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Concepts
Time Gating Concepts
signal parameters you chose in Step 1. If necessary, adjust span, but do not decrease resolution
bandwidth, video bandwidth, or sweep time.
“Quick Rules” for Making Time-Gated Measurements
This section summarizes the rules described in the previous sections.
Table 1 Determining Signal Analyzer Settings for Viewing a Pulsed RF Signal
Signal Analyzer Setting
Comments
Sweep Time
(gated video
only)
Set the sweep time to be equal to or
greater than
Because the gate must be on at least once per
trace point, the sweep time should be set such that
the sweep time for each trace point is greater than
or equal to the pulse repetition interval.
Gate Delay
The gate delay is equal to the signal
delay plus one-fourth the pulse width:
Gate Length
Resolution
Bandwidth
(number of sweep points - 1) × pulse
repetition interval (PRI):
Gate Delay = Signal Delay + τ /5
The gate delay must be set so that the gating
captures the pulse. If the gate delay is too short or
too long, the gating can miss the pulse or include
resolution bandwidth transient responses.
The gate length minimum is equal to
one-fourth the pulse width (maximum
about one-half):
If the gate length is too long, the signal display
can include transients caused by the signal
analyzer filters.
Gate Length = 0.7 x τ /4
The recommendation for gate placement can be
between 20 % to 90 % of the pulse width.
Set the resolution bandwidth:
The resolution bandwidth must be wide enough
so that the charging time for the resolution
bandwidth filters is less than the pulse width of
the signal.
RBW > 19.5/τ
Figure 13-21 Gate Positioning Parameters
Chapter 13
163
Concepts
Signal Analyzer
Function