AIS/VHF question

[drb1025]

Originally Posted by wwestman

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.

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.

[AnnapolisJoy]

Originally Posted by Delfin

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?

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.

[Ken E.]

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.

[Fletcher500]

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?

[Gordon J]

Originally Posted by wwestman

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.

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...

[AnnapolisJoy]

Originally Posted by Fletcher500

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?

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.

[JDCAVE]

Originally Posted by Delfin

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?

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

[LarryM]

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

[Delfin]

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.

[Skipper41]

Originally Posted by Delfin

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?

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.

[Djoub]

I just replaced my old VHF radio with a new Garmin VHF/AIS receiver. Also replaced a Raymarine chart plotter with Garmin MFD7610. I planned to use the existing antenna but after looking at it decided that the cable was starting to fray and the whip was showing signs of deteriorating. Replaced with a new antenna from West Marine. The VHF owners manual says connect to VHF antenna but nothing about a splitter or separate AIS or GPS antenna. Everything works fine but did not test it for any loss. It currently uses the internal GPS from the MFD. Perhaps there is some loss with this arrangement but it seems to work for me.

[Maerin]

Originally Posted by Delfin

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.

Therein you'll see advantage with AIS since you will be able to hail the ship with its name. It seems they are far less likely to ignore a hail by name than by "ship off my port bow".



One advantage of the dedicated antenna is that it's tuned for AIS rather than the whole VHF spectrum. Higher is better, I noticed a significant improvement when I changed to the AIS-tuned antenna and moved it to the masthead.

[twistedtree]

If at all possible, I would use two separate antennas. You will get better performance, and have fewer things to fail. But I understand the realities of adding stuff, especially cable runs .....

[Delfin]

Originally Posted by twistedtree

If at all possible, I would use two separate antennas. You will get better performance, and have fewer things to fail. But I understand the realities of adding stuff, especially cable runs .....

Anything is possible and if I see degradation I'll bite the bullet. But I'm curious what "degradation" will look like. Wouldn't you need a comparative range experiment or is it obvious with increased static or something concrete?

[Spinner]

Sure, that would work.

[diver dave]

The receive losses are advertised as quite small. As far a performance issues, the primary one is the ability to VHF transmit the same time as AIS transmit. You can't. The AIS connection is lost when VHF power is sensed. The models I've read do have the VHF com as the priority.

[FoxtrotCharlie]

But if you just have an AIS receiver, in a VHF radio, then the single antenna should be no problem since you are not transmitting AIS.

[twistedtree]

Originally Posted by Delfin

Anything is possible and if I see degradation I'll bite the bullet. But I'm curious what "degradation" will look like. Wouldn't you need a comparative range experiment or is it obvious with increased static or something concrete?

Yes, it’s nebulous. I just figure if I can eliminate possible issues, I like to do it. But I have suffered through enough exercises in pulling cables that I can hardly criticize anyone using a splitter. I used on on our tender when I added AIS because there wasn’t really space for a second antenna. And it’s so low to begin with....

[Alaskan Sea-Duction]

I have a Raymarine AIS650 transceiver with a separate antenna. As stated here separation of antennas is important. My AIS antenna is a Shakespeare. They recommend at least a 4ft separation.

[Delfin]

Originally Posted by twistedtree

Yes, it’s nebulous. I just figure if I can eliminate possible issues, I like to do it. But I have suffered through enough exercises in pulling cables that I can hardly criticize anyone using a splitter. I used on on our tender when I added AIS because there wasn’t really space for a second antenna. And it’s so low to begin with....

We installed the Sitex Metadata AIS transceiver and fancy splitter. We were able to use the cable for a dedicated GPS that was attached to a backup Simrad GPS, so that was simple. I was able to pick up targets around 40 miles out, which seems pretty good. According to the tech, the Sitex splitter, which costs about as much as the transceiver, handles the hand off between VHF and AIS seamlessly, at least in his experience. We'll see...