Hi,
You are seeing this because of the trace averaging you are performing. The trace averaging is being performed as dB, not in linear units, and thus will skew the results. You will want the “clear and write” trace type for noise floor measurement. To compensate for the noisier measurement without the additional averaging, you can increase the RBW/VBW ratio. Something like 100/1Hz would perform significant averaging. Increasing RBW would also have an averaging like effect (1000/1).
You will also want to leave the VideoUnits/Detector settings to Power/Average (as you already have them set).
Let me know if you have follow up questions,
Thanks
