RFI Signals Research Articles

Simulating Spectral Kurtosis Mitigation against Realistic RFI signals

Simulating Spectral Kurtosis Mitigation against Realistic RFI signals

Solar radio filtering algorithm based on improved long short-term memory

The effective observation of burst events in solar radio research has been impeded by various interference signals, especially interference signals with a wide frequency range and high intensity, as they can partially or completely obscure the observation of burst events. Image processing methods that directly remove the interference signal channels and subtract the average of the interference signal channel are not suitable for processing all types of interference signals. This paper proposes the use of a specific kind of recurrent neural networks, called long short-term memory networks, to predict the value of the radio frequency interference signals with high intensity of the burst event in the solar radio spectrum. The predicted interference can then be removed in accordance with the principle that signals can be linearly added. Therefore, predicted value is subtracted from the data containing the burst event signals and the RFI signals (The radio frequency interference signals to be processed in this article refer to the signal of the broadcast signal that can be received in the frequency range, the signal transmitted by the mobile phone, and the signal transmitted by the sea vessel, and the like) to remove the interference. Then, in order to reduce the error caused by the stepwise prediction in the network and further improve the prediction accuracy, this paper analyzes the characteristics of the value of the radio interference and applies the digital mapping method to convert the prediction problem into the classification problem in the time series. The experimental results show that the proposed method can effectively remove the radio interference in the solar spectrum and clearly show the burst events.

A method for the automated detection of solar radio bursts in dynamic spectra

The variability of the solar corona, including flares and coronal mass ejections, affects the space environment of the Earth (heating and ionization of the atmosphere, magnetic field disturbances, and bombardment by high-energy particles). Electromagnetic emissions are the first signatures of a solar eruptive event which by modifying the electron density in the ionosphere may affect airborne technology and radio communications systems. In this paper, we present a new method to detect automatically radio bursts using data from the Nançay Decametre Array (NDA) in the band 10 MHz–80 MHz. This method starts with eliminating unwanted signals (Radio-Frequency Interference, RFI and Calibration signals) by analyzing the dynamic spectrum of the signal recorded in time. Then, a gradient median filter is applied to smooth and to reduce the variability of the signal. After denoising the signal, an automated solar radio burst detection system is applied. This system is based on a sequential procedure with adaptive constant-false-alarm rate (CFAR like detector) aimed to extract the spectra of major solar bursts. To this end, a semi-automatic software package is also developed to create a data base of all possible events (type II, III, IV or other) that could be detected and used for our performance assessment.

Three Years of SETI@home: A Status Report

The SETI@home project has recently completed its third year of active data analysis. Over 4 million volunteers have joined the search, providing a combined total of over 1 million CPU-years of processing power. SETI@home performs a sensitive search for extraterrestrial signals in a 2.5 MHz band centered on 1420 MHz. SETI@home searches a wide parameter space including 14 octaves of signal bandwidth and 15 octaves of pulse period with Doppler drift corrections from −50 Hz/s to +50 Hz/s. We will briefly describe the SETI@home project and the algorithms used in the SETI@home client. We will describe the post-processing methods we use to reject RFI and select candidate signals from the nearly 4 billion “hits” returned by SETI@home clients.

Driftscan Surveys in the 21 cm Line with the Arecibo and Nançay Telescopes

AbstractDriftscan methods are highly efficient, stable techniques for conducting extragalactic surveys in the 21 cm line of neutral hydrogen. Holding the telescope still while the beam scans the sky at the sidereal rate produces exceptionally stable spectral baselines, increased stability for RFI signals, and excellent diagnostic information about system performance. Data can be processed naturally and efficiently by grouping long sequences of spectra into an image format, thereby allowing thousands of individual spectra to be calibrated, inspected and manipulated as a single data structure with standard tools that already exist in astronomical software. The behaviour of spectral standing waves (multi-path effects) can be appraised and excised in this environment, making observations possible while the Sun is up. The method is illustrated with survey data from Arecibo and Nançay.

Signal shapes and single‐boundary measurements in flow injection analysis with amperometric detection

AbstractThe shapes of normal and reverse flow injection (nFI and rFI) signals have been studied using single‐channel manifolds, amperometric and visible spectrophotometric detection, and small and large (> 1.5 mL) injection volumes. The shapes of nFI and rFI signals are fundamentally different because in rFI the sample, being the carrier stream, is present in essentially infinite volume. For this reason, rFI signals are broader and are prone to double‐peak formation at lower injection volumes than are nFI signals. Contributions to the final signal from dispersion at the front and rear boundaries of the injected bolus frequently are, or appear to be, unequal. With loop injection, the rear boundary travels further than the front boundary and is dispersed more: injection by stream switching removes this factor. With spectrophotometric detection, correction for large and opposite refractive index effects at the two boundaries may be required. In amperometric detection, differences in acidity of carrier stream and injectate can cause significant changes in background current on switching and can distort the signal at low concentrations of monitorand. When these factors are eliminated, however, other factors causing peak height and peak shape differences remain: differences in dispersion rates of reactants, and of reaction rates, appear to be the major factors.

Macromodel Predictions for EMI in Bipolar Operational Amplifiers

A macromodel containing two transistors can accurately predict how amplitude-modulated RF signals with RF carrier frequencies in the 0.05-to 100-MHz range are demodulated in a bipolar operational amplifier (μ A741 op amp) to cause undesired low-frequency responses related to the modulation envelope of the RF signals. The original op-amp macromodel, which was developed by Boyle et al., was modified by adding four capacitors (each 4 pF) to account for parasitic-capacitance effects in the integrated-circuit op amp. The macromodel can be used when the RFI signals are incident upon the op-amp input terminals. The use of the macromodel leads to a substantial reduction in computer time and expense.

The Performance of Suppressed Carrier Receivers in a Pulsed RFI Environment

This paper investigates the tracking performance of a Costas loop in the presence of single and multiple in-band pulsed RFI signals and receiver additive noise. It is shown that the loop's tracking performance is very sensitive to the pulse durations of the RFI signals, as well as their repetition rates and peak powers relative to those of the desired signal. The presence of in-band RFI can affect the loop's tracking performance in basically three ways. 1) The loop tracks the composite phase of the RFI instead of the phase of the desired signal when the effective RFI power is greater than that of the signal. 2) When the effective RFI power is not sufficiently large to capture the loop, there still will exist static phase error biases which cause the loop to lock at a phase between that of the desired signal and the composite RFI. 3) There is an increase in the rms phase jitter over the nominal design. These latter two effects degrade the bit error probability performance of the receiver. More significantly, if the nominal loop bandwidth is not designed properly to account for the increase in jitter phenomenon, frequent cycle slipping may result.