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The Noise Level of
the Reference Source
Unless it is below the system's noise floor, the noise level of
the source you are using as the reference source will set the
noise floor for the measurement. When you set up your
measurement, you will want to use a reference source with a
noise level that is below the level of the source you are
going to measure.
The following graph demonstrates that as the noise level of
the reference source approaches the noise level of the DUT,
the level measured by the HP 3048A (which is the sum of
all noise sources affecting the system) is increased above the
actual noise level of the DUT.
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AMOUNT EXPECTED DUT NOISE
EXCEEDS REFERENCE NOISE (dB)
Figure 2-4. Increase in Measured Noise as
Reference Source Noise Approaches DUT Noise
Note
To help you select the appropriate reference source
for your measurement, the noise plots for the various
Hewlett-Packard signal source options are included in the
HP 3048A Reference Manual.
Signal Source Fundamentals
2-9
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