3 Spectrum Analyzer Mode
3.2 Swept SA Measurement
Couplings Switching to Zero Span:
–
Turns off Signal Track
–
Turns off the auto-coupling of Res BW and sweep time
–
Places the instrument in Center/Span frequency entry mode
When you enter Zero Span, the instrument changes the displayed frequency span to
0 Hz. The horizontal axis changes to time rather than frequency. The amplitude
displayed is the input signal level at the current center frequency. This is a time-
domain mode that changes several measurement functions and couplings. The
instrument behavior is similar to an oscilloscope with a frequency selective detector
installed in front of the oscilloscope. See Application Note 150 for more information
on how to use Zero Span.
While in Zero Span, setting Span to a non-zero value through SCPI or the front
Panel returns the instrument to Swept Span. You can also return to your last Swept
Span by pressing the Swept Span/Zero Span toggle on the Span control.
The following table summarizes the differences between Zero Span and Swept
Span:
Zero Span Swept Spans
X axis is time X axis is frequency
There is no auto-Res BW selection unless the EMC
Standard is CISPR or MIL
Res BW coupled to Span when Res BW in
Auto
There is no auto sweep time Sweep time coupled to Res BW when
sweep time in auto
Interval Power calculated in Mkr Function Band Power calculated in Mkr Function
Can only define time limits when in zero span Can only define frequency limits when in
Swept SA
Marker Count counts at the center frequency Marker Count counts at the marker
frequency
CF Step size set to Res BW value CF Step autocouples to 10% of Span
Some Marker -> commands not available Other Marker -> commands not available
Freq entry mode always Center/Span Freq entry mode can be Center/Span or
Start/Stop
N dB points reports a time difference N dB points reports a frequency
difference
Full Span
Changes the frequency span of the instrument to the Preset frequency span of the
instrument and sets the Frequency entry mode to Center/Span.
Spectrum Analyzer Mode User's &Programmer's Reference 291
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