From an analysis of galactic H I spectra acquired over a period of seven months, we investigate the accuracy of H I profiles obtained with the dual circular feed at Arecibo Observatory. The H I stray radiation contribution is estimated from a comparison of H I spectra toward the moon with H I spectra in the same direction when the moon is absent. The profile areas of corrected H I spectra are accurate to 3%, while individual features are accurate to 15%. At velocities where the H I emission is less than 3 K, the observed stray radiation is less than 0.5 K.
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