ResBW Mode (ResBW)

The choice of resolution-bandwidth mode in conjunction with the choice of resolution-bandwidth coupling mode affects both resolution and measurement speed.

Keysight 89600 VSA offers two levels of flexibility in selecting a resolution bandwidth setting: 1-3-10 and Arbitrary:

1-3-10 mode is more restrictive than Arbitrary mode. In 1-3-10 mode, the VSA always sets the resolution bandwidth using the pattern { ..., 1, 3, 10, 30, 100, 300, ... } MHz Megahertz: A unit of frequency equal to one million hertz or cycles per second. (emulating many existing spectrum analyzers).
Arbitrary mode allows an arbitrary resolution bandwidth setting. The choice of bandwidth mode in conjunction with the choice of ResBW Coupling affects both resolution and measurement speed. To get the best resolution-to-speed tradeoff when changing the measurement span, specify Auto ResBW coupling and Arbitrary ResBW mode.