While scanning the VHF spectrum with a SDR USB dongle, I found something that sounded like an old 56k modem (at around 160MHz, FM modulation, Europe region).
After some research, I found out that is relatively common to broadcast digital messages and warnings with sound tones (ACARS)... so I decided to try to demodulate the signal.
With the help of minimodem, and after some trial and error baud rate estimation (1200 baud, ASCII, 8N1), I finally got some text out of those recordings:
CAL/I0M039D042#EXAN:09158700403:250/END CAL/I0M042D039#OKEY:151/END CAL/I0M055D053#EXAN:15171500380:244/END CAL/I0M041D039#EXAN:10139400412:237/END CAL/I0M039D041#OKEY:150/END
Anyone knows something about these messages?
Wheater forecast? Airport broadcast? Thank you.
Thank you all for your comments.
I collected the signal for 24h, in order to determine if there was any kind of correlation with the weather (like temperature vs hour etc.). Afterward, I plotted the number following the EXAN keyword in the received string (here in bold: CAL/I0M055D053#EXAN:15171500380:244/END).
Here 4 of the resulting graphs (x-axis represent the sample number, not time). Judge by yourself:
As you can see, every signal seems to behave differently from the others, without any apparent correlation with wheater (pressure, temperature...).
I would exclude any boat tracking system because I live in a mountain valley, at least 80km from the sea. Moreover, the source does not seem to move and the packets signatures are recurrent day after day (at least for the moment).
PS: Thank you all for the interest, please feel free to move the question if inappropriate for "Electrical Engineering".