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post #1 of 18 Old 01-09-2008 Thread Starter
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Dual channel vs single channel AIS

Can anyone educate me on the differences/advantages/disadvantages of dual channel vs single channel AIS units. I'm trying to decide between the Sitex AIS Radar which has it's own display unit or going with the Furuno FA30 and integrating with my Furuno chartplotter. The Sitex unit is single channel while the Furuno is dual channel. Dual something or other always sounds better than single but in this case I would like to know why one is better or worse than the other. Thanks.
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post #2 of 18 Old 01-09-2008
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Class A AIS transceivers transmit on two frequencies (I believe alternating between them) so an AIS receiver that is genuinely two frequency (like Class A) will get twice as many updates as one that works with only one frequency at a time. A lot of the early receivers for pleasure craft are "dual" frequency, but only in the sense that the receiver listens sequentially to one frequency and then to the other. Theoretically, such a receiver could miss transmissions all together, but this is unlikely as the Class A transceivers randomly change their transmission time a little.

The Furuno combination is likely to be better for you, as you already have the chartplotter, which is hopefully compatible.

Some chartplotters can't take the higher data rate output by some AIS receivers.

The expert story can be found at www.panbo.com

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post #3 of 18 Old 01-09-2008 Thread Starter
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Idiens,
Thanks. The Furuno FA30 is listed as "dual parallel channel". I have a newer Furuno chartplotter and it is set up for AIS so the FA30 would be a clean installation without the need for another GPS antenna. The down side is then I have all my eggs in one basket if the chartplotter goes down.
A ton of info on AIS on Panbo that I'm still sorting through.
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post #4 of 18 Old 01-09-2008
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I may be off base here and it was something else. But my memory says that Cam posted a link to a small inexpensive unit about 6 months back or so.

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post #5 of 18 Old 01-09-2008
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AIS receivers have been around for a couple of years. The Class B transceivers - intended for pleasure craft / non-SOLAS - have yet to receive FCC approval IIRC.

I have a NASA AIS radar (that's its name). It's a receiver with its own screen. I chose it as I don't have a chart plotter and my JRC radar doesn't take AIS inputs.

http://www.nasamarine.com/AIS/AIS.html

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post #6 of 18 Old 01-09-2008 Thread Starter
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Idiens,
That is the stand alone unit I'm considering. I started a thread on it a short time back and those who responded, I think you were one, seemed pleased with it. It is a single channel unit. If you were doing it over again and had a chartplotter that was AIS capable would you have just installled the black box or would you go with the unit you have now?
Freesail,
In searching the threads on AIS I saw Cam's post, thanks.
I'm still thinking the Furuno unit is the best bet for me.
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post #7 of 18 Old 01-09-2008
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I am happy with the NASA AIS radar unit for my situation, but I still have a Class B transceiver on my shopping list. It does show up all the big targets I can see visually or on radar.

I don't like single points of failure, so the snag for me with just a receiver feeding a chartplotter, is that if the chartplotter were to fail, I would loose some nav capability and AIS. (Also I would have to buy a suitable chartplotter ) As my chartplotter is a Yeoman unit, AIS overlay has to be with a pencil.

However, I recognise that having the AIS targets on the chartplotter's screen is a major advantage, even better, if the radar can be overlayed too. That would give maximum situation awareness.

In your situation, I would go for the Furuno combination.

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post #8 of 18 Old 01-09-2008
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What about the idea of using a PC as a chartplotter? I want to have stand-alone RADAR with the ability to send its display to a PC as an overlay, but I want a laptop/mini-PC to also display a chartplot with AIS info over that.

I see the RADAR as best used as a stand-alone, but with the ability to feed its "screen" to the chartplotter on the PC or laptop screen. One is "raw data" in the sense that "there's a big fast blip out there moving in this direction", with the option to identify said blip and get closing speeds, precise vectors relative to one's own bearing, and so on.

I certainly don't want a multifunction display. Eggs/basket, as has been pointed out.
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post #9 of 18 Old 01-09-2008 Thread Starter
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Valiente,
What I have is my Furuno chartplotter/radar display at the helm. My radar does not overlay to the charts. I also have a Garmin 478 at the nav station so in terms of GPs I have good redundancy. The Furuno GPS connects to my laptop also but not the radar. I think the Garmin can download to the laptop but it's new and I haven't tried it yet. I don't feel the need for AIS redundancy. So what I'm struggling with is AIs at the helm where I think it would be most usefull vs a separate stand alone SiTex at the nav station that would still be functional if the Furuno craps out(no room at the helm for it). If I go with the Furuno unit it can also send it's input to the laptop but the SiTex cannot. Costs are about the same as is ease of installation. Furuno unit is dual channel, SiTex is single channel. How did I ever live in the old days with my simple RDF!
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post #10 of 18 Old 01-09-2008
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No doubt that if you're interested in implementing an AIS system within a reasonable time frame, at least 6 mos. you'd be wise to consider any of the currently advertised receivers. These will be class A, receive only, and it doesn't make any difference at all from a pleasure craft perspective whether it's a dual simultaneous channel device or not...you'll never see a difference. You can put your own vessel accurately on your chart plotter, the position of the target of your choice (there may be several) and fuse the whole thing with a radar overlay...bathymetric data may appear on your plotter too depending on the ENC software / firmware you'r running.
If you're considering going offshore you may actually 'need' a transponder. Maybe so, but class B doesn't offer any special performance perks, and there is some speculation that B may not be so universally accepted as A currently is. Go to www.panbo.com and follow the various threads for up to date info on AIS
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