Chapter 2
81
Programming Fundamentals
Improving Measurement Speed
automatically setting the value of the attenuator. It requires measuring
an initial burst to identify the proper attenuator setting before the next
burst can be measured properly. If you know the amount of attenuation
or the signal level needed for your measurement, just set it.
Note that spurious types of measurements must be done with the
attenuator set to automatic (for measurements like: output RF
spectrum, transmit spurs, adjacent channel power, spectrum emission
mask). These types of measurements start by tuning to the signal, then
they tune away from it and must be able to reset the attenuation value
as needed.
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:
1.
:STATus:OPERation:EVENt?
This query of the operation event
register is to clear the current register contents.
2.
: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.
3. 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.
These two commands are repeated until the condition is set, so we
know that the trigger is armed and ready.
4. Trigger your DUT to send the burst.
