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Indonesia, located in the zone of “Ring of Fire,” has a high tsunami risk, specifically from those induced by earthquakes. The 2004 Aceh Tsunami and the 2006 Pangandaran Tsunami demonstrated that tsunamis could cause major damage to coastal areas. The Indonesian Tsunami Early Warning System (Ina-TEWS) typically relies on buoys connected to satellites, transmitting information about 5 minutes after the tsunami earthquake begins. Though Indonesia relies on this system, many buoys have gone missing, emphasizing the need for a faster and more reliable backup early warning system. This study proposes a new early warning system by integrating maritime wireless communication between vessels in the open sea and coastal radio stations in the Pangandaran coastal area by using VHF and HF radio communication systems. 200 Gross Tonnage (GT) fishing vessels equipped with the VHF radio communication system are used for the first signal propagation option. The HF radio communication system is applied as a second option, for when there is a hop number limit. Three scenarios of tsunami numerical modeling were carried out using Delft3D and Delft Dashboard based on the earthquake and fault parameters from PUSGEN. The output from this study is the propagation time of VHF and HF signals of the early warning system for each scenario, which was less than 1 minute. The development of an early warning system based on maritime wireless communication is expected to be a part of Indonesia’s tsunami mitigation system in place of buoys.

Recently, artificial intelligence and data science have witnessed dramatic progress and rapid growth, especially Automatic Speech Recognition (ASR) technology based on Hidden Markov Models (HMMs) and Deep Neural Networks (DNNs). Consequently, new end-to-end Recurrent Neural Network (RNN) toolkits were developed with higher speed and accuracy that can often achieve a Word Error Rate (WER) below 10%. These toolkits can nowadays be deployed, for instance, within aircraft cockpits and Air Traffic Control (ATC) systems in order to identify aircraft and display recognized voice messages related to flight data, especially for airports not equipped with radar. Hence, the performance of air traffic controllers and pilots can ultimately be improved by reducing workload and stress and enforcing safety standards. Our experiment conducted at Tangier's International Airport ATC aimed to build an ASR model that is able to recognize aircraft call signs in a fast and accurate way. The acoustic and linguistic models were trained on the Ibn Battouta Speech Corpus (IBSC), resulting in an unprecedented speech dataset with approved transcription that includes real weather aerodrome observation data and flight information with a call sign captured by an ADS-B receiver. All of these data were synchronized with voice recordings in a structured format. We calculated the WER to evaluate the model's accuracy and compared different methods of dataset training for model building and adaptation. Despite the high interference in the VHF radio communication channel and fast-speaking conditions that increased the WER level to 20%, our standalone and low-cost ASR system with a trained RNN model, supported by the Deep Speech toolkit, was able to achieve call sign detection rate scores up to 96% in air traffic controller messages and 90% in pilot messages while displaying related flight information from ADS-B data using the Fuzzy string-matching algorithm. [ABSTRACT FROM AUTHOR]

In this article, an active electrically small Horn antenna for very high frequency (VHF) and ultra-high frequency (UHF) frequencies is presented. The proposed horn antenna has a height of 5 cm and a diameter of 4.28 cm which can cover 6-12 GHz without a special active circuit with the VSWR of less than 2. A Non-foster Active Adaptation Circuit is used to reduce the antenna input frequency from 164 MHz to 880 MHz. Good matching is visible between the simulation results and the measurement of the antenna reflection coefficient with the active matching circuit. The proposed structure has more than 137 % bandwidth. With the proposed active antenna, the problem of non-portability of VHF and UHF Horn antenna antennas has been solved. Finally, by analyzing the time domain, the stability of the circuit is examined, and the results of the stability test show that the system, including the antenna and the circuit, is stable. The antenna and the matching circuits are simulated by CST microwave studio and advanced design system, respectively.

The eastern spotted skunk (Spilogale putorius) is of increasing conservation concern across its range, with managers requiring information on the species' spatial ecology to design conservation actions. The Florida spotted skunk (Spilogale putorius ambarvalis) is the smallest and least-studied subspecies, with little known about its home range size and movement ecology. We fitted Florida spotted skunks with VHF radio-transmitters and tracked them to diurnal den sites in 2016 and 2017 to estimate home range sizes. We were able to calculate 95% kernel density estimates of home range size for 12 skunks (7 males, 5 females) and found that males had significantly larger (mean ± SE) home range sizes (1.60 km2 ± 0.38) than females (0.36 km2 ± 0.06). Additionally, to gather information on the nightly activity patterns and fine-scale movements of Florida spotted skunks, we fitted skunks with Global Positioning System (GPS) collars in 2017 and successfully retrieved location data from 24 individuals (12 males, 12 females). We tracked GPS-collared skunks over an average of 5.7 days (range = 1–9 days) and a mean of 115.75 locations per skunk (range = 4–223). The mean distance traveled per night for a skunk in our study area was 1874 m (range = 437–3451 m). Mean distance traveled per night was positively influenced by mean nightly temperature, but did not differ significantly by sex, moon illumination, or rainfall. Florida spotted skunks were most active ~ 2 h after sunset and nightly activity declined from that period on. Home range estimates (100% minimum convex polygons) derived exclusively from daytime den locations were significantly smaller than those derived from nighttime locations. Our research advances our understanding of Florida spotted skunk spatial ecology, including the first use of GPS collars on the subspecies, and provides novel information for future ecological comparisons with other populations. Our results suggest that the frequent practice of relying solely on daytime locations when tracking spotted skunks may under-represent their areas of habitat use and might fail to capture important nocturnal foraging areas. [ABSTRACT FROM AUTHOR]

In this article, an active electrically small Horn antenna for very high frequency (VHF) and ultra-high frequency (UHF) frequencies is presented. The proposed horn antenna has a height of 5 cm and a diameter of 4.28 cm which can cover 6-12 GHz without a special active circuit with the VSWR of less than 2. A Non-foster Active Adaptation Circuit is used to reduce the antenna input frequency from 164 MHz to 880 MHz. Good matching is visible between the simulation results and the measurement of the antenna reflection coefficient with the active matching circuit. The proposed structure has more than 137 % bandwidth. With the proposed active antenna, the problem of non-portability of VHF and UHF Horn antenna antennas has been solved. Finally, by analyzing the time domain, the stability of the circuit is examined, and the results of the stability test show that the system, including the antenna and the circuit, is stable. The antenna and the matching circuits are simulated by CST microwave studio and advanced design system, respectively. [ABSTRACT FROM AUTHOR]

Summary: Background: High Consequence Infectious Diseases (HCIDs), have the potential to cause pandemics and require particular focus for preparedness due to their high mortality rates. The application of Personal Protective Equipment (PPE) for HCIDs is complex and carries significant risk of Health Care Worker (HCW) contamination if done incorrectly. Previous reviews have reported a lack of information on the nature of training provided and the ideal timing of repeat training to best retain skills. Simulation Based Mastery Learning (SBML) is a methodology for skill acquisition which encompasses deliberate practice and repeated assessment until the learner achieves a pre-set Mastery standard. SBML has been demonstrated to improve competence, skill retention and patient outcomes in other clinical procedures. SBML has not been previously studied or utilised in HCID PPE training. Aim: We aimed to increase the likelihood of safe clinical practice by evidencing that Lothian modified SBML for PPE effectively prepares our priority learners. Methods: A quasi-experimental within group post-test design was used. Learners undertook a modified SBML programme which included two-hour asynchronous and two-hour synchronous components. Findings: 11 learners (10 infectious diseases registrars and 1 infectious diseases consultant) were enrolled in the programme with 8 completing all stages, all of whom achieved the Mastery passing standard. The resources were highly rated by learners with the exemplar videos of skills highlighted as particularly useful. Self-assessed preparedness for each skill increased following pre-learning and synchronous sessions. Conclusion: Modified SBML can be used as an effective methodology for the training and assessment of HCWs in the donning and doffing of HCID PPE.

Space-based communications at the very high frequency (VHF) band for air traffic management is a new technology application under development that requires energy-efficient architectures to mitigate the power limitations of satellite platforms. The usage of high-efficiency radiofrequency (RF) transmitters can help reduce the power consumption, but nonlinearities concerning the amplified signal in wide fractional bandwidth systems are a problem to solve. This paper proposes a high-efficiency (RF) power amplifier (PA) for satellite communications at the VHF band that aims to reduce the envelope distortion inherent to wide fractional bandwidth multicarrier polar-mode transmitters. Its design is based on a solution called hybrid-coupled switching voltage PA in combination with gallium nitride (GaN) high electron mobility transistor (HEMT) technology. The developed VHF PA prototype delivers up to 95 W from a 28 V power supply, with a drain efficiency about 80% within the 118 MHz to 138 MHz operating band. To test its linearity performance, operating in a polar-mode configuration, a GaN-based wideband envelope amplifier (EA) has been developed to modulate the RF PA supply port. This EA improves its power efficiency by combining it with a slow envelope power supply (SEPS). Some measurements have been taken for a 100 W peak envelope power (PEP) and 10 MHz (maximum carrier spacing) four-tone digitally-modulated test signal, where any distortion product is attenuated 46 dB below the average power of the amplified signal without applying any digital predistortion (DPD) technique. [ABSTRACT FROM AUTHOR]

This research aims to analyze the impact of the Earth-Space link on the Automatic Identification System (AIS) signals of ships. To achieve this, we established a simulation system that measures the receiving power of AIS signals via satellite platforms. We validated the system by utilizing observation data from Tiantuo-5. Through this simulation, we quantitatively analyzed the effects of ionospheric TEC (Total Electron Content) and space loss on the received power. During the processing of observation data, we construct a geometric propagation model utilizing the measured positions of both the satellite and the ship. We then calculate the antenna gain and remove any system errors. Additionally, we eliminate the deviation of elevation and azimuth angles caused by satellite motion. This allows us to determine the actual power of different ships reaching the receiving platform. Upon comparing the measured power data with the simulated power, it was noted that both exhibited an increasing trend as the elevation angle increased. This led to an RMSE (Root Mean Square Error) result of approximately one, indicating the accuracy of the simulation system. These findings hold significant implications for analyzing interference factors in satellite-ground links. [ABSTRACT FROM AUTHOR]

Indonesia, located in the “Ring of Fire” zone, is a tsunami-prone area, especially those earthquake-induced. Therefore, a tsunami early warning system is crucial for reducing potential damage. Ina-TEWS is an Indonesian tsunami early warning system that relies on buoys, uses seismic sensors to detect a tsunami, sends out its warning within 5 min. Ina-TEWS requires maintenance and supervision, especially since 22 buoys were declared lost or damaged in 2012–2018. Therefore, Indonesia needs a faster and more reliable backup early warning system. This study proposes a new method by integrating maritime wireless communication between ships on the open sea and ship-to-coastal radio stations in the Palu Port. The ships used are passenger ships equipped with VHF radio communication which is the main working frequency for signal propagation. Numerical modeling of tsunamis was carried out using Delft3D and Delft Dashboard, using earthquake and fault parameters from PUSGEN. The output of this study is the required VHF signal propagation times for each tsunami scenario less than 1 min. Standard operating procedure (SOP) has also been developed based on the worst scenario. The development of this system is expected to enhance tsunami mitigation systems in Indonesia by replacing the buoys in the future.

This article presents a comprehensive evaluation of the performance of a super-large-coverage mobile communication system for wireless regional area networks (WRANs) in the very-high-frequency (VHF) band. The system was standardized as ARIB STD-T103 and IEEE 802.16n. It can transmit data over a distance of 10 km or more at a transmission rate of several megabits per second (Mbps). It is particularly suitable for transmitting sensor and monitoring information, including moving images, over a wide area. First, we present some use cases and determine the feasibility of implementing WRANs for vehicle-to-everything (V2X) and the Internet of Things applications. Subsequently, we evaluate the transmission performance and estimate the transmission distance in the VHF-band radio propagation environment through computer simulations and experimental evaluations with our WRAN prototype. In the evaluation, we also adopt several channel estimation methods for a particular pilot pattern in the downlink. Moreover, we demonstrate the transmission distance that can be achieved with and without a multihop relay based on the evaluation results. Single-hop transmission reaches up to approximately 10 km while maintaining transmission speeds of several Mbps on the uplink, when QPSK is used. Conversely, by using multihop transmission, although the transmission speed is approximately 1/2 to 1/6, the maximum transmission distance is approximately 50 km.

In a range of IoT applications, edge nodes require minimal size, mass, and power/energy use. When node complexity is severely constrained, the burden of detection falls to the receiving system. In this paper we present a method of detection for RF signals motivated by wildlife radio telemetry, where miniature transmitters emit VHF pulses that are used to detect and localize animals in the field. We address the challenges of limited transmit power and large path losses that lead to low received SNR. In addition, the pulse train structure requires joint frequency acquisition, time synchronization, and detection; our approach addresses the key challenge of large uncertainty in signal parameters. Our algorithm explicitly integrates frequency acquisition and time synchronization, using nearly phase-coherent matched filtering followed by non-coherent pulse combining and a multiple hypotheses test to provide near-optimal detection performance in low SNR scenarios. We provide quantitative results showing performance as a function of SNR and signal uncertainty. When compared to the single pulse detection case as used in existing systems, our multipulse combining approach pulses improves detection performance by 4 dB, even under the conditions of temporal and frequency/phase uncertainty resulting from transmitter design and manufacturing. We also describe an efficient real-time signal processing implementation of the algorithm, including signal tracking that supports localization after initial signal detection.

Short burst continuous phase modulation transmission is of practical relevance in e.g. frequency hopping systems applied in sensor or tactical networks. The channel conditions can be seen as mutually uncorrelated for each burst due to spectral and or temporal separation of those. Because of this time variant nature, a recurring acquisition of the impairment parameters is required for each burst. In this work, a blind joint estimation of several parameters in a flat fading environment for continuous phase modulation bursts is realized by the expectation maximization algorithm. The main contributions are first the formulation of the expectation and maximization steps to enable the joint computation of the maximum likelihood parameter estimates and second the analysis of the likelihood functions to obtain an optimized initialization for the algorithm. It is shown, that the joint estimator produces unbiased estimates and its performance in terms of the mean squared estimation error achieves the theoretical limits, i.e. the modified Cramér-Rao-Vector-Bound and slightly outperforms a state of the art pilot based estimator. Furthermore, the effective throughput is discussed and bit and frame error rates are compared to each other and to the perfectly synchronized estimator. Its computational complexity is analyzed and efficient computation steps and further approaches are outlined to decrease it.

This paper proposes a radio-protected area (RPA) estimation model that achieves full protection and avoids overprotection by adding an appropriate margin to the extended-Hata (EH) model, for realizing efficient spectrum sharing in the V-High-band. This additional margin, called location gain, is a location-dependent value that accounts for knife-edge losses calculated from topographic information. This study experimentally obtains the location gain by conducting VHF-band-based propagation experiments in urban and suburban areas. Subsequently, we developed an estimation formula for the location gain using topographic data, which include correction terms based on the experimental data. As a result, RPA can be estimated using only the topographic data, excluding the need for propagation experiments. The proposed model resolved the problems of the EH model (incomplete protection) and free-space (FS) model (overprotection). In urban and suburban areas, the proposed model achieved full protection and over 99.7% reduction in the RPA size of the FS model when the threshold of the received power for determining the RPA was set to –80 dBm.

In this paper, computation of very high frequency (VHF) signal strength for point to area network was carried out using machine learning modeling techniques. Seven different machine learning models were adopted: Decision Tree, Random Forest, AdaBoost, k-Nearest Neighbor, Support Vector Machine, Artificial Neural Network and Linear Regression. A total of 120 data points was used in computing the signal strength. 72 data points (60%) was used to train the model, while the remaining 48 data points (40%) were used as test data to determine the accuracy of the computation for all the models. From the results, it was observed that the accuracy of the computations was greatly influenced by the amount of training data that was used. Also, from the results, in highest order of accuracy, AdaBoost was adjudged the best model. This was followed by the Artificial Neural Network model. Generally, the error margin of computation obtained for these two models were low, hence indicating that the models can be effectively relied on for computation of signal strength in the study area.

ABSTRACTThis paper is introducing analyses of new design of the automatic identification system (AIS) ships antenna that will serve for both VHF-band radio and satellite tracking and identification system for maritime applications. The current AIS network is an automatic tracking system used by ships of vessel traffic service for identification and location of vessels by electronically exchanging data between nearby ships and on-shore base station. In the AIS system for the electronic data exchange, the very high frequency (VHF) range is used. Utilizing of the VHF range makes the AIS as short-range communication, identification and collision avoidance system between AIS equipped ships and base station is possible in the antennas line-of-sight . In order to widen the range of the AIS from short range up to long or global range, AIS communication should be used via a satellite. In order to provide communication via satellite as well should be designed multifunctional antenna for both radio AIS (R-AIS) and satellite AIS (S-AIS) communication antenna. The analyses and design of a new multifunctional antenna, calculation and development, including implementation and testing of helical VHF antenna for R-AIS and S-AIS equipment are discussed.

An as-produced epoxy material reinforced with ZnO (nano)rods for outdoor use was produced for the purpose of enclosing VHF/early UHF transceiving elements. Three different ZnO (nano)rod percentages were dispersed (0.1 wt%, 0.5 wt% and 2 wt%) in epoxy samples and were consequently exposed to an artificial weathering environment for a total period of 2880 h. SEM and XRD characterizations were followed by gravimetric, colorimetric and dielectric measurements that were conducted every 576-h AWE treatment intervals and were complemented by FTIR, UV-Vis, contact angle and gloss measurements. The composite exhibited favourable dielectric behaviour: ZnO presence inflicted minimal impact to the composites' loss tangent, while dielectric permittivity was reduced for low ZnO content (0.1 wt%/0.5 wt%), especially until the 1152-h interval, while it suffered an increase for 2 wt% samples that was maintained from the beginning until the end of the experiment. Hence, the low-k (4–5.2) constructed material, compared to bare epoxy resin, maintained moderate loss tangent levels (0.55–0.7) in the VHF/early UHF spectrum, throughout the full AWE treatment, and also attained reduced dielectric permittivity, thus exhibiting moderate radio frequency transparency, together with enhanced endurance against environmental fatigue. [ABSTRACT FROM AUTHOR]

Today’s practice of developing VHF radio systems paths widely uses MMIC as low-noise amplifiers. This approach is acceptable for radio systems operating in a relatively quiet electromagnetic environment. However, for systems operating in a complex interference environment of the VHF band, low-noise amplifiers with a lower gain and increased overload capacity are desirable. This requires maintaining a low noise figure and manufacturability of the device. Therefore, the solution to this problem requires the development of a low-noise amplifier of the VHF band with increased overload capacity, made on commercially available MMIC. This paper presents the results of a logical-heuristic synthesis of a VHF low-noise high-linear amplifier performed on an MMIC, utilising noiseless negative feedback technique. Analytical expressions are given for calculating the gain, the input gain compression point, input intercept points of the J-th order, and the noise figure of the structure. The analysis of the performance of the amplifier implemented on the MGA 62563 MMIC showed that, in comparison with other integrated solutions, increased overload capacity and structure linearity are provided. The high noise immunity and ease of manufacture of the device using commercially available components, make it a promising element in the design and modernization of VHF receiving and amplifying paths operating in a complex electromagnetic environment.

Mid-latitude sporadic-E (Es) is an intermittent phenomenon of the lower E region of the ionosphere. Es clouds are thin, transient, and patchy layers of intense ionization, with ionization densities which can be much higher than in the background ionosphere. Oblique reflection of radio signals in the very high frequency (VHF) range is regularly supported, but the mechanism for it has never been clearly established—specular reflection, scattering, and magnetoionic double refraction have all been suggested. This article proposes using the polarization behaviour of signals reflected from intense midlatitude sporadic-E clouds as an indicator of the true reflection mechanism. Results are presented from a measurement campaign in the summer of 2018, which gathered a large amount of data at a receiving station in the UK using 50 MHz amateur radio beacons as signal sources. In all cases the signals received were elliptically polarized, despite being transmitted with linear polarization; there were also indications that polarization behaviour varied systematically with the orientation of the path to the geomagnetic field. This represents, for all the examples recorded, clear evidence that signals were reflected from midlatitude Es by magnetoionic double refraction. [ABSTRACT FROM AUTHOR]

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This paper presents a low-power CMOS temperature and process compensated 150.9 MHz Very-high-frequency (VHF) voltage-controlled-ring-oscillator (VCRO) for on-chip integration. The design employs a CMOS temperature-sensor and novel feedback control circuitry to generate the internal control-voltage for the VCRO which ensures oscillation in the vicinity of the desired frequency despite variations in temperature. The control circuitry is the implementation of an empirical equation expressing a temperature sensor-voltage into a specific control-voltage for three different process corners using three different switches. The control-voltage calibrates against temperature variation for the specific process-corner in order to maintain the same frequency of oscillation. Simulations shows that the proposed design maintains the oscillator’s frequency within 0.39% from −10°C to 90°C. The fabricated chip implemented in 130-nm GF 8HP Si-Ge BiCMOS process, occupies an area of 0.0242-mm2 and consumes 325 $\mu \text{W}$ while operating with a 1 V supply-voltage. The performance was verified through experimental immersion of DUT (device-under-test) in a temperature-controlled water-bath in the range 22.5°C–70°C.

To solve the poor quality of Very high frequency (VHF) speech communication in the navigation field, a VHF speech enhancement model based on an improved transformer (VHFSE) is proposed in this paper. The long-term and short-term noise are the reasons for the poor quality of VHF voice communication. VHFSE can reduce these two aspects of noise. We select the Two-stage Transformer based Neural Network (TSTNN) as the baseline. The Transformer structure pays attention to global information and parallel computing, which can reduce the long-term noise. In order to strengthen the ability of the model to reduce short-term noise, we add CNN module to the transformer according to the ability of revolutionary neural networks (CNN) to extract local information. Meanwhile, to improve the real-time performance, this study employs the lightweight convolution module (Depthwise Separable Convolution) to efficiency of VHF speech communication. Experimental results show that the proposed model VHFSE obtains the highest PESQ and STOI values than other compared modules. Besides, we apply the self-built dataset in our proposed model. The spectrum diagram shows that our model has the best enhancement effect on navigation VHF speech.

This research aims to analyze the impact of the Earth-Space link on the Automatic Identification System (AIS) signals of ships. To achieve this, we established a simulation system that measures the receiving power of AIS signals via satellite platforms. We validated the system by utilizing observation data from Tiantuo-5. Through this simulation, we quantitatively analyzed the effects of ionospheric TEC (Total Electron Content) and space loss on the received power. During the processing of observation data, we construct a geometric propagation model utilizing the measured positions of both the satellite and the ship. We then calculate the antenna gain and remove any system errors. Additionally, we eliminate the deviation of elevation and azimuth angles caused by satellite motion. This allows us to determine the actual power of different ships reaching the receiving platform. Upon comparing the measured power data with the simulated power, it was noted that both exhibited an increasing trend as the elevation angle increased. This led to an RMSE (Root Mean Square Error) result of approximately one, indicating the accuracy of the simulation system. These findings hold significant implications for analyzing interference factors in satellite-ground links.

Viral hemorrhagic fever (VHF) is a term referring to a group of life-threatening infections caused by several virus families (Arenaviridae, Bunyaviridae, Filoviridae and Flaviviridae). Depending on the virus, the infection can be mild and can be also characterized by an acute course with fever accompanied by hypervolemia and coagulopathy, resulting in bleeding and shock. It has been suggested that the course of the disease is strongly influenced by the activation of signaling pathways leading to RIG-I-like receptor-dependent interferon production. RIG-I-like receptors (RLRs) are one of two major receptor families that detect viral nucleic acid. RLR receptor activation is influenced by a number of factors that may have a key role in the differences that occur during the antiviral immune response in VHF. In the present study, we collected data on RLR receptors in viral hemorrhagic fevers and described factors that may influence the activation of the antiviral response. RLR receptors seem to be a good target for VHF research, which may contribute to better therapeutic and diagnostic strategies. However, due to the difficulty of conducting such studies in humans, we suggest using Lagovirus europaeus as an animal model for VHF. [ABSTRACT FROM AUTHOR]

Viral hemorrhagic fever (VHF) is a term referring to a group of life-threatening infections caused by several virus families (Arenaviridae, Bunyaviridae, Filoviridae and Flaviviridae). Depending on the virus, the infection can be mild and can be also characterized by an acute course with fever accompanied by hypervolemia and coagulopathy, resulting in bleeding and shock. It has been suggested that the course of the disease is strongly influenced by the activation of signaling pathways leading to RIG-I-like receptor-dependent interferon production. RIG-I-like receptors (RLRs) are one of two major receptor families that detect viral nucleic acid. RLR receptor activation is influenced by a number of factors that may have a key role in the differences that occur during the antiviral immune response in VHF. In the present study, we collected data on RLR receptors in viral hemorrhagic fevers and described factors that may influence the activation of the antiviral response. RLR receptors seem to be a good target for VHF research, which may contribute to better therapeutic and diagnostic strategies. However, due to the difficulty of conducting such studies in humans, we suggest using Lagovirus europaeus as an animal model for VHF.

The motivation of this paper increases the bandwidth of power amplifier to multioctave by matching circuit, which consists of ferrite balun, 4:1 transformers and RC network feedback to make atrade-off between gain and VSWR. So this work discusses the design of a push-pull power amplifier demonstrating over more than a decade bandwidth using matching networks to achieve [30–800] MHz bandwidth. Matching transformer techniques can be used in order to minimise the return loss and increase the gain. Modification of the classical topology, based on inductive compensation of the parasitic capacitance of ferrite, has been proposed and used to design a 1:4 transformer. Practically, miss-match and heating is the main concern for broadband performance of high power amplifier. Coaxial cable and ferrite are also used to dissipate the heat (high temperature) resulting from the amplification power, in addition to installing the board on a cooler with appropriate dimensions, so we get the best match and stability. The simulation results are compared with the measurements. The measured results show that 20.5–17.46 dB of gain, 50.5–47.46 dBm of output power, and 50.9 of drain efficiency are delivered. [ABSTRACT FROM AUTHOR]

Recent observations from LOFAR indicate that multiple, spatially distributed corona bursts can occur in lightning processes with a timescale of 10 microseconds. The close proximity of the corona bursts in space and time poses a great observation challenge for short‐baseline (typically ≤100 m) radio interferometers. This paper reports simulations to show the interferometry results that would be obtained with such an interferometer. In particular, spatially‐separated corona bursts at fixed locations may be seen as a fast (>107 m/s) propagating source with large power variation if the resolution of the instrument is greater than the spatial separation of the bursts. The implications and suggestions for lightning interferometry studies are discussed in the paper. Plain Language Summary: Lightning evolution contains brief processes that are critical to its channel formation, but their physical mechanisms are poorly understood at present. Those processes emit very high frequency radio emissions, and radio sensor arrays have been used to detect those emissions to investigate their source processes. The latest observations from the large radio telescope LOFAR show that multiple, intense bursts of radio emission at discrete locations occur in those processes. Here we report simulations to show that such bursts are seen as a fast propagating wave for a short‐baseline lightning radio sensor array. Our study suggests that caution is required when interpreting the observations made with such a radio sensor array. Key Points: Complications of lightning radio interferometer data interpretation due to random nature of the emission sources are investigatedCorona bursts observed by LOFAR may be seen as a fast (>107 m/s) moving source with power variation by short‐baseline interferometersRequirements for radio interferometers to resolve corona bursts occurring in close spatial and temporal proximity are examined and discussed [ABSTRACT FROM AUTHOR]

Sound insulation with rear‐ventilated rainscreen façades As early as 1992–1994, more than 30 suitability and type tests on rear‐ventilated rainscreen façades were carried out in the test stand of ita Ingenieurgesellschaft für Technische Akustik mbH. At that time, 60 mm and 120 mm thick thermal insulation was used for the measurements. Since the thickness of the thermal insulation has increased in the course of progressive requirements for energy saving, more than 40 measurements of the airborne sound insulation were again carried out in the laboratory of ita Ingenieurgesellschaft für Technische Akustik mbH on rear‐ventilated rainscreen façades. Most of the measurements were carried out with mineral wool insulation with a thickness of d = 180 mm. Furthermore, the variety of façade claddings and fastening systems has increased, which again underlines the necessity of a new measurement campaign. Since DIN 4109‐34:2016‐07 "Sound insulation in buildings – Part 34: Data for the analytical verification of sound insulation (component catalogue) – Facing constructions in front of solid building components" does not yet contain any elaborations for rear‐ventilated rainscreen façades, the measurement results presented in this article provide useful information for the planning of sound insulation. [ABSTRACT FROM AUTHOR]

Coherent backscatter radar observations made at the Jicamarca Radio Observatory (JRO) have contributed significantly to our understanding of equatorial F-region irregularities. Radar observations, however, have been made predominantly at the Very-High Frequency (VHF) band (50 MHz), which corresponds to measurements of 3-m field-aligned irregularities. The deployment of the 14-panel version of the Advanced Modular Incoherent Scatter Radar (AMISR-14) at Jicamarca provided an opportunity for observations of Ultra-High Frequency (UHF - 445 MHz) echoes which correspond to measurements of irregularities with 0.34 m scale sizes. Here, we present what we believe to be the first report describing the quiet-time climatology of sub-meter equatorial F-region irregularities derived from UHF radar measurements. The measurements were made between August 2021 and February 2023 using a 10-beam AMISR-14 mode that scanned the F-region in the magnetic equatorial plane. The results show how F-region sub-meter irregularities respond to variations in season and solar flux conditions. The results also confirm, experimentally, that the occurrence of UHF F-region echoes is controlled by the occurrence of equatorial spread F (ESF). Higher occurrence rates were observed during pre-midnight hours and during Equinox and December solstice. Reduced occurrence rates were observed during June solstice. The results show that an increase in solar flux was followed by an increase in the altitude where noticeable occurrence rates (≳ 10%) start and in the maximum altitude of these occurrence rates. The observations also show that occurrence rates lasted longer (in local time) during low solar flux conditions. Comparisons with collocated VHF radar observations showed that, despite differences in radar parameters, observation days, and the scale size (one order of magnitude) of the scattering irregularities, the two systems show similar climatological variations with only minor differences in the absolute occurrence rates. Finally, the analysis of the occurrence rates for different beams did not show substantial climatological variations over local (within a few 100s of km) zonal distances around JRO. We point out, however, that observations on a single day can show strong local variations in echo detection and intensity within the AMISR-14 field of view due to the intrinsic development and decay of ESF structures. • We report for the first time the climatology of nighttime F-region echoes observed by a UHF radar at the magnetic equator. • We present the response of the occurrence rate of UHF echoes to variations in season and solar flux that are related to ESF. • We show that the climatology of irregularities from AMISR-14 is similar to that observed by the collocated VHF JULIA radar. • Analysis of the 10-beam observations confirms that the ESF echo climatology does not change within local zonal distances. [ABSTRACT FROM AUTHOR]

Parasitic currents on the sheaths of the coaxial cables will deteriorate the performance of the antenna, so the choke structures are needed. While a-quarter-wavelength choke sheaths at VHF and UHF are very long, miniaturized ferrite-EBG composited choke structures are proposed. The ferrite refers to ferrite magnetic beads. Electromagnetic bandgap (EBG) element is consisted of multi-section metal tubes with length relatively shorter than a-quarter-wavelength. The integrated structures are formed by arranging EBG elements and beads alternately along the coaxial line. The proposed choke structures combine the wideband choke performance of the ferrite beads and the high efficiency of the EBG structures. Furthermore, due to the difficulty of the quantitative measurement of the choke structures in an open space, a measuring setup designed in a transmission line model is devised. The choking effects of the proposed structures can be characterized by the $\vert \text{S}_{21}\vert $ parameter of the measuring device, as the direction of the currents flowing on the sheaths of feeding cables are the same as that of the currents on the inner conductor of the measuring device. Meanwhile, choking bandwidth, efficiency and size of the ferrite-EBG composited choke structures are compared with that of EBG structures and beads. The influence of different numbers of the proposed structures is studied. A prototype is fabricated and measured. The overall size of the ferrite-EBG composited choke structures is $0.25\,\,\lambda _{\mathrm {L}} \times 0.024\,\,\lambda _{\mathrm {L}} \times 0.024\,\,\lambda _{\mathrm {L}}$ (415 mm $\times40$ mm $\times40$ mm) ( $\lambda _{\mathrm {L}}$ is the wavelength of the lower end of the operating frequency band). The measured choking band ( $\vert \text{S}_{21}\vert < -10$ dB) is in the region of 181–343 MHz.

An as-produced epoxy material reinforced with ZnO (nano)rods for outdoor use was produced for the purpose of enclosing VHF/early UHF transceiving elements. Three different ZnO (nano)rod percentages were dispersed (0.1 wt%, 0.5 wt% and 2 wt%) in epoxy samples and were consequently exposed to an artificial weathering environment for a total period of 2880 h. SEM and XRD characterizations were followed by gravimetric, colorimetric and dielectric measurements that were conducted every 576-h AWE treatment intervals and were complemented by FTIR, UV-Vis, contact angle and gloss measurements. The composite exhibited favourable dielectric behaviour: ZnO presence inflicted minimal impact to the composites’ loss tangent, while dielectric permittivity was reduced for low ZnO content (0.1 wt%/0.5 wt%), especially until the 1152-h interval, while it suffered an increase for 2 wt% samples that was maintained from the beginning until the end of the experiment. Hence, the low-k (4–5.2) constructed material, compared to bare epoxy resin, maintained moderate loss tangent levels (0.55–0.7) in the VHF/early UHF spectrum, throughout the full AWE treatment, and also attained reduced dielectric permittivity, thus exhibiting moderate radio frequency transparency, together with enhanced endurance against environmental fatigue.

This paper investigates the effect of number and shape of membership function (MF) and training data size on the performance of ANFIS model for predicting path losses in the VHF and UHF bands in built-up environments. Path loss propagation measurements were conducted in four cities of Nigeria over the cellular and broadcasting frequencies. A total of 17 broadcast transmission and cellular base stations were utilized for this study. From the results obtained, it can be concluded for the broadcasting bandsthat the generalized bell MF shows better performance with an average RMSE of 3.00 dB across all the routes, followed by gaussian, Pi, trapezoid, and triangular MFs in that order with average RMSE values of 3.09 dB, 3.11 dB, 3.16 dB, and 3.23 dB, respectively. For the cellular systems, triangular MF outperformed other MFs with the lowest average RMSE. The generalized bell MF was found to be suited for WCDMA band, while triangular MF is most suited for GSM band. Furthermore, it can also be concluded that the higher the number of membership functions, the lower the RMSE, whereas a decrease in the data size leads to a reduction in the RMSE values. The findings of this study would help researchers and network planners make a more informed decision on choosing appropriate system parameters when modeling ANFIS models for path loss prediction. [ABSTRACT FROM AUTHOR]

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The Ionospheric Continuous‐wave E region Bistatic Experimental Auroral Radar (ICEBEAR) has been reconfigured using a phase error minimization and stochastic antenna location perturbation technique. The resulting 45‐baseline sparse non‐uniform coplanar T‐shaped array, ICEBEAR‐3D, is used for aperture synthesis radar imaging of low elevation targets. The reconfigured receiver antenna array now has a field of view ±45° azimuth and 0°–45° elevation at 0.1° angular resolution. Within this field of view no aliasing occurs. Radar targets are imaged using the Suppressed Spherical Wave Harmonic Transform (Suppressed‐SWHT) technique. This imaging method uses precalculated constant coefficient matrices to solve the integral transform from visibility to brightness through direct matrix multiplication. The method then suppresses image artefacts (dirty beam) due to undersampling by combining brightness maps of differing harmonic order. Measuring elevation angles of targets at low elevations with radar interferometers has been a long standing problem. ICEBEAR‐3D elucidates the underlying misinterpretations of the conventional geometry for vertical interferometry especially for low elevation angles. The proper phase reference vertical interferometry geometry is given which allows radar interferometers to unambiguously measure elevation angles from zenith to horizon without special calibration. The receiver antenna array reconfiguration, Suppressed‐SWHT imaging technique, and proper geometry for vertical interferometry are validated by showing agreement of the meteor trail altitude distribution with numerous data sets from other radars. Key Points: Ionospheric Continuous‐wave E region Bistatic Experimental Auroral Radar receiver antenna array reconfiguration design based on a phase error minimization techniqueAperture synthesis imaging using the Suppressed Spherical Wave Harmonic Transform (Suppressed‐SHWT)Application of the proper geometry for vertical interferometry resolves low elevation angles unambiguously [ABSTRACT FROM AUTHOR]

To further explore the machining characteristics of very high-frequency micro-electrical discharge machining (VHF micro-EDM), the range of radio frequency (RF) power amplifier was expanded to 110 MHz, and the power of the RF power amplifier was also greatly increased up to 91 W. The principle of the VHF pulse generator was discussed in detail, and an electro-thermal model suitable for VHF micro-EDM was established to determine the diameter of the plasma channel and the energy distribution ratio. Experimental studies for VHF micro-EDM were also carried out, and the effects of power and frequency on machining characteristics were then analyzed and discussed. The results show that at the same frequency, the higher the power is, the higher the material removal rate (MRR) and the larger the number of discharge craters. At the same power, both the MRR and the size of discharge craters first increase and then decrease with increasing frequency and peak at 65 MHz. For a copper workpiece, when the frequency is 110 MHz and the total power of the power amplifier is 8.0 W, 5.6% of the energy is used for the material removal of the workpiece and the finest processing surface is obtained with the surface roughness Ra = 12 nm. The average diameter of the discharge craters is as small as 0.268 μm, and the diameter of the plasma channel is only 0.350 μm. In addition, the effects of different workpiece materials and dielectric fluids are also analyzed in this paper. [ABSTRACT FROM AUTHOR]

Copyright of Przegląd Elektrotechniczny is the property of Przeglad Elektrotechniczny and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The first true common volume observations of the PMSE source region with 4 radars are presented in this paper. Radar frequencies of 8, 56, 224, and 930 MHz are used in this study. Three days of experimental observations at EISCAT are presented. Numerical simulations of mesospheric dusty/ice plasma associated with the observed radar frequencies are presented. The effect of neutral air turbulence on the generation and strength of plasma density perturbations associated with PMSE using four radar frequencies and in the presence of various dust parameters is investigated. Using the model it is shown that the well‐known neutral air turbulence in the presence of heavy dust particles and neutral air turbulence combined with dust density (dusty turbulence) can largely explain the observed radar cross‐section at four radar frequencies. The effect of neutral air turbulence amplitude along with dust charging and diffusion in the presence of various dust parameters is investigated using the computational model. Specifically, the response of diffusion to charging time scales, plasma density fluctuation amplitude and background dusty plasma parameters are discussed. Several key parameters in the dusty plasma responsible for the PMSE observations are determined. Qualitative comparison of radar echo strength at 4 frequencies with numerical results is provided. Unlike the previous studies that required large dust particles of 20 nm for PMSE formation, the present work demonstrates the possibility of small dust particles to explain the experimental observations. Key Points: The first simultaneous four radar frequency observation of the PMSE is presentedThe computational results and observations validate the fossil theory proposed to 14 produce the PMSEThe effect of initial turbulence amplitude along with dust charging and diffusion 16 in the presence of various dust parameters is investigated for the first time [ABSTRACT FROM AUTHOR]

This paper presents simulation-based design and analysis of a broadband dual-polarized magnetoelectric dipole antenna element that can be used to construct VHF astronomical antenna arrays. The antenna consists of two pairs of radiating structures, each fed by a G-shaped feeding section. The feeding section and radiating parts are physically disconnected from each other. The antenna is evaluated by simulation, and its-10 dB impedance matching bandwidth ranges from 115 to 340 MHz. The maximum gain of the antenna is about 8 dB over the operating range. Isolation of about 20 dB is observed between the two input ports. [ABSTRACT FROM AUTHOR]

In practical applications, system time delay (STD) of a VHF lightning mapping system, resulting from system manufacturing, installation, site differences, and signal channel inconsistency etc., is unavoidable and will affect the localization accuracy of the direction finding algorithm. In this article, a multiantenna VHF radiation continuous observation system (MARCOS) consisting of 7 channels is used as an example to make a quantitative analysis for the relationship between STD and localization error. The array is in an “L” shape, with a 9 m baseline. And its STD is obtained through actual measurement, using sweep-frequency method. The analysis results show that STD reduces the localization accuracy significantly. Especially, emissions with lower elevation are more vulnerable to STD. In order to correct localization error caused by STD, we utilize the actual measured STD of MARCOS to correct the error during the implementation of the algorithm. Field experiments are designed to verify the effectiveness of this correction method, with an unmanned aerial vehicle (UAV) and a portable radiation source. For MARCOS used in this article, the UAV experimental results show that the error caused by STD exceeds at least 2°, and even worse for the low elevation. However, after the STD is compensated, the localization error is alleviated within 1°. Finally, STD correction is applied to a triggered lightning data. Comparisons and analyses of the results are presented before and after STD compensation. [ABSTRACT FROM AUTHOR]

Copyright of Baghdad Science Journal is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The main issue to tune controlled devices by the application of a DC magnetic field comes up against the high value of the field’s intensity required for their implementation. This work presents an implementation of magneto-dielectric materials (MDM) specifically manufactured for their integration in antenna devices operating in VHF band. The twofold objective is: (i) reduction in antenna size, (ii) frequency tuning of the antenna using a low intensity magnetic control. A notable permeability variation of MDM samples is observed when the symmetry of the lines of the control field, with an intensity less than 10 Oe, is consistent with the one of the structures in the magnetic domains. The MDM allows a miniaturization of 20% of an inverted-F antenna (IFA) antenna structure, and an agility of about 2.5% for a control field of 1.5 Oe.