Fast cheap AIS using $20 rtl-sdr DVB-T SDR Dongles !

[seandepagnier]

I can see clearly when I transmit on various vhf channels in the fft graph a spike. I can play any vhf or fm chanel out the sound card. I see nothing at the ais frequencies.

I can run the ais script.. but I never get anything.. I think maybe because there are no ships transmitting here..

[larsed]

Well rgleason , to be perfectly honest, you were one of four. But, never mind, I would never have written those lines if the guy hadn't been so eager. As I said, I have no objections or complaints, I know how busy people in forums like this normally are and I respect that. I can say I learned a lot about that experience! For one to respect my own time and priorities, and for that I am grateful!

If I don't misunderstand, you ask me a very "impossible" question, "a good simple linux installation (dual boot or wipe a Windows install)"?
It's really a Q to your conscience! Having been an SuSE-enthusiast for almost a decade it's hard to admit that their releases are getting buggier and buggier, almost presented in a furious speed and slovenly. I really have come to like Slackware with it's traditional way of solving things but would not even recommend it to my worst enemy. It's not "friendly" to it's users.
To make my answer in anyway have a limit, I would go with the mainstream here on OpenCPN since that is what you want to primarily do with you Linux-dist: Ubuntu or LinuxMint. I myself prefer real Debian, have tried both Ubuntu and its derivative: LinuxMint. The two latter are very easy to install, almost "selfinstalling" (which I personally dislike. I like to set my own preferences during install) and from them I definitively like the "straight" LinuxMint. Hope that is at least a beginning of an answer?
If you're used to and familiar with Windows I would keep it and install Linux as second and use the 3rd party bootloader EasyBCD in Windows (works in Vista, 7 and 8) instead of the somewhat anarchistic, flashy grub2 that I would install in the Linux root partition. Think that will spare you some trouble?

By Jean I guess you mean Jean-Eaudes? Him I owe great thanks. He helped me a lot with
the confusing build-process i SuSE.

Finally about the USB-units:
I bought Lifeview LIFEVIEW NO DVB-T USB DELUXE LV5T with rtl2832 chipset and fc0013 tuner, easily found here in sweden.
My friend bought NEWSKY TV28T COAX DVB-T DAB DAB+ FM STICK SDR with rtl2832 chipset and e4000 tuner. Think he ordered it from GB.
Both worked equally well!

Best regards
Lars

PS. The desciption will be up in due time, clean and hopefully understandable. Computing must be fun, else you could... well, I won't go deeper into that!

[rgleason]

Dear Lars,
As always you are full of very good knowledge and forgiving. I very much appreciate your suggestions and will be doing 3rd party bootloader EasyBCD and probably one of the ones you mention! Like the info about USB DVB.
Thanks again.

[seandepagnier]

I got mine working.

Run:
gr-ais.py -d -e X

where X is a very important value you must find from running a fft spectrum analyzer. Easy way is to tune to a known vhf frequency and transmit with your vhf radio. There is a script gr-ais.grc which you can run in gnuradio-companion that makes calibration easier.

On the hardware side, you need a good vhf antenna, and must solder both inner and shield of coax to the cable going to the radio card.

That is it. If anyone has difficulties let me know. I'll begin pondering a plugin for opencpn now.. It can pick up any vhf station, so it would be cool to be able to listen for channel 16 in the background, and also get weather updates.

Next challenge is weather fax..

[seandepagnier]

run gr_ais.py with -t and it is a source for gpsd on port 9987, then opencpn reads from gpsd.

I am plotting ships with my $8 free shipping dongle.

[larsed]

First a PS. to rgleason:
The USB-units I mentioned are only two possibilities, you have got an updated list of rtl-sdr compatible units here: RTL-SDR compatibility list v.2 [work in progress, please help!] : RTLSDR. I found it easier to start there when looking for one since the retailers, and sometimes not even the manufacturers, are not shure what chipsets their dongles contain.

Then to boat_alexandra: From what I could understand from your posts you are in an quite different and more advanced corner in these rtl-sdr matters. It seems as your aim is to get the USB-reciever simultaneously work as an AIS-receiver and VHF-tuner? I can only wish you good luck!
Our goal was just to get "free" actual AIS-messages to use in OpenCPN.
Then I really must thank you! It seems you have solved all my problems concerning the documentation .

[rgleason]

Boat_Alexandra Glad it is working. I'm going to give this a shot, but I think I'll also need linux... but maybe not for AIS

[larsed]

Some late answers to boat_alexandra. The reason I did't answer them before is simply that I didn't have them when you asked, further investigation was necessary and the time lacked.

First it would be great if you could be more specific in your asking, what OS, if Linux what dist, and what you already had installed when you met the problem you describe. It would make it much easier to answer or even consider if I at all could be of any help.

Also.. did you get both channels? The two ais channels (161.975 and 162.025)

You could read the answer here: https://www.cgran.org/wiki/AIS. I found no way of objectively verifying this though, but if you set the frequency error-correction right (using SDR# or the gr-ais.grc found here: http://steve-m.de/files/rtl2832/gr-ais.grc) I can see no reason that it shouldn't receive both channels.

I can see clearly when I transmit on various vhf channels in the fft graph a spike. I can play any vhf or fm chanel out the sound card. I see nothing at the ais frequencies.

I think I met the same problem, but gave up those efforts when I found out that the AIS-pulses only last 30 ms. They should be very hard to see visually?

I think maybe because there are no ships transmitting here.. AND ...you need a good vhf antenna, and must solder both inner and shield of coax to the cable going to the radio card.

Maybe that's the reason to your problem getting any ais-messages (or the important -e -value that you stressed) both could be true. -If your -e-value is as little as 30 ppm wrong, + or -, you'll probably get no signal.
But the antenna, as you mention (or the distance to the sending ships) could also be the reason? I can mention that my friend (the picture I posted) lives about 1 km from the harbour with no visual contact to it. There are houses in the way. I myself have got a limited view of Lake Mälaren, live about 35 m above sealevel and never have visual contact with any ais-sending ship. But I get signals from ships about 3-4 NM from here.
We both use the small toy-like antennas that followed the sticks. -I'm certain though that if we both had got tuned VHF-antennas on our roofs our reception would improve a lot!

Also it (the plugin) could automatically play signals on other vhf channels at the same time on the speakers. AND
I'll begin pondering a plugin for opencpn now.. It can pick up any vhf station, so it would be cool to be able to listen for channel 16 in the background, and also get weather updates.

That's where I wished you good luck! I wouldn't say it's impossibel, too experienced for such a statement! But today I can say that me and my friend have had no success trying to make the USB-reciever simultaneously receive different frequencies (except ais-signals), nor running two gnuradio modules at the same time. Not even with two different modulations.
I mean it though: Wish you good luck there! And of course, Congratulations to your success with gr-ais!

Regards
Lars

[larsed]

rgleason, I get a little confused about your aimings when I read your posts from 25th and 26th of april. I mean about Linux/Windows, OpenCPN and AIS.

But, if you should try a Linux-install and chose Debian or one of its derivatives AND choose to use that for OpenCPN and AIS I've found an informative instruction here: DE8MSH *** German Shortwave Listener Station: RTL-SDR.

When starting these efforts getting AIS to OpenCPN in SuSE me and my friend made one mistake: We thought we had to have kernel 3.6 or higher because 3.6 was the first kernel with native support for the modules rtl2832 and fc0013 (my tuner) and e4000 (his tuner). It was just the other day we found out that this was not true! Kernelsupport for those modules are only necessary if you want to use the USB-dongle to what it's intended: Watching DVB-TV.
To use the dongles for gnuradio, rtl-sdr, osmosdr, gr-ais and gr-air-modes you do not need those modules. It works without them. -We both noticed that gr-ais when starting detached the kernel modules and reattached them when stopping. Finally we decided to try that out: shutting down our modules using blacklist resp rmmod and, much to our surprise, found that gnuradio and gr-ais et c worked without them.

Ubuntu 10.04LTS has kernel version 2.6 and the guy obviously got it working. LinuxMint with kernel version round the same should work.

Hope you come to the decision that's best for you!

Regards

Lars

[rgleason]

Thanks Lars! I'll let you know what I end up doing, w results no doubt.

[larsed]

Well Viking Sailor, boat_alexandra, rgleason and sailias...
We meet a problem here!
I've just cleaned up the gr-ais-install description in swedish and made it as instructive (read easy) as possible and added a few, not very large pictures. That made 4 MB as an OO-doc, 1,8 MB as a pdf.
I was just going to start translating it to english when I found out that the forum only allowed some 500 kB uploads.

I can say I won't go through the work reeiditing it again.
And my only reason for translating it was to post it to this forum.

Has anyone got a solution? Is there any other way for me to upload it?

Regards

Lars

[RhythmDoctor]

Originally Posted by boat_alexandra

...Also.. did you get both channels? The two ais channels (161.975 and 162.025) should be close enough so as one of these modules can pick up both channels at the same time...

This brings up a very interesting point. Some inexpensive AIS receivers scan between the two channels. In general, a dual tuner AIS is much preferred because nothing "falls through the cracks."

If this TV tuner is a single tuner, it will not have dual channel capability.

If its selectivity is so poor that it picks up both channels at the same time, wouldn't that create a problem with the digital transmissions interfering with each other? I believe AIS has some sophisticated timing algorithms to prevent ships from obscuring each other's transmissions. Does that timing coordinate between both channels, or does each channel operate independently?

[larsed]

Originally Posted by RhythmDoctor

This brings up a very interesting point. /.../
If its selectivity is so poor that it picks up both channels at the same time, wouldn't that create a problem with the digital transmissions interfering with each other? I believe AIS has some sophisticated timing algorithms to prevent ships from obscuring each other's transmissions. Does that timing coordinate between both channels, or does each channel operate independently?

It's possible that you've got a point there?
Yes it was Håkan Lans who wrote the patented STDMA datalink algoritm that should prevent AIS-transmissions to block each other, or as you say, obscuring each other's transmissions. As far as I've heard it coordinates between both channels, but I may be wrong.
These lines from Automatic Identification System - Wikipedia, the free encyclopedia when searching on stdma coordination channels

Each AIS station determines its own transmission schedule (slot), based upon data link traffic history and an awareness of probable future actions by other stations. A position report from one station fits into one of 2,250 time slots established every 60 seconds on each frequency. AIS stations continuously synchronize themselves to each other, to avoid overlap of slot transmissions. Slot selection by an AIS station is randomized within a defined interval and tagged with a random timeout of between 0 and 8 frames. When a station changes its slot assignment, it announces both the new location and the timeout for that location. In this way new stations, including those stations which suddenly come within radio range close to other vessels, will always be received by those vessels.

indicate that I could be wrong. On the other hand some lines in STDMA analyse report could indicate that what I heard is right?
As far as I can see (which sometimes is not very far) and STDMA coordinates between both bands this is mainly a problem on the transmission side, not reception, since there will be no simultaneous transmission.
It's still possible that you've got a point with that dual tuner?
I would ask the author of gr-ais https://www.cgran.org/wiki/AIS

And, as you could possibly have noted above, my problems for the moment are of another kind ...

Regards

Lars

[seandepagnier]

Originally Posted by RhythmDoctor

This brings up a very interesting point. Some inexpensive AIS receivers scan between the two channels. In general, a dual tuner AIS is much preferred because nothing "falls through the cracks."

If this TV tuner is a single tuner, it will not have dual channel capability.

Single tuner, yes, but it samples a full 2.2mhz, so it can pick up many channels if they are within this range. I can pick up 3 or 4 fm radio stations at once, or about a dozen vhf channels.

If its selectivity is so poor that it picks up both channels at the same time, wouldn't that create a problem with the digital transmissions interfering with each other?

No, because it filters them with bandpass fir filters. It works perfectly. If you have more detailed questions on these lines, refer to the source code.

[rgleason]

Larsed,

I have a program called PDF Converter Professional which will "compress" pdf files, sometimes significantly, sometimes not. It is unlikely it can be compressed down to below the 500kb allowed. However one approach is to spllit it into 500kb chunks and upload sequentially. I think that would be fine.

If you want to send it to me, or upload to my server, I can try to compress it and then split it up. Then I'd post it in your name to this thread.