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Ann. Geophys., 23, 39-46, 2005
www.ann-geophys.net/23/39/2005/
© European Geosciences Union 2005
A procedure to correct the effects of a relative delay between the quadrature components of radar signals at base band
Grydeland1, La Hoz1,2, Belyey1, and Westman3
1Dept. of Physics, University of Tromsø, N-9037 Tromsø, Norway
2currently at; Earth and Atmospheric Science Department, Cornell University, Ithaca NY 14853, USA
3EISCAT Scientific Association, PO Box 164, SE-981 23, Kiruna, Sweden
Abstract. The real and imaginary parts of baseband signals are obtained from a real
narrow-band signal by quadrature mixing, i.e. by mixing with cosine
and sine signals at the narrow band's selected center frequency. We address
the consequences of a delay between the outputs of the
quadrature mixer, which arise when digital samples of the
quadrature baseband signals are not synchronised, i.e. when the real and
imaginary components have been shifted by one or more samples with respect
to each other.
Through analytical considerations and simulations of such an error on
different synthetic signals, we show how this error can be expected to
afflict different measurements.
In addition, we show the effect of the error on actual incoherent
scatter radar data obtained by two different digital receiver systems used
in parallel at the EISCAT Svalbard Radar (ESR). The analytical
considerations indicate a procedure to correct
the error, albeit with some limitations due to a small singular region.
We demonstrate the correction procedure on
actually afflicted data and compare the results to simultaneously
acquired unafflicted data.
We also discuss the possible data analysis strategies, including some that
avoid dealing directly with the singular region mentioned above.
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