Stanford Research Systems SR780, Operating Manual And Programming Reference

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1-20 Triggering and the Time Record
SR780 Network Signal Analyzer
Select (Auto Arm) with the knob and press
[Enter].
Free Run means the measurement is free running
(requires no trigger). Auto Arm means the trigger is
armed automatically and the measurement is
triggered.
Press <Trigger Level>
The default Trigger Source is the Ch1 input (our
pulse signal). Adjust the trigger level to trigger on
the pulse.
Press [3] [0] and [Enter]. Set the trigger level as a percentage of full scale.
Adjust the level for a stable time record in
DisplayB.
Press [Auto Scale B] DisplayB (bottom) should display the pulse
waveform at the left edge. Remember, the FFT span
is baseband so the time record is entirely real and
non-heterodyned. In this case, the display shows the
signal pulse as a digital oscilloscope would.
6. Press [Window]
Select the Window menu.
Because the pulse is much shorter than the time
record, we need to use the Uniform (or Force)
window. The other window functions taper to zero
at the start and end of the time record. Always be
aware of the effect windowing has on the time
record and the FFT.
Press <Window> Select a new window type for both displays
(window type is linked by default).
Select (Uniform) with the knob and press
[Enter].
Notice how the spectrum in DisplayA is changed by
the Uniform window.
Press [Auto Scale A]
The spectrum in DisplayA is the sinx/x envelope of
a rectangular pulse. The zeroes in the spectrum
occur at the harmonics of 1/pulse width (1/100
µ
s or
10 kHz.)
7. Press <Window>
Choose a non-optimum window.
Select (Hanning) with the knob and press
[Enter].
Choose the Hanning window. Notice how the
spectrum in DisplayA goes away.
Press [Display Setup]
Select the Display Setup menu.
Press <Measurement> Change the Measurement of DisplayB to show the
effect of the Hanning window on the time record.