Can VHF and AIS run on the same aerial?

I’m planning to fit an AIS transceiver to my yacht and I can’t decide if I should fit a splitter or not, so that my AIS can share the same aerial as my VHF radio.

Also, I am unclear about the difference between passive and active splitters.

Can you offer any help?

Robert Campbell

James Turner replies:

Regarding the antenna, the most important VHF channel for voice is Ch16 because that’s the ‘help me, I’m sinking’ channel.

And the frequency for AIS is absolutely at the other end of the marine VHF spectrum.

So, whereas Ch16 is on 156MHz, AIS is at 162MHz.

For any antenna, its length dictates its centre frequency, so if you use a splitter on a VHF voice antenna that is centred on 156MHz it’s not going to be very good at the 162MHz that AIS requires– so what’s the point?

If you can separate the antenna systems, that’s really the way to go.

Another thing important to the whole subject is that if we’re talking sailboats, an antenna at the top of the mast gives a fantastic 20-mile-plus VHF range.

But does anyone really need AIS at 20 miles range?

That ship might change course, you might change course, tack, gybe or whatever, and things are very different at 20 miles than they are at closer to four miles.

So I’ve always been very keen on having a separate AIS antenna and hanging it on a short pole attached to the back of the boat, out of the way of everything.

In an emergency, it also serves as a voice VHF antenna, should the mast come down.

Splitters are a compromise and a route not worth going down if you can avoid it.

If you can possibly do separate antennas, then do separate antennas.

About the expert

James Turner worked in the antenna business and can be found on the YouTube channel Boating Equipment Reviews.

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