Noise figure measurments
i agree marcomdd.
I would add just a warning.
Increase Averaging will reduce jitter only if the NOISE is WHITE (or until the white part of the noise is dominant).
Whit long integrating times, the detected 1/F NOISE (also called DRIFT) became dominant, and the effect is a reduction on the measurement accuracy.
Dritf is not related to RFI or generically called SPUR, drift is maily related to physical temperature of all electronic components.