Frequency Interference Research Articles

EZOA: Nançay Hi follow-up observations in the Zone of Avoidance

We present follow-up 21cm line observations made with the Radio Telescope (NRT) of 99 weak or potential detections of galaxies from the EZOA catalogue in the northern Zone of Avoidance (ZoA), which were extracted from the shallow version of the EBHIS blind survey performed with the Effelsberg radio telescope. The new NRT observations are on average almost three times as sensitive as those from EBHIS. Of the 99 observed sources, we confirmed 72, while three yielded inconclusive results. We find that the quality assessment of the EZOA catalogue entries correlates well with the NRT recovery rate; for instance, only four of the 22 potential detections could be confirmed. Due to the higher sensitivity as well as the large north-south extent of the NRT beam, the NRT observations also yielded five serendipitous detections, which we include here. We updated the EZOA catalogue with the improved parameters and detections. To test the mitigation of radio frequency interference signals we also observed selected sources using a dedicated receiver and data processing system.

COSMIC’s Large-scale Search for Technosignatures during the VLA Sky Survey: Survey Description and First Results

Abstract Developing algorithms to search through data efficiently is a challenging part of searching for signs of technology beyond our solar system. We have built a digital signal processing system and computer cluster on the backend of the Karl G. Jansky Very Large Array (VLA) in New Mexico in order to search for signals throughout the Galaxy consistent with our understanding of artificial radio emissions. In our first paper, we described the system design and software pipelines. In this paper, we describe a postprocessing pipeline to identify persistent sources of interference, filter out false positives, and search for signals not immediately identifiable as anthropogenic radio frequency interference during the VLA Sky Survey. As of 2024 September 1, the Commensal Open-source Multi-mode Interferometric Cluster had observed more than 950,000 unique pointings. This paper presents the strategy we employ when commensally observing during the VLA Sky Survey and a postprocessing strategy for the data collected during the survey. To test this postprocessing pipeline, we searched toward 511 stars from the Gaia catalog with coherent beams. This represents about 30 minutes of observation during the VLA Sky Survey, where we typically observe about 2000 sources hr–1 in the coherent beamforming mode. We did not detect any unidentifiable signals, setting isotropic power limits ranging from 1011 to 1016 W.

RFSoC receiver calibration system for 21-cm global spectrum experiments from space: The CosmoCube case

Abstract The CosmoCube project plans to deploy a global 21-cm spectrometer with 10-100 MHz observation band in a lunar orbit. The farside part of such an orbit, i.e. the part of orbit behind the Moon, offers an ideal site for accurately measuring the 21-cm signal from the Dark Ages, Cosmic Dawn and Epoch of Reionization, as the effects of the Earth’s ionosphere, artificial radio frequency interference (RFI), and complex terrain and soil are all avoided. Given the limitations of a satellite platform, we propose a receiver calibration system design based on a Radio Frequency system-on-chip, consisting of a Vector Network Analyzer (VNA) sub-system, and a source switching sub-system. We introduce the measurement principle of the VNA, and discuss the effect of quantization error. The accuracy, stability and trajectory noise of the VNA are tested in laboratory experiments. We also present the design of the source-switching sub-system, generating mock datasets, showing that the imperfect return loss, insertion loss, and isolation of surface-mounted microwave switches have a minimal effect on the sky foreground fitting residuals, which are within ±10 mK under optimal fitting condition. When all possible measurement errors in reflection coefficients and physical temperatures are taken into account, the foreground fitting residuals for the 50-90 MHz part of the spectrum remain around ±20 mK.

Impacts and Statistical Mitigation of Missing Data on the 21 cm Power Spectrum: A Case Study with the Hydrogen Epoch of Reionization Array

Abstract The precise characterization and mitigation of systematic effects is one of the biggest roadblocks impeding the detection of the fluctuations of cosmological 21 cm signals. Missing data in radio cosmological experiments, often due to radio frequency interference (RFI), pose a particular challenge to power spectrum analysis as this could lead to the ringing of bright foreground modes in the Fourier space, heavily contaminating the cosmological signals. Here we show that the problem of missing data becomes even more arduous in the presence of systematic effects. Using a realistic numerical simulation, we demonstrate that partially flagged data combined with systematic effects can introduce significant foreground ringing. We show that such an effect can be mitigated through inpainting the missing data. We present a rigorous statistical framework that incorporates the process of inpainting missing data into a quadratic estimator of the 21 cm power spectrum. Under this framework, the uncertainties associated with our inpainting method and its impact on power spectrum statistics can be understood. These results are applied to the latest Phase II observations taken by the Hydrogen Epoch of Reionization Array, forming a crucial component in power spectrum analyses as we move toward detecting 21 cm signals in the ever more noisy RFI environment.

Analysis on dynamic characteristics and control strategy of medium structure network converter in new energy medium voltage flexible interconnection project

Abstract In view of the possible voltage and current overshoot problems in the process of new energy grid connection, the dynamic characteristics analysis and control strategy of the network converter in the new medium voltage flexible interconnection project are proposed. Firstly, a synchronous control strategy based on voltage phase and amplitude compensation is proposed. Then, based on the characteristics of new AC-DC hybrid distribution network, the new energy medium voltage flexible interconnection network is analyzed. The simulation experiment reveals the dynamic response characteristics of the new energy grid converter under frequency interference and load change.

Addressing Distribution Discrepancies in Pulsar Candidate Identification via Bayesian-neural-network-based Multimodal Incremental Learning

Abstract With the advancement of astronomical observation technology and the substantial increase in data volume, traditional methods for pulsar identification are increasingly challenged by the dynamic nature of data distributions. To address this, our study introduces a multimodal incremental learning approach utilizing Bayesian neural networks. This method enables the model to adapt to new data distributions while preserving the knowledge of previous data. In our experiments, we utilized pulsar data sets from two telescopes and compared our new method with traditional techniques. The research results demonstrate that our method performs comparably to traditional methods across all evaluation metrics, while showing a significant improvement in handling data distribution discrepancy, with the F1-score increasing from approximately 70% to over 95%. Specifically, our model achieved an accuracy of 97.93%, a recall of 96.13%, and an F1-score of 97.02% under conditions of distributional disparities. These findings not only confirm the model's capability to adapt to dynamic data environments but also effectively address the challenges of data distribution discrepancy, significantly enhancing the predictive accuracy of pulsar identification in the context of evolving and variable radio frequency interference environments.

Searching for short-timescale radio anomalies using nonlinear dimensionality reduction techniques

Abstract We have searched for anomalous events using 2,520 hours of archival observations from Murriyang, CSIRO’s Parkes radio telescope. These observations were originally undertaken to search for pulsars. We used a machine-learning algorithm based on ResNet and Uniform Manifold Approximation and Projection (UMAP) in order to identify parts of the data stream that potentially contain anomalous signals. Many of these anomalous events are radio frequency interference, which were subsequently filtered using multibeam information. We detected 202 anomalous events and provide their positions and event times. Our results show that the UMAP unsupervised machine learning pipeline effectively identifies anomalous signals in high-time-resolution datasets, highlighting its potential for use in future surveys. However, the pipeline is not applicable for standard searches for dispersed single pulses. We classify the detected events and, in particular, we are currently unable to determine the possible origin of events that last multiple seconds. For these we encourage follow-up observations.

Performance of the segment anything model in various RFI/events detection in radio astronomy

Abstract The emerging era of big data in radio astronomy demands more efficient and higher-quality processing of observational data. While deep learning methods have been applied to tasks such as automatic radio frequency interference (RFI) detection, these methods often face limitations, including dependence on training data and poor generalisation, which are also common issues in other deep learning applications within astronomy. In this study, we investigate the use of the open-source image recognition and segmentation model, Segment Anything Model (SAM), and its optimised version, HQ-SAM, due to their impressive generalisation capabilities. We evaluate these models across various tasks, including RFI detection and solar radio burst (SRB) identification. For RFI detection, HQ-SAM (SAM) shows performance that is comparable to or even superior to the SumThreshold method, especially with large-area broadband RFI data. In the search for SRBs, HQ-SAM demonstrates strong recognition abilities for Type II and Type III bursts. Overall, with its impressive generalisation capability, SAM (HQ-SAM) can be a promising candidate for further optimisation and application in RFI and event detection tasks in radio astronomy.

Handling class imbalance of radio frequency interference in deep learning-based fast radio burst search pipelines using a deep convolutional generative adversarial network

Handling class imbalance of radio frequency interference in deep learning-based fast radio burst search pipelines using a deep convolutional generative adversarial network

On-chip power efficient MHz to GHz tunable Brillouin microwave photonic filters

Stimulated Brillouin scattering (SBS) offers optically tunable, narrowband gain and loss resonances, which makes it ideal for optical filtering and signal processing applications. However, broadband filters utilizing Brillouin scattering typically necessitate multiple pump sources or linear frequency modulated waveforms, which necessitate the use of overall high pump powers to achieve broadband and multi-band filter configurations. To overcome the trade-off between bandwidth and power consumption, we introduce an on-chip broadband bandpass filter scheme leveraging the SBS response and the concept of radio frequency interference. We present the MHz to GHz reconfigurable microwave photonic filters on a chip. The bandwidth is tunable from 30 MHz to 1.2 GHz at a total pump power of only 15 dBm, corresponding to a figure of merit (maximum bandwidth/pump power) improvement of a factor of 25 compared to previously reported work. Furthermore, the filter exhibits frequency tuning capabilities ranging from 10 to 40 GHz (X to Ka-band) and can be configured from single- to multi-bandpass filter responses and switched from bandpass to bandstop.

Effects of molecular weight of chitosan on its binding ability with OSA starch and oil-water interface behavior of complex-stabilized emulsion.

This work examined the effects of molecular weight (2-15 kDa) and concentration (10-30 mg/mL) of chitosan (CTS) on the binding capacity and interface behavior between octenyl succinic acid sodium starch (OSS) and CTS, as well as their effects on the storage stability of emulsions. The results of the isothermal calorimetry titration demonstrated that OSS and CTS were complexed by electrostatic interaction and spontaneous hydrogen bonding driven by enthalpy (ΔH from -3931 to -7983 cal/mol, ΔS from -38.5 to -49.2 cal/mol/deg., ΔG from -6436.6 to -7542.0 cal/mol), and the affinity and binding capacity (N = 2.83-22.90 sites) were reinforced with CTS molecular weight. The interfacial adsorption kinetics revealed that the OSS/CTS complexes with high-molecular-weight CTS exhibited a markedly accelerated rate of interfacial diffusion and recombination, and rapidly reduced interfacial tension. CTS incorporation enhanced mass (1980.32-3522.56 ng/cm2), thickness (35.12-51.29 nm), viscosity (52.81-67.06 kPa), and elasticity (1.70-3.49 kPa) of interfacial film through the dissipative quartz crystal microbalance. OSS/CTS complexes displayed superior emulsification properties and adjustable interfacial viscoelastic ratio in response to frequency interference. Emulsions stabilized by the OSS/CTS complexes with high molecular weight and concentration of CTS exhibited more uniform spherical structures and superior storage stability. This work will facilitate the broader utilization of OSS and CTS in the emulsion delivery system.

Deep radio interferometric search for decametre radio emission from the exoplanet Tau Boötis b

Detection of electron cyclotron maser (ECM) emission from exoplanets in the 10-40 MHz radio band is likely the only way to measure an exoplanet's magnetic field directly. However, no definitive detection of exoplanetary ECM emission has been made to date. A detection of the hot Jupiter Tau Bo\"otis b was reported but with an observing mode that is not immune to confusion from off-axis interference, making the detection tentative. We searched for radio emissions from Tau Boötis b using the Low Frequency Array (LOFAR) in interferometric mode, which employs direction-of-arrival information to discriminate genuine signals from interference. Our aim was to confirm the previous tentative detection or establish an upper limit in the case of a non-detection. We conducted observations using LOFAR’s Low Band Antenna in interferometric mode, which totalled 64\, hours spread over 8\, nights. We created a custom data-processing pipeline to mitigate common challenges in decametric radio astronomy, including radio frequency interference, ionospheric distortions, and sidelobe noise from nearby bright radio sources. We used this pipeline to image the field around Tau Bo\"otis b, searching for both quiescent and bursting emission from the direction of Tau Bo\"otis b. Despite the high sensitivity of the interferometric observations and extensive data processing, no significant emission was detected from Tau Boötis b in Stokes V. We establish an upper limit of 2 sigma at 24 mJy for any continuous emission from the exoplanet. The previous tentative detection of 400 mJy is thus not confirmed by the interferometric observations. The previous tentative detection is unlikely to be a bona fide astrophysical signal. Our upper limit is lower than the flux density predicted by scaling laws, meaning either the scaling laws need to be revised or the emission from this particular system is beamed away from Earth.

Determining orientation using the earth's magnetic field

The structure and capabilities of the orientation device that uses the gravity vector and the Earth's magnetic field are considered. The device consists of three accelerometers and three magnetometrs, which are rigidly installed on the movable object. The possible characteristics of these sensitive elements, as well as the parameters of gravity and induction at a given point of the Earth (for example in Kiev). It are also shown the characteristics of devices AHRS. There are two algorithms for determining the magnetic course on the designated pitch and rolls: the algorithm of the triad and the Odintsov algorithm. Modeling shows that with relatively rough sensitive elements (accelerometers with an error more than 10 -2 m/s 2 , magnetometers with an error of more than 100 nT) it is advisable to use the triad method. With more accurate sensitive elements, the Odintsov method works better. When evaluating the characteristics, the systematic errors of the devices are taken into account, keeping in mind that noise interference are well filtered. Possible low - frequency interference when moving on the rough surface is not considered. The budget of errors for determining the true geographical course, which includes: errors of the сalculation of characteristics of the Earth's magnetic field parameters, magnetic deviation errors, seasonal and diligent variations of magnetic deviation, errors of magnetometers and accelerometers, as well as errors of algorithms.

Adaptive Ramanujan package decomposition method: a novel precise health indicator of rolling bearings

ABSTRACT In this paper, an adaptive Ramanujan packet decomposition (ARPD) method based on precise envelope segmentation is proposed to improve the accuracy of weak fault feature extraction and realise early non-destructive testing and condition evaluation of rolling bearings. Firstly, the power spectral density of the original signal is envelope-processed by accurate envelope segmentation method, so as to reduce the extreme points produced by interference frequency, and then realise the optimal frequency band division and reduce the influence of noise components. Secondly, the Ramanujan spectrum signal-to-noise ratio (RSSNR) index is introduced to quantify the fault characteristic information of the corresponding component in each frequency band. The largest component of the index is selected as the optimal mode, and the current number of layers is defined as the optimal number of modes. Finally, through the idea of iterative decomposition and RSSNR index, the problem that the optimal mode number is difficult to determine accurately is eliminated, and the optimal mode number is determined adaptively. The results of simulation and experimental signal analysis show that ARPD method can accurately divide the frequency bands and has excellent weak fault feature extraction ability, so it is an effective early non-destructive testing and condition evaluation method for rolling bearings.

Resource-Efficient FPGA Architecture for Real-Time RFI Mitigation in Interferometric Radiometers.

Interferometric radiometers operating at L-band, such as ESA's SMOS mission, enable crucial Earth observations providing high-resolution measurements of soil moisture, ocean salinity, and other geophysical parameters. However, the increasing electromagnetic spectrum utilization has led to significant Radio Frequency Interference (RFI) challenges, particularly critical given the sensors' fine temperature resolution requirements of less than 1 K. This work presents the hardware implementation of an advanced RFI detection and mitigation algorithm specifically designed for interferometric radiometers, targeting future L-band missions. The implementation processes 1-bit quantized signals at 57.69375 MHz from multiple receivers, employing time-frequency analysis and polarimetric detection techniques while optimizing Field Programmable Gate Array (FPGA) resource utilization. Novel optimization strategies include overclocked processing cores operating at 230.775 MHz, efficient resource sharing through operation serialization, and strategic memory management. The system achieves real-time processing capabilities while maintaining detection probabilities above 63% with false alarm rates below 1% for typical interference scenarios. Performance validation using synthetic datasets demonstrates robust operation across various RFI conditions, making this implementation suitable as part of the RFI detection and mitigation efforts for future interferometric radiometer missions beyond SMOS.

The costs of shifting from dual-task to single-task processing: Applying the fade-out paradigm to dual tasking.

Cognitive control processes mirror fast and dynamic adaptation toward a change in the environment. When performing dual tasks, mental representations of dual-task-specific control requirements and the task-pair set are established that help to manage dual-task processing (Hirsch et al., 2017, 2018; Hommel, 2004, 2020). In the present study, we investigated to which extent such higher order representations of dual-task processing persist even if major characteristics of the task context change, for example, if one of the tasks of a dual task becomes irrelevant. For this, we adapted the fade-out paradigm (Mayr & Liebscher, 2001) to a dual-task setting and tested whether fade-out costs appear. Performance of pure Task 1 single tasking was compared to the performance of Task 1 processing right after dual-task trials (fade-out phase). Results showed that performance in this fade-out block did not immediately drop to single-task performance (fade-out costs), indicating the persistence of task-pair set representations (Experiments 1 and 3, N = 40 each). In addition, automatic stimulus-response translation processes continued within the fade-out phase, resulting in ongoing between-task interference. Furthermore, the frequency of between-task interference in dual-task blocks was manipulated (75% vs. 25% incongruence) between participants to establish conflict-biased control states of increased versus relaxed task shielding. These different control states, however, did not modulate fade-out costs (Experiment 2, N = 80). Nevertheless, the persistence of these control adaptations was reflected in manipulation-dependent between-task interference during fade-out trials. Implications of this new evidence are discussed. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

3D-printed OAM beam generator with an enhanced out-of-band gain filtering characteristic

In this paper, a 3D-printed orbital angular momentum (OAM) beam generator is proposed with integrated gain-filtering characteristics. The proposed design is composed of an integrated all-resonator 1-to-8 filtering power divider, eight-phase delay lines with twisted waveguides, and an eight-horn circular array. Unlike conventional fabrication methods, the proposed OAM generator is monolithically fabricated using selective laser melting (SLM) 3D-printing technology. Experimental results demonstrate that the proposed design achieves OAM beams with mode number l =+1 and a mode purity of around 80%. Additionally, it exhibits a gain-filtering response with out-of-band suppression levels exceeding 30 dB in the main beam directions. The air-filled all-metal structure allows the OAM beam generator to achieve a maximum total efficiency of over 80%. The proposed OAM generator with gain filtering response not only enhances channel capacity but also helps to avoid adjacent frequency interference, demonstrating great potential in millimeter-wave (mm-Wave) wireless systems.

The legal regime of quantum communication lines in free space

The article discusses the features of regulating communication in free space as a key technology for quantum communication. An analysis of domestic and foreign experience in regulating this technology has been conducted, which has made it possible to highlight the advantages and disadvantages of its legal regime compared to other types of communication. It has been proved that communication via free space has advantages over wired communication since it does not require using other people’s land or establishing an easement as there is no need for a wire to create an atmospheric communication channel, while at the same time it is impossible to establish a security zone around atmospheric communication lines to protect wired communication lines from construction on them. It has been proved that communication in free space has advantages over radio frequency communication, as it does not require obtaining a permit/license for the use of radio frequencies. However, atmospheric communication lines do not have legal protection against technical interference. In order to improve the legal regime for quantum communication lines in free space, it has been proposed to eliminate terminological ambiguity in regulatory legal acts, define atmospheric optical communication as a special legal entity requiring equal protection with other communication channels, include atmospheric optical quantum communications in the security zone system for communication lines and structures, and establish administrative liability for interference with laser communications analogous to radio frequency interference.

The Impact and Sources of Radio Frequency Interference on GNSS Signals

AbstractThe utilization of the global navigation satellite systems (GNSS) services in both military and civilian applications as well as for scientific investigation has grown exponentially. However, the increasing reliance on GNSS applications has raised concerns about potential risks from intentional radio frequency interference (RFI) transmitters. RFI significantly affects GNSS's environmental monitoring capabilities by inflating the scintillation index and misleading the scientific community with scintillation indices not attributable to ionospheric dynamic events. Consequently, the existing climatological distribution of GNSS scintillations may require careful reevaluation, as it may not adequately filter out RFI induced scintillations. Thus, characterizing the global RFI occurrence regions and developing real‐time detection capabilities to mitigate its effects is critically important. Leveraging GNSS measurements from ground stations and six COSMIC‐2 satellite constellations, we have developed a technique to detect RFI events and identify RFI active regions. Additionally, for the first time, we have implemented techniques that differentiate RFI associated scintillations from scintillations caused by ionospheric turbulence.

Fault Feature Extraction Based on Variational Modal Decomposition and Lifting Wavelet Transform: Application in Gear of Mine Scraper Conveyor Gearbox

Vibration-based fault diagnosis of chain conveyor gearboxes is challenging under high load and strong shock conditions. This paper applies motor current characteristic analysis technology to scraper conveyor gearbox fault diagnosis and proposes a fault feature extraction method. Firstly, a variational mode decomposition algorithm combined with a genetic algorithm is used to divide the original current signal into several sub-bands with different frequency modulation information, and irrelevant information is preliminarily eliminated. Secondly, an intrinsic mode function (IMF) sub-band fault information extraction method based on lifting wavelet transform is proposed. The minimum entropy value is used to set the sensitive parameters involved in lifting wavelet transform, and the power supply current frequency and noise interference information of a scraper conveyor are removed from the current signal. Finally, it is proved that variational mode decomposition combined with lifting wavelet transform can effectively diagnose the fault of a scraper conveyor by comparative experiments.