The fft (Fast Fourier Transform) block that you're using, along with the Spectrum Analyser, outputs a frequency spectra of signals the fft signal. As such, it will only accept as input and output the spectrum units (dBm , dBV , dBW , Vrms , Watts).
If you would like to view the signal before the fast fourier transform is applied, I suggest that you connect another Scope block to display the signals you need.
