SDR's not receiving certain transponders

[ymmengin]

I picked up a new ONWA KS-200A+AIS transponder for my boat. It’s a class B device and uses SOTDMA technology.

AIS-catcher installed on a RPi with a SDR is not picking it up. I tested multiple SDR’s, antennas, LNA filters etc. Nothing….
If I use AIS-catcher with a device like a dAISy HAT or Quark-Elec QK-A021 USB Dongle I’m able to receive the ONWA transponder.

What could be preventing the SDR’s from picking up the transponder?

Thanks!

[jvde-github]

I am also keen to understand!

First thing might be that there is something in the signal that the decoder does not like (some frequency instability for example).
Can you run with a different decoding model:

AIS-catcher -m 4 -v

Can also try (-m 0 or -m 1) if you like. Does that make a difference?

If not, can you share with me the NMEA message? Perhaps there it is filtered out for some reason.

If that all does not work, I might ask you to share a raw recording with the RTL-SDR to have a closer inspection.

Thanks!

[ymmengin]

Some background info:
AIS-catcher running on 2 different RPi 5. AIS-catcher installed using abcd567a script.
One with a ShipXplorer SDR dongle + Uputronics LNA and one with a QK-A021 dongle.

SDR dongle setup:
-d 00000162
-v 10
-M DT
-gr TUNER auto RTLAGC on
-s 2304k
-p 3
-o 4
-N 8100 geojson on REALTIME on CDN /usr/share/aiscatcher/webassets
LAT xyz LON xyz SHARE_LOC ON
-N STATION PUFFIN-VAL
-S 10111 ##TCP Server
-N HISTORY 720
-N FILE /usr/share/aiscatcher/stat.bin BACKUP 60
-N PLUGIN_DIR /usr/share/aiscatcher/my-plugins
-X xxxyz
-t beast localhost 30005

QK-A021 dongle setup:
-e 38400 /dev/serial/by-id/usb-STMicroelectronics_STM32_Virtual_COM_Port_6D8A54695551-if00
-N 8100 geojson on REALTIME on CDN /usr/share/aiscatcher/webassets
-N STATION PUFFIN-AIS
-S 10111
-t gpsd localhost 2947
-N share_loc on
-N FILE /usr/share/aiscatcher/stat.bin BACKUP 60
-N PLUGIN_DIR /usr/share/aiscatcher/my-plugins
-N HISTORY 720
-N MSG on
-X xxxyz
-t beast localhost 30005

Messages received by QK-A021

[jvde-github]

Can you btw post the NMEA also as literal string, the markdown of Github corrupts the message. You would write it like:

````
!AIVDM,1,1,,B,13e;R001PNcD2MH48KQq>P0@;5,0*63
````

[ymmengin]

Also attached as text file in the original message.

[ymmengin]

Yes, looks like -m 4 is doing the trick.

I ran the NMEA string thru a decoder and it's giving out some ERROR: CHECKSUM. So the transponder could be sending bad strings.

[jvde-github]

Great! Just run with -m 4, will be slight more CPU consuming but will be more robust for these transponders.

There is nothing wrong with your device. You paste the NMEA from the webviewer which is scrambled to avoid scraping of the viewers.

I suspect your device has a slight frequency instability.

Thanks for flagging and hope it is resolved now.