N5511A Phase Noise Test System User’s Guide 75
Absolute Measurement Fundamentals
Changing the PTR
The Tuning Qualifications
Changing the PTR is accomplished by changing the tune range of VCO value or
the VCO tuning constant value or both. There are several ways this can be
done. However, when considering these or any other options for changing the
PTR, it is important to remember that the VCO source must always meet the
following tuning qualifications.
— The tuning response of the VCO source must always remain monotonic.
— The VCO source’s output level must remain constant across its tuning
range.
As long as these qualifications are met, and the software does not indicate any
difficulty in establishing its calibration criteria, an increase in PTR will not
degrade the system’s measurement accuracy.
The following methods may be considered for increasing or decreasing the
PTR.
Voltage controlled oscillators
1.
Select a different VCO source that has the tuning capabilities needed for
the measurement.
2.
Increase the tune range of the VCO source.
Be careful not to exceed the input voltage limitations of the Tune Port on the VCO source.
Increasing the tune range of the VCO is only valid as long as the VCO source is able to
continuously meet the previously mentioned tuning qualifications.
Summary of Contents for N5511A
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