Agilent Technologies E5500 Phase Noise Measurement System
6-7
Absolute Measurement Fundamentals
What Sets the Measurement Noise Floor?
Figure 6-4 Relationship Between the R Input Level and System Noise Floor
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 at or 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 UUT, the level measured by the
System (which is the sum of all noise sources affecting the system) is
increased above the actual noise level of the UUT.
Figure 6-5 Increase in Measured Noise as Reference Source Noise Approaches UUT Noise