Keysight Technologies N5511A, Руководство пользователя

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62 N5511A Phase Noise Test System User’s Guide
Absolute Measurement Fundamentals
The Phase-Lock Loop Circuit
Selecting the VCO Source
Although you must select a VCO source that provides a sufficient tuning range
to permit the system to track the beat note, keep in mind that a wide tuning
range typically means a higher noise level on the VCO source signal. When the
VCO source for your measurement is also the reference source, this trade-off
can make reference source selection the most critical aspect of your
measurement setup.
Specifying your VCO Source
When you set up your PLL measurement, you need to know four things about
the tuning characteristics of the VCO source you are using. The System
determines the VCO source's peak tuning range from these four parameters.
— Tuning Constant, estimated tuning sensitivity (Hz/V)
— Center Voltage of Tuning Range, (V)
— Tune Range of VCO, (±V)
— Input Resistance of Tuning Port, (ohms) if the tuning constant is not to be
measured.
The measurement examples in the next chapter that recommend a specific
VCO source provides you with the tuning parameters for the specified source.