462 Keysight N9927-90001 User’s Guide
Noise Figure Mode (Option 356 – CPU2 Only)
How to Define a Noise Figure Measurement
Calculating Noise Figure Measurement Uncertainty
The Noise Figure mode can calculate and display the uncertainty of the noise
measurement, whether it is a Noise Figure, Noise Factor, or Noise Temperature
measurement.
The uncertainty calculation accounts for the following sources of uncertainty,
both in the measurement and in the user calibration (Run User Cal):
— Noise power uncertainty caused by finite sample size (Jitter)
— Noise power uncertainty caused by mismatch
— ENR uncertainty of the noise standard
The following are not included because they have been determined to be
insignificant:
— Linearity (i.e., due to the linear wide dynamic range receiver, the automatic
gain adjustment, and the small power excursions of the hot/cold
measurement)
— Residual temperature drift of the FieldFox (i.e., due to the internal reference
switch)
Other possible causes of uncertainty that are not included in the uncertainty
analysis are temperature drift of the following:
—DUT,
— Noise source, or
— Preamplifier
Refer to ENR “Using ENR Tables” on page 467.
Reverse noise wave generation by the DUT or preamplifier
All amplifiers, including the DUT and preamplifiers used in the noise figure
measurement, are active devices which may generate noise power from both
their input and output ports. The Noise Figure mode uncertainty calculation
does not account for uncertainties caused when the input generated noise
reflects back into the amplifier and adds to the total measured noise power.
These types of uncertainties are minimized by using well matched noise
Generally, the drift immunity of the Y-factor noise figure measurement is
quite good. Nevertheless, caution is advised when temperature changes
are significant between the user calibration and measurement.
When any one of the four uncertainty values reads all "0.00" across the
band, a yellow
UNC? annotation is displayed on the left side of the FieldFox
display.
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