Stanford Research Systems SR780, Operating Manual And Programming Reference

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Triggering and the Time Record 1-21
SR780 Network Signal Analyzer
Select (WinTime1) with the knob and press
[Enter].
The Hanning window is zero at the beginning of the
time record and large in the center. This effectively
zeroes the signal pulse at the start of the time record
leaving nothing in the windowed time record. The
FFT operates on this windowed time record and
thus the spectrum shows no evidence of the signal
pulse.
8. Press [Trigger]
Select the Trigger menu again.
Press <DelayB> Change the Trigger Delay for the measurement in
DisplayB.
We can get the spectrum back by delaying the time
record relative to the trigger so that the pulse is
positioned in the center of the time record.
Press [-] [5] [0] [0] and [Enter].
A negative delay means that the time record starts
before the trigger event. In this case, the time record
is 1024 points long so we need about 500 bins
(points) of negative delay to put the signal pulse in
the center of the triggered time record.
The trigger delay is specified in time record bins at
the current span.
Press [Auto Scale B]
Note that the windowed time record in DisplayB
shows the signal at the center of the time record.
The amplitude of the windowed time record is not
the same as the amplitude of the time record itself.
This is because the window functions have gain and
attenuation at different parts of the time record. The
Hanning window is 2.0 at the center so the
amplitude of the signal in the windowed time record
is twice as large.
The Hanning, Flattop, BMH and Kaiser windows
are not intended for use with narrow pulse signals.
They are used for signals which last the entire time
record and normalized as such.
The Uniform (and Force) windows have no gain
and should be used with pulsed signals such as this.
Press <DelayA> We need to change the trigger delay for DisplayA
in order to recover the spectrum.