Setting the Bandwidths R&S FSH
1309.6275.12 4.14 E-2
Therefore, the following rules of thumb can be applied to setting the video bandwidth:
• If you are performing measurements on modulated signals, the video bandwidth must be sufficiently
large so that desired modulation components are not rejected ( RBW).
• If signals are to be kept free of noise, the smallest video bandwidth possible should be selected
(0.1 x RBW).
• If measurements are being performed on pulsed signals, the video bandwidth should be at least
three times greater than the resolution bandwidth so that the pulse edges are not distorted.
Like the resolution bandwidth, the video bandwidth has an effect on sweep speed. The spectrum
analyzer must pause before each measurement to allow the video filter to settle.
The R&S FSH has video bandwidths from 10 Hz to 3 MHz in a 1, 3, 10 sequence. When the default
settings are selected, they are coupled to the resolution bandwidth. The video bandwidth equals the
resolution bandwidth. When the resolution bandwidth is changed, the R&S FSH automatically sets the
appropriate video bandwidth. This means that, in many cases, the video bandwidth does not need to be
set separately. When the resolution bandwidth is changed, the video bandwidth is changed
automatically.
Operating sequence:
Press the BW key.
The menu for setting bandwidths opens. When the
default setting has been selected, the softkey label for
setting the bandwidth automatically is highlighted in
green.
Press the MANUAL VIDEO BW softkey.
The softkey label is highlighted in red and the video
bandwidth value entry box (VBW) indicates the current
bandwidth. To indicate that the video bandwidth is not
coupled to the resolution bandwidth (RBW), a small,
red circle is placed in front of the video bandwidth
readout on the screen.
Enter the video bandwidth you want with the
number keys and terminate the entry with the
appropriate unit (MHz, kHz or Hz), or
Change the video bandwidth to the value you want
using the rotary knob or the cursor keys.
The video bandwidth value entry box is closed by pressing the ENTER key.
Press the AUTO VIDEO BW softkey.
The video bandwidth is coupled to the resolution bandwidth that has been set. The AUTO VIDEO BW
softkey label is highlighted in green to indicate coupling and the red circle marking the VBW readout
disappears.
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