As the conductivity of a medium increases, the more a radio signal passing through it is attenuated. High frequencies are also attenuated more than low frequencies, and tend to reflect off the surface of the water more. As is well known communication with military submarines uses very low frequency electromagnetic radiation for this reason. Military frequencies are well below allocated hobby radio control bands, but the lowest hobby bands - typically around 27MHz/40MHz - can penetrate several feet of water at short distances, typically less than 45 meters. Penetration at these frequencies is easier in fresh water, but are difficult to impossible in sea water. Modern radio control sets using the 2.4GHz band penetrate water very poorly, and are thus not used by serious divers.