Common Measurement Settings
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User Manual 1173.9411.02 ─ 19
6.5.1.2
Smoothing the Trace Using the Video Bandwidth
The video filters are responsible for smoothing the displayed trace. Using video band-
widths that are small compared to the resolution bandwidth, only the signal average is
displayed and noise peaks and pulsed signals are repressed. If pulsed signals are to
be measured, it is advisable to use a video bandwidth that is large compared to the
resolution bandwidth (VBW = 10 x RBW) for the amplitudes of pulses to be measured
correctly.
The level of a sine wave signal is not influenced by the video bandwidth. A sine wave
signal can therefore be freed from noise by using a video bandwidth that is small com-
pared with the resolution bandwidth, and thus be measured more accurately.
RMS/Average detector and VBW
If an RMS or average detector is used, the video bandwidth in the hardware is
bypassed. Thus, duplicate trace averaging with small VBWs and RMS or average
detector no longer occurs. However, the VBW is still considered when calculating the
sweep time. This leads to a longer sweep time for small VBW values. Thus, you can
reduce the VBW value to achieve more stable trace curves even when using an RMS
or average detector. Normally, if the RMS or average detector is used the sweep time
should be increased to get more stable traces.
6.5.1.3
Coupling VBW and RBW
The video bandwidth can be coupled to the resolution bandwidth automatically. In this
case, if the resolution bandwidth is changed, the video bandwidth is automatically
adjusted.
Coupling is recommended if a minimum sweep time is required for a selected resolu-
tion bandwidth. Narrow video bandwidths require longer sweep times due to the longer
settling time. Wide bandwidths reduce the signal/noise ratio.
Table 6-1: Overview of RBW/VBW ratios and recommendations for use
Ratio RBW/VBW
Recommendation for use
1/1
Recommended for sinusoidal signals
This is the default setting for automatic coupling.
0.1
Recommended when the amplitudes of pulsed signals are to be measured
correctly. The IF filter is exclusively responsible for the pulse shape. No
additional evaluation is performed by the video filter.
10
Recommended to suppress noise and pulsed signals in the video domain.
Manually set (0.001 to 1000) Recommended for other measurement requirements
6.5.1.4
Coupling Span and RBW
The resolution bandwidth can be coupled to the span setting, either by a manually
defined factor or automatically. If the span is changed, the resolution bandwidth is
Bandwidth, Filter and Sweep Configuration
