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AIS transponder - SOTDMA vs CTDMA  

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Ludovic Francois
(@ludo)
Active Member
Joined:4 months  ago
Posts: 3
April 17, 2018 3:24 pm  

After some FOG experience few weeks ago on our way to Catalina. I am looking to add an AIS transponder/receiver to our Catalina 36.

Today I see some new system using SOTDMA, they look like a modern choice to do. Any inconvenient compared to CTDMA?

Now my products selection so far are:

  1. em trak b100 (if it has any advantages to stay with CTDMA, and the pretty low cost of this device)
  2. em trak b360 (SOTDMA version)
  3. amec widelink b600

Any comments/recommendations or any other products I should look at?

I already plan to set it up with its own antenna.

Ludo


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Ben Ellison
(@ben-ellison)
Member Admin
Joined:6 months  ago
Posts: 46
April 18, 2018 2:44 pm  

Hi Ludovic,

I've written about SOTDMA Class B and also used an EM-Trak B400. I think that CTDMA Class B works well for most recreational boats, but SOTDMA is particularly good for fast ones. Then again, it wasn't until your post that was aware of the B360, which is a lot of SOTDMA Class B for $749:

https://www.em-trak-usa.com/product-page/b360-high-powered-ais-class-b-waterproof-wifi-integrated-gps-antenna-uscg

And then again, if you're willing to spend that amount, you should also consider the Vesper XB8000, especially if you have a tablet to make use of its unique features. 

Sorry to just add to your decision process, but you can't go too far wrong.


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Steve Mitchell
(@stevemitchell)
Member Moderator
Joined:5 months  ago
Posts: 47
April 18, 2018 3:01 pm  

I wrote up a review on the AMEC B600 at  https://sailbits.com/amec-widelink-sotdma-ais/

I also have the XB-8000.

I sail in a fairly AIS congested area, so having SOTDMA from the AMEC appears to have helped with other people being able to see me. I've figured this out from having others look before/after and using online tools to track the frequency of updates also before/after. 

However, I prefer the management of the Vesper XB-8000 over the AMEC. The AMEC does not allow you to configure it over WiFi, which the Vesper does, and Vespers apps and ecosystem are far more developed than AMEC.

I've also had the XB-8000 for far longer, and although there have been some issues in the past with lockups, those appear to have been solved. The AMEC is fairly new, and has its share of bugs, so the jury is still out on its long term results.

I'm hoping that Vesper decides to put out a SOTDMA unit soon, as that would really be a great option if they had the same management and apps.

Editor, SailBits.com


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Geoff Roddick
(@geoff-roddick)
Active Member
Joined:4 months  ago
Posts: 3
April 19, 2018 10:35 am  

Steve,

I too am looking at the Amec B600 or Emtrack B350 after talking to Mitech. They seem quite similar..

You have said "However, I prefer the management of the Vesper XB-8000 over the AMEC".  If I am going with the non-wifi version how does that comment apply?

thanks!


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Steve Mitchell
(@stevemitchell)
Member Moderator
Joined:5 months  ago
Posts: 47
April 19, 2018 11:27 am  
Posted by: Geoff Roddick

Steve,

I too am looking at the Amec B600 or Emtrack B350 after talking to Mitech. They seem quite similar..

You have said "However, I prefer the management of the Vesper XB-8000 over the AMEC".  If I am going with the non-wifi version how does that comment apply?

thanks!

Geoff,

It still applies somewhat. The WiFi part of the AMEC is really only so you can connect to it from another machine or app and get AIS and GPS data. Even without WiFi, you may still have to do firmware updates every once in a while, or change settings, and that is where Vesper has an advantage over AMEC. AMEC requires a Windows machine with a USB cable and some really rather dated software to do the config. Vesper can be configured and updated from Mac and PC (and I believe updated as well from iOS and Android) and has better overall management for that stuff. 

Truth be told though, you won't be managing or changing settings on an AIS transponder that often, only if it needs software upgrades, so these features may not matter to you that much.

If I were choosing right now, I would choose an SOTDMA transponder for sure given the higher transmit wattage and better algorithm. 

Editor, SailBits.com


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Ludovic Francois
(@ludo)
Active Member
Joined:4 months  ago
Posts: 3
April 19, 2018 11:46 am  

Just saw a great deal for the B100 at $340. So I am going to take my chance with it for now:

https://us.binnacle.com/product_info.php?products_id=10043


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Steve Mitchell
(@stevemitchell)
Member Moderator
Joined:5 months  ago
Posts: 47
April 19, 2018 11:51 am  
Posted by: Ludovic Francois

Just saw a great deal for the B100 at $340. So I am going to take my chance with it for now:

https://us.binnacle.com/product_info.php?products_id=10043

The B100 is a great, compact unit. I don't believe it is SOTDMA nor has the higher wattage transmitter - it is using CTDMA and lower power, but if cost and space are an issue, it is a good choice.

Editor, SailBits.com


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Ben Ellison
(@ben-ellison)
Member Admin
Joined:6 months  ago
Posts: 46
April 19, 2018 2:55 pm  

Steve, have you been using the Vesper AIS target display and alerting features since they added them to the WatchMate app with their big SmartAIS update? I think that they're excellent, even award worthy:

https://www.sailmagazine.com/gear/vesper-smartais-app  

But I also agree that the B100 is a perfectly good CTDMA AIS transponder, and it's core is highly proven in many units with various brand names, though I've never before seen one for $340


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Steve Mitchell
(@stevemitchell)
Member Moderator
Joined:5 months  ago
Posts: 47
April 19, 2018 3:02 pm  

Yes to SmartAIS and the alerting stuff. I have used it a lot and it is definitely great stuff. That's one of the things I meant by the ecosystem and apps - they clearly are head and shoulders above anyone else out there. I have both the AMEC and the Vesper on Grace at all times, and depending on what I'm doing, flip back and forth between them being active. 

I have become very dependent on the anchor watch feature in Vesper along with my Android watch while on a mooring or at anchor.

Editor, SailBits.com


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Ben Ellison
(@ben-ellison)
Member Admin
Joined:6 months  ago
Posts: 46
April 19, 2018 3:06 pm  

Yes, the Vesper anchor watch is great. Off topic a bit, but do you have a way to use it when ashore?

PS:  https://www.panbo.com/new-in-safety-exposure-olas-float-on-vesper-smartais-deckwatch-and-digital-yacht-nomad-portable-ais/


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Steve Mitchell
(@stevemitchell)
Member Moderator
Joined:5 months  ago
Posts: 47
April 19, 2018 3:13 pm  
Posted by: Ben Ellison

Yes, the Vesper anchor watch is great. Off topic a bit, but do you have a way to use it when ashore?

PS:  https://www.panbo.com/new-in-safety-exposure-olas-float-on-vesper-smartais-deckwatch-and-digital-yacht-nomad-portable-ais/

I haven't used it that way, no, although I am now thinking of several ways that might be possible with a VPN from your phone/tablet back to the boat, but probably not practical.  I use my Siren MTC, Boat Command or one of a number of other devices for geofencing/movement when away from the boat. Not quite the same, but close.

Editor, SailBits.com


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Ben Stein
(@ben-stein)
Member Admin
Joined:6 months  ago
Posts: 39
April 19, 2018 9:02 pm  
Posted by: Steve Mitchell

I wrote up a review on the AMEC B600 at  https://sailbits.com/amec-widelink-sotdma-ais/

I also have the XB-8000.

I sail in a fairly AIS congested area, so having SOTDMA from the AMEC appears to have helped with other people being able to see me. I've figured this out from having others look before/after and using online tools to track the frequency of updates also before/after. 

However, I prefer the management of the Vesper XB-8000 over the AMEC. The AMEC does not allow you to configure it over WiFi, which the Vesper does, and Vespers apps and ecosystem are far more developed than AMEC.

I've also had the XB-8000 for far longer, and although there have been some issues in the past with lockups, those appear to have been solved. The AMEC is fairly new, and has its share of bugs, so the jury is still out on its long term results.

I'm hoping that Vesper decides to put out a SOTDMA unit soon, as that would really be a great option if they had the same management and apps.

Steve, 

I think you hit on a challenge with AIS.  How do I know my AIS is being transmitted adequately?  The short answer I've been able to figure out is... ask other people.  Not exactly what we're all hoping for with our high tech toys err tools.  Last fall while travelling with a friend for several hundred miles we noticed he would drop off our AIS diplays frequently.  He had a brand new Garmin suite of electronics including an AIS-600.  The AIS-600 has a VHF radio pass-through function that was employed on his boat.  When we had the opportunity we re-wired his AIS and radio so they each had their own antennas.  His AIS performance increased dramatically.  What fixed it?  Bad switch in the AIS-600?   Bad crimp somewhere?  Not sure.  

 

Ben

Contributing Editor, Panbo.com


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Steve Mitchell
(@stevemitchell)
Member Moderator
Joined:5 months  ago
Posts: 47
April 19, 2018 9:29 pm  
Posted by: Ben Stein

Steve, 

I think you hit on a challenge with AIS.  How do I know my AIS is being transmitted adequately?  The short answer I've been able to figure out is... ask other people.  Not exactly what we're all hoping for with our high tech toys err tools.  Last fall while travelling with a friend for several hundred miles we noticed he would drop off our AIS diplays frequently.  He had a brand new Garmin suite of electronics including an AIS-600.  The AIS-600 has a VHF radio pass-through function that was employed on his boat.  When we had the opportunity we re-wired his AIS and radio so they each had their own antennas.  His AIS performance increased dramatically.  What fixed it?  Bad switch in the AIS-600?   Bad crimp somewhere?  Not sure.  

 

Ben

I learned long ago that AIS transponders should never have a splitter or share antennas. I had a Vesper splitter on Grace for a few months because I had no choice, and removing that and using a properly tuned, dedicated AIS antenna caused my tracks to appear all the time. The dedicated antenna is on the stern radar mount vs the VHF antenna at the top of the mast! So even with the height, it didn't matter. 

On my previous boat Jammy, I always had a dedicated AIS antenna on the stern arch, and never had any issues. 

One strange way I know that I am always transmitting is because I am a mobile base station, and run software on the Linux boat computer to submit my data to 4 different online sources. If I am not submitting good data, including my own boat, within a 5-10 minute period, I get an alert. 

Not the most flexible or scalable approach for the average boater, but it is a start.

Vesper does show the stats of sent and received messages for your transponder, so that is at least one way you could check. Perhaps they could integrate an alarm if your antenna SWR is high, and you are not receiving data or something like that? 

Another way could be that the Vesper could check an online service every N number of minutes to see if your MMSI is fresh, using its WiFi radio. Interesting feature which could be a differentiator. 

To your point, though - no guarantees that you are actually showing up.

Editor, SailBits.com


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Geoff Roddick
(@geoff-roddick)
Active Member
Joined:4 months  ago
Posts: 3
April 19, 2018 10:07 pm  

A simple test, which won't show your signal strength, is to have another AIS receiver onboard to see if you see yourself. 


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Saffy The Pook
(@saffythepook)
Active Member
Joined:4 months  ago
Posts: 5
April 21, 2018 10:49 am  

Regarding SOTDMA vs CTMDA, just a data point here. I've got a Vesper 8000 connected to Vesper's active splitter, which feeds 30' of LMR-240UF within the boat and then 75' of LMR-400UF going up the mast, terminating in Vesper's hybrid VHF/AIS antenna, which is ~65' off the water. I'm moored at Shilshole in Seattle and routinely see large numbers of recreational class B transponders (presumably CTDMA units) 30 miles away at Port Townsend. Prior to the recent upgrade of my antenna and cabling, my AIS detection range limit was approximately 12 miles. 

From a spec standpoint, SOTDMA may be better than CTDMA but with a good install, even with long cable runs and a shared antenna, CTDMA works great. I'd be willing to bet that most AIS installations are limited by compromised cables/connectors/antennas rather than the technology of the AIS unit itself.


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