... calibration

During D $\rightarrow$A reconfiguration antennae are moved from the innermost to the outermost stations of the VLA. Our subarray therefore consisted of a mix of very short and very long baselines. In addition, the composition of the subarray changed frequently, as an antenna was checked out to be moved, and replaced by another antenna that had just been repositioned. The positions of the newly checked-in antennae were often not known precisely at the time of our observations, resulting in unusually large phase errors. These problems could be overcome in the analysis of the total intensities, but prevented us from performing a sufficiently reliable polarization calibration.

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