[PUP] AIS

[John Marshall]

Except if the antenna goes bad on that unit, you're really of out  
luck. The AIS and GPS electronics are integrated with the antenna.  
Antennas fail more often than electronics -- joys of wind, saltwater  
and weather -- and ordinary antennas are relatively cheap to replace.

I've got a 16' 10db antenna on my AIS, and I routinely pick up  
commercial Class A units beyond 50 miles, sometimes out to 70 miles.  
Albeit I usually only get the rapidly transmitted portion of the data  
(MMSI, COG, SOG and position data) that far out. That says that most  
packets are getting lost and the 6 minute packages aren't getting  
through as the repeat rate isn't high enough.

I use a Furuno Class A transceiver unit, but the receivers in my  
FA150 are nothing special. I think my range advantage over most  
setups is all antenna.

Of course, 50-70 miles range is useless for collision avoidance. But  
the extra margin ensures that a ship preparing to come around the end  
of an island 10 to 20 miles away (or go through a pass in the San  
Juans) is visible on my AIS long before I can see him. The nice thing  
about the 160Mhz frequency range is that its a bit better than line- 
of-sight, unlike our radar and eyeballs. But only if your receiver  
sensitivity is good enough.

John Marshall
N55-Serendipity
Sequim Bay, WA



On Nov 10, 2007, at 6:40 PM, Steven Dubnoff wrote:

>> Sounds to me like your AIS problem is really an antenna problem.
>
> All of these potential antenna connection problems provide a great
> argument for the SeaCAS AIS 300.  It has a GPS and AIS receiver built
> inside of the antenna housing and the whole unit talks to your
> computer by USB.  No antenna connections to go sour.
>
> I have one of these and it has been ticking along without problems
> for a couple of years.  Fred Pot, the developer, is a very nice guy
> and a big mucky muck in AIS circles.
>
>          www.seacas.com
>
> Best,
>
> Steve
>
>
>
> Steve Dubnoff
> 1966 Willard Pilothouse
> www.mvnereid.com
> sdubnoff at circlesys.com
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