Keysight M9421A - Noise Floor Extension

3 WLAN Mode
3.2 Channel Power Measurement
Noise Floor Extension
Lets you turn on/configure the Noise Floor Extension (NFE) function. Some Modes
(such as Spectrum Analyzer Mode), support two states of NFE, Full and Adaptive.
The ON state (in Modes which do not support Adaptive NFE) matches the FULL state
(in Modes that do support Adaptive NFE).
In ON or FULL NFE, the expected noise power of the instrument (derived from a
factory calibration) is subtracted from the trace data. This will usually reduce the
apparent noise level by about 10 dB in low band, and 8 dB in high band (>~3.6 GHz).
In Adaptive NFE, there is not the same dramatic visual impact on the noise floor as
there is in Full NFE. Adaptive NFE controls the amount of correction that is applied
based on other instrument settings like RBW, averaging and sweep time. Adaptive
NFE controls the degree of potential improvement in the noise floor to give more
improvement for those instrument settings that can make good use of the potential
improvement, such as settings that provide more averaging. The result is that when
not much averaging is being performed, the signal displays more like the NFE-off
case; and when lots of averaging is being performed, the signal displays more like
the full-NFE case.
Adaptive NFE (in Modes which support it) is recommended for general-purpose use.
For fully ATE (automatic test equipment) applications, where the distraction of a
person using the instrument is not a risk, Full NFE is recommended.
NFE works with any RBW, VBW, detector, any setting of Average Type, any amount
of trace averaging, and any signal type. It is ineffective when the trace is not
smoothed (smoothing processes include narrow VBWs, trace averaging, and long
sweep times with the detector set to Average or Peak). It works best with extreme
amounts of smoothing, and with the average detector, with the Average Type set to
Power.
In those cases where the cancellation is ineffective, it nonetheless has no
undesirable side-effects. There is no significant speed impact to having Noise Floor
Extension on.
The best accuracy is achieved when substantial smoothing occurs in each point
before trace averaging. Thus, when using the average detector, results are better
with long sweep times and fewer trace averages. When using the sample detector,
the VBW filter should be set narrow with less trace averaging, instead of a wide
VBW filter with more trace averaging.
NOTE
Noise Floor Extension has no effect unless the RF Input is selected, so it does
nothing when External Mixing is selected.
In Modes that support Adaptive NFE, the default state of NFE is Adaptive (ON). In
Modes that do not support Adaptive NFE, the default state of NFE is OFF. Prior to
WLAN Mode User's &Programmer's Reference 288