Applying I/Q Vector Modulation
R&S
®
SMW200A
425User Manual 1175.6632.02 ─ 16
To optimize the characteristics of signals with high adjacent channel power ratio
(ACPR)
For a given baseband signal (e.g. a 3GPP signal) and RF frequency, perform the fol-
lowing iterative steps:
1. In the block diagram, select "I/Q Mod > I/Q Settings > I/Q Modulator".
The I/Q modulator is enabled. Modulated is the internal baseband signal.
2. Select "Baseband Gain = 6 dB".
3. On a connected signal analyzer, monitor the signal characteristics.
4. Vary the value of the parameter "Baseband Gain" until the maximal signal-to-noise
ratio (SNR) is achieved.
To trigger the internal correction routine of the I/Q modulator
System error correction of the I/Q modulator permits precise and repeatable measure-
ments.
If a temperature fluctuation of several degrees occurs, trigger the correction routine
using one of the following:
1. Select "I/Q Mod > I/Q Modulator > Adjust I/Q Modulator Current Frequency"
2. Select SETUP > "System > Internal Adjustment > Adjust I/Q Modulator Current
Frequency".
See also "Internal Adjustments" on page 1153.
To generate a wideband modulation signal
1. In the block diagram, select "I/Q Mod > I/Q Settings > I/Q Modulator".
The I/Q modulator is enabled. Modulated is the internal baseband signal.
2. Select "I/Q Wideband > On".
The R&S SMW shifts the switching frequencies of the lowpass filters in the output
section and generates signal with higher I/Q modulation bandwidth.
The harmonic suppression, however, degrades.
How to Adjust the I/Q Modulator to Optimize Performance
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