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31 July 1998 Digital techniques for ground-based low-frequency radio astronomy
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Far prior to any other wavelength domains, decameter radioastronomy has become a challenging task because of man made interference due to the increasing needs in telecommunications. However most of the astrophysical studies in this frequency band, -- particularly those of non thermal radiations from magnetized objects --, require high gain multi-polarization antennas and the use of high sensitivity, high dynamic range spectroscopy techniques. New generation of wide band spectrum analyzers, well suited to overcome these constraints, are presently developed in Meudon observatory in collaboration with the Space Research Institute (Graz, Austria). They are based on the utilization of newly available, high performance, programmable digital circuits for signal processing, arranged in dedicated, parallel architecture, which can directly compute the power spectrum of the input signal. As an example, we describe here a specialized real-time analyzer for studying polarized decameter emissions from Jupiter and the Sun. With this device, the full spectral analysis (four Stokes parameters) of a 10 MHz bandwidth can be performed at the millisecond time scale, over 1024 channels and within a 70 dB dynamic range. The unprecedented capabilities of this analyzer were evaluated during the last Jovian opposition, by using the Decameter Array in Nancay, France. Some examples are presented, with emphasis on results on the shortest fine structures, which are characteristics of cyclotron maser radiations from planets. Perspectives for extending to shorter wavelengths (namely decimeter or centimeter ones) and for enhancing capabilities by implementing dedicated softwares are discussed. The offered possibility of processing the telescope signal in real time -- in order, for instance, to manage the man made radio interference problem --, indeed appears as a key to maintain acceptable sensitivity in any future, large radio telescope system operating on the ground.
© (1998) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Alain Lecacheux, Carlo Rosolen, V. Clerc, P. Kleewein, Helmet O. Rucker, M. Boudjada, and Wim van Driel "Digital techniques for ground-based low-frequency radio astronomy", Proc. SPIE 3357, Advanced Technology MMW, Radio, and Terahertz Telescopes, (31 July 1998);


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