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CACD Group
updated 2000.03.30
Author: Mike Smith

spec: generate a Fourier transform vector

General Form
spec start_frequency stop_frequency frequency_step vector
Calculates a new vector containing the Fourier transform of the input vector. This vector should be the output of a transient analysis. This command takes note of the following shell variables which can be set using the set command:
Variable Type Description
specwindow String Specifies the windowing function. Possible values are:

none
hanning or cosine
rectangular
hamming
triangle or bartlet
blackman
gaussian

If this variable is not defined, the hanning window is used.
specwindoworder Number Specifies the window order for the gaussian window only.
Note that the time axis of the input vector should be linearised first by using the linearize command because SPICE does not produce a linear time axis for transient analyses. After using the spec command, the spectrum can be displayed by plotting the magnitude of the resultant vector.
For example, after a transient analysis resulting in transient vector v(1), the spectrum can be plotted with the following commands:

linearize
spec 10 100000 5000 v(1)
plot mag(v(1))
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