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Using the Optical Spectrum Analyzer
The Bandwidth/Sweep Menus
The following functions affect video bandwidth:
• Changing the sensitivity value.
• Changing the reference level.
• Turning autoranging
ON
or
OFF
.
The range of video bandwidth available in Auto mode is much greater than can
be set manually from the front panel. A lower video bandwidth value requires
a longer sweep time. Because of the interdependence between the video
bandwidth and sensitivity, it is recommended that either the sensitivity
or
the
video bandwidth be changed, whichever is the most important to the measure-
ment task being performed.
To change the sweep time
1
Press the front-panel
Bandwidth/Sweep
key.
2
Press the
Sweep Time
softkey.
3
Toggle between selecting sweep time automatically or manually.
4
Use the knob, step keys or numeric entry pad to enter the desired value.
The sweep time is the amount of time required for the optical spectrum ana-
lyzer to sweep the current measurement range. The optical spectrum analyzer
automatically selects sweep times based on coupling of the following instru-
ment settings:
• Wavelength span
• Resolution bandwidth
• Video bandwidth
• Sensitivity
• Trace length
• Power level
Coupling of these parameters yields optimum amplitude accuracy. When cou-
pled, the optical spectrum analyzer always uses the fastest sweep possible
while still maintaining the specified accuracy. Coupled, sweep times range
from 50 ms to a maximum value that depends on the number of trace points
used to draw the trace. This relationship is shown in the following equation:
The default number of trace points is 1001, so the maximum sweep time is
normally 100 seconds. When coupling is disabled, the sweep time can be set
from 56.3 ms to a maximum of 1000 seconds. If you change the number of
trace points, the maximum sweep time changes as well.
50 ms sweep time 1s()trace points()≤≤
book.book Page 16 Monday, January 31, 2000 10:34 AM