[PUP] AIS pitfalls

[John Marshall]

Dave,
	That really speaks the virtues of digital comm... lower power and  
far longer range. It would be nice if Marine voice communications  
would move away from FM and join the 21st century. We'd get vastly  
better audio quality and apparently longer effective range.	

	To your sat compass question, we have a flux-gate compass in each of  
the two autopilots that can provide heading data on the bus if we  
enable it. Plus a good old fashioned properly swung compass on the  
dash in case something bright comes out of they sky. Fortunately  
thunderstorms are rare as hen's teeth in the Northwest.

	RE: what I'm transmitting. I can see what's being set for all the  
data streams in terms of manual input, but I don't have a way to  
receive my own signal to ensure its right or that computed SOG, COG  
or location is going out correctly. That's a weakness as you  
highlighted at the beginning of this thread. I almost wish I could  
call someone up for an "AIS check". Or spend the dollars for an AIS  
receiver only, but not until they get a lot cheaper. I'm waiting for  
the handheld variety to use as a "backup".

	RE: Class B... I'm not sure if I've picked up any Class B signals or  
how I'd know... some boats report 0's for things like beam and length  
and draft and so forth, but I've been assuming they simply haven't  
set their system up properly.

	RE: Messaging... Before I left Dana Point for the Northwest, an  
installation technician from Alcom transmitted a message to me via  
AIS, but I never noticed it coming in. Once in port, I powered the  
system down, only to have him come by and ask me if I'd gotten his  
message. We powered the AIS back up and there was no message. Not  
sure if it stores it in non-volatile memory or not. Have to play  
further with this when I've got a buddy close by to work with, but  
given that aspect is new (especially the emergency calling feature),  
I think we're a bit ahead of the curve there.

	Too bad I'm kittycorner across the US mainland from you or we could  
play. I know I'd learn a lot by exploring all the corners of AIS  
capabilities.

John Marshall
N5520-Serendipity


On Jun 4, 2007, at 4:11 PM, Dave Cooper wrote:

> <John wrote: Actually, the FA-150 is a transponder... our buddies  
> track us
> via AIS when we are in the area long before they can raise us on  
> VHF. Which
> I find interesting given AIS uses VHF as well.>
>
> Sorry I thought the FA-150 was just a receiver..my mistake.
>
> The 3 GPS's in their 38' high location must have quite a ride ;-)
>
> The reason they can see you when you can't reach them via VHF even  
> though
> you have 25 watts vs. the 4 of the transponder is due to the  
> wonderful world
> of digital transmission. It can get thru as it only looks for  
> thresholds vs.
> needing receive the full modulation of voice. Sort of like why  
> Morse code
> could always out do voice.
>
> One of those GPS's must be dedicated to input the location, speed and
> course...at least according to the spec. The other two are most  
> likely the
> differently pair to determine the ships heading.....hope you have a  
> compass
> as a back-up when it goes dark ;-)
>
> So I must ask how you know what you are transmitting in all of the  
> data
> streams? Many of which most folks can't see...yet.
>
> Have you received any Class B signals yet? Does your FA-150 have the
> software to pick them up and display there complete data or does it  
> leave
> missing files without the word "missing".
>
> You'd be a good guy to have around so I could talk to someone who  
> can see me
> and might actually be willing to talk back about the AIS. Not like the
> Master of the Tropic Palm who basically "hung up" on me today. Bet  
> we'd both
> learn a lot more about each others units and what the ranges are :-)
>
> And we haven't yet even got into the safety messages and DSC distress
> messages it can deal with......a much more powerful tool than the  
> current
> VHF DSC, IMHO. It also has a much wider range due to the all  
> digital nature.
> So if you have a distress then instead of 10 or perhaps 15 mile  
> radius you
> have the radius of the AIS transponders signal...
>
> Thanks for the correction :-)
>
> As always YMMV
>
> Cheers
>
> Dave & Nancy
> Swan Song
> Roughwater 58
> Caribbean Cruise '07
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