Waterfall-Scope plot an FFT with Simulink

Hi!

I'm relativly new to Simulink with the SDRu block libraray and the Digital Communications Toolbox. I'm using the Ettus UHD support package. I can connect to my USRP2. I want to plot the samples into a Waterfall-Scope Sink, but I face an issue with the data-types. The issue is very similar to the model shown below, but the source here is a simple Sine Wave.

Could somebody give me a short pointer which block there is to use for conversion here? It seems a Scalar Input is not possible.

Best, Marius