  The channel-to-channel migration of radio interferometric baselines for the
same antenna separation causes a flat spectrum source that should have remained
in the zeroth delay (line-of-sight) mode to become centered around a higher
mode - the geometric delay for that particular antenna separation with a spread
(spill-over) of the order of reciprocal bandwidth. While in principle an
errorless gridding interpolation can remove inter-channel migration,
intra-channel baseline migration exists due to the non-zero width (resolution)
of the instrument's spectral channel arising from the finite-period integration
in a DFT cycle. Here for the first time, we analyze this effect and quantify it
using the case of a flat-spectrum point source. We find that the visibility
undergoes an attenuation, the extent of which depends on the auto-correlation
of the window function used for DFT and is more towards the lower-end of the
band. This causes the spill-over of the delay mode to extend beyond the
reciprocal bandwidth order.
