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15
Evaluating Your Measurement Results
Problem Solving
Table 15-2 Potential Causes of Discontinuity in the Graph
Circumstance
Break at the upper edge of the
segment below PLL Bandwidth ³ 4.
Small Break at 100 kHz,
10 kHz, or 1 kHz
Higher Noise Level
Spurs on the Graph
15-14
E5500 Phase Noise Measurement System Version A.02.00
Description
Accuracy degradation of more than
1 or 2 dB can result in a break in the
graph at the internal changeover
frequency between the phase
detector portion of the
measurement and the voltage
controlled oscillator tune line
measurement. The accuracy
degradation can be caused by:
An inaccurate Tuning or Phase
Detector Constant
Injection locking, or
Noise near or above the small angle
line at an offset equal to the PLL
Bandwidth for the measurement.
The noise level measured by the test system reflects the sum of all of
the noise sources affecting the system. This includes noise sources
within the system as well as external noise sources. If the general
noise level measured for your device is much higher than you
expected, begin evaluating each of the potential noise sources. The
following table will help you identify and evaluate many of the
potential causes of a high noise floor.
Except for marked spurs, all data on the graph is normalized to a 1
Hz bandwidth. This bandwidth correction factor makes the
measurement appear more sensitive than it really is. Marked spurs
are plotted without bandwidth correction however, to present their
true level as measured.
Recommended Action
Check the Parameter Summary list
provided for your results graph to
see if any accuracy degradation was
noted. If the Tuning constant and
Phase Detector constant were not
measured by the phase detector
system, verify their accuracy by
selecting the Measured calibration
method and then initiating a New
Measurement. If you suspect
injection locking or noise above the
small angle line, refer to the Problem
Solving section of Chapter 3 for
specific actions.
Document Part No. E5500-90024 Ed. 1.0
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