3 VMA Mode
3.3 Monitor Spectrum Measurement
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 will make the buckets longer.
For best operation, the power scale (Average Type = Power) is optimum. 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. When using NFE,
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.
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 key 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.
Conversion
Access a menu of functions that enable you to control the frequency conversion type
for the current measurement. The following choices are available:
Auto
AUTO
Auto optimizes demodulation quality by selecting single conversion
when available. Default value
Single High
Side
SHSide
Single downconversion with the LO frequency above the receiver
frequency. Not image protected, and available only above 400 MHz
or at all frequencies under specific condition
Single Low
Side
SLSide
Single downconversion with the LO frequency below the receiver
frequency. Not image protected, and available only above 1.1 GHz
Image
Protect
IPRotect
Double downconversion with pre-selection filtering. Available at all
frequencies
645 Vector Modulation Analyzer Mode User's &Programmer's Reference
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