No AIS messages received - bad reception or configuration error?

[ferret5929]

Hi all,
first of all, thank you, jvde and all contributors, for this great piece of software!

I have been trying to set up AIS-catcher on my Raspberry Pi but so far was not able to receive any* valid AIS messages. As I'm completely new to SDR and radio technology in general I was wondering if anyone could help me shed some light on the issue.

I see two possibilities:

• Is it because of my setup using the small antenna that came with my usb dongle receiver and buildings blocking any signal?
• Is it because I made configuration errors?

I'm using a Raspberry Pi 3b+ with Raspberry OS Lite + the lastest version of AIS-catcher, an usb dongle receiver with rtl2838uhidir chip and the small 15cm antenna that came with it.
I was hoping to still receive some messages as I live in a city with a large port and vessels sending AIS signals should be passing less than 2 nmi from my home.

*the only message that ever came through in several hours was (probably) corrupted / incompletely received as it didn't have much information except being a class A base station and an incorrect MMSI.

I attached a screenshot from the webviewer in case it is of any help. Unfortunately I re-setup everything while trying some troubleshooting, so I don't have any screenshot from the one message received or singal strength etc. :(

I'd appreciate any tips or directions on how to improve the signal or fix configuration issues. Thanks a lot!

*Edited to add: On the console, I got two more message after several hours of running AIS-catcher:
AIS: invalid message of type 45 and length 6
AIS: invalid message of type 25 and length 38

So most probably signal strength / reception issues? Or is there something on the software-side I might be overlooking?

[jvde-github]

Hi, assume you are using a recent dongle with frequency stability, then you should be fine when running with the standard settings. Otherwise you have to calibrate the frequency offset.

I looks to be working. The issue is that if you are in a residential area, you have to put in a bit more effort, get a proper antenna (or at least calibrate it to 162 MHz and perhaps an AIS bandpass filter). If you have a laptop you might be able to get a bit closer to the ships and check there and experiment a bit.

Only thing you could try it so set the antenna at the proper length and try a run at maximum gain: -gr tuner 48.0 but in general this is not a good setting.

[ferret5929]

Hey Jasper,
thanks a lot for your quick reply and helping me troubleshoot.
You were absolutely right: this weekend I managed to put together a mobile setup and get closer to the ships without so many buildings in between - and it worked like a charm, valid messages started flowing in almost immediately. I was able to receive signals from ships in up to 2.1 nmi distance. I’m going to try your other suggestions for further expanding range.
Thanks again, really enjoying your useful project!