172 N5511A Phase Noise Test System User’s Guide
Residual and Additive Noise Measurement Fundamentals
What is Residual Noise?
Assumptions
The following are some basic assumptions regarding Residual Phase Noise
measurements. If these assumptions are not valid they will affect the measured
results.
— The source noise in each of the two phase detector paths is correlated at
the phase detector for the frequency offset range of interest.
— Source AM noise is comparatively small. A typical mixer-type phase
detector only has about 20 to 30 dB of AM noise rejection. If the AM
component of the signal is greater than 20 to 30 dB above the residual
phase noise, it will contribute to the residual phase noise measurement and
show the residual phase noise as being greater than it really is.
— The DUT does not exhibit a bandpass filter function. A bandpass filter type
response will cause the source noise to be decorrelated at the edge of the
filter. This decorrelation of the noise causes the system to measure the
source noise level directly at offsets beyond the filter bandwidth.
Summary of Contents for N5511A
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