Friday, October 31, 2008

gnuais - AIS decoding on Linux

Lately I've been working on the gnuais source code, improving it so that it could be used to decode AIS and feed aprs.fi using Linux. My changes are in the SVN trunk (not in any released version yet). It's generally working, I just haven't done the actual "feed aprs.fi" part yet. But it's getting closer. The decoder isn't as good as in aismon/shipplotter - if you have DSP coding experience, your help is welcome on this project!

I've also modified some Televa 703-LYVV VHF FM receivers from the cold war era to be used as AIS receivers. "Brand new" (but a bit over 30 years old - like myself) commercial NBFM receivers in their original factory boxes, built to be installed at bomb shelters and such, but (luckily) never needed. Going to install a couple of them here in Helsinki, with directional antennas pointing southeast and southwest on the Gulf of Finland. We installed the antennas and cables during the last couple weeks, they're just waiting for the gnuais feeding code.

6 comments:

kk5mr said...

I'm seeing old comment text when i click on my APRS symbol (KK5MR-9), but when I examine the raw packets, it shows the comments I expect (i.e., no comment text).

The old comment text was:
;roadwork *1111113305.20N\09607.51Wj I-30 Work Zone, 60mph

(I was attempting to formulate an object, which I found out that the OT2m cannot perform right now.)

oh7lzb said...

A new empty comment text will not overwrite an existing comment. You'll have to specify a new non-empty comment to overwrite the old one.

I did it this way, because there are quite a few stations (both digipeaters and mobile) sending a very good descriptive comment text only once out of every 3 or 5 transmissions, and the rest of the packets don't have any comment text (to reduce APRS channel congestion).

kk5mr said...

Ah... thanks for the insight.

pbsl said...
This comment has been removed by a blog administrator.
Chris said...

I am having trouble with gnuais...
It was working, but I had a hard drive crash and I installed Ubuntu 10.04 and now it does not work.

I dont think it's an ALSA issue, as I can run ACARS data with acarsd and it's not the scanner or discriminator as I can see the ais data in Ship Plotter on windows.....

I was wondering if you could please shed any light on what I might try to do....

It's sad I enjoyed this software, but there is no formal channels to get support or even developers anymore :(

oh7lzb said...

Chris, I suppose you could try the forums at sourceforge (https://sourceforge.net/projects/gnuais/forums/forum/753370) unless you're the other Chris over there already. :)

Please post a message there. Also try the latest svn version if possible, and confirm if decoding is working on your box with the testing recording found in SVN. If it decodes from the file, there is a problem with the audio.

src/gnuais -c gnuais.conf -l testmessages/gnuais-stereo-2rx.raw
2010/07/20 05:10:47.685021

(decoding follows)

gnuais[24909:3078527424] NOTICE: Closing down...
2010/07/20 05:10:48.488986 gnuais[24909:3078527424] INFO: A: Received correctly: 144 packets, wrong CRC: 47 packets, wrong size: 6 packets
2010/07/20 05:10:48.489015 gnuais[24909:3078527424] INFO: B: Received correctly: 46 packets, wrong CRC: 53 packets, wrong size: 5 packets