Abstract
In radio astronomy, the radio spectrum is used to detect weak emission from celestial sources. By spectral averaging, observation noise is reduced and weak sources can be detected. However, more and more observations are polluted by man-made radio frequency interferences (RFI). The impact of these RFIs on power spectral measurement ranges from total saturation to subtle distortions of the data. To some extent, elimination of artefacts can be achieved by blanking polluted channels in real time. With this aim in view, a complete real-time digital system has been implemented on a set of FPGA and DSP. The current functionalities of the digital system have high dynamic range of 70 dB, bandwidth selection facilities ranging from 875 kHz to 14 MHz, high spectral resolution through a polyphase filter bank with up to 8192 channels with 49 152 coefficients and real-time time-frequency blanking with a robust threshold detector. This receiver has been used to reobserve the IIIWZ35 astronomical source which has been scrambled by a strong satellite RFI for several years.
Highlights
Radio astronomy, in common with many other users of the radio spectrum, has the advantage of a few protected frequency bands
The current functionalities of the digital system have high dynamic range of 70 dB, bandwidth selection facilities ranging from 875 kHz to 14 MHz, high spectral resolution through a polyphase filter bank with up to 8192 channels with 49 152 coefficients and real-time time-frequency blanking with a robust threshold detector
If any radio frequency interferences (RFI) emission occurs during this averaging time, the whole power spectral estimation is corrupted, unless a fine time-frequency blanking of the input signal is applied prior to the averaging
Summary
In common with many other users of the radio spectrum, has the advantage of a few protected frequency bands. If any RFI emission occurs during this averaging time, the whole power spectral estimation is corrupted (see Figures 1b and 1c), unless a fine time-frequency blanking of the input signal is applied prior to the averaging. In this case, the time-frequency slots detected as polluted are removed so that only free timefrequency slots will be averaged. Their spectral resolution and channel selectivity are often too limited to extract the free channels from the corrupted ones Their hardware architecture is too specific to allow additional functions, such as RFI detection, to be implemented.
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