AIS-VHF Antenna Splitter

[Lee Hadjiosif]

I have a VHF and and AIS with a active splitter but I'm not happy with the setup. The splitter is always hot with lots of lights blinking and I'm thinking of the battery power draw just to manage the splitter. I never use the fixed VHF for transmission because is below and I always use a handheld in the cockpit. I'm thinking of removing the active splitter and install a non-active antenna splitter instead. Given that I don't transmit on the VHF radio, are there any technical issues that I'm overlooking with doing this? PS. And if I ever needed to transmit on the vhf radio below, I could use the AIS silent switch which is right next to the radio. Opinions please. Thanks.

 

[Don S/V ILLusion]

I have a VHF and and AIS with a active splitter but I'm not happy with the setup. The splitter is always hot with lots of lights blinking and I'm thinking of the battery power draw just to manage the splitter. I never use the fixed VHF for transmission because is below and I always use a handheld in the cockpit. I'm thinking of removing the active splitter and install a non-active antenna splitter instead. Given that I don't transmit on the VHF radio, are there any technical issues that I'm overlooking with doing this? PS. And if I ever needed to transmit on the vhf radio below, I could use the AIS silent switch which is right next to the radio. Opinions please. Thanks.

Good idea. I was never a fan of splitters as they can fail and you won’t know until it’s too late.

In buying a coax switch, the primary consideration is it’s isolation rating. That is important to ensure sufficient isolation to prevent RF from overloading/ damaging the inactive radio. If a switch mfg doesn’t specify isolation rating, that’s a good reason to ignore it.

Good switches are rated at 60dB isolation.

 

[dlochner]

I have a VHF and and AIS with a active splitter but I'm not happy with the setup. The splitter is always hot with lots of lights blinking and I'm thinking of the battery power draw just to manage the splitter. I never use the fixed VHF for transmission because is below and I always use a handheld in the cockpit. I'm thinking of removing the active splitter and install a non-active antenna splitter instead. Given that I don't transmit on the VHF radio, are there any technical issues that I'm overlooking with doing this? PS. And if I ever needed to transmit on the vhf radio below, I could use the AIS silent switch which is right next to the radio. Opinions please. Thanks.

In theory this will work. In practice it is an accident waiting to happen. If the VHF is used to transmit and the the AIS is not disconnected the AIS will be toast. If the VHF is disconnected from the antenna and an emergency broadcast is necessary, then the broadcast won't go out.

In one case you are out an expensive piece of equipment, in the other you will be talking to yourself during an emergency, neither are desirable outcomes.

The splitter is probably drawing less than 1 amp, which is pretty minimal. If the splitter power is on the same switch as the VHF it will only draw power when needed, i.e., when the VHF might be used is active. Another alternative is adding a dedicated AIS antenna.

 

[Lee Hadjiosif]

In theory this will work. In practice it is an accident waiting to happen. If the VHF is used to transmit and the the AIS is not disconnected the AIS will be toast. If the VHF is disconnected from the antenna and an emergency broadcast is necessary, then the broadcast won't go out.

In one case you are out an expensive piece of equipment, in the other you will be talking to yourself during an emergency, neither are desirable outcomes.

The splitter is probably drawing less than 1 amp, which is pretty minimal. If the splitter power is on the same switch as the VHF it will only draw power when needed, i.e., when the VHF might be used is active. Another alternative is adding a dedicated AIS antenna.

Are you saying that if I turn off the power to the splitter and the VHF, the AIS will transmit normally? I thought that VHF had priority during a splitter failure.

 

[stephen_i_w]

Antennas are not really expensive. A second antenna will work much better than a splitter. I simply use another (power boat type) antenna for my AIS transponder attached to the frame of my Bimini. The set up works very well.

 

[dlochner]

Are you saying that if I turn off the power to the splitter and the VHF, the AIS will transmit normally? I thought that VHF had priority during a splitter failure.

Check with the splitter instructions, not all splitters are alike. If I recall the instructions for my Vesper Splitter (it has been a few years) the instructions were clear that the splitter needed to tied to the AIS power so the splitter was always powered when the AIS was on.

 

[Don S/V ILLusion]

Are you saying that if I turn off the power to the splitter and the VHF, the AIS will transmit normally? I thought that VHF had priority during a splitter failure.

Failure and loss of power are different things.
How a splitter defaults in loss of power is predictable and the manufacturer tells you how it defaults.
In a failure of the splitter, it’s a crap-shoot what happens - both transmitters could be damaged in a worst case scenario.

 

[LloydB]

I am theoretically opposed to adding a point of failure in between two perfectly good radios and one good antenna, but that's me.

 

[jviss]

If the VHF is disconnected from the antenna and an emergency broadcast is necessary, then the broadcast won't go out.

And if you key the mic with no load on the output, the VHF could be toast!

 

[dlochner]

A lot of ifs in this thread. In the end, turning off the splitter creates a lot of risk for very little gain. The small amount of power consumed by the splitter, maybe 6 or 7 ah in a long day, is quickly replaced by the alternator.

 

[jviss]

You could add an antenna. I have two VHF antennas on my boat, one on top of the mast, another on the radar tower. I have two fixed-station VHFs and a splitter for my AIS transponder, but I confess I don't know what antenna is wired to what! (Yet.).

I'm guessing the radar tower antenna is for the cockpit VHF, and the nav station and AIS use the masthead antenna via the splitter.

 

[LloydB]

popcorn emoji

 

[NYSail]

My ais has a built in splitter(Garmin 800). So far no issues, unit never gets hot and simple install. AIS targets on the plotter screen and remote mic at helm are invaluable pieces of equipment on my boat here in NE with potential travel days in fog……. Whatever route you take with or without splitter just make sure they both are working all the time.
Good luck!

 

[jssailem]

That is a sensible theory @LloydB and one to enhance the use of ones radios. Yet, it means to optimize ones transmission and reception of the radios you need to utilize the limited real estate on the top of the mast with 2 antennas. Both are line of site transmitter/receivers. The frequencies they use are close together. It is one reason a splitter works. The mast head gets you further distance, especially if you are in the trough of a wave.

It would be sensible to carry a back up antenna or 2 onboard to address a failure condition.

 

[dLj]

I don't think you need a mast head AIS antenna. I would put that antenna lower down and leave the VHF antenna at the mast head. I'm a fan of independent antennas and no splitter.

dj

 

[quadrille38]

I don't think you need a mast head AIS antenna. I would put that antenna lower down and leave the VHF antenna at the mast head. I'm a fan of independent antennas and no splitter.

dj

Then downside with a lower antenna (that’s what I have) is that range is less. Perhaps only 5 miles or so. Not a huge issue on a sail boat where we don’t move all that fast but it Is less. My AIS can see down the lake about 6 miles but friends with mast head antenna can see down the lake, over the dunes, and miles beyond.

 

[jssailem]

downside with a lower antenna (that’s what I have) is that range is less.

The waters you sail influences the way you sail and the equipment you use. How you configure that equipment and the physics of the equipment will affect the performance.

Sailing in the PacificNW’s Puget Sound we share the waters with many much larger craft. They prickle with antennae more than a hundred feet in the air. Their antennae look downward on my sail boat as they power through the waters at 15-20 knots. Unless hidden by a tall bluff, an AIS antenna on the stern pulpit can see their transmission. Yet, if I am out near the ocean and the wave heights rise, when I am in the trough my boats Signal can become intermittent and I can disappear from their view as well as they from mine. Mounting my antenna on the 40 ft mast becomes an aide to safe navigation.

I do not expect to sail in 40 ft waves. I do enjoy knowing the freighter doing 18 knots coming up behind me is 10 miles away when I consider crossing his path.

His boat is so big and mine is so small, Lord I pray keep me safe.

 

[dLj]

Then downside with a lower antenna (that’s what I have) is that range is less. Perhaps only 5 miles or so. Not a huge issue on a sail boat where we don’t move all that fast but it Is less. My AIS can see down the lake about 6 miles but friends with mast head antenna can see down the lake, over the dunes, and miles beyond.

I have my AIS antenna mounted on my stern railing and I'm able to see and be seen at around 25 NM. Certainly far beyond 5 nm! I've used it extensively - as in when I'm sailing it is turned on - I just finished crossing the North Atlantic Sailing in all kinds of weather and waves. Traveling up the North East Coast to Nova Scotia and Newfoundland, I had to sail in dense fog and was traveling 24/7. There were many commercial freighters and fishing boats that I could watch both where they were, where they were going and what my heading required. When I neared the European coast, I had extensive commercial traffic to contend with. My AIS was a godsend for navigating in those conditions. I could see the heading and speed of the freighters and my AIS would calculate the closest point of contact. Numerous times that was 0 NM - or stated in more blunt terms - predicting a collision course! Most freighters adjusted their rumb line, some did not and it was clear they weren't going to. So I followed the law of the jungle - bigger wins, I changed course!

No idea where you got the 5 nm, perhaps it's the unit you are running, but my AIS with antenna mounted on the stern rail works well, even in large waves (where I could see boats appear and disappear at the 25 nm range) at pretty much 25 nm, sometimes further.

dj

p.s. why would you care to see beyond the lake you are sailing in? What does that do for you? Just a question...

p.p.s. - OK ignore this post - I just discovered that my AIS antenna is indeed on my mast head! So I'm sending and receiving for my AIS at roughly 65 feet above sea level... see later post in this thread....

 

[dlochner]

No idea where you got the 5 nm, perhaps it's the unit you are running, but my AIS with antenna mounted on the stern rail works well, even in large waves (where I could see boats appear and disappear at the 25 nm range) at pretty much 25 nm, sometimes further.

5 NM is roughly the distance to the horizon when standing from about 8 feet above sea level, the height an antenna would be if mounted on the pushpit. You could see ship's up to 25 miles away because their antennas are mounted much higher on the ship than 8 feet, some as much as 80 to 100 feet above sea level.

 

[dLj]

5 NM is roughly the distance to the horizon when standing from about 8 feet above sea level, the height an antenna would be if mounted on the pushpit. You could see ship's up to 25 miles away because their antennas are mounted much higher on the ship than 8 feet, some as much as 80 to 100 feet above sea level.

Let me understand - if my antenna is 8 feet above the water, and the other boat's antenna is 8 feet above the water then the two boats can see each other only at about 5 nm. Correct?

Now, if one of the two boats has the antenna much higher, do both boats still see each other at the 25 nm? Or does one see the other and not vice versa? Let me restate that, while I can see the commercial ship at 25 nm, are they still able to see me at 25 nm or no?

I am assuming that both can see each other as I've watched commercial ships change course due to my heading at much further away than the 5 nm.

Now let me ask a second question - say both ships have their AIS antenna's way up high - I believe you are still only going to get about the same 25 nm range due to atmospheric attenuation. Maybe you get 30 nm....

Are these correct assumptions?

dj