National Instruments Toolkit Figure 7. Center Frequency and Span Combinations

© National Instruments Corporation 19 NI Spectral Measurements Toolkit User Guide
The left side of Figure7 shows examples of the four combinations of
center frequency and span that you can encounter in the case of a real
input signal. The right side of Figure 7 shows the actual coerced values of
center frequency and span that the VI sets in each example.
Figure 7. Center Frequency and Span Combinations
Figure 7a demonstrates that if you enter appropriate values for both center
frequency and span, the values do not change. The spectrum represents the
frequency response of the input antialiasing filter on the data acquisition
device. Figure7b demonstrates that if you enter a center frequency value
Effective Band
fl
Span
fcfhfs/2
Effective Band
Span
flfc
fhfs/2
Effective Band
Span
flfcfhfs/2
Effective Band
Span
flfcfhfs/2
Effective Band
Span
flfcfhfs/2
Effective Band
flfhfs/2
Effective Band
fl
Span
fcfhfs/2
Effective Band
Span
flfc +f
hfs/2
Antialiasing Filter Response
Span
fc = (fl + fh)
2
a.
b.
c.
d.
User Input Coerced Result