Yes avoid splitters. Most AM /Fm radios will work quite well in a f/g boat with just a piece of wire run from the antenna socket for about 2 metres inside the hull ie along a shelf. give it a try. If that is inadequate try attaching that wire to the rigging or try an external wire or rod. olewill
I've used the active (powered) splitters and they work well, very good vhf reception of fairly weak stations and no noticeable effect on the transceiver.
I have a splitter from Pacific. It works well. No noticable loss on either VHF or FM. Before buying I tried extending the aerial and touched it down to the rigging chain plates. Didn't seem to make any real difference.