HP ESA-L1500A, Руководство пользователя и калибровки

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88 Chapter 4
Front-Panel Key Reference
Measure
Limits Fixed Rel
allows you to choose fixed or relative limit lines. The
fixed (
Fixed
) type uses the current limit line as a
reference with fixed frequency and amplitude values.
The relative (
Rel
) setting causes the current limit line
value to be relative to the displayed center frequency
and reference-level amplitude values. When limit lines
are specified with time, rather than frequency, the
Rel
setting only affects the amplitude values. The current
amplitude values will be relative to the displayed
reference- level amplitude, but the time values will
always start at the left edge of the graticule.
As an example, assume you have a frequency limit line.
If the limit line is specified as fixed, entering a limit
line segment with a frequency coordinate of 300 MHz
displays the limit line segment at 300 MHz. If the same
limit line table is specified as relative, it is displayed
relative to the spectrum analyzer center frequency and
reference level. If the center frequency is at 1.0 GHz, a
relative limit line segment with a frequency coordinate
of 300 MHz will display the limit line segment at 1.3
GHz. If the amplitude component of the relative limit
line segment is –10 dB, then
−
10 dB is added to the
reference level value to obtain the amplitude of the
given component (reference level offset included).
A limit line entered as fixed may be changed to relative,
and one entered as relative may be changed to fixed.
When changing between fixed and relative limit lines,
the frequency and amplitude values in the limit line
table change so that the limit line remains in the same
position for the current frequency and amplitude
settings of the spectrum analyzer. If a time and
amplitude limit line is used, the amplitude values
change but the time values remain the same.
Key Access:
Measure
,
Limits
Edit Limits
allows you to edit the current limit line tables by
accessing the
Select Line Upper Lower
, and
Edit Line
keys. Use
Delete Limits
in the
Limits
menu to dispose of
the current limit line table. Key Access:
Measure
,
Limits
Select Line Upper Lower
selects upper or lower limit line
tables.
With Lower selected on the
Select Line Upper Lower
softkey,
Edit Line
allows you to view or edit the lower
limit line table. Up to 30 entries are allowed for the
lower limit line table. With the lower limit line table
format, the coordinates for the lower limit line are
specified, but none are specified for the upper limit line.