Keysight Technologies CXA N9000B, Руководство пользователя

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N9069C Noise Figure Measurement Guide 41
Making Noise Figure Measurements
Using the U7227-Series USB Preamplifiers in Noise Figure Measurements
Guide for Using U7227-Series USB Preamplifier and the Internal
Preamplifier inside X-Series Signal Analyzer
This section provides a rough guide for using the U7227-Series USB
Preamplifier, the internal preamplifier, and the internal attenuator together to
make accurate noise figure measurements.
Amplitude Concerns in the Noise Figure Test System
Before talking about the guide, let us look at some signal amplitude concerns
in the test system. Figure 2-15 shows all the possible blocks in the signal path
of the noise signal in the noise figure measurement. The blocks with dotted
lines indicate that you can choose whether to use them or not. The USB
preamplifier, the internal preamplifier and input mixer inside the signal analyzer
are non-linear components and have a limit on the largest signal that can be
processed. The power limits of the noise signal are for the following places:
— before the USB preamplifier
— before the internal preamplifier
— before the input mixer
To make an accurate noise figure measurement, the noise power should be
below the maximum allowable power at all these three places. You can refer to
the technical overview of the U7227-Series USB Preamplifier and the
specification guide of the X-Series signal analyzer to check the maximum
allowable powers. For power levels before the internal preamplifier and before
the input mixer, the internal attenuator inside the signal analyzer can be
applied to reduce the power level. But at the same time, the instrument noise
figure will increase with using the internal attenuator.
The rough guide for the noise figure test system configuration in the following
section is based on the noise power calculation before the non-linear
components. For more details about noise power calculation in different stages
of the test system, refer to “Calculating the Noise Power into Different Stages
of the Noise Figure Measurement System” on page 85 .
Figure 2-15 Blocks in the Signal Path of the Noise Signal in the Noise Figure Measurement
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