Above 200 kHz span, only the 10.7 MHz IF is used, and the LO is injected first low side, then high side. The noise figure of the 10.7 MHz IF is maybe 5 dB higher, so this can affect measurements where the level of noise present is low.
As long as your VBW is much lower than your RBW, you can still make decent noise measurements, with the caveat that you’re measuring the combined noise from RF and image.
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