Agilent Technologies E4438C - Manual (Page 86)

Performance Tests
Phase Noise and Residual FM (Manual Test - Option UNJ or Option 506 Only)
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Figure 3-34
Measuring Residual FM
Residual FM is closely related to phase noise. Good phase noise typically implies good residual FM. Directly
measuring residual FM at very low levels is difficult, but the Agilent E5500 Series phase noise measurement
system can integrate the phase noise results to determine an accurate value. This is done under the Trace
Integration menu, of the Agilent E5500 Series phase noise measurement system, by selecting a data type of
Snu(f) or Spectral density of frequency fluctuations .
In signal generators with Option UNJ, residual FM is defined only within a 300 to 3000 Hz bandwidth and
with a specified frequency response within this band. That frequency response is specified by a CCITT filter
characteristic. In the Agilent E5500 Series phase noise measurement system, software revision 5.0 or higher,
use of this filter response can be achieved by simply checking the
CCITT weighting box under the Trace
Integration menu.
If you use the older Agilent 3048 phase noise system, there is no direct way to measure residual FM, but
because residual FM and phase noise are so closely related and interdependent, it is safe to assume that if the
DUTs phase noise meets specification, looks typical (between 300 and 3000 Hz), and shows no unexpected
large spikes in the response, it will most likely also meet the residual FM specification.