Agilent Technologies VXI E1439 - Manual (Page 37)

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Using the Agilent E1439
Delay and phase in triggered measurements
Due to the pretrigger delay of 32, the desired trigger point would have been at the 32nd sample of
the time record. However, the delay_actual value of 16 indicates that the sample corresponding
to the actual trigger is number 32+16/2
4
or the 33rd sample. The measured phase of the 33rd
(complex) sample, found via the atan2() function, is 159 degrees. The phase of the LO at this
sample is 19697*360/65536=108 degrees. Adding these together to get the corrected phase of the
input signal results in 267 degrees = -93 degrees, which is close to the expected phase of a sine
wave triggered at its zero-crossing, which would be -90 degrees.