№ 2 (2024)

Introduction. The advancement of modern digital technology, the increase in productivity and operating clock frequency, and the development of specialized architectures for generating output signals have led to the creation of high-speed digital-to-analog converters (DACs). These converters are a crucial component of digital computing synthesizers, which are used to develop digital radio frequency signal generators. Goal. This paper aims at comparing methods for constructing digital signal generators based on high-speed DACs and analyze their noise characteristics. Methodology. The study presents various configurations for designing digital signal generators using high-speed DACs, including configurations with a mixer, a quadrature modulator, and special operating modes that enhance the efficiency of utilizing reference frequency images. Results. Analysis of simulation results indicates that the third configuration – a digital generator based on a high-speed DAC operating in special modes – exhibits the lowest level of phase noise. In RFZ3 mode, this configuration shows a phase noise level that is 10-14 dBn/Hz lower than that of the quadrature modulator-based generator and approximately 6-8 dBn/Hz lower than the mixer-based configuration. In RFZ4 mode, when utilizing the third positive image, a reduction of 15-22 dBn/Hz below the power spectral density (PSD) phase noise of the quadrature modulator-based generator and about 15-20 dBn/Hz below the mixer-based configuration is achieved. Additionally, the highest efficiency in utilizing images is obtained in higher Nyquist zones, where the increase in the output signal spectrum's envelope in special modes surpasses that in the DAC's primary NRZ mode. Conclusion. To effectively employ a digital signal generator based on high-speed DACs, frequency planning and the selection of optimal modes for analog signal restoration according to the image number used are necessary. Practical significance. The evaluation of the noise characteristics of the considered configurations, based on the proposed models, demonstrates that the use of the special operating modes of the DAC can significantly reduce the phase noise level of signal generators. Moreover, the use of high-speed DACs allows for the exclusion of analog elements from the signal generator structure, thereby significantly enhancing energy efficiency.

Introduction. Receiving telemetry information from a high-speed mobile object that rotates around its axis presents significant challenges. The wide range of changes in flight altitude and range, coupled with continuous shifts in signal direction and reflections from the underlying surface, necessitate the use of multiple reception points (RP) spaced over long distances and methods for joint signal processing. Consequently, the problem of optimal placement of radio telemetry system (RTS) reception points within an area arises. The aim of this work is to create and implement a method and software for multifactorial optimization of the placement of reception points for a radio telemetry system transmitting information from a mobile object. Research methods. The problem of optimal RP placement is addressed by numerically searching for the extremum of the target function, which is the average signal-to-noise ratio (SNR) in the radio channel across all points of a given trajectory of the mobile object. The SNR is calculated using a model of the signal propagation medium and an algorithm for joint processing of signals from all RPs. The propagation medium model primarily relies on well-known analytical expressions describing radio wave propagation, accounting for the influence of the underlying surface, and partially employs simulation techniques to calculate the power of signal components scattered over a large area of the surface. Results. We developed a software for the automated search of the optimal RP placement within an area given the trajectory of the mobile object and specified RTS parameters. Practical use of the developed optimization software has demonstrated its effectiveness. Conclusion. The practical benefit of the developed software lies in its ability to determine the coordinates of reception points that ensure the highest possible quality and reliability of telemetry information reception, given the specified RTS parameters. The scientific significance of the work includes: 1) the creation of a new tool for the automated search of optimal RP locations to maximize communication quality with the mobile object through a complex dynamic radio channel in a telemetry system; and 2) the optimization results and subsequent RTS modeling demonstrate the possibility of continuous high-quality reception of telemetry information from the mobile object during its descent trajectory, with continuous changes in the spatial position of radiation patterns from two transmitting antennas when using simple dipole receiving antennas.

Introduction. Touchscreens and panels are integral to modern life, actively replacing various push-button, lever, and rotary control devices. However, existing touchscreen solutions are often unsuitable due to their fragility, lack of waterproofing, or vulnerability to vandalism. This study proposes a new information input device system designed to be resistant to harsh conditions. The aim is to develop and research mathematical and software models for accurately positioning the touch point. Research objectives: 1) Develop a mathematical model for touch point positioning; 2) Develop a software model for touch point positioning; 3) Develop an experimental model of a computing system for a sensory input device. The proposed system operates by registering acoustic waves generated by tangential contact with the panel. When a touch occurs, a sound wave propagates across the surface, and several microphones can register this wave. The obtained data is then used to localize the touch point. Results. The study demonstrates the limitations of using an analytical model and proposes a numerical model instead. Modeling was carried out in the SciLab 2023.1.0 software environment, and a mathematical program for a microcontroller was written in C. Conclusion. The best arrangement of microphones was found to be at the corners of the panel, with the optimal initial approximation for calculating unknowns set to the average possible value or zero. Experimental simulations confirmed these findings, showing that the placement of microphones and the initial approximation, except when set to zero, matched the simulation results and proved more accurate. Additionally, a square shape was determined to be the best for the touchpad. Practical significance. The results of this study will be integrated into the microcontroller of the touch panel. This integration is crucial for further investigations into the localization of sound waves on the surface of solid bodies under conditions of multiple touches and potential external influences.

Introduction. Two-component one-address fiber Bragg structures (AFBS), a type of fiber-optic sensor, offer significant advantages. They enable the multiplexing of sets and microwave photonic interrogation at unique address frequencies. This capability allows for the construction of multi-sensor, multi-parameter networks with high accuracy and low-cost measurements by substituting optoelectronic interrogators with microwave photonic ones. Despite these advantages, AFBS also have notable drawbacks, primarily the occurrence of inter-address collisions, or false addresses, when structures move relative to each other during measurements. This can lead to situations where some address components of the AFBS coincide or are multiples of frequency. To significantly mitigate the impact of inter-address collisions, both software and hardware methods can be employed. The latter includes the formation of AFBS structures with three or more spectral components, known as multi-addressed fiber Bragg structures (MAFBS). However, the manufacturing technologies for three-component MFBS are significantly more complex than for AFBS, further complicated by the need to vary the address frequencies between the three components to ensure uniqueness. The aim of this research is to develop scientifically-based principles for constructing combined two-component multi-addressed fiber Bragg structures (CMAFBS). CMAFBS must combine the simplicity of recording and controlling address frequencies characteristic of two-component AFBS with the advantages of three-component MAFBS, which are resistant to address collisions. Methods and results. Numerical modeling of AFBS employed the gear matrix method, which is well-regarded for constructing mathematical models of fiber Bragg gratings (FBG), including those with phase inhomogeneities and AFBS. Analysis of the obtained spectral characteristics revealed that the range of changes in additional address frequencies could be formed in the range of 1.2 to 7.2 GHz, which is an order of magnitude smaller than for classical two-component AFBS. It was found that the main parameter influencing the operating mode of the structure (reflection or transmission) is the value of the induced refractive index n_mod,​ as it affects the narrowband performance requirement of both the λ-FBG component and the λ/π-FBG transparency window, as well as the ability to control additional address frequencies. This influence, along with the impact of the physical length of each FBG on the characteristics of the CMAFBS, is detailed in the paper. The final section of the paper discusses the prospects for CMAFBS use and examples of their application in multi-sensor systems within the framework of the Smart Grid Plus concept for smart energy grids. Modeling has shown that CAFBS can achieve potential temperature measurement accuracy when assessing the recorded signal by wavelength to within ±0.01 °C with a sensitivity of approximately 13 pm/°C, and by amplitude to within ±0.1 °C, depending on the parameters of the ADC used. Conclusion. The paper presents new sensitive elements for constructing addressable multi-sensor networks for monitoring various physical parameters – combined two-component multi-addressed fiber Bragg structures.

Introduction. Ventricular late potentials (VLPs) are low-amplitude potentials located at the terminal part of the QRS complex in electrocardiogram (ECG) signals. The presence of VLPs indicates a high probability of heart function deviations. Currently, no single-channel devices are available to detect VLPs. Therefore, designing devices and developing algorithms to detect VLPs is a topical task. The aim of this research is to analyze the feasibility of registering VLPs using single-lead ECG signals. Materials and methods. X-lead signals were selected for this study. A total of 271 signals were analyzed using MATLAB. Preliminary estimates to detect VLPs were performed using the standard Simson method, which analyzes X-, Y-, and Z-lead signals through coherent accumulation and averaging of heartbeat signals to increase the signal-to-noise ratio. This study proposes analyzing only X-lead signals using the same method. Results. According to the standard method, 46 signals had VLPs. Using the proposed algorithm, 61 signals were detected to have VLPs. The probability of a correct decision when testing the algorithm exceeded 80%. Conclusion. The proposed algorithm can detect VLPs in X-lead signals. The results of this study will be useful in designing single-channel ECG analyzers with enhanced functionality.