1-22 Triggering and the Time Record
SR785 Dynamic Signal Analyzer
9. Press [Display Setup]
Select the Display Setup menu.
Press
<Measurement>
Change the Measurement of DisplayB back to Time
Record.
Select (Time1) with the knob and press [Enter].
Time1 is the un-windowed time record.
Press
[Window]
Select the Window menu.
Press
<Window>
Change the window type for both displays.
Select (Uniform) with the knob and press
[Enter].
Use the Uniform window (which is the correct
window for this measurement).
10. Press [Trigger]
Select the Trigger menu.
Press <Trigger Source>
Change the Trigger Mode.
Select (Cont) with the knob and press [Enter].
The continuious trigger source triggers
measurements as fast as the analyzer can go.
If the generator is set to 256 Hz pulse rate, the
signal will drift slowly in the time record. This is
because the SR785 time records are exactly
1/256 Hz (3.90625 ms) long (400 lines at full span)
and the analyzer is running in real time (no missed
data).
The drift in the time record is because the analyzer
and the generator are using different time bases.
Adjust the generator frequency to 255 Hz.
The time record is now unstable and the pulse
moves through the entire time record.
The spectrum in DisplayA is mostly unaffected
since the Uniform window allows the pulse to be
anywhere in the time record.
Only when the pulse is not entirely within the time
record is the spectrum disturbed.
This concludes this measurement example. You
should have a feeling for triggered time records and
the effect of windowing on the resulting FFT.
Содержание SR785
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