Figure 2-77 Setup Time For Interpulse Measurement - Agilent Technologies 8560E User Manual

Making Measurements
Example 11: Time-Gated Measurement
You can set the gate length to any value you desire that lets you
select the proper portion of the signal of interest to measure.
Choosing a narrower gate length forces you to select a wider video
bandwidth, as will be discussed in step 5.
Note that the signal need not be an RF pulse. It could be simply a
particular period of modulation in a signal that is continuously
operating at full power, or it could even be during the off time
between pulses. Depending on your specific application, adjust the
gate position to allow for progressively longer setup times (ensuring
that the gate is not left on over another signal change such as a
pulse edge or transient), and select the gate delay and length that
offer the best signal-to-noise ratio on the display.
If you were measuring the spectrum occurring between pulses, you
should use the same (or longer) setup time after the pulse goes away,
but before the gate goes on. This lets the resolution-bandwidth
filters fully discharge the large pulse before the measurement is
made on the low-level interpulse signal.
Figure 2-77 Setup Time for Interpulse Measurement
5. Adjust the resolution bandwidth and video bandwidth. Adjust the
resolution bandwidth to greater than two divided by the setup time.
If you want to use a narrower bandwidth, you can increase the setup
time. See the previous step for more information. Adjust the video
bandwidth to greater than one divided by the gate length.
Resolution Bandwidth
The resolution bandwidth you can choose is determined by the gate
position, so you can trade off longer setup times for narrower
resolution bandwidths. This trade-off is due to the time required for
the resolution-bandwidth filters to fully charge before the gate comes
on. Setup time, as mentioned, is the length of time that the signal is
present and stable before the gate comes on.
146 Chapter 2