Specifications

11
Figure 12.
Uncertainty
calculator display
Noise figure uncertainty
calculator
When making a noise figure measure-
ment, there are many aspects of the
measurement setup that can affect
the uncertainty of that measurement.
The instrument uncertainty is one
element of measurement uncertainty
where the instrument itself adds to
the measurement uncertainty; this is
the instrument uncertainty we read
in the specifications. Other factors
like the noise source and the system
mismatch also add to the measure-
ment uncertainty. A measurement
uncertainty calculator is used to
incorporate all of these factors to
determine the total measurement
uncertainty.
The noise figure measurement per-
sonality, Option 219, has a built-in
uncertainty calculator. To calculate
the overall measurement uncertainty,
simply choose the default noise source
(346C for example), enter the input
and output match of the device under
test and the gain/noise figure of the
DUT from the measurement display
and the value of the uncertainty will
be calculated. There are some default
values for the instrument (PSA)
already entered.
Instructions Keystrokes
Select uncertainty calculator. [Mode Setup] {Uncertainty Calculator}.
Choose 346C as default source. Use right/left tab keys to highlight “Noise
Source Model” box. Press {346C}.
Enter the noise figure and gain values from Use tab keys to highlight “DUT Noise Figure”
the measurements graph or marker table. and enter [3.2] {dB}. (To view the marker table,
press [Return] and to return to the calculator
press {Uncertainty Calculator}). Then highlight
“DUT Gain” and enter [25] {dB}.
The input and output match of the DUT is Highlight “DUT Input Match” and enter [1.5].
determined from the specifications sheet Highlight “DUT Output Match” and enter [1.5].
or measured using a network analyzer. The measurement uncertainty is then calculated
and the results is display at the bottom of the
form (Figure 12).
Use the built-in uncertainty calculator.