Bandwidth decorrelation of a point source ($V_{\mathrm{avg}}=V({\nu }_0)\mathrm{sinc}(\pi \Delta \nu \tau )$)

A point source away from the tracked direction has residual geometric delay $\tau$. Averaging its frequency-dependent phase over a top-hat band gives the displayed sinc attenuation times its central-frequency complex phase. The first bandwidth null is complete cancellation, not a small-loss operating limit. Fine frequency channels preserve the information needed for later frequency-aware imaging.