Keysight Technologies N9040B UXA Manual page 40

Making Noise Figure Measurements
Using the U7227-Series USB Preamplifiers in Noise Figure Measurements
Figure 2-14 Signal Analyzer Display after USB Preamplifier is Ready For Use
5. The USB preamplifier is ready for use.
When the instrument is in the Noise Figure mode and the external U7227
Series USB preamplifier is plugged in, the internal preamplifier will turn off
to avoid compression. The user can turn it on at any point (Amplitude,
Signal Path, Internal Preamps, On)
40 N9069C Noise Figure Measurement Guide