AIS/VHF two antennae's or one?

[BAD ORCA]

I have a VHF with integrated AIS. I have never used the AIS feature but want to in the future. I am pulling my mast next week and running new LMR400 cable for the new VHF antennae. Are you guys using the same cable/antennae for integrated VHF AIS or are you running a seperate cable and antennae? If i need to add other cable for future upgrades i may want, it will be much easier to do this while the mast is down.

To add, i would like to be able to receive AIS positions from other boats but also send one of my own. Just very quickly reading from googles, and it seems i may need a seperate cable and antennae for each? VHF at masthead and AIS on a spreader? Same cable and antennae's just separate locations?

 

[jssailem]

I have installed:

• Vesper Marine XB-8000 AIS Transponder
• Vesper VHF/AIS antenna splitter
• Standard Horizon GX2200 MATRIX AIS/GPS

One Antenna cable to antenna. The antenna is tuned to cover the VFH and AIS frequencies.

AIS/VHF Antennas

The Milltechmarine site has information on all of these capabilities.

Garmin bought Vesper about 2-3 years ago. Some of their products are no longer available. The tech is still available through other sources.

 

[Don S/V ILLusion]

Combining them is fairly common, however, if your are a purist, there are two compromises with doing so:
1. The frequency split between marine VHF and AIS is about 5MHz so one end will be a higher SWR detuning the respective transmit signal, and
2. the requisite splitter or duplexer has both an inherent insertion loss and potential for failure

Not advocating one over the other but only to make an informed decision before choosing to combine/not combine them.

 

[Tally Ho]

I bought a new B&G radio several years ago, with AIS. I just hooked it up to my existing antennae. Works fine or me. I networked with Garmin Chart plotter, so I get AIS targets on my CP at the helm.

Greg

 

[capta]

Standard Horizon makes an AIS/VHF antenna, all in one, designed for their upper line of VHF radios. I bought the VHF because it had fog, NOC, towing etc. sound signals built in, thinking the AIS would be fun to mess with.
At least in Narragansett Bay, it was a nightmare. The alarm went off every 20 seconds, and after I had shut that off, it seemed as if every vessel broadcasting an AIS signal was headed for me as fast as they could.
The other day, my ophthalmologist said I had 20/20 distance vision (no kidding, at 78), so I believe I'll rely on my sight, as I have for the last 6 decades plus, with the aid of my newfangled Cannon Image Stabilized Binoculars.

 

[AndyBC]

I have an Emtrak AIS transceiver, which has a built-in splitter. So I use 1 cable and 1 antenna that is rated for both VHF and AIS. The receive and transmit have worked great so far - approx 20 nm range.

 

[NYSail]

I have a Garmin 800 that has a splitter for the antenna. Works perfectly. Consider the upgrade so people can see you as well….. it really is a great tool in the fog here in the NE.

Greg

 

[colemj]

What specific VHF do you have? There are more of them containing AIS receive-only, and only a few expensive ones containing an AIS transponder. If yours is AIS receive, then you do not need a separate antenna, and there is no place to connect one. If yours is a true transponder, then it will have separate connections on the back for AIS and VHF antennas. VHF/AIS radios are not allowed to have internal splitters like pure AIS units can (at least that was the case when the first models came out - it could have changed).

In the latter, your choice will be two separate antennas, or use a splitter to combine them after they leave the radio into a single antenna.

Things to consider in making this choice:
1. Height is the most important variable in seeing targets and being seen. An antenna on the mast top is far more effective than one down on the rail. Avoiding large ships is easy because their antenna is high and they transmit with greater power and higher frequency. But many recreational boats not only have their antenna on the rail, they have questionable rf connections to those antenna, and only broadcast position every 30sec with the weakest power level. We encounter a lot of boats like this who can see us at 10nm, but they only show up on ours at 1-2nm. They think their system is working great because they can see far, not realizing that is the easy part.

2. Related to the above, there will be directional and other issues if two antennas are mounted close together, like closer than 3' in the horizontal plane. So this puts a constraint on having two antennas on the mast top. Your idea of mast top and spreader is a good compromise for separate antennas if you don't use a splitter.

3. There are several antennas designed specifically for combined VHF/AIS use. These have a widened peak frequency response (usually 6MHz) that puts both Channel 16 and AIS frequencies within this peak response. I've tested a couple of them and they are very good at this. We have the Vespar version which is very good, but don't think they sell it anymore after the Garmin takeover.

4. Active splitters have <1db insertion loss in real-life. They are often spec'd at "1.5db or less", but at least ours operates on the "less" side. This loss is less in practice than that which occurs from mounting a separate antenna on the rail instead of the mast top through a splitter. The failure mode of all active splitters is to leave the VHF connected.

Mark

 

[Captain Larry-DH]

Standard Horizon makes an AIS/VHF antenna, all in one, designed for their upper line of VHF radios. I bought the VHF because it had fog, NOC, towing etc. sound signals built in, thinking the AIS would be fun to mess with.
At least in Narragansett Bay, it was a nightmare. The alarm went off every 20 seconds, and after I had shut that off, it seemed as if every vessel broadcasting an AIS signal was headed for me as fast as they could.
The other day, my ophthalmologist said I had 20/20 distance vision (no kidding, at 78), so I believe I'll rely on my sight, as I have for the last 6 decades plus, with the aid of my newfangled Cannon Image Stabilized Binoculars.

Turn off the alarm and connect the AIS receive over NMEA to your chartplotter. It’s a game changer.

 

[Captain Larry-DH]

What specific VHF do you have? There are more of them containing AIS receive-only, and only a few expensive ones containing an AIS transponder. If yours is AIS receive, then you do not need a separate antenna, and there is no place to connect one. If yours is a true transponder, then it will have separate connections on the back for AIS and VHF antennas. VHF/AIS radios are not allowed to have internal splitters like pure AIS units can (at least that was the case when the first models came out - it could have changed).

In the latter, your choice will be two separate antennas, or use a splitter to combine them after they leave the radio into a single antenna.

Things to consider in making this choice:
1. Height is the most important variable in seeing targets and being seen. An antenna on the mast top is far more effective than one down on the rail. Avoiding large ships is easy because their antenna is high and they transmit with greater power and higher frequency. But many recreational boats not only have their antenna on the rail, they have questionable rf connections to those antenna, and only broadcast position every 30sec with the weakest power level. We encounter a lot of boats like this who can see us at 10nm, but they only show up on ours at 1-2nm. They think their system is working great because they can see far, not realizing that is the easy part.

2. Related to the above, there will be directional and other issues if two antennas are mounted close together, like closer than 3' in the horizontal plane. So this puts a constraint on having two antennas on the mast top. Your idea of mast top and spreader is a good compromise for separate antennas if you don't use a splitter.

3. There are several antennas designed specifically for combined VHF/AIS use. These have a widened peak frequency response (usually 6MHz) that puts both Channel 16 and AIS frequencies within this peak response. I've tested a couple of them and they are very good at this. We have the Vespar version which is very good, but don't think they sell it anymore after the Garmin takeover.

4. Active splitters have <1db insertion loss in real-life. They are often spec'd at "1.5db or less", but at least ours operates on the "less" side. This loss is less in practice than that which occurs from mounting a separate antenna on the rail instead of the mast top through a splitter. The failure mode of all active splitters is to leave the VHF connected.

Mark

This is excellent advice. To add to this, for those who use a tablet for navigation apps I recommend you either buy a a Wi-Fi bridge to your boat’s NMEA instrument network, or buy an AIS transceiver that comes with Wi-Fi built-in. I find it very helpful having the AIS information overlaid on my nav charts in Navionics and Aqua Maps, in addition to having it on my Raymarine chartplotter. (Aqua Maps has the best interface for displaying AIS).
I also recommend buying a unit that uses AIS class B+.
A class B+ AIS Transponder (also called Class B SOTDMA or Class B 5W ) is a new standard that utilizes SOTDMA format transmissions which offer a 5W power output (2.5 x more powerful than a regular Class B), a guaranteed time slot for transmission in busy traffic areas and faster update rates depending upon the speed of the boat.
I’m using an AMEC B600w Widelink SOTMA transceiver with Wi-Fi and an AMEC AIS splitter. It‘s been great for me. I also recommend Milltech Marine as a vendor because they provide excellent phone support as a small business, and competitive prices (I have no financial interest in that recommendation, just a happy customer.) AMEC WideLink B600W Class B SOTDMA AIS transponder with WiFi

 

[stephen_i_w]

When I purchased my AIS transponder, I bought a 6db VHF antenna (like the ones power boats use) for less than $100. I mounted the antenna for it on the stern pulpit. It works great. Everywhere I go on the Great Lakes, I can see my AIS symbol on the "Marine Traffic" website, verifying that my AIS transmission is received.

Using a separate antenna for the AIS transponder has certain advantages. For one thing, it costs less, a decent active splitter is expensive and draws additional power. For another, it simply works better. Also, the installation is more straightforward. Finally, the redundancy adds to safety in case of equipment failure.

 

[BarryL]

Hello,

To those of you with AIS transponders and a single antenna, what happens when you try to listen to an VHS broadcast (say one of the long messages from the coast guard) and then the AIS transponder sends your AIS information? My VHF receiver seems to cut off for a second or two. I assume that's because the AIS is broadcasting and you can't broadcast and receive at the same time?

I have a Vesper 8000 transponder and standard horizon VHF.

Barry

 

[colemj]

To those of you with AIS transponders and a single antenna, what happens when you try to listen to an VHS broadcast (say one of the long messages from the coast guard) and then the AIS transponder sends your AIS information? My VHF receiver seems to cut off for a second or two. I assume that's because the AIS is broadcasting and you can't broadcast and receive at the same time?

I have a Vesper 8000 transponder and standard horizon VHF.

We have the same AIS and a SH VHF and have never experienced this. The AIS transmission length is <30msec, so shouldn't be noticeable. Definitely not a second or two. We do often experience mic keys from close boats that can interrupt a broadcast.

Using a separate antenna for the AIS transponder has certain advantages. For one thing, it costs less, a decent active splitter is expensive and draws additional power. For another, it simply works better. Also, the installation is more straightforward. Finally, the redundancy adds to safety in case of equipment failure.

Cost is dependent on variables. The cost of coax, another antenna, connectors, deck gland, and a mount is often the same price or less of a splitter. Splitters draw no appreciable power - 200mA for 26msec every 30sec when underway, and every 3 minutes when stationary. Running full-time, that is <0.5Ah/day. For sure, the installation of a splitter is much more straightforward than running more coax through a boat, through a deck, and to a separately mounted antenna. A splitter requires only a short coax pigtail and you are done. Redundancy is a valid point if you mean equipment failure to be an antenna or loss of mast (if mounted there). There is no redundancy in the radios themselves. One should carry a spare antenna and a length of coax that will reach out a port or hatch otherwise.

I think something is getting lost in this thread. The OP stated they had a combination VHF/AIS radio, but most of the comments are about independent AIS transceivers and how to coordinate those with the VHF.

The OP needs to clarify which particular VHF they have.

Mark

 

[colemj]

When I purchased my AIS transponder, I bought a 6db VHF antenna (like the ones power boats use) for less than $100. I mounted the antenna for it on the stern pulpit. It works great. Everywhere I go on the Great Lakes, I can see my AIS symbol on the "Marine Traffic" website, verifying that my AIS transmission is received.

Marine Traffic is not a good test of your system. They have towers up high everywhere (often using Seatow, BoatUS, and others equipment), use satellites, and have commercial ships rebroadcasting nearby data to them. The poorest installed and performing system will usually show up there.

A better test of your system would be how far a buddy boat can see you while sailing heeled over. Or can boats on the other side of land masses see you. Coming visually blind around a large breakwall or inlet lined with condos is where rail-mounted antennas sometimes struggle. These situations are also one of the most useful aspects of AIS.

Mark

 

[Captain Larry-DH]

I think something is getting lost in this thread. The OP stated they had a combination VHF/AIS radio, but most of the comments are about independent AIS transceivers and how to coordinate those with the VHF.

Good point! To clarify to the OP: If you are only receiving there is never a need for a second antenna. Your radio handles the split internally and there is no connector for the second antenna. I recommend you connect the VHF radio to the NMEA network so that you can display the AIS info overlaid in the chart display of your chartplotter.

 

[BAD ORCA]

What specific VHF do you have? There are more of them containing AIS receive-only, and only a few expensive ones containing an AIS transponder. If yours is AIS receive, then you do not need a separate antenna, and there is no place to connect one. If yours is a true transponder, then it will have separate connections on the back for AIS and VHF antennas. VHF/AIS radios are not allowed to have internal splitters like pure AIS units can (at least that was the case when the first models came out - it could have changed).

In the latter, your choice will be two separate antennas, or use a splitter to combine them after they leave the radio into a single antenna.

Things to consider in making this choice:
1. Height is the most important variable in seeing targets and being seen. An antenna on the mast top is far more effective than one down on the rail. Avoiding large ships is easy because their antenna is high and they transmit with greater power and higher frequency. But many recreational boats not only have their antenna on the rail, they have questionable rf connections to those antenna, and only broadcast position every 30sec with the weakest power level. We encounter a lot of boats like this who can see us at 10nm, but they only show up on ours at 1-2nm. They think their system is working great because they can see far, not realizing that is the easy part.

2. Related to the above, there will be directional and other issues if two antennas are mounted close together, like closer than 3' in the horizontal plane. So this puts a constraint on having two antennas on the mast top. Your idea of mast top and spreader is a good compromise for separate antennas if you don't use a splitter.

3. There are several antennas designed specifically for combined VHF/AIS use. These have a widened peak frequency response (usually 6MHz) that puts both Channel 16 and AIS frequencies within this peak response. I've tested a couple of them and they are very good at this. We have the Vespar version which is very good, but don't think they sell it anymore after the Garmin takeover.

4. Active splitters have <1db insertion loss in real-life. They are often spec'd at "1.5db or less", but at least ours operates on the "less" side. This loss is less in practice than that which occurs from mounting a separate antenna on the rail instead of the mast top through a splitter. The failure mode of all active splitters is to leave the VHF connected.

Mark

Thanks Mark. Its an older Standard Horizon. I forget model but i'm pretty sure its only a receiver. It was not very expensive. I was eying the ICOM M605 but appears to be just a receiver as well.

I'm starting to think a standalone AIS transponder might be a better solution. It appears most of the VHF/AIS units only receive AIS signals but dont broadcast one if im understanding them correctly. Also, as CAPTA mentions nuisance signals. If its a standalone transponder, I'm guessing it would be as easy as flicking a breaker to turn it off if i'm just day sailing in the local bay.

I think i will run another piece of LRM400 cable to the spreader just in case thats the route I go. I can easily pull it later if i change my mind or use it for a backup VHF. The AIS install is still months away, i just want to get some idea on what i may do so i can run the cable now while the mast is down. Im leaning towards a second antennae at the spreader. Sounds like it will give me a slightly better signal and could be a backup VHF antennae in an emergency. I already have the cable and connections, would just need a second antennae.

 

[stephen_i_w]

Marine Traffic is not a good test of your system. They have towers up high everywhere (often using Seatow, BoatUS, and others equipment), use satellites, and have commercial ships rebroadcasting nearby data to them. The poorest installed and performing system will usually show up there.

A better test of your system would be how far a buddy boat can see you while sailing heeled over. Or can boats on the other side of land masses see you. Coming visually blind around a large breakwall or inlet lined with condos is where rail-mounted antennas sometimes struggle. These situations are also one of the most useful aspects of AIS.

Mark

Marine Traffic is actually an excellent way to test your transmission. Ask yourself, why even bother to have an AIS transponder? As I see it, there are two reasons.

One is to avoid collisions with local traffic. Local means close by. You do not need to blast your signal 20 nm for a boat approaching you within a few nm to see your signal. As for being seen behind a breakwall, typically sailboats have tall masts that can be easily seen above brakewalls. Personally, I have yet to see a 50' tall breakwall. I hope other boaters also look where they are going.

The second reason to have an AIS transponder is to allow rescue authorities to track you. As far as I know, the Coast Guard also has those large radio towers. I am pretty confident that if Marine Traffic can see me, so can the Coast Guard.

I know that boaters like to brag about their fancy, expensive electronic gear. The less than $100 Shakespear antenna I used came with a nice long cable and all needed connectors. I admit, I used a mounting clamp I already had. But I see rail mounts advertised for less than $30 online. I fed the cable through an existing vent so no gland was needed. No splitter means one less piece of electronics to fail. To me, that seems like a good thing.

Somehow, power boaters manage to communicate using the same antennas mounted in a similar fashion.

 

[kappykaplan]

I have a Simrad RS35 VHF radio with a Simrad HS35 that connects to the main unit via bluetooth. The other piece of kit is a Raymarine AIS700 splitter. All coexist happily with the masthead-mounted antenna. They were installed in 2018.

 

[colemj]

Marine Traffic is actually an excellent way to test your transmission.

It is not, and I explained why. It is similar to why calling the Coast Guard is not a good way to test the quality of your VHF transmission. You even elude to this when you mention how easy it is for the CG and Marine Traffic to see you with large radio towers.

Seeing a mast is not a good way to avoid a collision coming in a blind breakway or inlet. There is no easy way to tell direction, or timing. Then there are boats like tugs and barges that can't be seen at all. If you haven't seen visually obstructed breakwaters or inlets, then you've had it easy. Right now, I'm at the mouth of the Panama Canal, where there the breakwater is tall enough to hide container ships, and avoiding the ships while coming in the breakwater is a blind game of frogger. AIS makes this a piece of cake, but it is tough visually, and is mostly guessing, hoping, and reacting quickly at the last minute without it.

I've never questioned having an AIS transponder. Quite the opposite - I'd like to see every boat have one.

I agree that running a second antenna COULD be less expensive than a splitter, and it was in your case, but it isn't necessarily so. It would cost more than a splitter on our boat, for example. I was just pointing this out, because being less expensive than a splitter is not universally true.

Rail mount works fine for what it is. There just isn't any argument that lower height is better, or that one only cares about other slow boats a mile or so away, and not anything at larger distances. As someone who regularly sails short handed in large sea states, with strong winds, at night or in poor visibility, often with sails prevented, I am grateful to have notice of an unseen boat 10nm away so that I have time to chose my option, prepare the boat, and safely make a course change if needed. I appreciate when my signal gets out 10nm or more and the other ship has an equal opportunity. Detection distance isn't as critical in calmer conditions and good visibility.

Yes, power boaters have height constraints and still manage (although they get a bit of help with higher-gain antennas). So do kayakers with handheld radios. I don't see how this matters, as each is using their best option. It would be like telling a power boater that putting his antenna in the cabin below is just as good as above on the rail.

Mark

 

[colemj]

Thanks Mark. Its an older Standard Horizon. I forget model but i'm pretty sure its only a receiver. It was not very expensive. I was eying the ICOM M605 but appears to be just a receiver as well.

I'm starting to think a standalone AIS transponder might be a better solution. It appears most of the VHF/AIS units only receive AIS signals but dont broadcast one if im understanding them correctly. Also, as CAPTA mentions nuisance signals. If its a standalone transponder, I'm guessing it would be as easy as flicking a breaker to turn it off if i'm just day sailing in the local bay.

I think i will run another piece of LRM400 cable to the spreader just in case thats the route I go. I can easily pull it later if i change my mind or use it for a backup VHF. The AIS install is still months away, i just want to get some idea on what i may do so i can run the cable now while the mast is down. Im leaning towards a second antennae at the spreader. Sounds like it will give me a slightly better signal and could be a backup VHF antennae in an emergency. I already have the cable and connections, would just need a second antennae.

OK, so that is much clearer now. You have a receive-only AIS in your VHF that naturally uses the same antenna. No splitting is required because there is no AIS transmission that needs splitting.

A stand alone AIS transponder is an excellent idea. For this, you will make decisions discussed in this thread as to its installation and antenna hows and wheres.

LMR400 is a beast of cable. Make sure your mast has the conduit room for two runs of it, along with other wires needed up there for the usual stuff.

It doesn't sound like Capta understood his AIS system. The alarms can be highly customized as to distance, speed, time, etc, and can be turned off completely. Turning the alarms off does not immediately make all boats zoom toward you at high speed. None of this is any different than the identical functions on a modern ARPA radar. For sure, eyeballs and good binoculars are important, but they are pretty useless in the conditions where AIS is invaluable, like heavy fog or rain, or targets visually blocked by land or other boats. And plotting out and calculating positions over many minutes while bouncing around in the middle of the night is more fraught with potential error than a quick glance at a target on AIS telling you that you will pass its stern by 0.5nm in 26min.

Mark