Arcetri Astrophysical Observatory

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logosmallarcetri Arcetri Technical Reports 3/2003


Phase effects in a hybrid correlator 

G. Comoretto

INAF - Arcetri Astrophysical Observatory

Abstract

In an hybrid correlator, the signal to be analyzed is divided into several sub-bands, that are separately analyzed. Edge effects are thus particularly important, as they determine the accuracy of the reconstructed spectrum across junction points. In this report these effects are analyzed. It is shown that, using a real valued correlator, errors of up to 30% in amplitude, and 20 degrees in phase, could be expected. After appropriate calibration for correlator response, these errors can be reduced by a factor of 3-4, but not eliminated. Accurate spectra, to a level of a fraction of a percent or a few tenths of a degree, can be obtained only using overlapping sub-bands, and discarding the more troublesome edge channels. The effects of the digital filter shape is also analyzed. It is shown that filter ripple translates in a calibration error that depends on signal gradient. This must be corrected for high dynamic range observations.

Postscript version of this report.

PDF version of this report.