The Resolution Bandwidth (RBW) plays and important role in resolving signals that are close together in the frequency domain.

The RBW defines the bandwidth of the IF filter in a heterodyne receiver, and it controls the frequency resolution of the resulting spectrum – the smaller the RBW, the higher the spectral resolution, which means more peaks of frequencies are shown and distinguishable. If the resolution bandwidth is too broad, two frequencies can easily be combined into one and it can be difficult to tell them apart.

The RBW also defines the minimum sweep time, since smaller RBWs require longer sweep times, because narrow filter have longer settling times than wideband filters.

Typical resolution bandwidth values range from 1 Hz to 10 MHz.