Simulating Fading, Adding Noise and Predistortions, and Impairing the Signal
R&S
®
SMW200A
407User Manual 1175.6632.02 ─ 16
An external analog signal can thus be impaired twice, analog and digital. If both
types of impairments are enabled, they superimpose each other in the signal.
Impairments caused by the I/Q modulator are automatically corrected by the Adjust I/Q
Modulator Current Frequency function. See also "Internal Adjustments" on page 1153.
5.3.2.1 Gain and Gain Imbalance
An I/Q gain is a multiplication of all I/Q amplitudes by a common factor. The effect is
equivalent to two identical I and Q gain factors. The effect of an increased gain factor
in the I/Q constellation diagram is shown on Figure 5-5.
Figure 5-5: Effect of an increased amplitude in the I/Q constellation diagram
An I gain multiplies the I amplitudes by a factor, leaving the Q amplitudes unchanged.
A Q gain has the opposite effect. Different I and Q gain factors result in an I/Q imbal-
ance, which is due to different gains of the amplifiers in the I and Q channels of the I/Q
modulator. The effect of a positive and negative gain imbalance is shown on Fig-
ure 5-6.
Figure 5-6: Negative gain imbalance (left) and positive gain imbalance (right) in the I/Q constellation
diagram
Impairing the Signal
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