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Measurements and Results

R&S

FSW

144User Manual 1173.9411.02 ─ 43

7.1.5.2 Measuring the Modulation Depth of an AM-Modulated Carrier in the Frequency

Domain

In the frequency range display, the AM side bands can be resolved with a narrow

bandwidth and measured separately. The modulation depth of a carrier modulated with

a sinusoidal signal can then be measured. Since the dynamic range of a signal ana-

lyzer is very large, extremely small modulation depths can also be measured precisely.

For this purpose, the R&S FSW provides measurement routines that output the modu-

lation depth numerically in percent directly.

Figure 7-9: Test setup

Table 7-4: Signal generator settings (e.g. R&S SMW)

Frequency 128 MHz

Level -30 dBm

Modulation 50 % AM, 10 kHz AF

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 mea-

surement.

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.

Basic Measurements

R&S FSW Series User Manual

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