This article discusses modern techniques of implementation of a wideband digital modulator in an FPGA kit for use in electrical engineering communications laboratory. Previous configurations proposed ...in literature present limitations, as lack of details about the methods used in the algorithm developed and test procedures. Those key details can help researchers to develop this modulator more effectively. From technical point of view, previous works were also implemented for small bandwidth output signals. The proposed digital modulator has low cost and can generate signals based on several modulation schemes with various output roll-off filters. This proposed kit allows researchers to change digital signal characteristics through dip-switches, customizing the modulated signal. Advanced techniques such as parallelism of processes and fast access to look up tables using an FPGA were used to achieve the desired objective, and are detailed in the article. Besides this implementation, this article also shows test procedures to validate the performance of digital modulators using lab test equipment. Those procedures were used to validate the FPGA modulator developed. The paper shows how researchers can analyze the performance of digitally modulated output signals using an Oscilloscope, a Spectrum Analyzer, and a Vector Signal Analyzer. Features such as symbol rate, modulation constellation, roll-off output filter, and EVM are covered.
A new hi-accuracy method for slight-shift determination of low-resolution spectra is proposed. The method allows determining a spectrum shift with an accuracy exceeding the spectrum analyzer ...resolution to more than three orders of magnitude due to the mathematical post-processing. The method is based on representing the spectrum as a continuous and everywhere differentiable function; expanding it into the Taylor series; approximating all the function derivatives by finite differences of a given order. Thereafter, the spectrum shift is determined using the least-squares method. The method description, its mathematical foundation and the simulation results are given. The advantages of the application of the proposed method are shown.
This study is aimed to synthesize ZrB2-SiC composite powders by boro-carbothermal reduction of zircon using two different carbon sources, namely expanded graphite and carbon black. The effect of ...carbon sources on the phase composition and microstructure of composite powders was studied using an X-ray diffractometer, a scanning electron microscope, and an energy spectrum analyzer. Pure-phase ZrB2-SiC composite powders were prepared in 2 h at 1550 and 1500 °C 1500 °C using expanded graphite and carbon black, respectively. In the former case, anisotropic ZrB2-SiC composite powders were synthesized. Their ZrB2phase grains had an average diameter of 2.0 μm and regular hexagonal shape, while SiC phase grains were whisker-shaped, had an average diameter of 0.15 μm and aspect ratio exceeding 20. For carbon black, finer ZrB2grains and shorter rod-shaped SiC grains were obtained.
In order to intensively study the exterior transient electromagnetic interference characteristics caused by disconnector operation in Gas Insulated Switchgear, experimental research of exterior ...transient electromagnetic interference under switching conditions is performed in this paper. Based on 330kV GIS test platform, with the method of resistive impedance divider, TEV is measured with Pintech P6039A high-voltage probe and Yokogawa DLM2054 oscilloscope by using resistor voltage divider GIS exterior radiation electromagnetic circuit is also established using antenna theories, biconical antenna and spectrum analyzer etc. The exterior transient electromagnetic interference waveform and characteristics are precisely measured. By the contrast analysis of TEV and radiation electromagnetic waveforms, results can be summarized as followed: ① The TEV waveform caused by opening and closing of disconnecting switch is front sparse and rear dense, and its amplitude is low at the fore and high over the back; The electric field strength is weaker compared to the electromagnetic compatibility of normal substation.
The rolling-out of 5G networks is recently including 5G Base Stations (BSs) operating on millimeter-Wave (mm-Wave) frequencies. The goal of this work is to shed light on the exposure assessment from ...commercial 5G mm-Wave 5G BSs, by focusing on the impact of downlink traffic on the exposure levels. To this aim, we adopt an innovative measurement framework, based on hardware and software components, able to satisfy the challenging measurement requirements of mm-Wave frequencies. In addition, we design a completely softwarized algorithm, called M-WAVE, in order to measure the mm-Wave exposure with a programmable spectrum analyzer. Results, obtained from a commercial 5G scenario, reveal that the exposure from the mm-Wave BS is directly proportional to the amount of traffic injected on the wireless link. However, the electric field is always lower than 0.08 V/m, while the downlink traffic is even larger than 800 Mbps.
A filter bank consisting of switches and band‐pass filters is one method for configuring a spectrum analyzer preselector. A long‐life switch with high isolation is key to this development. We propose ...a novel horizontal‐moving waveguide switch designed for easy addition of ports compared to commercial rotating switches. The switch has a small gap between the fixed and moving parts with the gap surrounded by chokes. This configuration offers high isolation and long life. It also reduces the size of the filter bank. This paper describes 2 proposed switch prototypes for frequency ranges from 90 to 140 GHz and from 255 to 315 GHz. The measured switch isolation is better than 50 dB and the insertion loss is less than 3 dB for both prototypes.
Filterless optical networks (FONs) have been proposed as a feasible solution for optical metro networks. In addition, as a result of the shorter distance compared to core optical networks, direct ...detection optical transmission systems can be used in metro FONs, which reduces costs, as compared to coherent detection systems. In this work, we present two optical signal tracking approaches for FONs that allow to detect small frequency laser drift problems and enable safely reducing channel spacing. Additionally, we study the most proper resolution for optical spectrum analyzers continuously scanning the whole C-band. Proposed approaches are: (1) feature-based tracking and (2) residual-based tracking. Experiments are carried out to compare the performance of the approaches for both direct detection and coherent detection systems, in the case of a single optical signal with no neighboring signals nearby in the spectrum, as well as in the case of a group of optical signals closely allocated in the spectrum. The results show that the residual-based approach enriched with contextual information enables to better track and correct the wavelength drifts before they reach their limits (e.g., ± 2.5 GHz), leading to the guard band reduction for what concerns wavelength drifts.
In some previous reports about frequency-modulated continuous-wave (FMCW) Lidar, observing the longer waveform of a de-chirped signal is considered an effective scheme for further improving the ...ranging resolution. In this work, the ranging resolution of a FMCW Lidar is experimentally investigated, and the feasibility of such a scheme is tested. During the experiment, a FMCW signal is generated via a Mach–Zehnder modulator in the transmitted port. In the received port, the de-chirped signal is extracted based on a homodyne detection scheme and is analyzed by an electrical spectrum analyzer. Two different methods are adopted to determine the ranging resolution. One is based on a single target, for which the ranging resolution is obtained through inspecting the shift of spectral peak position as the target moves. The other is based on two targets, for which the ranging resolution is acquired through inspecting the variation of spectrum distribution as the spacing of two targets changes. The experimental results demonstrate that extending the observed duration of the de-chirped signal cannot improve the ranging resolution, and the corresponding physical mechanism is revealed.
In this paper, an optical fiber fluid sensing system based on optoelectronic oscillator (OEO) was proposed and studied numerically. The fluid sensor head is constructed by splicing two sections of ...side-polished fiber (SPF) to one section of photonic crystal fiber (PCF). Fluid sample can flow continuously through the holes of PCF. The refractive index (RI) change of the fluid sample can lead to the effective RI change of the fiber, resulting in frequency change of microwave signal generated by OEO. By monitoring the oscillation frequency using an electronic spectrum analyzer (ESA), the RI of fluid sample can be measured. Thanks to the fast interrogation speed of ESAs, the measuring speed can be increased significantly compared to traditional optical fiber RI sensing systems using optical spectrometers. The sensing principle of the system was studied. The sensitivity of the proposed system was evaluated by simulation, and an RI sensitivity of −14.20 MHz/RIU can be achieved. The results show that with proper system design, real-time RI measurement with high sensitivity can be achieved. Increasing the length of the PCF while under the premise of the fluid parameters will be the most reasonable way to improve the sensitivity. The proposed design and simulation results can provide suggestions for the fabrication and optimization of fluid sensing systems used for real-time detection and measurement of biological elements and heavy metal ions in liquid environment.
A machine learning (ML)-based multifunctional optical spectrum analysis technique is proposed to perform not only the conventional analysis functions but also the extended analysis functions, ...including center wavelength detection, optical signal-to-noise (OSNR) calculation, bandwidth recognition, as well as spectral distortion diagnosis. We have investigated four widely used ML algorithms, including support vector machine (SVM), artificial neural network, k-nearest neighbors, and decision tree. First, the wavelengths, OSNRs, and bandwidths of optical signals are processed by four ML methods based on the spectral data. The good performance and fast processing speed are obtained, especially for SVM, achieving the optimal accuracy (100%) and the least test time. For the need of the practical application, we also investigate the more complicated case, where wavelength, OSNR, and bandwidth are variable simultaneously so that the ML should analyze these three parameters comprehensively. Even in this case, the overall accuracy is still larger than 99.1%. In addition, the extended analysis functions are also studied to diagnose the spectral distortion caused by the cascaded filtering effect and off-center filtering effect. The number of cascaded filters and the offsets of filter shift and laser drift can be effectively estimated by the SVM with high average accuracy and low standard deviation, which are useful for failure detection and distortion recovery. This technique has the potential to be applied in the optical spectrum analyzer to implement the multifunctional spectrum analysis or in the optical performance monitor to execute the spectral distortion diagnosis.
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