I have a Raymarine 240 vhf radio. The problem I am having is I have to turn to squelch to the lowest level to receive a transmission. Even on the lowest squelch I am only receiving nearby signals. AIS is also only seeing close by vessels. Even the weather channels only comes in if I turn the squelch to zero. I have a shared antenna between the vhf and AIS. Is this an antenna or a transceiver problem?