[aprssig] Objects Of Boats Along Waterways

Joe Della Barba joe at dellabarba.com
Sun Jan 21 20:21:28 CST 2007

AIS is secret???
I have an AIS receiver on my boat, along with VHF and HF ham gear. The 
AIS targets display on SeaClear, my marine navigation program. Since I 
already have all the pieces, I thought it might be fun to see what could 
be done with it. I wonder what the timeline between APRS and AIS is? I 
can;t help but think AIS was at least partly inspired by APRS. I also 
wonder if the TMD-700A could be an AIS transceiver. I know it wouldn't 
be legal, but it would seem to be able to do 9600 baud.
73 Joe

Kai Gunter Brandt wrote:
> Tapio Sokura wrote:
>> Joe Della Barba wrote:
>>> I am very interested in AIS>APRS. If anyone has any info on this, 
>>> could they send it my way.
>> Basically you just decode the AIS traffic (9600 bps GMSK) from marine 
>> vhf band per the AIS specification and re-encode suitable parts of 
>> the information to form an APRS packet. You probably want to cache 
>> some information at the conversion
> My program uses ShipPlotter and relays the trafic to UI-View.
> Next version is going to have filters and posibilities to connect 
> directly to an aprs server.
> ShipPlotter is storing MMSI,callsign and names in a "library" so that 
> theres no need to do this job every time.
>> point as well, as static data (ship name, dimensions, etc) is sent 
>> less often in AIS than location updates. And you'll probably want to 
>> do considerable rate-limiting, if 1200 bps APRS on the band is 
>> involved. A 2-channel AIS network has 4500 time slots (~ location 
>> updates) per minute. That's a 100-fold difference in capacity 
>> compared to APRS.
> This is no really a problem if you configure i.e UI-View to limit the 
> amount of traffic. But yes you should check before and after to see if 
> you are making to much traffic.
> The ships is sendig lots of updates when turning etc. But the 
> digi-functions in UI-View you can limiting this.
> Setting it to i.e 20-40sec then redusing it a lot. Its working just 
> like TinyTrack smart beaconing. lotz of traffic in curves etc.
>> I just haven't really gotten the point in it, why would you want to 
>> see AIS targets in the APRS network? Maybe that can be useful in a 
>> special event situation that includes both APRS stations and AIS 
>> equipped ships, but in the general case? Ok, this is a hobby, so 
>> "just for fun" is a valid answer as well.. just watch out for those 
>> that might not like it. I've heard stories of some players in the 
>> marine world that consider AIS information to be "secret".
> SAR, spesial event or maybe filter out just som nice ships and not 
> everything.
> Hobby, just4fun, developing things and combine with the HAM hobby and 
> another thing is that you can see everything in the same program.
> If you disable the digipeat function then only you can see it on your 
> computer.
> And yes there is some "issue" that goverment do not want this 
> information on internet etc because its supposed to be antiterror not 
> to show the positions... crap but thats politics. For terorists doesnt 
> need either aprs, internet or shippositions to make unwanted things to 
> happen.
> Kai Gunter
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