LeCroy 6000 SERIES, Operator'S Manual

Page: 215 / 409

WR6K-OM-E Rev A ISSUED: October 2003
213
8.
Touch the Suppress DC checkbox if you want to make the DC bin go to zero. Otherwise,
leave it unchecked.
9.
Touch inside the Output type field, and make a selection from the pop-up menu.
10.
Touch inside the Window field, select a window type.
11.
Touch inside the Algorithm field and select either Least Prime
3
from the pop-up menu.
2
Zero-fill is useful when the source data for the FFT comes from a math operation that shortens the record. This is
commonly encountered in filtering operations like enhanced resolution. The missing data points are replaced by data
values, whose amplitudes are interpolated to fit between the last data point and th first data point in the record. This
guarantees that there is not a first-order discontinuity in the filled data. Since the data at the end of the record is "filled"
data, it is advisable to select a weighting window other than rectangular to minimize the effect of the fill on the resulting
spectrum.
3
The default algorithm is a least primes algorithm that computes FFTs on transform sizes having lengths that can be
expressed as factors of 2
N
*5
K
. This is very compatible with the record lengths encountered in the oscilloscope, which are
often multiples of 1, 2, 4, 5, or 10. or Power of 2 The other choice is a power of two algorithm where the record lengths are
in the form of 2
N
. The power of 2 algorithm generally runs faster than the least primes algorithm. The price that is paid is a
record length that is not the same as the acquired signal. The power-of-two FFT uses the first 2
N
points of the record. For
example, if you acquire 500 points in your trace, the power-of-two FFT would only use the first 256 points.