Hi,

You should use the PERIODIC option of the amplitude module (you were right). Here is one example of null load ratio:

*AMPLITUDE, NAME=cosinus_R0, DEFINITION=PERIODIC

1, 6.283, 0., 1.

-1., 0.

Please have a look into the documentation (Keyword Reference at the *Amplitude location) to have more details on the data provided. If this is not clear, I will give you more informations.

Hi

why are you not using tabular option instead of periodic? 

 Because if the signal is periodic, this choice seems the most appropriate. However, your solution also works...