The Spectrum Application
R&S
®
FPC
108
User Manual 1178.4130.02 ─ 07
Automatically selects an appropriate resolution bandwidth depending on the
current
Automatic adjustment of the sweep time
In its default mode, the R&S
FPC automatically adjusts the sweep time when you
change the resolution bandwidth. This ensures that the settling time required for the
selected resolution filter is properly taken into account.
For narrow resolution filters and large spans, the maximum sweep time would be
exceeded. To avoid this, the R&S
FPC adjusts the span automatically as soon as the
maximum sweep time is reached.
14.5.2
Video Filter
The video filter is a lowpass filter located after the
which filters the
higher frequency parts of the voltage from the signal. This process makes the trace
smoother and makes it easier to read out level values.
Video voltage is the (DC) voltage that results from the IF signal passing through the
envelope detector which removes the IF components and outputs the envelope only.
This output is also known as the video signal.
The figure below shows that process on an AM modulated signal in the time domain.
In case of an AM modulated signal, the envelope (or video) signal contains a DC com-
ponent that corresponds to the level of the carrier. The video signal also contains an
AC component whose frequency is the same as the AM frequency.
Figure 14-11: Video voltage of an AM signal
If the video filter bandwidth is less than the frequency of the AC component, it is sup-
pressed depending on its maximum frequency. If the AM component should be dis-
played truly, the cutoff frequency of the filter has to be greater than the modulation fre-
quency.
If there is noise on the sine signal, the modulation signal can be thought of as noise. If
the video bandwidth is reduced, the high-frequency noise components above the cutoff
Bandwidth Configuration
