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14
Evaluating Your Measurement Results
Table 52 Potential causes of discontinuity in the graph (continued) (continued)
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
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.
Spurs on the graph
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.
Refer to Table 53. The spur marking criterion is a detected upward change of
more than X dB (where X is the value shown below) within 4 data points (a
single data point noise peak will not be marked as a spur). Note that the
effective noise floor for detecting spurs is above the plotted 1 Hz bandwidth
noise by the bandwidth correction factor.
336
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.
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.
Agilent E5505A User's Guide
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