Keysight Technologies CXA N9000B, Manual

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N9069C Noise Figure Measurement Guide 43
Making Noise Figure Measurements
Using the U7227-Series USB Preamplifiers in Noise Figure Measurements
Below is the procedure for using Figure 2-16 and Figure 2-17 to find the proper
system configuration. See “Examples for Using the Guide to Find the Test
System Configuration” on page 46 for examples of using this procedure.
1. Check the DUT and get the rough data for the DUT bandwidth (BW), noise
figure (NF), and gain.
2. Calculate the bandwidth adjust factor (AF) using the following equation.
1
Then subtract the AF from the DUT Gain. The resultant value is called
DUT_Gain_Modified.
3. Use the DUT_NF and DUT_Gain_Modified values to search in Figure 2-16
or Figure 2-17 from bottom to top and find an approximate place for them.
4. Find the corresponding system configuration. If the system configuration
includes the internal attenuation, do the following to find the proper
attenuation level:
a. Set the attenuation to 0 dB and note the noise figure of your DUT.
b. Increase the attenuation by one step (4 dB). If the noise figure
changes too much, such as 0.3 dB, this attenuation is required for
accurate measurement.
c. Repeat step (b) until you find the proper value.
1. The Ref BW is the bandwidth used in
Figure 2-16
or
Figure 2-17
to calculate the
noise power, which is 3.59 GHz.
AF 10 = Ref_BW DUT_BW
⁄ ( )
10 3.59 10
9
×
DUT_BW
⁄ ( )
log
×
= log
×
DUT_Gain_Modified DUT_Gain AF
–
=
As in the calculation of the supported DUT characteristics in
Figure 2-16
and
Figure 2-17
, the most precise data is used in most cases, it is recommended to
try the system configuration below the one you find using DUT_NF and
DUT_Gain_Modified first.