(S) = Simplex — the transmit and receive frequencies are the same, with no offset (no “+” shown on your display).

If you cannot hear another station on a simplex frequency, it simply means you are out of that station’s range. Unlike a repeater, a simplex station does not re-broadcast your signal locally — the RF travels directly from the other station to you, point to point, with nothing in between to extend its reach.

However, you will hear stations connecting in via IRLP or AllStar, because that audio is coming directly out of the simplex radio you are tuned to.