Agilent Technologies Signal Analyzer N9030a - Manual (Page 1215)

6 RLC Swept SA Measurement Front-Panel & SCPI Reference
Sweep/Control
This feature selects the internal periodic timer signal as the trigger. Trigger occurrences are set by
the Periodic Timer parameter, which is modified by the Sync Source and Offset.
The figure below shows the action of the periodic timer trigger. Before reviewing the figure, we’ll
explain some uses for the periodic trigger.
A common application is measuring periodic burst RF signals for which a trigger signal is not
easily available. For example, we might be measuring a TDMA radio which bursts every 20 ms.
Let’s assume that the 20 ms period is very consistent. Let’s also assume that we do not have an
external trigger source available that is synchronized with the period, and that the signal-to-noise
ratio of the signal is not high enough to provide a clean RF burst trigger at all of the analysis
frequencies. For example, we might want to measure spurious transmissions at an offset from the
carrier that is larger than the bandwidth of the RF burst trigger. In this application, we can set
the Periodic Timer to a 20.00 ms period and adjust the offset from that timer to position our
trigger just where we want it. If we find that the 20.00 ms is not exactly right, we can adjust the
period slightly to minimize the drift between the period timer and the signal to be measured.
A second way to use this feature would be to use Sync Source temporarily, instead of Offset. In
this case, we might tune to the signal in a narrow span and use the RF Burst trigger to
synchronize the periodic timer. Then we would turn the sync source off so that it would not mis-
trigger. Mis-triggering can occur when we are tuned so far away from the RF burst trigger that it is
no longer reliable.
A third example would be to synchronize to a signal that has a reference time element of much
longer period than the period of interest. In some CDMA applications, it is useful to look at
signals with a short periodicity, by synchronizing that periodicity to the "even-second clock" edge
that happens every two seconds. Thus, we could connect the even-second clock trigger to Ext1
and use then Ext1 as the sync source for the periodic timer.
The figure below illustrates this third example. The top trace represents the even-second clock. It
causes the periodic timer to synchronize with the leading edge shown. The analyzer trigger occurs
at a time delayed by the accumulated offset from the period trigger event. The periodic timer
continues to run, and triggers continue to occur, with a periodicity determined by the analyzer
time base. The timer output (labeled "late event") will drift away from its ideal time due to
imperfect matching between the time base of the signal being measured and the time base of the
analyzer, and also because of imperfect setting of the period parameter. But the synchronization
is restored on the next even-second clock event. ("Accumulated offset" is described in the in the
Offset function section.)
Remote Language Compatibility Measurement Application Reference 1215