New rtlsdr Plugin

[rgleason]

Dear the_muck

Let's see if we could test this without a genuine signal via antenna.

To do that we would have to issue the appropriate ais signal at one of the two AIS frequencies so that the rtldsr USB would pick it up. Then you would be able to test if it were working ok. So you would need a transmitter that would transmit any typical ais signal (probably in the form of a .wav).

The only thing I can think of that would transmit at these frequencies is a VHF with DSC and I am guessing that "faking" it would be illegal...

Maybe I need to get that VHF antennae off the boat now that she's on the hard and make a short coax cable and try this again...

[the_muck]

Hallo,
i try panis and another "chinese" Software, AISrec. Both without any ppm correction.

Panis recieved ships in 10sm. The AISrec up to 30sm and 10 times faster than panis. So my stick and antenna is working.

The problam, AISrec is a demo 20min or 5000 Massages...

Sent from my Nexus 5 using Cruisers Sailing Forum mobile app

[the_muck]

Sorry PNAIS

https://sites.google.com/site/f4eyuradio/ais-decoder

and

New Windows AIS Decoder For the RTL-SDR: AISRec - rtl-sdr.com

We tested the trial version on our machine and found that it worked well at decoding AIS messages. To download the trial go to 百度云 请输入æ��å�–密ç*� and enter the code kn44.

AISRec have the better perfomance to test the stick and antenna.

[McElch]

Originally Posted by boat_alexandra

did you try with rtl_fm and aisdecoder?

You will need the latest plugin to be able to pass command line paramters to rtl_fm to specify which dongle to use

I tried both RTL_fm aisdecoder and ais_rx (gnuradio).

Error message with ais_rx (gnuradio) is

"Execution failed: ais_rx -d -r 256000 -e 0"

and with rtl_fm aisdecoder the error is

Execution failed: "aisdecoder -h 127.0.0.1 -p 10110 -a file -c mono -d -f /dev/stdin"

Plugin Version is 0.10, downloaded and installed a few days ago...

Any suggestion? THX in advance!!!

[McElch]

No advise?

As my Linux skills are poor, i abandoned my hope to get it work.

Ordered a dedicated USB AIS Receiver with GPS instead:

www.aisspotter.com

More expensive than the RTL SDR thing, but less expensive than other AIS Receivers. Works out of the box under Kubuntu 14.04 as well as Windows 8.1 (both OpenCPN 4.0) with only one COM port for both AIS and GPS...

[martin_br]

Dear Boat-Alexandra;

There seems to be a bug in tha latest version currently on git. I had it all working 100% on a Cubietruck with 1.02v Lubuntu. Now with only the new plugin (btw I like the additional cli option fields) an error is occuring: Cannot open rtlsdr when OpenCPN is starting. It appaear however that both rtl_fm and aisdecoder are both launched and running. Also when checked in a terminal rtl_fm launches without a hick. Do you have any suggestions to overcome this error that has been mentioned sometime before in the very thread?

Thanks in advance and enjoy your day

Martin J.

[the_muck]

Originally Posted by McElch

No advise?

As my Linux skills are poor, i abandoned my hope to get it work.

Ordered a dedicated USB AIS Receiver with GPS instead:

www.aisspotter.com

More expensive than the RTL SDR thing, but less expensive than other AIS Receivers. Works out of the box under Kubuntu 14.04 as well as Windows 8.1 (both OpenCPN 4.0) with only one COM port for both AIS and GPS...

Hey can you please make a range + update time test with the RTL_SDR dongle + AISrec (under Windows) and aisspotter?

Malte

Sent from my Nexus 5 using Cruisers Sailing Forum mobile app

[piluso]

Hello all

Looking for a two channels receiver for AIS using rtl-sdr I found the rtl_ais prototype at https://github.com/keenerd/rtl-sdr-misc/tree/master/ais , tagged as "work-in-progress ideas"

I compiled the program without effort, but it didn't work, so after some debugging and tweaking, I managed to make it work, piping data to aisdecoder.

I added a conditional compilation for Windows in both rtl_ais and aisdecoder with a little modification that lets rtl_ais and aisdecoder to work the same way they do on Linux using pipes.

The command line I used to test the program, with OpenCPN for showing targets is:

(path_to_rtl_ais)/rtl_ais -p73 | (path_to_aisdecoder)/aisdecoder -a file -f- -d -h 127.0.0.1 -p10110

With this, aisdecoder can decode both AIS channels simultaneously.

The source code is here:
https://github.com/dgiardini/rtl-sdr...ree/master/ais

and here:
https://github.com/dgiardini/aisdecoder

I've made a pull request on both, still no news.

Hope this helps, feedback is welcome

Regards, David

[rgleason]

For windows users, still using OpenCPN v 4.0 there are several versions available if you would like to try them.

OpenCPN Beta File Thingie rguser rgpass

Look under 4.0 PI Win directory and under Earlier PI directories.
I have tried this plugin and almost got it working but did not have the proper antenna at the time, so I am no expert. Sean is sailing on a long voyage. When he reconnects, he'll be able to assist, as he uses it a lot. Good Luck.

[piluso]

This is a great plugin I use a lot too, but there are a couple of details to take care to get it working. Besides a good antenna, we need the calibration factor error , and is not trivial to know. Once you have it, you don't need to change it anymore, and is the same for any platform.

Here my way to find the ppm:

First, you need a working sdr radio environment, I use HDSDR software. The instructions for get it working are here:http://hdsdr.de/RTLSDR_with_HDSDR.pdf

You'll need some AIS traffic too.

Tune the AIS channel A at 161.975 Mhz. Choose a bandwidth of 12khz, and zoom in the spectrum waterfall as shown:


The AIS traffic is encircled in yellow.

As you see, the traffic is _outside_ of the tuning window, and that is because the dongle cristal errror. To correct this, you need to enter the ppm error value. Click the "ExtIO" blue button, and change the value until the signal enters the tuning window:


You can also calculate the value using the first screen, using the tuning freq and the center of the AIS signal:

1000000* (161975000-161963000)/161975000 =74 ppm

Then use that value for the plugin.

Before doing anything, you can try with a value of 73, that is typical for a lot of these dongles ;-)

Aside this, my previuos reply was for sharing a working two channels AIS receiver for this dongle, I hope Sean could go ahead with his plugin.

Regards, David

[duichan]

Hi David

Good find! It was well hidden.

Originally Posted by piluso

The source code is here:
https://github.com/dgiardini/rtl-sdr...ree/master/ais

Your fork appears to be the same code as Keenerd's original. Were no changes necessary to get rtl_ais itself working?

Regards

Andrew

[piluso]

Your fork appears to be the same code as Keenerd's original. Were no changes necessary to get rtl_ais itself working?

I'm sorry, I'm new at github; the code is in this branch:

https://github.com/dgiardini/rtl-sdr.../ais/rtl_ais.c

The main problem I found was that "stereo.bl_len" didn't compute correctly (probably a portability issue)
Then I added the "droop compensation" filter as rtl_fm

Still yet, 12k sampling didn't work properly , because the audio bandwidth drops -3db @ 3khz, but still get some messages. So, I change the default to 24k; with better performance.
I change the file mode of stdout to binary for using on windows with aisdecoder

Regards; David

[duichan]

Many thanks David. I will try it out in a couple of days.
Regards
Andrew

[rgleason]

It is great that you are making progress and it is even better that you seem to understand details about adjusting and finding the ppm. I initially banged my head against this particularly getting the proper drivers and then getting the USB RTL receiving, and finally failing (I think) because the antenna was not good enough.

The problem was I had no experience and could not determine when things were working properly because there was no step by step description of the process and what we need to be looking for and adjusting. I did try an use several other programs and I found HDSDR to be one of the better one.

I hope we can get a step by step with some photos, put together. The dual band improvements are exciting.

[seandepagnier]

Originally Posted by piluso

I'm sorry, I'm new at github; the code is in this branch:

https://github.com/dgiardini/rtl-sdr.../ais/rtl_ais.c

The main problem I found was that "stereo.bl_len" didn't compute correctly (probably a portability issue)
Then I added the "droop compensation" filter as rtl_fm

Still yet, 12k sampling didn't work properly , because the audio bandwidth drops -3db @ 3khz, but still get some messages. So, I change the default to 24k; with better performance.
I change the file mode of stdout to binary for using on windows with aisdecoder

Regards; David

David,

Thanks for looking into this. I have crossed the indian ocean which took almost a month, and internet here is neither fast or reliable so it make take me time to catch up.

As for error calculation, yes you can use a graphical tool and see the ppm directly. Currently the plugin implements a bad algorithm to try lots of different error codes to try to find one it can hear ais messages on.

The future development of this plugin really should do two things:

1. Incorporate rtl_rm and aisdecoder directly into the plugin (executing in two different background threads) to avoid issues with process execution and to simplify the distribution of the plugin.

2. Once rtl_fm is integrated, it should now be possible to write code to at least display the fft needed for calibration within the plugin itself as well as automatically compute the error code as soon as only one ais message is received (with care to avoid confusing channel a and b.. so the message would actually need to be decoded to determine.


Basically I see two important