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3-10 Defining Laser-Line Peaks
Peak excursion The peak excursion defines the rise and fall in ampli-
Examples of
valid and
invalid signals
tude that must take place in order for a laser line to be
recognized. The rise and fall can be out of the noise, or
in the case of two closely spaced signals, out of the filter
skirts of the adjacent signal. The peak excursion's
default value is 15 dB. Any laser line that rises by 15 dB
and then falls by 15 dB passes the rule. You can set the
peak excursion value from 1 to 30 dB.
In the following figure, three laser lines are identified:
responses ➀, ➂, and ➃. Response ➁ is not identified
because it is below the peak threshold. The portion of
each signal that is within the peak excursion limits is
shown in bold lines.
Because of the peak excursion rule, responses ➃ and ➄
are identified as one laser line—the minimum point
between ➃ and ➄ does not drop to the peak excursion
limit. This response has the highest power shown,
which is peak ➃.
Whenever the peak threshold limit or peak excursion
value is changed, the new limits are applied to the cur-
rent displayed measurements even if the instrument is
in the Single measurement mode.
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