Keysight Technologies N5511A, Руководство пользователя

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82 N5511A Phase Noise Test System User’s Guide
Absolute Measurement Fundamentals
Evaluating Noise Above the Small Angle Line
Evaluating Noise Above the Small Angle Line
If the average noise level on the input signals exceeds approximately 0.1
radians RMS integrated outside of the Phase Lock Loop (PLL) bandwidth, it
can prevent the system from attaining phase lock.
The following procedure allows you to evaluate the beat note created between
the two sources being measured. The intent is to verify that the PLL bandwidth
is adequate to prevent the noise on the two sources from causing the system to
lose lock.
If the computer is displaying the hardware Connect Diagram you are ready to
begin this procedure. (If it is not, begin a New Measurement and proceed until
the hardware Connect Diagram appears on the display.)
Determining the Phase-Lock-Loop bandwidth
1. Determine the Peak Tuning Range (PTR) of your VCO by multiplying the
VCO Tuning Constant by the Tune Range of VCO value entered. (If the
phase noise software has measured the VCO Tuning Constant, use the
measured value.)
PTR = VCO Tuning Constant X Voltage Tuning
For Example:
2. Estimate the Phase Lock Loop (PLL) bandwidth for the measurement
using the PTR of your VCO and the graph in Figure 5-20 .
Observing the beat note
If the beat note frequency is below 100 kHz it appears on the analyzer’s display
in both the frequency domain and the time domain. If the beat note does not
appear on the RF analyzer, then the beat note is either greater than 100 kHz or
it does not exist.
If incrementing the frequency of one of the sources does not produce a beat
note within 100 kHz, you need to verify the presence of an output signal from
each source before proceeding.