Impairments; I And Q Offset; Gain And Gain Imbalance - R&S SGT100A User Manual

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R&S SGT100A

7.3.2 Impairments

The R&S SGT allows the digital I/Q signal to be impaired before it is passed on to the
I/Q modulator. These settings are available in the block diagram in the "Impairements"
functional block.
7.3.2.1

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 usually due to carrier feedthrough in the I/Q modulator. Possi-
ble reasons are interfering signals at the RF carrier frequency, e.g. an unsuppressed
RF carrier subchannel. The effect of a positive I and Q offset in the I/Q constellation
diagram is shown below.
Figure 7-4: I offset (left) and Q offset (right) in the I/Q constellation diagram
7.3.2.2

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 below.
User Manual 1176.8674.02 ─ 07
Signal Generator Settings
I/Q Modulation and Impairment Settings
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