Has anyone been able to undertake a Random Response analysis in Abaqus CAE?

I am trying to undertake a Random Response analysis in Abaqus 6.14, but am unable to specify the random excitation. I have been referring to the user guide:http://localhost:2080/v6.14/books/usb/default.htm?startat=pt03ch06s03at16.html#usb-anl-arandomresponseI can follow the guide up to the section titled "Defining the frequency functions". however when i try to create a load amplitude i get the following dialogue, suggesting that i am unable to create a load. I understand that the loads are created under the model, and not the step but i cant find how i do this. 

Any ideas?