Users of extremely narrow bandwidths should be aware that when observing in continuum mode the VLA bandwidths narrower than 6.25 MHz suffer large closure errors because the quadrature networks do not work well. If such narrow bandwidths are essential for your observations, consider observing with the spectral-line system, where these problems are avoided. Unfortunately, the VLA spectral-line system is not a panacea for eliminating chromatic aberration: it cannot support continuum polarimetry in all 4 ``IFs".
Chromatic aberration effects at the VLA are well estimated by
the expressions given by
Bridle & Schwab (1989) for a square bandpass
and Gaussian tapering in the u-v plane. In the regime ( 
) where the amplitude reduction for a point source is moderate,
the exact expression for the reduction (their Equation 13-23)
can be approximated by
using the standard expansion for the error function, erf, at small values of its argument.
