AIS Antenna??

[mvweebles]

I'm headed back to Weebles in a few weeks to resume our journey south through Central America. I've had AIS issues since the start (boat symbol I broadcast is intermittently 90-degrees off direction of travel - Simrad hasn't been able to help). I have a Sat Compass and run the antenna through a Simrad AIS/VHF Splitter. My gut tells me it's a setting within the MFD (3-year old EVO3) but since Simrad hasn't been able to assist, I'm thinking I'll try replacing the antenna and bypass the splitter - since the problem is intermittent, wondering if the VHF interferes with the AIS signal somehow (doubtful, but worth a try).

Getting an antenna down to southern Mexico is a pretty expensive. Wondering if a whip antenna (AIS) for a sailboat would be helpful - It's short enough I can bring it with me in checked luggage.

Amazon.com

Thoughts?

Thanks in advance -

Peter

 

[Diep]

Most of the Shakespeare AIS antennas are only 3' or 4' so you should be able to check or carry on. The one you linked is available with 2 different bases depending on what would work best for your location.

The only other thing to think about is if you have a place to mount it with good separation from your other VHF antennas.

 

[rslifkin]

A separate antenna is a good thing, but I wouldn't expect it to fix an issue with incorrect heading being transmitted.

In our case, I installed a Morad 159HD as an AIS antenna. About 4.5 feet long, better performance than a 3db gain sailboat style whip, and very wide banded so it covers the regular AIS channels as well as the AIS 3 and 4 channels used for satellite reception with low enough SWR across all of them.

 

[JackConnick]

Be sure to buy an antenna that's compatible with your system. Some want an "AIS" rated model, others (Raymarine) just a regular VHF. That could be some of the issue you're having...

 

[twistedtree]

A separate antenna is a good thing, but I wouldn't expect it to fix an issue with incorrect heading being transmitted.

In our case, I installed a Morad 159HD as an AIS antenna. About 4.5 feet long, better performance than a 3db gain sailboat style whip, and very wide banded so it covers the regular AIS channels as well as the AIS 3 and 4 channels used for satellite reception with low enough SWR across all of them.

I agree. A good antenna is a good thing to have, but there is zero chance it will fix the heading issue. The messed up heading is almost certainly some sort of data communications problem between the AIS and other devices, probably with a software bug compounding the problem.

 

[O C Diver]

Agree that changing the antenna won't have any effect. The more important question is whether it appears that way on another boats AIS screen.

I would dive into the sub menus for the AIS receiver as that's what's showing your image on the MFD.

Ted

 

[boomerang]

I've had AIS issues since the start (boat symbol I broadcast is intermittently 90-degrees off direction of travel - Simrad hasn't been able to help). I have a Sat Compass and run the antenna through a Simrad AIS/VHF Splitter. My gut tells me it's a setting within the MFD (3-year old EVO3)

If you are in fact broadcasting an incorrect vessel orientation ,or for that matter ,even if it's just showing up incorrectly on your MFD screen, you might have too many or conflicting PGN's on your nmea 2000 buss. You said you have a satellite compass, which I'm assuming is your primary compass for your autopilot. If you've verified that the sat compass remains steady but your ships icon jumps, do you have any other heading devices on the buss? If possible, access the pgn list and remove or turn off redundant PGN's. Also, you're possibly merging another heading source ,via a multiplexer (your MFD,AIS or similar unit that has nmea 2000 and nmea 0183 connect to it), and the extra heading data might be causing a burp in the system.
Save your $$ trying another antenna but if you want a 3' Shakespeare AIS whip antenna, I have one that I took off and replaced with an 8' that is almost new that I'll give you.

 

[mvweebles]

Agree that changing the antenna won't have any effect. The more important question is whether it appears that way on another boats AIS screen.

It does appear that way on other boats screens. Bit embarrassing to get a VHF hail alerting to the problem. And could be a safety issue in slow, close quarters (such as Canal Zone - Panama).

Peter

 

[mvweebles]

If you are in fact broadcasting an incorrect vessel orientation ,or for that matter ,even if it's just showing up incorrectly on your MFD screen, you might have too many or conflicting PGN's on your nmea 2000 buss. You said you have a satellite compass, which I'm assuming is your primary compass for your autopilot. If you've verified that the sat compass remains steady but your ships icon jumps, do you have any other heading devices on the buss? If possible, access the pgn list and remove or turn off redundant PGN's. Also, you're possibly merging another heading source ,via a multiplexer (your MFD,AIS or similar unit that has nmea 2000 and nmea 0183 connect to it), and the extra heading data might be causing a burp in the system.
Save your $$ trying another antenna but if you want a 3' Shakespeare AIS whip antenna, I have one that I took off and replaced with an 8' that is almost new that I'll give you.

Thanks @boomerang - and thanks to all others who responded. What you and other knowledgeable folks have said - it's a config issue - makes sense to me. What I don't understand is why Simrad was never able to resolve. This started out as a 100% Simrad system. I added the Sat Compass to resolve some mild serpentining on the A/P. And replaced the Simrad AIS (combined with Simrad VHF with AIS B) with an Emtrek AIS. I've been chasing this problem for a while, have over a dozen calls into Simrad (and a couple into Emtek) with many long hours on hold waiting to chat with a well-meaning but not overly helpful Tech Support CSR. Email is no better - days between responses.

I'll hold off on the antenna. Maybe when I get to Weebles, I'll try Simrad Tech Support again - it's been over a year. Maybe they have better tech support process and talent these days.

Thanks - Peter

 

[Marco Flamingo]

Just saw a "45 degree off" AIS thing yesterday with a sailboat along side of us. When he became a "dangerous AIS target", his red COG direction was correct (and parallel to us), but his vessel icon was still off by 45 and pointing at us. I didn't hail him, but I'm curious as to what causes that. We were going through Dodd Narrows, so having the icon pointed wrong was probably a bit concerning to other boaters as well.

 

[rslifkin]

On a basic level, what I expect is happening is that you're getting intermittent or invalid heading data sent onto the NMEA network at some point and the AIS is picking that up. If you have both a satellite compass and a fluxgate on the network, try unplugging the fluxgate compass and see if that resolves the issue.

I've noticed that my Emtrak B951 won't accept a magnetic heading, only true heading (as that's what AIS broadcasts). So my setup only broadcasts COG and doesn't provide heading data to other boats, as the heading sensor in the system is a Furuno PG700 which only outputs magnetic heading to the network.

 

[Ron Hopkins]

I've had great luck with a stainless whip, cut specifically and loaded at 162 for AIS channels, TX/RX. I gave up on the smart splitter and it's issues (made by Smart Radio). Gam antenna's are made in the USA, high quality, recommended.
Mini Series | USA made VHF/UHF Antennas & Accessories

 

[ranger58sb]

It does appear that way on other boats screens. Bit embarrassing to get a VHF hail alerting to the problem. And could be a safety issue in slow, close quarters (such as Canal Zone - Panama).

Thanks @boomerang - and thanks to all others who responded. What you and other knowledgeable folks have said - it's a config issue - makes sense to me. What I don't understand is why Simrad was never able to resolve.

I'll hold off on the antenna. Maybe when I get to Weebles, I'll try Simrad Tech Support again - it's been over a year. Maybe they have better tech support process and talent these days.

If you appear sideways on other boat's receivers... yep, I'd think first that's a configuration thing on your systems.

I didn't have to do it all, installers did most... but I know our AIS configuration process asks for things like boat orientation, AIS/GPS antenna placement relative to boat dimensions and so forth. I'd guess heading is one of those too, but don't have it in front of me just now to confirm. Maybe take a fresh look at it when you get back, see if anything maybe now more likely to be associated pops up... and then as you say, get with Simrad again with the menus and buttons at your fingertips.

-Chris

 

[O C Diver]

First, your AIS is a stand alone unit. It has its own GPS antenna, does its own calculations as far as speed and direction, and doesn't pick up information from the NEMA 2000 network.

So, the heading information is generated from the AIS program. As I said earlier, go into the menus and sub menus to see if there's a correction. For black box versions, the software should be accessible from the MFD. If you don't have success contact the manufacturer. I'm sure you're not the first user that this has happened to.

Ted

 

[rslifkin]

First, your AIS is a stand alone unit. It has its own GPS antenna, does its own calculations as far as speed and direction, and doesn't pick up information from the NEMA 2000 network.

So, the heading information is generated from the AIS program. As I said earlier, go into the menus and sub menus to see if there's a correction. For black box versions, the software should be accessible from the MFD. If you don't have success contact the manufacturer. I'm sure you're not the first user that this has happened to.

Ted

Not quite. The AIS will derive course over ground from its internal GPS, but it has no way to figure out heading as there's no internal heading sensor. Heading is not a required input for class B AIS, but it's optional. So normally if true heading data is available on the network it will be used. The issue happening here seems to be the heading data being incorrect, leading to the AIS broadcasting a heading and COG that differ significantly.

 

[mvweebles]

If you don't have success contact the manufacturer. I'm sure you're not the first user that this has happened to.

Ted

That was my thought too, of course. But when I called both Simrad and Em-Trak (953), sure seemed like they had little input or knowledge about what the issue might be. To their defense, it was about 1-1/2 years ago so I may try them again to see if their knowledge base has improved (and perhaps Simrad's customer service has improved).

Despite Navico (Simrad/Lowrance/B&G) being a major player, they didn't seem to have much familiarity with settings except to contact Navico.

Of course, DIY install runs this risk of finger-pointing.......

Peter

 

[DDW]

For true heading there is something else involved, that knows the local variation. That could involve the chartplotter. I think I'd start by disabling the sat compass, as it is the most complex piece of gear, and see if it works with the fluxgate.

I see this somewhat frequently from other boats. Including 180 degrees, which is disconcerting.

 

[O C Diver]

Not quite. The AIS will derive course over ground from its internal GPS, but it has no way to figure out heading as there's no internal heading sensor. Heading is not a required input for class B AIS, but it's optional. So normally if true heading data is available on the network it will be used. The issue happening here seems to be the heading data being incorrect, leading to the AIS broadcasting a heading and COG that differ significantly.

If that's the case then disconnect the heading sensor (electronic compass) to see if that solves the problem.

Maybe in the AIS menus there an electronic switch to disengage the heading sensor.

Ted

 

[heysteve]

Not sure how far down the rabbit hole you want to go, but consider putting an Actisense NGX-1/USB device on your NMEA 2000 network. This allows you to use their free NMEA Reader software on your PC to analyze the traffic. You should be able to filter out various PGNs and look for anything strange. There's a really terrific site called NMEA Revealed (here) where you can see the expected formats.

On a similar but different note, after setting up my DIY network I noticed that I wasn't getting heading deviation information (HDG PGN) despite having a Raymarine EV-1 sensor. Turns out it was because my Digital Yachts AIS device was also sending an HDG PGN sans deviation and it was a lower NMEA device instance so it was taking priority over the EV-1. Fortunately, I found this informative article on TimeZero's website (here) that explained how to fix it.

 

[SteveK]

FWIW, I recall reading others reporting this issue with antenna splitters. I think your separate antenna is the best first attempt at repair.

 

[twistedtree]

It does appear that way on other boats screens. Bit embarrassing to get a VHF hail alerting to the problem. And could be a safety issue in slow, close quarters (such as Canal Zone - Panama).

Peter

I have seen other boat's broadcasting the same erroneous heading, so you are not alone. Someone out there has a bug, but I don't know who or where.

 

[boomerang]

I first encountered a skewed boat icon when Vesper introduced their Cortex unit with an internal heading sensor. No matter how hard I tried, there was an onboard deviation that couldn't be removed and that would cause the heading of our ship to be displayed incorrectly oriented. There was no provision in the Cortex software to turn the internal sensor off, either, which was a pain because it caused my navigation charts to be incorrectly oriented too. Garmin had just bought Vesper and I spent most of our trip back up the ICW on the phone with them trying to remedy the solution. They ended up sending me a Smart cast nmea 2000 compass which I installed below (the Vesper was under the fly bridge) and the skewing problem went away since the Cortex defaulted to the external heading sensor on the nmea2000 buss.
Most every time I'd see a boat that showed up on our plotter with their icon skewed, I'd hail them on the VHF and ask if they had a Vester Cortex AIS and each time ,the answer was yes.
I bought and installed another Garmin Cortex AIS on our current boat ( mainly because I like the anchoring app but this one will be the last Garmin) and we haven't seen any issues with the heading but I am also using a Simrad hi-performance rate compass for the autopilot so the Vespers internal compass has never been used.

 

[twistedtree]

To diagnose, I'd start by disconnecting your AIS from N2K and NMEA 0180 such that it is operating stand alone. Make sure it's working correctly like this where it is only using its own internally derived data, and not anything external. Just be aware that when set up like this your nav system won't show any AIS targets because you AIS device isn't sending data to your nav system.

Also check to be sure the AIS in your Simrad VHF is completely disabled, assuming it can be disabled. Otherwise try turning the VHF off completely. It's possible that both AIS devices are sending data with one being correct and the other incorrect.

If none of this works then you will need to hook up N2K and 0183 again and start to figure out where the bad data is coming from.

See if you can find an app or device that will show you the individual data elements being received. As has been mentioned, AIS B sends COG and HDG, and a first step would be to see which is getting messed up. It's probably HDG, but good to confirm so you know what to focus on.

HDG can come from a number of different sources. Some data (whether PGN in N2K or sentence in 0183) provides true heading directly, like from a sat compass. In other cases only magnetic heading is sent like from a rate compass. In the case of a magnetic heading, it would then be up to the AIS device to also look for someone sending Variation data so that true heading can be computed. I'm presuming an AIS device is smart enough to do this if the data is available. I have been told by people who I think are reliable sources that the unwritten rule is that you should never send computed data (like magnetic heading plus variation), only original data. And computation should be done by whoever is going to consume the data. So in this case, if magnetic heading is being combined with Variation to get true heading, it should be the AIS doing it. If something other than the sat compass is transmitting true heading, try to shut it off.

 

[rslifkin]

HDG can come from a number of different sources. Some data (whether PGN in N2K or sentence in 0183) provides true heading directly, like from a sat compass. In other cases only magnetic heading is sent like from a rate compass. In the case of a magnetic heading, it would then be up to the AIS device to also look for someone sending Variation data so that true heading can be computed. I'm presuming an AIS device is smart enough to do this if the data is available. I have been told by people who I think are reliable sources that the unwritten rule is that you should never send computed data (like magnetic heading plus variation), only original data. And computation should be done by whoever is going to consume the data. So in this case, if magnetic heading is being combined with Variation to get true heading, it should be the AIS doing it. If something other than the sat compass is transmitting true heading, try to shut it off.

I have a similar AIS unit (Emtrak B951) and despite having mag heading plus variation available on the network, I haven't seen mine transmit heading data. It seems that it will only transmit it if true heading is provided to the AIS unit (such as from a sat compass, which I don't have).

 

[twistedtree]

I have a similar AIS unit (Emtrak B951) and despite having mag heading plus variation available on the network, I haven't seen mine transmit heading data. It seems that it will only transmit it if true heading is provided to the AIS unit (such as from a sat compass, which I don't have).

OK, good info. That suggests that something other than Weebles Sat Compass is sending bad heading data. Or the sat compass is sending bad data...

 

[rslifkin]

OK, good info. That suggests that something other than Weebles Sat Compass is sending bad heading data. Or the sat compass is sending bad data...

For some additional info, I just checked the manual. The B95x units accept PGN 127250 for heading, as well as the NMEA 0183 HDT and THS sentences. They do not accept PGN 127258 for mag variation or any NMEA 0183 sentences for magnetic variation or magnetic heading, which seems to confirm the behavior I've seen where they'll only transmit heading if something is providing true heading.

Although it looks like the variation data can be included in PGN 127250, so it's possible in my case that it's just not doing that and the heading is being ignored as a result. I might see if I can get my AP or plotter to output heading data with variation included and see if the AIS transceiver uses it.

I'd be inclined to look into the NMEA data going over the network and see what devices are sending heading info and what it looks like.

 

[mvweebles]

@rslifkin - I believe the difference between my B953 and your B951 is mine has an integral antenna splitter (back-story: I originally went with the Simrad VHF with integral AIS and separate Simrad splitter, but it never worked properly (not the same issue) so I returned it to Simrad and got a refund - then bought the EmTrak) . Much of my problem is the problem is intermittent; and I don't see the problem - only those to whom receive my broadcast see it. QUESTION: Any tips on how I can see what I'm broadcasting in real time?

@twistedtree - thanks so much for the tips (I owe you yet another adult beverage). I will run the traps you offer. I do have one novice question. I am apparently broadcasting my heading information correctly, but the boat-icon is rotated so I appear to be crabbing on other's screen. I don't really understand the whole PGN stuff (except that it's a config setting). Why would the boat's apparent heading be different than the actual heading?

The one item I do recall from EmTrak tech is they only use True, not Mag heading information. I wish I still had the email where I sent them the sys log information. I'll repeat the process when I return to the boat in a few weeks.

Peter

 

[FWT]

I have Simrad, and use a Simrad black box VHF including AIS send.

1) I agree it does not sound like an antenna issue, however my installer insisted on a separate dedicated AIS antenna for the send. Said a splitter won't work well.

2) Do a recalibration of the AIS compass. Find a quiet empty spot on the water, find the AIS antenna in the Devices menu, and hit the button to recalibrate. On that one I think the pattern is to do a slow 360 degree turn. It will guide you with on screen instructions. Might work. Might be something else.

 

[rslifkin]

Much of my problem is the problem is intermittent; and I don't see the problem - only those to whom receive my broadcast see it. QUESTION: Any tips on how I can see what I'm broadcasting in real time?

I normally look at what Marinetraffic shows for us. Or find a nearby friend with AIS and ask them what they're seeing.

 

[twistedtree]

For some additional info, I just checked the manual. The B95x units accept PGN 127250 for heading, as well as the NMEA 0183 HDT and THS sentences. They do not accept PGN 127258 for mag variation or any NMEA 0183 sentences for magnetic variation or magnetic heading, which seems to confirm the behavior I've seen where they'll only transmit heading if something is providing true heading.

Although it looks like the variation data can be included in PGN 127250, so it's possible in my case that it's just not doing that and the heading is being ignored as a result. I might see if I can get my AP or plotter to output heading data with variation included and see if the AIS transceiver uses it.

I'd be inclined to look into the NMEA data going over the network and see what devices are sending heading info and what it looks like.

That's great info, and I agree the next step is to start examining messages. I'm guessing this is an all N2K setup?