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[Discuss-gnuradio] Approaches for cross-spectra

From: Marcus D. Leech
Subject: [Discuss-gnuradio] Approaches for cross-spectra
Date: Wed, 10 Aug 2011 22:02:31 -0400
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I'm working on a continuum interferometer project (actually resurrecting one that has been dormant for several years). I'm currently playing with approaches for spectral estimating with a two-antenna interferometer system. I think, ideally, since you have two antennae, you'd like to take advantage of that for producing spectral estimates that have channel-electronics-induced-spurs reduced in magnitude, and the spectral components that are common to the two antennas enhanced. I've tried various approaches:

    o Add the magnitudes of the FFTs for two antennae, low pass filter that

This produces a *composite* spectral estimate, including the components due to independent spurs on the two channels.

o Complex multiply the two FFT outputs, then compute the magnitude, low-pass filter that

This seems to produce some suppression of distinct components that aren't common to the two sides The absolute magnitudes of non-suppressed components are obviously larger, due to the multiply.

The second approach seems very similar to what ALMA is doing for their FX correlators.

Any words of wisdom/advice?

Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium

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