When observing at two bands with the ATCA, it is generally sensible to
set the two bands so that they do not overlap. In terms
of sensitivity, there is
nothing to be gained by setting the bands to the same frequency as the noise
will be common to the the bands.
However having the bands overlap complicates the data reduction
process in Miriad.
The best approach is to avoid the problem, by setting the bands so that
they do not overlap at all, or overlap by a comparatively small amount.