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?

Use a splitter. You will have some signal loss, but not enough to worry about.

Gordon

Most units use a pass through where the VHF goes through the AIS. I would at least try it with the splitter.

Ted

I have a sitex and use a splitter. No problem whatsoever.

Thanks all! That is kind of what I thought, but I think my installer is a bit of a perfectionist...

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.

Hardly a PITA, much less bother than routing ship's power. One cable clam, three screw holes. 20 minute job.

All boat jobs start out at 20 minutes. It is just how many multiples you use.

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 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.

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.

wwestman said:

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.

Click to expand...

Sounds like good advice to me also

Spinner said:

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

Click to expand...

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.

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.

Spinner said:

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

Click to expand...

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.

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.

I have a Raymarine AIS650 Class B with a Raymarine 100 Active VHF/AIS Splitter & Existing VHF antenna. Works great!

diver dave said:

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.

Click to expand...

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....

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.

DDW said:

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.

Click to expand...

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.

wwestman said:

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.

Click to expand...

A benefit of AIS having its own GPS is that it can be used as a primary or backup with your navigation software. I use Coastal Explorer and have the AIS integrated with it and I can select whether to use the primary Furuno GPS or the signal from the AIS transceiver. Good redundancy.

Splitter: just say no.

Delfin said:

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?

Click to expand...

My boat had an AIS receiver with a short VHF antenna laying across the back of the wiring under the console. Bad bad bad.

I could barely get a boat next to me.

The first thing I did was swap the receiver for a transceiver. A Garmin AS600 I had on my sailboat.

Still bad.

I then installed a splitter with on of the two VHF antennas. Bad and worse.

The AIS coverage was poor. A new wrinkle appeared. The VHF on the splitter became erratic. Marinas and out her boaters complained of weak signal and static.

The best and only solution for me was a dedicated VHF on the arch.

Everything now works.

I have a Sitex splitter with my Comnav AIS...no problems. I didn't want to add another vhf antenna and the splitter solved the problem.

AJ, very nice Fleming.

You appear to have 4 antennas? One for VHF and one for AIS. I assume you put these on opposite sides of the arch?

What are the other two being used for? VHF back up?

Really

wwestman said:

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.

Click to expand...

So, just curious about how you know the splitter is most likely place for failure? In my 40 years of working with communications equipment I would say cable and connectors are most likely failure. Never saw a splitter fail, but it could happen.

Just sayn...

Fletcher500 said:

AJ, very nice Fleming.

You appear to have 4 antennas? One for VHF and one for AIS. I assume you put these on opposite sides of the arch?

What are the other two being used for? VHF back up?

Click to expand...

Thanks!

Two big VHFs that I can drop for low bridges.

What I did was even better. The boat came with a Furuno Weather FAX that had an antenna on the arch. Since I no longer had a use for the Furuno I replaced the antenna with a new VHF and used it for the AIS. I did have to install a pivot on the base as it was now a few feet over the mast light.

Delfin said:

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?

Click to expand...

I have Sitex and use a dedicated antenna and a gps antenna as well. I used a upper end Shakespeare antenna, as recommended. It’s not a specific AIS one though.

Remember the signal from the Class B units is quite weak, so you want to do everything possible to maximize success.

Sitex provides good support. Give them a call.

Jim

I also have a Sitex and use dedicated Shakespeare Galaxy VHF and AIS antennas. They work perfectly. I originally used a less expensive Shakespeare Classic antenna with a splitter and found the Garmin VHF200 range was somewhat reduced. It was restored with the installation of separate antennas. It's also possible that the new antenna's use of RG-8X low-loss cables instead of RG-58 helped the performance. Anyway, my vote is for separate, high quality dedicated antennas and cables

I had the installer out on the boat yesterday, and we're going to use the cable for the backup GPS connected to the Simrad radar for the dedicated GPS of the Sitex AIS. A good quality splitter is more $ than a new and separate AIS antenna, but to save the 6 hours or so of labor on running a new cable for that antenna, I'll start with the splitter and see how it goes on this Spring/Summer's trip to Alaska. The tech thought that since cable length would just be a few feet I'd have no problem, so I guess we'll see.

Again, many thanks for the input and advice. It's help like this that makes TF such a great site.

Delfin said:

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?

Click to expand...

Get separate antennas. I tried a splitter with a Garmin AIS and Radio. It seriously degraded the radio performance. Range dropped by about 2/3. I even got a replacement AIS unit and had the same result.