3 Spectrum Analyzer Mode
3.2 Swept SA Measurement
Sample Works well, but never better than Average , because it does not smooth as well
Normal A combination of peak and negative peak behaviors, and works about as well as
these
For best operation, extreme smoothing is desirable, as already stated. Using narrow
VBWs works well, but using very long bucket durations and the average detector
works best. Reducing the number of trace points makes the buckets longer.
For best operation, Average Type = Power (RMS) is optimal (when this option is
available). When making CW measurements in the presence of noise without NFE,
averaging on the decibel scale has the advantage of reducing the effect of noise.
Using NFE with Average Type = Log-Power (LOG) is not synergistic, though; NFE
with Average Type = Power (RMS) works a little better than NFE with LOG.
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 -174dBm/Hz. This
is expected and useful behavior, because NFE is designed to report the amount of
input signal that exceeds 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.
Recalibration of Noise Floor
In instruments with the NF2 license installed, the calibrated noise floor used by
Noise Floor Extension should be refreshed periodically. Keysight recommends that
the Characterize Noise Floor operation be performed after the first 500hours of
operation, and once every calendar year. To do this, use "Characterize Noise Floor"
on page 2149, under System, Alignments, Advanced. If you have not done this
yourself at the recommended interval, then when you turn on Noise Floor Extension,
the instrument will prompt you to do so with a dialog stating:
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.
Noise Source
Lets you turn the noise source power on or off and select the type of Noise Source to
be used when making manual noise figure measurements.
See "More Information" on page 449.
448 Spectrum Analyzer Mode User's &Programmer's Reference
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