text: The video bandwidth filter or VBW filter is the low-pass filter directly after the envelope detector.  It's the bandwidth of the signal chain after the detector.  Averaging or peak detection then refers to how the digital storage portion of the device records samples—it takes several samples per time step and stores only one sample, either the average of the samples or the highest one.  The video bandwidth determines the capability to discriminate between two different power levels.  This is because a narrower VBW will remove noise in the detector output. This filter is used to "smooth" the display by removing noise from the envelope. Similar to the RBW, the VBW affects the sweep time of the display if the VBW is less than the RBW. If VBW is less than RBW, this relation for sweep time is useful:
  Here t is the sweep time, k is a dimensionless proportionality constant, f &minus; f is the frequency range of the sweep, RBW is the resolution bandwidth, and VBW is the video bandwidth.