Determining whether signal meets the 12 dB SINAD voltage
I don't see how I can calculate the voltage level of a signal


Well, you know it has to be 0.15 uV RMS and, if you assume a 50 ohm impedance at the antenna electrical terminals, then you know the power (\$V^2/R\$) = 0.45 femto watts.

This will be the power transferred by the antenna to your circuit. Given that the antenna will likely have gain you'll have to factor this in to things but, the basic equation you need is the Friis link loss formula. That will tell you what power you need to transmit at over the distance between send and receive.