Standard FFT function in SIGVIEW operates on real-valued sequences, i.e. real signal. If your
signal is complex, i.e. contains complex samples, you can still calculate its FFT by using
Complex-FFT function in
Signal calculator . Good examples
of such signals are complex signals
used in for signal analysis in radio communication.
Before applying this function, you need to load both real and complex part of your signal as
separate signal windows in SIGVIEW. Alternatively, you can perform 2-channel data acquisition
where the first channel contains real values and the second one complex values. Afterwards,
simply open Signal calculator window, choose real signal component, then press Complex FFT
button, and then finally choose your imaginary signal component. The result should look like this:
Press OK button in Signal calculator dialog and a new window containing complex FFT will
appear. As expected, its frequency axis will contain both negative and positive frequencies.
If your real and complex signals have different lengths, SIGVIEW will use only a part of the longer
signal (starting from its first sample) which has the length of the smaller signal.