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First results from the FPGA/NIOS Adaptive FIR Filter Using Linear Prediction Implemented in the AERA Radio Stations to Reduce Narrow Band RFI for Radio Detection of Cosmic Rays  [PDF]
Zbigniew Szadkowski,D. G?as,C. Timmermans,T. Wijnen for the Pierre Auger Collaboration
Physics , 2014,
Abstract: The FPGA/NIOS FIR filter based on linear prediction (LP) to suppress radio frequency interference (RFI) has been installed in several radio stations in the Auger Engineering Radio Array (AERA) experiment. AERA observes coherent radio emission from extensive air showers induced by ultra-high-energy cosmic rays to make a detailed study of the development of the electromagnetic part of air showers. Radio signals provide complementary information to that obtained from Auger surface detectors, which are predominantly sensitive to the particle content of an air shower at the surface. The radio signals from air showers are caused by the coherent emission due to geomagnetic and charge-excess processes. These emissions can be observed in the frequency band between 10 - 100 MHz. However, this frequency range is significantly contaminated by narrow-band RFI and other human-made distortions. A FIR filter implemented in the FPGA logic segment of the front-end electronics of a radio sensor significantly improves the signal-to-noise ratio. In this paper we present first results of the efficiency of the adaptive LP FIR filter, deployed in real AERA station on pampas, with a comparison to the currently used IIR notch filter with constant coefficients. The laboratory tests confirms the stability of the filter. Using constant LP coefficients the suppression efficiency remains the same for hours, which corresponds to more than $\bf 10^{12}$ clock cycles. We compared in real conditions several variants of the LP FIR filter with various lengths and various coefficients widths (due to fixed-point representations in the FPGA logic) with the aim to minimize the power consumption for the radio station while keeping sufficient accuracy for noise reduction.
A new technique to improve RFI suppression in radio interferometers  [PDF]
D. Anish Roshi,R. A. Perley
Physics , 2003,
Abstract: Radio interferometric observations are less susceptible to radio frequency interference (RFI) than single dish observations. This is primarily due to : (1)fringe-frequency averaging at the correlator output and (2) bandwidth decorrelation of broadband RFI. Here, we propose a new technique to improve RFI suppression of interferometers by replacing the fringe-frequency averaging process with a different filtering process. In the digital implementation of the correlator, such a filter should have cutoff frequencies $< 10^{-6}$ times the frequency at which the baseband signals are sampled. We show that filters with such cutoff frequencies and attenuation $>$ 40 dB at frequencies above the cutoff frequency can be realized using multirate filtering techniques. Simulation of a two element interferometer system with correlator using multirate filters shows that the RFI suppression at the output of the correlator can be improved by 40 dB or more compared to correlators using a simple averaging process.
Design of UWB Filter with WLAN Notch
Harish Kumar,MD. Upadhayay
International Journal of Antennas and Propagation , 2012, DOI: 10.1155/2012/971097
Abstract: UWB technology- (operating in broad frequency range of 3.1–10.6 GHz) based filter with WLAN notch has shown great achievement for high-speed wireless communications. To satisfy the UWB system requirements, a band pass filter with a broad pass band width, low insertion loss, and high stop-band suppression are needed. UWB filter with wireless local area network (WLAN) notch at 5.6 GHz and 3 dB fractional bandwidth of 109.5% using a microstrip structure is presented. Initially a two-transmission-pole UWB band pass filter in the frequency range 3.1–10.6 GHz is achieved by designing a parallel-coupled microstrip line with defective ground plane structure using GML 1000 substrate with specifications: dielectric constant 3.2 and thickness 0.762 mm at centre frequency 6.85 GHz. In this structure a λ/4 open-circuited stub is introduced to achieve the notch at 5.6 GHz to avoid the interference with WLAN frequency which lies in the desired UWB band. The design structure was simulated on electromagnetic circuit simulation software and fabricated by microwave integrated circuit technique. The measured VNA results show the close agreement with simulated results.
International Journal of Engineering Science and Technology , 2011,
Abstract: The design of analog filters at low frequencies is not possible because the size of inductors becomes very large. In such cases, the simulated inductors using operational amplifiers are used. This paper deals with the implementation of notch filter using band pass filter which uses simulated inductor where the direct implementation of notch filter using simulated inductor is not possible because of floating inductor. The design of notch filter and the simulation done in PSPICE is presented.
Random RFI Suppression in Impulse Radar

Li Yu,Su Yi,Huang Chun-lin,Gao Shou-chuan,

电子与信息学报 , 2004,
Abstract: Based on the study on the features and characteristics of random Radio Frequency Interference (RFI) in impulse radar, this paper firstly analyzes the RFI supperession in Ultra Wide Band(UWB) time domain receivers. Taking Mean Square Error (MSE) as principle, the wave-average filtering and the median filtering methods of random RFI suppression are raised. The performance of the two methods is demonstrated on data collected from impulse radar and the experimental results also show their consistence.
Notch Filtering Suitable for Real Time Removal of Power Line Interference
P. Zahradnik,M. Vlcek
Radioengineering , 2013,
Abstract: This paper presents a high performance notch filtering for real time suppression of power line interference in a general signal. The disturbing signal is suppressed using an optimal notch FIR filter with tunable notch frequency. The tuning of the filter preserves its selectivity, most importantly the specified attenuation at the notch frequency. One example and two Matlab functions demonstrate the performance, robustness and usefulness of the proposed procedure for the design and tuning of optimal notch FIR filters suitable in the real time notch filtering.
Researching on Random Phase-Coded to Suppress RFI in SFGPR

Li Ting-jun,Kong Ling-jiang,Zhou Zheng-ou,

电子与信息学报 , 2009,
Abstract: The Radio Frequency Interference(RFI) makes the most performance degradation for the Synthetic Aperture Imaging(SAI) and the object detection of Stepped-Frequency Ground Penetrating Radar(SFGPR).This paper proposes a random phase-coded method to transform RFI into zero-mean random signal without effect on the object's echo.Then the RFI can be suppressed easily by a classical average filter.Analysis indicates that the proposed method makes the SFGPR have the same anti-RFI performance as that of noise radar.I...
A Wide Passband SAW Notch Filter  [cached]
Zhiqun Lin,Jiuling Liu,Wenhui Ren,Shitang He
Modern Applied Science , 2009, DOI: 10.5539/mas.v2n5p46
Abstract: Wide passband notch filter is fulfilled by combining LC-all-pass filter with one-port-SAW resonator by means of its impedance characteristics. It possesses good frequency selectivity and low insertion loss due to good frequency selectivity of resonance-frequency resonator and low insertion loss of LC filter. Higher attenuation of specified frequency can be achieved by cascade. Compared with LC notch filter, it posses sharp cutoff frequency and narrower notch?width. This paper first discusses the principle of this filter, and then proceeds with theoretical simulation and experimental demonstration.
Notch filter feedback controlled chaos in buck converter
Lu Wei-Guo,Zhou Luo-Wei,Luo Quan-Ming,

中国物理 B , 2007,
Abstract: A method of controlling chaos in the voltage-mode buck converter is presented by using an improved notch filter feedback control in this paper. The proposed control part comprises a notch filter and a low-pass filter. The discrepancy between the outputs of the two filters is introduced into the control prototype of the power converter. In this way, the system period-1 solution is kept unchanged. The harmonic balance method is applied to analysing the variation law of the system bifurcation point, and then the stable range of the feedback gain is ascertained. The results of simulation and experiment are also given finally.第一段]
An Adaptive Notch Filter For Noise Reduction and Signal Decomposition.
Vikas S. Mane,Amrita A. Agashe
International Journal of Computer Science Issues , 2011,
Abstract: Detection, estimation and filtering of desired signal in the presence of noise are some of the most common and practical problems in the analysis of time series. The analysis in the time domain often involves the comparison of two different signals and stochastic signals are usually more profitably analyzed in the time domain. Extraction of signal are considerably improves quality of signal. In many signal processing applications is to decompose an original signal into its primitive or fundamental constituents and to perform simple operations separately on each component, thereby accomplishing extremely sophisticated operations by a combination of individually simple operations. An adaptive notch filter is able extract the desired signal from noisy signal. In this paper proposed filter is parallely connected adaptive notch filter which is able to extract the fundamental frequency from the noise corrupted signal and each filter able decompose 'n' sinusoid which is harmonically related to its constituent component.
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