Service manual

WLAN TX Measurements
R&S
®
FSV-K91/91n/91ac/91p
44Operating Manual 1176.7649.02 ─ 04
3.8.1.1 IQ Offset
An IQ-Offset indicates a carrier offset with fixed amplitude. This results in a constant
shift of the IQ axes. The offset is normalized by the mean symbol power and displayed
in dB.
3.8.1.2 Gain Imbalance
An ideal I/Q modulator amplifies the I and Q signal path by exactly the same degree.
The imbalance corresponds to the difference in amplification of the I and Q channel
and therefore to the difference in amplitude of the signal components. In the vector dia-
gram, the length of the I vector changes relative to the length of the Q vector.
The entry is displayed in dB and %, where 1 dB offset is roughly 12 % according to the
following:
Imbalance [dB] = 20log (| GainQ |/| GainI |)
Positive values mean that the Q vector is amplified more than the I vector by the corre-
sponding percentage:
Measurement Result Types