Agilent Technologies 8560E User Manual page 150

Making Measurements
Example 11: Time-Gated Measurement
"Rules" for Making a Time-Gated Spectrum
Measurement
This section summarizes the rules described in the previous sections.
Table 2-6 Determining Spectrum Analyzer Settings for Viewing a Pulsed
RF Signal
Spectrum Spectrum Analyzer Setting
Analyzer
Function
Sweep Set the sweep time to be 601
Time times greater than the pulse
repetition interval (PRI):
Sweep time > 601 × PRI
Gate Delay The gate delay is equal to the
signal delay plus half of the
pulse width:
Gate Delay = Signal Delay + τ/2
Gate The gate length is equal to
Length one-fourth the pulse width:
Gate Length = τ/4
Video Set the video bandwidth to a
Bandwidth value greater than 1 divided by
the gate length:
Video Bandwidth >1/gate length
Resolution Set the resolution bandwidth to
Bandwidth a value greater than 2 divided
by the gate delay minus the
signal delay:
Resolution Bandwidth >
2/(Gate Delay - Signal Delay)
150
Comments
Because the gate must be on at least
once per trace point, the sweep time has
to be set to the pulse repetition interval
times for every point of the trace. (Each
trace has 601 points.)
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.
If the gate length is too long, the signal
display can include transients caused by
the spectrum analyzer filters.
The video bandwidth must be wide
enough so that the rise times of the video
bandwidth do not attenuate the signal.
The maximum video bandwidth for
time-gate measurements is 1 MHz.
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.
Chapter 2