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Applying I/Q Vector Modulation
R&S
®
SMBV100B
284
User Manual 1178.4460.02 ─ 03
5.5
How to Adjust the I/Q Modulator to Optimize Perform-
ance
With its default settings, the I/Q Modulator provides vector modulated signal that is
optimized for time sensitive measurements and lower noise.
Adjusting the settings helps to improve signal quality in the following cases:
●
To optimize the intermodulation characteristics of the signal
●
To optimize the signal-to-noise ratio (SNR) of the signal
●
To improve the flatness of the RF signal
In the following examples, we assume that:
●
The R&S
SMBV100B generates a baseband signal
●
A spectrum analyzer is connected to the R&S
SMBV100B, the analyzed is config-
ured, and measures the required signal characteristics.
To improve signal flatness
For a given baseband signal and RF frequency, perform the following:
1. In the block diagram, select "I/Q Mod > I/Q Settings > I/Q Modulator > On".
The I/Q modulator is enabled. Modulated is the internal baseband signal.
This mode generates flat signal but requires longer settling time and leads to signal
interruption.
2. Select "Optimization Mode > High Quality"
Note:
Do not use the mode "I/Q Modulator > Optimization Mode > High Quality" in combi-
nation with the modes "RF Level > Setting Characteristics > Uninterrupted/Strictly
Monotone".
The high quality I/Q optimization leads to RF signal interruption. The requirements
of the RF level modes "Uninterrupted" and "Strictly Monotone" can not be fulfilled.
3. On a connected signal analyzer, monitor the signal characteristics.
To optimize the intermodulation characteristics of signal
For a given baseband signal and RF frequency, perform the following iterative steps:
1. In the block diagram, select "I/Q Mod > I/Q Settings > I/Q Modulator > On".
The I/Q modulator is enabled. Modulated is the internal baseband signal.
2. If activated, disable the "I/Q Wideband > Off".
3. Select "Baseband Gain = - 2 dB".
4. On a connected signal analyzer, monitor the signal distortion characteristics.
5. Vary the value of the parameter "Baseband Gain" until the maximal suppression of
the intermodulation products is achieved.
How to Adjust the I/Q Modulator to Optimize Performance