Measurements
R&S
®
FSW
127
User Manual 1173.9411.02 ─ 19
1. Select PRESET to reset the instrument.
2. Set the center frequency to
128
MHz
.
3. Set the frequency span to
50
kHz
.
4. Select MEAS > "AM Modulation Depth" to activate the modulation depth measure-
ment.
The R&S
FSW automatically sets a marker to the carrier signal in the center of the
diagram and one delta marker each to the upper and lower AM sidebands. The
R&S
FSW calculates the AM modulation depth from the level differences of the
delta markers to the main marker and outputs the numeric value in the marker
information.
Fig. 5-10: Measurement of the AM modulation depth
The modulation depth is displayed as "MDepth". The frequency of the AF signal can be
obtained from the frequency display of the delta marker.
5.2.4.3
Measuring AM-Modulated Signals
The R&S
FSW rectifies the RF input signal (that is, removes the negative parts) and
displays it as a magnitude spectrum. The rectification also demodulates AM-modulated
signals. The AF voltage can be displayed in zero span if the modulation sidebands fall
within the resolution bandwidth.
Displaying the AF of an AM-modulated signal (Zero Span)
Signal
Generator
R&S FSW
Fig. 5-11: Test setup
Basic Measurements
