Stanford Research Systems SR785, Руководство по эксплуатации и программированию

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Triggering and the Time Record 1-21
SR785 Dynamic Signal Analyzer
Press <Measurement> Change the Measurement of DisplayB to show the
effect of the Hanning window on the time record.
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 <Delay1> Change the Trigger Delay for the signal on Ch 1.
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 [-] [2], select (ms) with the knob, and
[Enter]. A negative delay means that the time record starts
before the trigger event. In this case, the time
record is about 4 ms long so a delay of -2ms will
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.