OpenMarine
Does openCPN get AIS from the internet or just SDR? - Printable Version

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Does openCPN get AIS from the internet or just SDR? - Techstyle - 2020-01-20

I installed an RTL-SDR USB and have connected a an antenna, but the one that came with it - not a marine VHF antenna.

In OpenCPN I can see a couple of base stations, one 7.3NM away and 16.1 NM away.

I don’t think these were on the map previously but my question is - Does OpenCPN (ver 4.8.4) use the Internet and the SDR for AIS info?

I know there are a few boats closer than those base stations but I cannot see them. The two base stations are both south of me and the boats are north. It is pretty built up to the north of me

Pi ver 3B, OP ver 1.0.0 alpha


RE: Does openCPN get AIS from the internet or just SDR? - Luckbert - 2020-01-20

Hello Techstyle
OpenCPN can only display records which it receives.
In the original state no inputs are made.
So if you have not set up a data flow from the internet, OpenCPN can't display anything either.
You have installed a USB dongle. If you now see objects that were not there before, the dongle will work.
Not every ship is obliged and/or equipped with an AIS transponder.

Take a screenshot and we will see.
If it is an AIS object you can double click on it to see all available details.
I hope this brings you a bit further now.
Greetings Jürgen

Translated with www.DeepL.com/Translator (free version)


Does openCPN get AIS from the internet or just SDR? - Techstyle - 2020-01-20

Thanks for this info, that makes a lot of sense. I don’t have anything setup to provide OpenCPN with internet based AIS.

I am in MILWAUKEE and last night there were two boats showing up in the port/river on Marinetraffic.com, but both were docked and like you said, may not have been transmitting. Right now one of them is leaving so this would be a good time to check but I am not at home. The grey and pink dots on the screen shot below are the ones I can see and when I look in openCPN I get AIS information on them and and the age of the last contact is usually seconds or a few mins - not longer than that.

[Image: 0be50ea2ac7fd28e9b6155c7832b766b.jpg]

When I look at the frequency analyzing tool for the SDR the screen is greeny-blue but does have yellow blips every so often. The boat is on the hard right now so I am doing this in my (walk out) basement


RE: Does openCPN get AIS from the internet or just SDR? - Luckbert - 2020-01-20

OK, keep testing and asking questions.
Take a screenshot of your OpenCPN.

I recommend to change the antenna. There are instructions on the internet for do-it-yourself construction.
http://muck-solutions.com/?p=1324
http://vk2zoi.com/articles/half-wave-flower-pot/
Greetings Jürgen


Does openCPN get AIS from the internet or just SDR? - Techstyle - 2020-01-22

I made an antenna based on one of the many sites guides but did not get very good results, I am in the basement though.

When I change the antenna, I expect I have to go through the calibration process again?


RE: Does openCPN get AIS from the internet or just SDR? - Techstyle - 2020-01-22

this is typical of what I am seeing with the original Antenna - see attachment, the second file shows my OpenCPN screen and there was for a brief time over the weekend a base station showing up where the green circle is about 7 miles south of my location

I might need to get a proper Marine VHF antenna, or head to my boat and try it there with the one fitted


RE: Does openCPN get AIS from the internet or just SDR? - Luckbert - 2020-01-22

You need to get out of the basement and get a better antenna.
The calibration refers to the stick, not the antenna.

The stick has a dispersion due to the manufacturing process.
And as the temperature rises, there's additional drift.

That means and should calibrate the stick when it is warm (so it was connected for a while).

If you want to use it on a boat I recommend a better stick. For example one of
rtl-sdr.com

These are of higher quality than the DVB-T Stick

Greetings Jürgen

Translated with www.DeepL.com/Translator (free version)