to improved visual inspection and fast digital signal processing capabilities, a number of additional tools may be provided for the purpose of computer-aided auscultation, physiological monitoring systems and computer-aided cardiological diagnostic systems.

A new crystal filter F 106

In modern communications, it is of great importance to implement quality modules for signal transmission, transfer and reception. One of the most important components of those modules is crystal filter. This is especially true for digital communications. In this paper, we propose antenna-filter F 106, suitable for high frequencies. This new filter is based on crystal units. We describe its design and present the final product.

Improvements in Image Segmentation by Applying Hopfield Neural Networks

Hundreds of algorithms for different aspects of image segmentation have been developed. In this paper goals of using segmentation in video and multimedia systems are considered. Thus direction of improvements is towards forming masks and matte signals. The idea is to spread locally dominant segment in already segmented image. This problem is set as optimization problem and solution can be achieved by Hopfield neural network. Presented results are obtained applied to color detected segmentation, performed by mean shift algorithm

Defining steaming conditions for a thin metal film electrode for the new SC cut crystal unit

In order to obtain fine contacts over the crystal unit, it is necessary to apply a thin layer of metal electrodes on its surface. The structure of the thin metal film formed by evaporation and condensation under the vacuum depends on many parameters and therefore it is very important to define the terms of steaming. This paper describes a method for achieving a good structure of thin metal films in high quality crystal units with SC cuts, which are designed for high quality OCXO oscillators.

Matched crystal filters

Crystal oscillators and filters are still very important devices in modern telecommunication and measurement equipment. Quartz crystal units are basic elements for those oscillators and filters, due to their extremely stable resonant frequency and Q-factor. Matched crystal filters are consisted of filter sections with the same phase characteristics. In this paper the design and realization of a new type of matched filters with quartz crystal units is described.

Adaptive fractal filtering of echocardiograms

Echocardiograms are inherently corrupted by the speckle noise. Elimination of the noise is usually treated with low-pass filters which can degrade edges in the image. Adaptive approaches employ masks for edges and restrict low-pass filtering mainly to homogeneous regions. Masks are based on statistical parameters or gradients. In this paper are applied local dimension matrices from fractal model as masks. Experimental tests are conducted for two simple low-pass filters (i) average filter and Gaussian filter (ii) and using three multifractal measures known from the literature - MIN, MAX and OSC measure. Obtained results for adaptive approaches show improvements over non-adaptive approaches in all analyzed scenarios.