152 Chapter2
Making Measurements
Example 11: Time-Gated Measurement
Table 2-8 Suggested Sweep Times for a Known Pulse Repetition Interval
(PRI) or Pulse Repetition Frequency (PRF)
Pulse Repetition
Interval (PRI)
Pulse Repetition
Frequency (PRF)
Sweep Time (minimum)
≤50 µs ≥20 kHz 50 ms
100 µs 10 kHz 61 ms
500 µs 2 kHz 301 ms
1 ms 1 kHz 601 ms
5 ms 200 Hz 3.01 s
10 ms 100 Hz 6.01 s
16.7 ms 60 Hz 20 s
33.3 ms 30 Hz 30 s
50 ms 20 Hz 40 s
100 ms 10 Hz 60 s
>170 ms Use the MAX HOLD trace function and take several measurement sweeps.
Table 2-9 If You Have a Problem with the Time-Gated Measurement
Symptom Possible Cause Suggested Solution
Erratic analyzer trace with
random vertical lines or
dropouts extending below
the peak trace amplitude.
Sweep rate too fast to
ensure at least one gate
occurrence per trace point.
Increase sweep time until
dropouts disappear.
Erratic analyzer trace with
dropouts that are not
removed by increasing
analyzer sweep time;
oscilloscope view of gate
output signal jumps
erratically in time domain.
GATE DLY may be greater
than trigger repetition
interval.
Reduce GATE DLY until it
is less than trigger interval.
Gate does not trigger. Gate triggervoltage maybe
too low, or gate may not be
activated.
Ensuregatetrigger reaches
5.0 volts. Check to see if
other connections to trigger
signal may be reducing
voltage. If using
oscilloscope, check that all
inputs are high impedance,
not 50 Ω.
Display spectrum does not
change when the gate is
turned on.
Insufficient setup time. Increase setup time for the
current resolution
bandwidth, or increase
resolution bandwidth.
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