AIS transponder AND integrated AIS receiver/VHF radio

[redneckrob]

Like many people I originally bought a VHF radio that had an AIS receiver built into it. I just upgraded to a standalone SOTDMA AIS transceiver with an integrated splitter. I get the theory, and in theory there shouldn't be any issues with having the two going to the same antenna because of how the splitter works. But I was wondering if anyone has any real-world experience running a receiver and transceiver on the same antenna using a splitter and any potential issues?

[River Cruiser]

I have the same setup except for a dedicated antenna for the AIS transceiver. I have one mfd wired to the vhf and it will show my boats AIS location and the gps icon location separately. I know this isn’t a answer to your question but thought it may be useful.

[carstenb]

we've run an AIS and VHF on a splitter for 5 years now all over the world - no issues

[wingssail]

Originally Posted by redneckrob

Like many people I originally bought a VHF radio that had an AIS receiver built into it. I just upgraded to a standalone SOTDMA AIS transceiver with an integrated splitter. I get the theory, and in theory there shouldn't be any issues with having the two going to the same antenna because of how the splitter works. But I was wondering if anyone has any real-world experience running a receiver and transceiver on the same antenna using a splitter and any potential issues?

We installed a AIS transponder and a splitter (to share a single antenna) in 2010 and it has worked perfectly.

[tkeithlu]

If you'd like to avoid the splitter, workable as they seem to be, realize that the AIS antenna only needs a view of the sky, not altitude as in a VHF.

I'm glad you went to the transceiver. There is always the slim chance that that container ship is actually keeping a watch and will at least wake you up before it runs over you.

Has it got its own display? If so, it makes a back-up navigator.

[Marathon1150]

We have been using a Vesper XB-8000 transponder with Vesper splitter for about 5 years coastal cruising and a bluewater crossing from Mexico to French Polynesia. It seems to work well - we detected tankers etc when they were a long way off and contacted those that were going to get close to us. By the time we contacted them (usually about 20nm distant) they were already aware of us and without exception, volunteered to change their course after I offered to change ours.

[redneckrob]

I fear I didn't explain my question well, I think @River Cruiser was the only one to get it (thanks, that was helpful). I have no questions about using a splitter or about AIS in general. The question is that I plan to have both an AIS transceiver AND an AIS receiver using the same antenna (they're just doing so via a splitter). My question is if having an AIS receiver on the same antenna as a separate AIS transceiver is going to be an issue.

[Auspicious]

Originally Posted by redneckrob

I fear I didn't explain my question well, I think @River Cruiser was the only one to get it (thanks, that was helpful). I have no questions about using a splitter or about AIS in general. The question is that I plan to have both an AIS transceiver AND an AIS receiver using the same antenna (they're just doing so via a splitter). My question is if having an AIS receiver on the same antenna as a separate AIS transceiver is going to be an issue.

No. Sharing the antenna won't be a problem per se. Two issues.

One. You'll have to set the threat threshold in the VHF AIS setup to 0. Some radios with built-in AIS are smart enough not to alarm on the same MMSI programmed into them but many are not. You don't want your VHF alarming due to the transponder signal.

Two. Splitters are really not a good idea. First, they reduce signal inbound and outbound on both legs. Second, if/when they fail they can connect the two source together and the AIS transponder can damage the VHF receiver front-end. Technical term: bad. A separate AIS antenna is a better solution.

[Martkimwat]

Originally Posted by tkeithlu

If you'd like to avoid the splitter, workable as they seem to be, realize that the AIS antenna only needs a view of the sky, not altitude as in a VHF.

I'm glad you went to the transceiver. There is always the slim chance that that container ship is actually keeping a watch and will at least wake you up before it runs over you.

Has it got its own display? If so, it makes a back-up navigator.

I'm not sure that is correct, it is still line of site, and if your AIS antenna is down low, you will have much less range and be seen at a much lower range than if it is up high, at the top of the mast. There is an interesting article in the July issue of Yachting Monthly that touches on this and it is a way to check if your antenna is working properly. If you are only seeing vessels out to a couple of miles when you know that there areAIS targets at say 10 miles, then you know your antenna is suspect. It's a way of checking your antenna instead of doing a radio check, especially in a busy area where Ch 16 or Coastwatch is busy.

[Dsanduril]

Think of it this way. If your AIS transmitter decides to transmit (you said SOTDMA so it has a reserved slot) then no one else will be transmitting at the same time (should even be the case with a traditional class B). So, your AIS receiver isn't missing anything. It is only you transmitting in that time slot.

If you don't use a splitter then your own receiver, on a separate antenna, will receive your transmitted signal. That could mean, as noted above, that you see yourself as a collision risk. It could also result in an overload (probably temporary) of the receiver's input circuits depending on how close the receive antenna is to your transmit antenna.

With a splitter you automatically take the receiver offline when you are transmitting.

I like the redundancy of multiple systems and distinct antennas, but in this case a splitter may actually be a cleaner setup.

[Telemark43]

Originally Posted by Marathon1150

We have been using a Vesper XB-8000 transponder with Vesper splitter for about 5 years coastal cruising and a bluewater crossing from Mexico to French Polynesia. It seems to work well - we detected tankers etc when they were a long way off and contacted those that were going to get close to us. By the time we contacted them (usually about 20nm distant) they were already aware of us and without exception, volunteered to change their course after I offered to change ours.

my experience as well, pick up tankers at least 20 nm away, no interference with

VHF

[waterman46]

Originally Posted by Martkimwat

I'm not sure that is correct, it is still line of site, and if your AIS antenna is down low, you will have much less range and be seen at a much lower range than if it is up high, at the top of the mast. There is an interesting article in the July issue of Yachting Monthly that touches on this and it is a way to check if your antenna is working properly. If you are only seeing vessels out to a couple of miles when you know that there areAIS targets at say 10 miles, then you know your antenna is suspect. It's a way of checking your antenna instead of doing a radio check, especially in a busy area where Ch 16 or Coastwatch is busy.

You are correct, the AIS antenna height does matter, though not quite as important as the VHF antenna in general. If you don't use a splitter but want to use two separate antennas, then be sure to place them at a different heights as far away as possible.

The method above checks your AIS receiver. To check your AIS transmit, on the internet you can find AIS trackers (Google "ship tracker") that can be used to check if your AIS is signal is getting out. If you are near any port, your signal will be picked up on a land based receiver connected to the internet.

[Sailmonkey]

Originally Posted by tkeithlu

If you'd like to avoid the splitter, workable as they seem to be, realize that the AIS antenna only needs a view of the sky, not altitude as in a VHF.

Not even remotely correct.

AIS between vessels at sea is line of sight VHF transmission. The higher the antenna, the further the horizon.

Mount the antenna down low and you’ve drastically reduced your range. If both vessels have their antennas down low range is even worse.

[Cpt Pat]

Originally Posted by Auspicious

No. Sharing the antenna won't be a problem per se. Two issues.

One. You'll have to set the threat threshold in the VHF AIS setup to 0. Some radios with built-in AIS are smart enough not to alarm on the same MMSI programmed into them but many are not. You don't want your VHF alarming due to the transponder signal.

Two. Splitters are really not a good idea. First, they reduce signal inbound and outbound on both legs. Second, if/when they fail they can connect the two source together and the AIS transponder can damage the VHF receiver front-end. Technical term: bad. A separate AIS antenna is a better solution.

I agree with Auspicious' caveats, especially point two above. I have, and have used, the Vesper splitter to combine both my VHF and AIS transponder to use my masthead antenna. I had four issues:

1) The splitter reduced the measured transmit power of both transceivers. I have access to good RF test instruments. My VHF transceiver power to the antenna was reduced from 25 watts to 18 watts. Not a big deal, in terms of decibels, but why waster power?
2) The splitter punched a hole in VHF reception every time the AIS transmitted. While a 20 millisecond hole isn't very long, it's audible. I got tired of hearing "pifft" every time the AIS transmitted during VHF reception.
3) Using only one antenna creates a single-point-of-failure. If the antenna or splitter fails -- you've got nothing. Complexity and Coupling are the mortal enemies of reliability. The splitter adds complexity, and it couples two independent systems (VHF radio and AIS). A simpler configuration with two antennas, and decoupling the two radios, is naturally more reliable.
4) If you sail in an area with a lot of traffic, the AIS reception range added by an antenna way up high at your masthead can overwhelm the CPU in your AIS display device. The CPU doesn't have infinite processing power, and plotting and calculating the CPAs on all that data isn't free. I sail offshore near the S.F. Bay, and when using the masthead antenna, I was often receiving 100 stations from the Bay. The CPU on my chartplotter groaned under the load. All functions slowed way down from the load of processing all that data. While it's fun to see vessels over 20 miles away: what is the usefulness of that?

Plus, the cost of a good splitter (Vesper is one of the best) costs more than a separate antenna and coax for the AIS transponder.

I am now using a Shakespeare 5215 1/2 wave antenna at the masthead, and a Morad 162 HD antenna on its own mast at the stern that is 12 feet above the waterline at its base. The Vesper splitter is powered up and ready for emergency use in case I ever lose use of either antenna. I consider that to be the only appropriate use for an antenna splitter (a free solution -- since I already owned it).

[StoneCrab]

The way I understand it, the transmission of AIS data only takes a few milliseconds, so the sharing is sort of a non event. Your radio can even broadcast the AIS info while you are transmitting. The interruption is so brief that you or the receiving station can't tell it happened. This is the magic of modern computing.

I'm not a salesman for Vesper, but I did get excited about their new Cortex product that I saw in fall. I was thinking about buying their XB-8000 AIS transceiver when I stopped in the booth, but when I saw the Cortex, I decided to hold off until the Cortex hit the market.

Vesper Cortex is a new integrated VHF with AIS transceiver and base maps onboard. It is due to hit the US market in June, 2020. The Cortex is unique in that the handset looks like a smartphone and is wirelessly connected to the base-station. Like a smartphone, it has a touchscreen which displays the AIS targets and allows for DSC calling by tapping on the target who you want to call. Pretty slick.

The base is also a multiplexor for NMEA 0183, NMEA 2000, and WiFi. Since it has a built in GPS and heading sensor for the AIS functions, it can do Anchorwatch. It also allows for monitoring of a built in barometer, NMEA 2000 sensors and five additional sensors ( 5 Inputs, Digital (0-24V), Analog (0-10V). Now if they can only figure out how to overlay RADAR on the display, it will be like having a MFD in your pocket.