HP 54750A, User Manual, Page: 157 / 478

The Digital Communications
Analysis Menus
Mask T est Menu
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Mask Align
Mask align is only enabled with Mask T est on.
After a mask is selected, or created, it is aligned to the waveform. F or
example , an eye-diagram for a laser transmitter will typically require the
mask to be placed in the center of the eye . In this case , the center of the eye
is measured relative to the eye crossing points and the most prevalent one
and zero levels .
Mask alignment is automatically performed. However , the algorithm used
to determine where the mask is placed acts on all the data currently in the
database . If the display is set to variable persistence , the alignment of the
mask can be aected by data that is in the database , but not displayed.
N O T E
T o ensure all of the data in the database is displa yed, mask testing should be performed in Innite
P ersistence mode .
T o ensure proper mask alignment:
set the time base to display 2.3 bit periods
set the vertical scaling so the complete magnitude of the waveform is
displayed
Once a mask alignment is performed, the database is cleared and data
acquisition begins again. Mask hits are only measured from the most recently
acquired data.
K ey Path 4 Shift 5 4 Mask test 5
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Mask align
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