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Absolute Measurement Fundamentals
Evaluating Noise Above the Small Angle Line
6. Using the --> key on the RF analyzer, offset the marker by the PLL
bandwidth. Read the offset frequency and noise level indicated at the
bottom of the display. (If the noise level falls below the bottom of the
display, the marker reading will still be correct. To increase the vertical
scale, press [[ VERT SCALE ]] press [[, DEFINE DB/DIV, and enter 20
dB.)
7. Compare the average noise level at the PLL bandwidth offset to the
small angle criterion level shown on the graph in
page
small angle line at all offset frequencies beyond the PLL bandwidth.
(The small angle line applies only to the level of the average noise. Spur
levels that exceed the small angle line will not degrade measurement
accuracy provided they do not exceed -40 dBc.)
Figure 6-12
Graph of Small Angle Line and Spur Limit
8. Continue moving the marker to the right to verify that the average noise
level remains below the small angle line.
9. Increase the span by a factor of ten by selecting FREQ and DEFINE
SPAN. Continue comparing the noise level to the graph.
10. Continue to increase the span width and compare the noise level out to
100 kHz. (If the noise level exceeds the small angle line at any offset
frequency beyond the PLL bandwidth, note the offset frequency and
level of the noise. Use the graph in
determine the Peak Tuning Range (PTR) necessary to provide a
sufficient PLL bandwidth to make the measurement.
6-22 Agilent Technologies E5500 Phase Noise Measurement System
6-22. The average noise level of the signal must remain below the
Figure 6-12 on
Figure 6-13 on page 6-23
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