IWR1642: Maximum theorical distance equation

Hi,

I'm trying to understand how we can determine the theorical distance and I found the 3 following formulas :  

1. f_{IF_max} = (S2d_max)/c
2. F_s ≥ (S2d_max)/c
3. d_max = (F_s*c)/(2*c).

I understand the first and the third formulas but I don't understand how we get the second one. The F_s frequency is the sampling rate but this frequency should not be at least twice the frequency of the IF signal to respect the Nyquist-Shannon sampling theorem?

Thanks,

François.