Mitigation of Non-Narrowband Radio Frequency Interference Incorporating Array Imperfections

2019 ◽  
Vol 08 (01) ◽  
pp. 1940013
Author(s):  
Jan-Willem W. Steeb ◽  
David B. Davidson ◽  
Stefan J. Wijnholds
Keyword(s):  
Radio Frequency ◽  
Software Defined Radio ◽  
Mutual Coupling ◽  
Low Frequency ◽  
Radio Frequency Interference ◽  
Digital Audio ◽  
Signal Model ◽  
Narrowband Signal ◽  
Calibration Step ◽  
High Band

In a recent paper, we presented a non-narrowband spatial radio frequency interference (RFI) mitigation algorithm for radio astronomy arrays. The algorithm constructs a 2nd-order filter by combining a 1st-order subspace subtraction method with a non-narrowband signal model. The model is based on the assumption that the frequency response is approximately flat and that the array is calibrated. In this paper, we consider the effects of array imperfections such as unknown complex gains and mutual coupling, incorporate these into the non-narrowband signal model and extend the RFI mitigation algorithm to include a calibration step. With a calibration step and no mutual coupling, the proposed algorithm was able to process twice the bandwidth per channel when compared to conventional narrowband techniques. This performance declines to 1.6 times greater bandwidth when the effect of mutual coupling is included. The evaluation of the algorithm was done using the layout of a Low Frequency Array (LOFAR) High Band Antenna (HBA) station and a digital audio broadcast recorded with a software defined radio.

Low-frequency technology for a lunar interferometer

2020 ◽  
Vol 379 (2188) ◽  
pp. 20190575 ◽  
Author(s):  
Kristian Zarb Adami ◽  
I. O. Farhat
Keyword(s):  
Radio Frequency ◽  
Signal Detection ◽  
Radio Astronomy ◽  
Lunar Surface ◽  
Low Frequency ◽  
Radio Interferometer ◽  
Radio Frequency Interference ◽  
The Moon ◽  
Single Antenna ◽  
Global Signal

This work sketches a possible design architecture of a low-frequency radio interferometer located on the lunar surface. The design has evolved from single antenna experiments aimed at the global signal detection of the epoch of reionization (EoR) to the square kilometre array (SKA) which, when complete, will be capable of imaging the highly red-shifted H 1 -signal from the cosmic dawn through to the EoR. However, due to the opacity of the ionosphere below 10 MHz and the anthropogenic radio-frequency interference, these terrestrial facilities are incapable of detecting pre-ionization signals and the moon becomes an attractive location to build a low-frequency radio interferometer capable of detecting such cosmological signals. Even though there are enormous engineering challenges to overcome, having this scientific facility on the lunar surface also opens up several new exciting possibilities for low-frequency radio astronomy. This article is part of a discussion meeting issue ‘Astronomy from the Moon: the next decades’.

scholarly journals A New Restoration Method for Radio Frequency Interference Effects on AMSR-2 over North America

2019 ◽  
Vol 11 (24) ◽  
pp. 2917 ◽  
Author(s):  
Wangbin Shen ◽  
Zhengkun Qin ◽  
Zhaohui Lin
Keyword(s):  
Radio Frequency ◽  
Land Surface ◽  
Interpolation Method ◽  
Low Frequency ◽  
Principal Component ◽  
New Method ◽  
Radio Frequency Interference ◽  
Data Restoration ◽  
Order Of Magnitude ◽  
Restoration Method

Observations from spaceborne microwave imagers are important sources of land surface information. However, the low-frequency channels of microwave imagers are easily interfered with by active radio signals with similar frequencies. Radio frequency interference (RFI) signals are widely distributed because of the lack of frequency protection, which seriously hinders the application of microwave imager data in data assimilation and retrieval research. In this paper, a new data restoration method is proposed based on principal component analysis (PCA). Both the ideal and real reconstruction experiments show that the new method can effectively repair abnormal observations interfered by RFI compared with the commonly used Cressman interpolation method because observation information over the whole selected domain is used for restoration in the new method, whereas Cressman interpolation uses only a selection of data around the target observation. The observation errors in the data with RFI can be reduced by one order of magnitude by means of the new method and little artificial information is introduced. One-week restoration validation also proves that the new method has a stable accuracy and broad application prospects.

scholarly journals A survey of spatially and temporally resolved radio frequency interference in the FM band at the Murchison Radio-astronomy Observatory

2020 ◽  
Vol 37 ◽  
Author(s):  
S. J. Tingay ◽  
M. Sokolowski ◽  
R. Wayth ◽  
D. Ung
Keyword(s):  
Radio Frequency ◽  
Radio Astronomy ◽  
Angular Resolution ◽  
Low Frequency ◽  
Earth Orbit ◽  
Radio Frequency Interference ◽  
Astronomy Observatory ◽  
Frequency Range ◽  
Radio Astronomy Observatory ◽  
Imaging Mode

Abstract We present the first survey of radio frequency interference (RFI) at the future site of the low frequency Square Kilometre Array (SKA), the Murchison Radio-astronomy Observatory (MRO), that both temporally and spatially resolves the RFI. The survey is conducted in a 1 MHz frequency range within the FM band, designed to encompass the closest and strongest FM transmitters to the MRO (located in Geraldton, approximately 300 km distant). Conducted over approximately three days using the second iteration of the Engineering Development Array in an all-sky imaging mode, we find a range of RFI signals. We are able to categorise the signals into: those received directly from the transmitters, from their horizon locations; reflections from aircraft (occupying approximately 13% of the observation duration); reflections from objects in Earth orbit; and reflections from meteor ionisation trails. In total, we analyse 33 994 images at 7.92 s time resolution in both polarisations with angular resolution of approximately 3.5 $^{\circ}$ , detecting approximately forty thousand RFI events. This detailed breakdown of RFI in the MRO environment will enable future detailed analyses of the likely impacts of RFI on key science at low radio frequencies with the SKA.

scholarly journals A Radio Frequency Magnetoelectric Antenna Prototyping Platform for Neural Activity Monitoring Devices with Sensing and Energy Harvesting Capabilities

Electronics ◽  
2020 ◽  
Vol 9 (12) ◽  
pp. 2123
Author(s):  
Diptashree Das ◽  
Mehdi Nasrollahpour ◽  
Ziyue Xu ◽  
Mohsen Zaeimbashi ◽  
Isabel Martos-Repath ◽  
...  
Keyword(s):  
Energy Harvesting ◽  
Integrated Circuits ◽  
Radio Frequency ◽  
Software Defined Radio ◽  
Low Frequency ◽  
Software Radio ◽  
Operating Conditions ◽  
Time Signal ◽  
Modulated Signals ◽  
Wireless Energy Harvesting

This article describes the development of a radio frequency (RF) platform for electromagnetically modulated signals that makes use of a software-defined radio (SDR) to receive information from a novel magnetoelectric (ME) antenna capable of sensing low-frequency magnetic fields with ultra-low magnitudes. The platform is employed as part of research and development to utilize miniaturized ME antennas and integrated circuits for neural recording with wireless implantable devices. To prototype the reception of electromagnetically modulated signals from a sensor, a versatile Universal Software Radio Peripheral (USRP) and the GNU Radio toolkit are utilized to enable real-time signal processing under varying operating conditions. Furthermore, it is demonstrated how a radio frequency signal transmitted from the SDR can be captured by the ME antenna for wireless energy harvesting.

scholarly journals Comparison of the Radio Frequency Interference (RFI) in the Region of Solar Burst Type III Data at Selected CALLISTO Network

2014 ◽  
Vol 29 ◽  
pp. 38-45
Author(s):  
Zety Sharizat Hamidi ◽  
N.N.M. Shariff ◽  
C. Monstein
Keyword(s):  
Radio Frequency ◽  
Low Cost ◽  
Low Frequency ◽  
Electronic System ◽  
Specific Region ◽  
Global Network ◽  
Radio Frequency Interference ◽  
Type Iii ◽  
Solar Burst ◽  
Spectrometer System

Compact Astronomical Low-frequency, Low-cost Instrument for Spectroscopy in Transportable Observatories (CALLISTO) is a global network of spectrometer system with the purpose to observe the Sun’s activities. There are 25 stations that are used for this purpose. Radio Frequency Interference (RFI) is a major obstacle when performing observation with CALLISTO. We have confirmed at least 2 stations out of 10 stations with a complete overview spectral (OVS) made available to us showed clear detection of these consistent types of RFI for each specific region. In Malaysia, these RFI are also clearly detected. The major RFI affecting CALLISTO within radio astronomical windows below 1 GHz are local electronic system specifically radio navigation (at 73.1 MHz and 75.2 MHz), broadcasting (at (i) 151 MHz, (ii) 151.8 MHz and 152 MHz), aeronautical navigation (at (i) 245.5 MHz, (ii) 248.7 MHz and (iii) 249 MHz and fixed mobile at (i) 605 MHz, (ii) 608.3 MHz, (iii) 612.2 MHz, (iv) 613.3 MHz). It is obviously showed that all sites within this region are free from interference at 320-330 MHz and is the best specific region to be considered for solar burst monitoring. We also investigate the effect of RFI on detection of solar burst. We have considered type III solar bursts on 9th March 2012 in order to measure the percentage of RFI level during the solar burst. The RFI level is as low as 6.512% to 80.769% above solar burst detection.

scholarly journals Nonlinear Behavior of the Radio Frequency Interference (RFI) Sources at Faculty of Applied Sciences, MARA University of Technology

2014 ◽  
Vol 34 ◽  
pp. 39-47
Author(s):  
Zety Sharizat Hamidi ◽  
N.N.M. Shariff
Keyword(s):  
Applied Sciences ◽  
Radio Frequency ◽  
Low Frequency ◽  
Nonlinear Behavior ◽  
Current Status ◽  
Radio Frequency Interference ◽  
Monitoring Frequency ◽  
University Of Technology ◽  
Current Scenario ◽  
A Current

In this article, we describe and compare several sources of the nonlinear of Radio Frequency Interference (RFI) based on classification methods. It is very important to characterize and understand the nature of interference in as much of the candidate spectrum as possible. Preliminary analysis has been done in 2011. As data sizes of observations grow with new and improved solar monitoring system, the need for completely automated, robust methods for RFI mitigation is highlighted. The current status of RFI noise level is being compared at two different sites (i) indoor and (ii) outdoor. The main objective is to evaluate and find the best range of low frequency in MHz for the solar monitoring purpose. Our findings are consistent with those of previous studies. There is not much different in terms of the sources of RFI. However, the level of RFI is become increase. Based on the results, it was found that the distribution of RFI sources in indoor site is in the range from -(80-105) dBm. A strong and moderate RFI can be identified in the range of -100 dBm. The dominant sources in this region are due to the fixed mobile signal with 10 points of this signal from 1-2000 MHz. If we compare with outdoor site, the distribution of RFI sources in indoor site is in the range from -(75-105) dBm. It means that the signal of noise is larger compared with indoor site. While new sources strive to remain the increasing of RFI signal levels, numerous factors interact to influence the pattern of this noise. Reporting to the authoritative body should be made to make sure the allocation of the solar monitoring frequency region was not used by other applications. This work is a current scenario of the nonlinear RFI level at our site.

scholarly journals Protecting Space-Based Radio Astronomy

2001 ◽  
Vol 196 ◽  
pp. 324-334 ◽  
Author(s):  
V. Altunin
Keyword(s):  
Radio Frequency ◽  
Radio Astronomy ◽  
Low Frequency ◽  
Radio Frequency Interference ◽  
Lagrangian Point ◽  
Radio Telescopes ◽  
The Moon ◽  
Microwave Background ◽  
Distant Future ◽  
First Results

This paper outlines some of the radio frequency interference issues related to radio astronomy performed with space-based radio telescopes. Radio frequency interference that threatens radio astronomy observations from the surface of Earth will also degrade observations with space-based radio telescopes. However, any resulting interference could be different than for ground-based telescopes due to several factors. Space radio astronomy observations significantly enhance studies in different areas of astronomy. Several space radio astronomy experiments for studies in low-frequency radio astronomy, space VLBI, the cosmic microwave background and the submillimetre wavelengths have flown already. The first results from these missions have provided significant breakthroughs in our understanding of the nature of celestial radio radiation. Radio astronomers plan to deploy more radio telescopes in Earth orbit, in the vicinity of the L2 Sun-Earth Lagrangian point, and, in the more distant future, in the shielded zone of the Moon.

scholarly journals The Low-Frequency Environment of the Murchison Widefield Array: Radio-Frequency Interference Analysis and Mitigation

2015 ◽  
Vol 32 ◽  
Author(s):  
A. R. Offringa ◽  
R. B. Wayth ◽  
N. Hurley-Walker ◽  
D. L. Kaplan ◽  
N. Barry ◽  
...  
Keyword(s):  
Radio Frequency ◽  
Low Frequency ◽  
Digital Tv ◽  
Frequency Resolution ◽  
Interference Detection ◽  
Radio Frequency Interference ◽  
Receiver Design ◽  
Square Kilometre Array ◽  
Atmospheric Propagation ◽  
Murchison Widefield Array

AbstractThe Murchison Widefield Array is a new low-frequency interferometric radio telescope built in Western Australia at one of the locations of the future Square Kilometre Array. We describe the automated radio-frequency interference detection strategy implemented for the Murchison Widefield Array, which is based on the aoflagger platform, and present 72–231 MHz radio-frequency interference statistics from 10 observing nights. Radio-frequency interference detection removes 1.1% of the data. Radio-frequency interference from digital TV is observed 3% of the time due to occasional ionospheric or atmospheric propagation. After radio-frequency interference detection and excision, almost all data can be calibrated and imaged without further radio-frequency interference mitigation efforts, including observations within the FM and digital TV bands. The results are compared to a previously published Low-Frequency Array radio-frequency interference survey. The remote location of the Murchison Widefield Array results in a substantially cleaner radio-frequency interference environment compared to Low-Frequency Array’s radio environment, but adequate detection of radio-frequency interference is still required before data can be analysed. We include specific recommendations designed to make the Square Kilometre Array more robust to radio-frequency interference, including: the availability of sufficient computing power for radio-frequency interference detection; accounting for radio-frequency interference in the receiver design; a smooth band-pass response; and the capability of radio-frequency interference detection at high time and frequency resolution (second and kHz-scale respectively).

scholarly journals Practical Lessons from Low Frequency Imaging with the VLA

2002 ◽  
Vol 199 ◽  
pp. 455-458
Author(s):  
Christina K. Lacey ◽  
Namir E. Kassim
Keyword(s):  
Radio Frequency ◽  
Data Reduction ◽  
Low Frequency ◽  
Practical Interest ◽  
Radio Frequency Interference ◽  
Wide Field ◽  
Self Calibration ◽  
Field Imaging ◽  
Wide Field Imaging

Many lessons gained in imaging 74 and 330 MHz VLA data are of practical interest to future users of the GMRT and other low frequency observers. Three important issues are 1) radio frequency interference excision, 2) self-calibration, and 3) wide-field imaging. Recently developed tasks to address these and other problems encountered in low frequency VLA data reduction now exist or are being developed in both AIPS and AIPS++. We will describe how we use some of these new tools to routinely generate wide-field, low frequency images with sensitivities approaching thermal or classical confusion limits.

scholarly journals Investigation of Radio Frequency Interference (RFI) Profile and Determination of Potential Astronomical Radio Sources

2013 ◽  
Vol 24 ◽  
pp. 43-49
Author(s):  
Zety Sharizat Hamidi ◽  
N.N.M. Shariff
Keyword(s):  
Radio Frequency ◽  
Low Cost ◽  
Low Frequency ◽  
Astronomical Observation ◽  
Radio Frequency Interference ◽  
Analysis Process ◽  
Significant Region ◽  
Network Project

In this article, we have recognized a Radio Frequency Interference (RFI) sources that can potentially affect for radio astronomical observation. The main objective of this surveying is to test and qualify the potential of radio astronomical sources that can be observed in Malaysia generally. Analysis process focuses on the high sources that contribute the pollution and the significant region that can be considered for astronomical purpose beginning 1-2000 MHz. It was found that 13 individual sources contribute as a noise and mostly are telecommunication and radio navigation applications. We then compared of the RFI profiles based on three different periods in order to observe the variety of the signals. The main regions that still excellent to do an observation are: 13.36 -13.41 MHz (solar), (25.55-25.67) MHz (Jupiter) and (37.50-38.25) MHz (Continuum) respectively. This work is also an initiative of the International Space Weather Initiative (ISWI) project where Malaysia is one of the countries that involve in e- CALLISTO (Compound Astronomical Low Cost Low Frequency Transportable Observatory) network project. Some suggestions are recommended in order to improve the quality of the radio frequency profile.

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