Time record processing
The relationship between a time record and the frequency data is relatively straight
forward if the minimum resolution bandwidth (and therefore the maximum time
record length) is used. In this case the time record size is equal to the time record
size required by the FFT (which is dictated by the number of frequency points and
must be a power of 2
n
). Therefore, the FFT converts the samples in the time record
directly to display points.
If a higher resolution bandwidth is selected, the time length necessary to acquire
the time samples is shorter and fewer samples are required. However, the FFT
must still operate on the same time record length for display purposes, so the extra
time record length is set to zero (zero padded) before the FFT process. This
enables the FFT to properly convert the time record to the required number of
display points without adversely affecting the frequency data.
The time record calculations
The length of the time record determines how long a given measurement will take
and the maximum frequency resolution you can measure. As described above the
FFT time record size may differ from the size dictated by the resolution bandwidth.
The FFT record size must be a power of 2 equal to or greater than the number of
frequency points.
TP = INTEGER
T
∆T
TP (FFT)=2
n
≥ FP for zoom mode
TP (FFT)=2
n
≥(FP × 2) for baseband mode
Fundamental Measurement Interactions
19 - 20
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