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Chapter 2 71
Programming Fundamentals
Improving the Speed of Your Measurements
These types of measurements begin tuned to the signal, then tune away
from it and must be able to reset the attenuation value as needed.
Optimize your GSM output RF spectrum switching
measurement.
For ORFS (switching), setting the break frequency to zero (0) puts the
analyzer in a measurement setup where it can use a direct time
measurement algorithm, instead of an FFT-based algorithm. This
non-FFT approach is faster. (However, remember that your break
frequency for ORFS (modulation) measurements must be >400 kHz for
valid measurements, so you will need to change the break frequency if
you are making both types of measurements.)
Avoid using RFBurst trigger for single burst signals.
RFBurst triggering works best when measuring signals with repetitive
bursts. For a non-repetitive or single burst signals, use the IF(video)
trigger or external trigger, depending on what you have available.
RFBurst triggering depends on its establishment of a valid triggering
reference level, based on previous bursts. If you only have a single
burst, the peak detection nature of this triggering function, may result
in the trigger being done at the wrong level/point generating incorrect
data, or it may not trigger at all.
Are you making a single burst measurement?
To get consistent triggering and good data for this type of measurement
application, you need to synchronize the triggering of the DUT with the
analyzer. You should use the analyzer’s internal status system for this.
The first step in this process is to initialize the status register mask to
look for the “waiting for trigger” condition (bit 5). Use
:STATus:OPERation:ENABle 32
Then, in the measurement loop:
• :STATus:OPERation:EVENt? This query of the operation event
register is to clear the current register contents.
• :READ:PVT? initiates a measurement (in this example, for GSM
power versus time) using the previous setup. The measurement will
then be waiting for the trigger.
Make sure the attenuation is set manually. Do NOT use automatic
attenuation as this requires an additional burst to determine the
proper attenuation level before the measurement can be made.
• Create a small loop that will serial poll the instrument for a status
byte value of binary 128. Then wait 1 msec (100 ms if the display is
left on/enabled) before checking again, to keep the bus traffic down.