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Figure 3. The user-settable parameter, frequency points, begins to determine the
boundaries of the time record length and frequency span operating region
5.2 Operating region curves for Agilent Acqiris digitizers
Several interrelated characteristics of both the Acqiris digitizers and the 89600 VSA
software combine to form a region within which the VSA is constrained to operate.
The 89600 VSA software characteristics that affect this operating region include
maximum number of time points, the minimum number of time points (not user
settable), a maximum acquisition record size (not user settable) and a maximum
decimation factor (not user settable). The Digitizer characteristics that affect the
operating region are sample rate and memory depth. This section describes the
effects each of these parameters has on the VSA operating region.
The operating region is described in terms of span and time record length. For a
given window type it could just as easily be described in terms of span and RBW.
Figure 3 shows the effects of the number of time points the 89600 VSA software is
allowed to collect. Because sample spacing is inversely proportional to span, the
record length decreases as span increases. Although a family of lines is shown,
only two defi ne the operating region at any one time. The lowest line gives the
smallest time record length allowed for any given span. The position of this line
is determined by minimum number of time points (16) the VSA requires in a time
record. The line that defi nes the upper time record length boundary is positioned
by the maximum number of time points the VSA allows in a time record . The maxi-
mum number of time points is determined by the Frequency Points setting (Meas-
Setup/ResBWFrequency Points). The 89600 VSA is constrained to operate in the
region between these two lines. Note that the operating lines of Figure 3 are the
same for all digitizer models.
1.E-08
1.E-07
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
1.E-01
1.E+00
1.E+01
1.E+02 1.E+03 1.E+04 1.E+05 1.E+06 1.E+07 1.E+08 1.E+09 1.E+10 1.E+11
Span (Hz)
Time record length (sec)
Minimum
Operating region: number of frequency points limits
Number of frequency points
204801
409601
102401
51201
25601
12801
6401
3201
1601
801
401
201