Keysight x-series User Manual

3 Spectrum Analyzer Mode
3.2 Swept SA Measurement
When NFE is On or Full, 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).
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 when
External Mixing is selected, it does nothing.
For more details, see "Optimal Detector & Averaging Selections" on page 447 and
"Recalibration of Noise Floor" on page 448.
Pros & Cons of Adaptive NFE
Adaptive NFE provides an alternative to fully-on or fully-off NFE. Fully-on NFE can,
notably in cases with little or no averaging of the spectrum, result in a display that is
distractingly unfamiliar in the variability in response to low level signals. Fully-off
NFE fails to achieve the potential improvement in dynamic range and associated
accuracy of measurement of low-level signals. 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—those
settings with high degrees of variance reduction through some variant of averaging.
When the potential improvement is small, the display acts like the fully-off case, and
when it is high, it acts like the fully-on case, and in-between, application is a
compromise between attractiveness and effectiveness.
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 fully-off
Spectrum Analyzer Mode User's &Programmer's Reference 445

Keysight x-series Specifications

General

Analysis Bandwidth	Up to 1 GHz (depending on model)
Real-Time Bandwidth	Up to 1 GHz (depending on model)
Form Factor	Benchtop
Connectivity	LAN, USB, GPIB
Resolution Bandwidth	1 Hz to 10 MHz (depending on model)