Simulating Fading, Adding Noise and Predistortions, and Impairing the Signal
R&S
®
SMW200A
408User Manual 1175.6632.02 ─ 16
5.3.2.2 I and Q Offset
An I offset adds a constant value to all I amplitudes, leaving the Q amplitudes
unchanged. A Q offset has the opposite effect. A combination of I and Q values results
in an I/Q offset, which is due to carrier feedthrough in the I/Q modulator. Possible rea-
sons are interfering signals at the RF carrier frequency, e.g. an unsuppressed RF car-
rier subchannel. The effect of a positive I and Q offset in the I/Q constellation diagram
is shown on Figure 5-7.
Figure 5-7: I offset (left) and Q offset (right) in the I/Q constellation diagram
5.3.2.3 Quadrature Offset
Changes the phase angle between the I and the Q vectors from the ideal 90 degrees,
while the amplitudes are maintained. A positive quadrature offset results in a phase
angle greater than 90 degrees. The effect of a positive quadrature offset in the I/Q con-
stellation diagram is shown on Figure 5-8.
Figure 5-8: Positive quadrature offset in the I/Q constellation diagram
Impairing the Signal
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