Specifications

Chapter 15 143
Concepts
Time Gating Concepts
Concepts
View/Trace (ESA) or Trace/View (PSA) menu) to determine the frequency
of peak energy.
To optimize measurement speed, set the span narrow enough so that
the display will still show the signal characteristics you want to
measure. For example, if you wanted to look for spurious signals within
a 200 kHz frequency range, you might set the frequency span to just
over 200 kHz.
Step 4. Determine the setup time and signal delay to set up the gate signal.
Turn on the gate and adjust the gate parameters including gate delay
and gate length as shown below.
Generally, the gate should be positioned over a part of the signal that is
stable, not over a pulse edge or other transition that might disturb the
spectrum. Starting the gate at the center of the pulse gives a setup time
of about half the pulse width. Setup time describes the length of time
during which that signal is present and stable before the gate comes on.
The setup time (SUT) must be adequately long enough for the RBW
filters to settle following the burst-on transients. Signal delay (SD) is
the length of time after the trigger, but before the signal of interest
occurs and becomes stable. If the trigger occurs simultaneously with the
signal of interest, SD is equal to zero, and SUT is equal to the gate
delay. Otherwise, SUT is equal to the gate delay minus SD. See Figure
15-16.
Figure 15-16 Positioning the Gate
There is flexibility in positioning the gate, but some positions offer a
wider choice of resolution bandwidths. A good rule of thumb is to
position the gate from 20% to 80% of the burst for PSA, and 25% to 80%
of the burst for ESA. Doing so provides a reasonable compromise
between setup time and gate length.