I mounted a regular marine VHF antenna on the transom, which I use as my AIS antenna. It doesn't have as good range as if it were at the masthead, but my logic was that if I got de-masted I could use it as a backup VHF marine antenna.
Don't use a splitter - one good enough to prevent your marine VHF from overwhelming your AIS receiver would probably cost more than just a separate antenna and feedline.
Don't use a splitter - one good enough to prevent your marine VHF from overwhelming your AIS receiver would probably cost more than just a separate antenna and feedline.