In Simulink Library - RF Blockset 's Sources how to make the Continuous Wave's Carrier frequencies tunable?

Dear Sir,

I am a beginer user to Matlab and i have ran into some issue which i don't know how to resolve.

1. I am trying to use a Rotary Knob to vary the Carrier Frequencies of the Continuous Wave from the Simulink Library - RF Blockset 's Sources, but i can't and it show some error.
2. The Rotary Knob can't seem to connect to the Continuous Wave, it will display the following error.

3. What i want to acheive is that, when the simulation is running, i want to change the Continuous Wave's Carrier Frequencies and let it display on the Spectrum Analyzer.

So please provide me with some feedbacks/suggestion on how to make this work.

kind regards

Kei Lam