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Old 27-10-2010, 13:54   #1
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Can AIS Share VHF Antenna with Existing VHF Radio ?

Hi, I just bought West Marine AIS-1000 class-B AIS.
I have existing VHF radio (Horizon Intrepid GX1260S) that are hooked with mast head antenna.
Both AIS and VHF allow antenna input and no output.

Question: can I buy T-type antenna connector and connect the main antenna to both VHF radio and AIS that I bought?

If I cannot do, i should be using handheld VHF radio and/or put up separate VHF antenna to AIS I guess.

Thanks for reading.

y.lee
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Old 27-10-2010, 14:01   #2
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There are special splitters that are available for this reason, Vesper marine and Digital Yacht both make them. What you don't want to do is mount a separate antenna that is any closer than 3 feet from the existing VHF antenna.
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Old 27-10-2010, 14:06   #3
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Do not use a T-connector -- you will probably burn out the receiver, and it will certainly not work very well for either the VHF or the AIS units.

There are active antenna splitters you can buy which will let you share one antenna. Go to Milltech Marine to see examples of these. There are others out there as well.

I prefer to use a separate antenna though. You can certainly use your handheld VHF, but you're going to give up a lot of range and convenience.
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Old 27-10-2010, 14:22   #4
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Quote:
Originally Posted by cool2848 View Post
Hi, I just bought West Marine AIS-1000 class-B AIS.
I have existing VHF radio (Horizon Intrepid GX1260S) that are hooked with mast head antenna.
Both AIS and VHF allow antenna input and no output.

Question: can I buy T-type antenna connector and connect the main antenna to both VHF radio and AIS that I bought?
Simple answer: NO!

Not quite so simple answer: It would work for a while. But if you just physically join the cables, besides impedence and intereference issues, the second you key down the VHF transmitter you're probably going to fry the AIS unit. Maybe even the VHF unit too, depending on how robust the finals are (I would think they would be able to handle 2W, I imagine they see more reflected power than that in normal operation).

There are more expensive units (which means nothing, as you've already invested, and they don't seem cost effective anyway) that have a built in duplexer that allows for antenna sharing. You could make, or even purchase, such a duplexer yourself, but a quick google search didn't turn up anything promising.

Quote:

If I cannot do, i should be using handheld VHF radio and/or put up separate VHF antenna to AIS I guess.

Thanks for reading.

y.lee
The installations I have seen, and I am awaiting parts to do my own at the moment, pretty much have the AIS antenna mounted on a spreader. That's how I was advised to do it by my local electronics guru. There is some thought to swapping out and mounting the AIS antenna at the masthead and using the spreader antenna for the VHF, to give the more often used unit more range. I'm still chewing on this one. I doubt it really matters much, but I'll await the opinion of someone more experienced than I.

JRM
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Old 27-10-2010, 16:11   #5
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If you buy a proper ais active splitter designed for transmit ais. The it works fine. You can't use a simlple "T" at all don't even try it.

Dave.
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Old 01-11-2010, 10:25   #6
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If you decide to use a separate VHF antenna, which has the benefit of redundancy in your systems, you can mount the AIS antenna on the stern rail.

AIS signals come from ships which have their antennae mounted high up on their superstructure and this helps to provide a reasonable receiving distance even with your antenna mounted low down. You should get 12 miles and, for a ship steaming at 24 knots, that's a half hour in which to react.

If you carry the appropriate adapter you can switch the AIS antenna with the masthead antenna in case of a dismasting or bird strike or other event that takes out the masthead unit.
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Old 01-11-2010, 10:34   #7
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The cheap solution is a second ariel, which we have, mounted on a pole on the stern. Also I wasn't too keen on another split int he VHF cable. There is one at the base of the mast but didn't fancy another.

Pete
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Old 12-02-2013, 11:48   #8
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Re: Can AIS Share VHF Antenna with Existing VHF Radio ?

From JRM:

"The installations I have seen, and I am awaiting parts to do my own at the moment, pretty much have the AIS antenna mounted on a spreader. That's how I was advised to do it by my local electronics guru. There is some thought to swapping out and mounting the AIS antenna at the masthead and using the spreader antenna for the VHF, to give the more often used unit more range. I'm still chewing on this one. I doubt it really matters much, but I'll await the opinion of someone more experienced than I."

I'm considering the same solution. If you've completed yours I'd be interested to know if the mast disrupts the coverage of the AIS antenna on the spreader?

Thanks
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Old 12-02-2013, 14:50   #9
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Re: Can AIS Share VHF Antenna with Existing VHF Radio ?

FWIW:

We had the AIS antenna mounted on the solar panel arch, about 12 feet above the WL. Routinely got ship transmissions from 20+ mile distances. Now on masthead, and we get them at 50+ miles. Interesting, but really, not very useful. In fact, these distant contacts only clutter up the screen and target lists.

BTW, our AIS receiver (Icom) has a built in splitter which works very well. The insertion losses are not perceptible for either AIS or normal VHF usage.

Cheers,

Jim
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Old 12-02-2013, 15:28   #10
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Re: Can AIS Share VHF Antenna with Existing VHF Radio ?

The cheap solution IS a second antenna! The splitter costs more than an antenna.
I put a new antenna on the aft rail so I could switch between the mast head one for the AIS or the VHF depending on what I needed the best range. So its always on the AIS!

I did have a splitter but I was never happy with it and took it back.

Now I know how good an AIS is I reckon its worth its own masthead antenna.
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Old 12-02-2013, 22:25   #11
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Re: Can AIS Share VHF Antenna with Existing VHF Radio ?

I have an AIS 600 and my VHF signal goes through it then out to the (one) antenna.
If your AIS doesn't have a splitter or a pass-through like mine, cheapest option is a 2nd antenna. Also, you'll get a spare VHF into the bargain, in case one breaks off at an inconvenient moment.
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Old 18-02-2013, 08:39   #12
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Quote:
Originally Posted by CptnHornblower View Post
From JRM:

"The installations I have seen, and I am awaiting parts to do my own at the moment, pretty much have the AIS antenna mounted on a spreader. That's how I was advised to do it by my local electronics guru. There is some thought to swapping out and mounting the AIS antenna at the masthead and using the spreader antenna for the VHF, to give the more often used unit more range. I'm still chewing on this one. I doubt it really matters much, but I'll await the opinion of someone more experienced than I."

I'm considering the same solution. If you've completed yours I'd be interested to know if the mast disrupts the coverage of the AIS antenna on the spreader?

Thanks
I totally cheated, and put a second antenna mounted to the rear of the bimini (easier cabling). It worked fine for what we wanted on the Catalina, which is to spot shipping in the channel without the expense of radar.

I'm moving all those electronics to our new boat, and pulling the mast next month. I'm back to debating the placement again. Although this time I'm investing in radar also, so I'll have to figure that into the equation.

And not that it matters, but when I bought the WM AIS transponder the documentation stated that it could not be reprogrammed. I asked at the local store, they made some phone calls, and turns out it can be done for like $40 or so.

JRM
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Old 18-02-2013, 09:15   #13
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Re: Can AIS Share VHF Antenna with Existing VHF Radio ?

Quote:
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when I bought the WM AIS transponder the documentation stated that it could not be reprogrammed. I asked at the local store, they made some phone calls, and turns out it can be done for like $40 or so.

JRM
You can still use it with the wrong MMSI number in it. it still works. You can have the correct boat name, so doesnt really matter.
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Old 03-03-2013, 23:39   #14
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You can't use a transponder with the wrong MMSI in it! It's a federal crime in most jurisdictions internationally.
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Old 04-03-2013, 07:12   #15
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Re: Can AIS Share VHF Antenna with Existing VHF Radio ?

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You can still use it with the wrong MMSI number in it. it still works. You can have the correct boat name, so doesnt really matter.
Mark

You are absolutely wrong, at least if you want to obey the law.

International Maritime Organization is the world regulator of marine laws. Most nations are members of the IMO and taylor their own laws to the IMO regulations.

Legally, you can not operate an AIS with an incorrect MMSI.... Refer to IMO SN/Circ. 227 or if the vessel is US Flagged, 33 CFR 164.46 for details.

As far as just ignoring the law and runing the AIS with the wrong MMSI...

Many countries (Like the US) are using AIS as part of Homeland Security and routinely run the MMSI numbers through the data base for confirmation of the vessel's status, similar to when a local cop runs a license plate on car.

If they see your vessel is transmitting the wrong MMSI number, you are most likely going to be visited by people with large guns and have some epxplaining to do.....
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