3 Spectrum Analyzer Mode
3.8 Spurious Emissions Measurement
the NFE does an even better job than using the log scale ever could. Using NFE with
the log scale is not synergistic, though; NFE with the power scale works a little
better than NFE with log averaging type.
The results from NFE with internal preamp can often be lower than the theoretical
noise in a signal source at room temperature, a noise density of -174 dBm/Hz. This
is expected and useful behavior, because NFE is designed to report the amount of
input signal that is in excess of the thermal noise, not the amount that includes the
thermal noise. This can be a useful behavior because thermal noise often interferes
with what you want to measure, instead of being part of what you want to measure.
Note that NFE is not adequately accurate to always be able to read below kTB.
Adaptive NFE provides an alternative to fully-on and -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 NFE-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.
On instruments with the NF2 license installed, the calibrated Noise Floor used by
Noise Floor Extensions should be refreshed periodically. Keysight recommends that
the Characterize Noise Floor operation be performed after the first 500 hours of
operation, and once every calendar year. The control to perform this is located in the
System, Alignments, Advanced menu. If you have not done this yourself at the
recommended interval, then when you turn on Noise Floor Extensions, the
instrument will prompt you to do so with a dialog that says:
“This action will take several minutes to perform. Please disconnect all cables from
the RF input and press Enter to proceed. Press ESC to cancel, or Postpone to
postpone for a week”
If you Cancel, you will be prompted again the next time you turn NFE on. If you
postpone, you will be prompted again after a week passes and you then turn NFE
on.
3.8.8.4 Global
The controls in this menu apply to all Modes in the instrument.
Some controls (for example, "Global Center Freq" on page 2034) allow you to switch
certain Meas Global parameters to a Mode Global state. These switches apply to all
Modes that support global settings. For example, no matter what Mode you are in
1490 Spectrum Analyzer Mode User's &Programmer's Reference
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