N9069C Noise Figure Measurement Guide 11
Introduction to Noise Figure
How does the Noise Figure Measurement Work?
Process
1.
A calibration (
) is done without the DUT in place to measure the
instrument itself. The noise source is usually connected directly to the
input of the instrument.
In calibration, the analyzer makes two measurements with the noise
source ON and OFF respectively.
Note that if the ENR of the noise source is much smaller than the
instrument noise figure (for example, ENR 6 dB, instrument noise figure
30 dB), the CAL will not work well. In this case, it is recommended to
use a USB preamplifier and/or the internal preamplifier, to reduce the
instrument noise figure. If the preamplifier can
not
be used for some other
concerns, you can use a noise source with a higher ENR.
2.
A measurement is done with the DUT inserted and the test system
consists of the DUT (stage 1) followed by the instrument (stage 2). The
analyzer makes another two measurements with the noise source ON and
OFF respectively.
In the measurement, if the DUT has gain, the measurement with the noise
source ON is the largest signal case in the four measurements. In some
high-gain cases, especially with an external preamplifier, there is a risk of
overloading the instrument that must be addressed.
With these four measurements in the two stages, the analyzer can calculate
the noise figure and gain of the DUT. The DUT discussed above is assumed to
have two ports, input and output.
If the DUT is frequency translating, the ENR values of the noise source used in
the calibration and measurement are for different frequency ranges. See
“Making Frequency Converting DUT Measurements” on page 20
for more
details.
If the frequency range of the DUT is beyond the frequency range of the
analyzer, a system down-converter is needed. See
System Downconverter” on page 28
for more details.
Figure 1-2
Y factor Noise Figure Measurement Requires Two Steps: Calibration and
Measurement of the DUT
Summary of Contents for CXA N9000B
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