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5
Absolute Measurement Fundamentals
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 beatnote 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
For Example:
2
Observing the beatnote
If the beatnote frequency is below 100 kHz it appears on the Agilent E4411A
RF analyzer's display in both the frequency domain and the time domain. If
the beatnote does not appear on the RF analyzer, then the beatnote is either
greater than 100 kHz or it does not exist.
If incrementing the frequency of one of the sources does not produce a
beatnote within 100 kHz, you need to verify the presence of an output signal
from each source before proceeding.
124
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
Estimate the Phase Lock Loop (PLL) bandwidth for the measurement using
the PTR of your VCO and the graph in
Tuning
Constant
X
Hz
PTR
=
100
X
10
V
=
V
Figure
Voltage
Tuning
1
kHz
82.
Agilent E5505A User's Guide
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