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Old 01-12-2019, 08:44 PM   #1
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AIS/VHF question

Finally installing an AIS, but I am unclear on the required antenna setup. The unit is a Sitex and it suggests a VHF splitter. However, the installer says that the AIS requires a slightly different frequency, so advises a new and separate antenna. This is certainly doable, but a pita, so my question is for those with AIS, do you use a splitter, and have you ever had any problems as a result?
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Old 01-12-2019, 09:07 PM   #2
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Use a splitter. You will have some signal loss, but not enough to worry about.

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Old 01-12-2019, 09:44 PM   #3
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Most units use a pass through where the VHF goes through the AIS. I would at least try it with the splitter.

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Old 01-12-2019, 10:01 PM   #4
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I have a sitex and use a splitter. No problem whatsoever.
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Old 01-12-2019, 10:14 PM   #5
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Thanks all! That is kind of what I thought, but I think my installer is a bit of a perfectionist...
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Old 01-12-2019, 10:26 PM   #6
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I used a separate antenna. If you have a transceiver the most likely place for a failure will be the splitter. Why take a chance on safety to save the cost of another antenna and a little work.

If all you have is a receiver, go with the splitter.
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Old 01-12-2019, 10:54 PM   #7
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Hardly a PITA, much less bother than routing ship's power. One cable clam, three screw holes. 20 minute job.
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Old 01-12-2019, 11:14 PM   #8
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Old 01-12-2019, 11:44 PM   #9
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I had a Vesper Marine AIS transponder installed this year. It required a separate VHF antenna AND a separate GPS antenna (included with the unit). I am very happy with the configuration :-)
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Old 01-13-2019, 12:01 AM   #10
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I believe it is a requirement for any AIS transmitter to have its own GPS receiver. It cannot use data from a shared GPS receiver for some reason.
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Old 01-13-2019, 05:10 AM   #11
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I had our Vesper AIS on an amplified Vesper splitter that was connected to a run of the mill VHF antenna. Now I've reconfigured the antennas so that the AIS is on the antenna by itself & I can't tell any difference although I don't know what difference antennas and splitters could make concerning reception other than maybe distance. I'm not too concerned about long range targets.
AIS uses a frequency that is on the high end of a regular vhf antennas capability but again, I can't tell much difference between a regular VHF antenna and an AIS antenna that's made exclusively to work in the AIS frequency.
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Old 01-13-2019, 05:43 AM   #12
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Quote:
Originally Posted by wwestman View Post
I used a separate antenna. If you have a transceiver the most likely place for a failure will be the splitter. Why take a chance on safety to save the cost of another antenna and a little work.

If all you have is a receiver, go with the splitter.
Sounds like good advice to me also
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Old 01-13-2019, 05:48 AM   #13
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Quote:
Originally Posted by Spinner View Post
I had a Vesper Marine AIS transponder installed this year. It required a separate VHF antenna AND a separate GPS antenna (included with the unit). I am very happy with the configuration :-)
I have a Digital Yacht (DY) transceiver. I also have the combo GPS/VHF antenna in a little 6 inch antenna. Works well, though in my laziness i mounted it pretty low on the fly-bridge cowling.

I don't believe my DY cares about the source. I like having many sources for my travels. My AIS data is displayed using Coastal Explorer on my 24" monitors. I can change the input for GPS if I so choose, since the Maretron data, with GPS and compass are also in input.
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Old 01-13-2019, 09:38 AM   #14
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A really good splitter (Vesper @ $260) is speced at about 1dB of Transmit loss, on both VHF and AIS. That's like adding 20 feet of RG8x to your coax line. Also, when you transmit, the AIS function will be lost. This should be a minor issue. Saying that, since the cost of a decent splitter is much more than a AIS antenna, I go with the separate antenna. My 17' runabout has a separate ais antenna.
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Old 01-13-2019, 09:57 AM   #15
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Quote:
Originally Posted by Spinner View Post
I had a Vesper Marine AIS transponder installed this year. It required a separate VHF antenna AND a separate GPS antenna (included with the unit). I am very happy with the configuration :-)
I have the same unit. Separate VHF and GPS antenna. The splitter was more expensive, and don't believe mounting the separate antenna took more that 20 minutes.

One advantage to the splitter might be a higher antennae, which on a sail boat would be signifiant rather than climbing up there to mount another antenna.

Mine works fine with the VHF antenna about 15ft above the water. My VHF antennas for the radio are about 5 ft higher.
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Old 01-13-2019, 10:04 AM   #16
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Your electronics installer is correct. Separate whips for the VHF and AIS is the preferred method. And, an adequate separation distance between the two should be maintained.
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Old 01-13-2019, 10:09 AM   #17
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I have a Raymarine AIS650 Class B with a Raymarine 100 Active VHF/AIS Splitter & Existing VHF antenna. Works great!
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Old 01-13-2019, 10:41 AM   #18
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Quote:
Originally Posted by diver dave View Post
A really good splitter (Vesper @ $260) is speced at about 1dB of Transmit loss, on both VHF and AIS. That's like adding 20 feet of RG8x to your coax line. Also, when you transmit, the AIS function will be lost. This should be a minor issue. Saying that, since the cost of a decent splitter is much more than a AIS antenna, I go with the separate antenna. My 17' runabout has a separate ais antenna.
That's good feedback, thanks. Since we use VHF to transmit about once every three months, and since those who use splitters seem to see no issue with performance, I'll probably go that route and follow Sitex's guidance on installation that splitters are fine as long as they are rated for transmission.

And I do wish adding an antenna was a 20 minute job, but alas....
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Old 01-13-2019, 10:45 AM   #19
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An advantage of having a separate antenna is that now you have two. You can move the VHF to the AIS antenna if you ever need to.
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Old 01-13-2019, 10:58 AM   #20
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An advantage of having a separate antenna is that now you have two. You can move the VHF to the AIS antenna if you ever need to.
That would be an advantage. However, I've found that off shore, the odd ship you encounter frequently doesn't respond to VHF, and in shore other boats only sometimes do. We keep the VHF on for safety, and put up with the 100db DSC alarm that causes you to snort your coffee when someone's 10 year explores what the red button on daddy's radio does but rarely use it. So a small loss of utility in the VHF doesn't worry me too much, and it sounds like those with appropriate splitters don't see much downside to combining antennas.
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