Receiving Automatic Identification System (AIS) Messages
We need an antenna, a receiver and some software for processing.
Facts
The transmit frequency is around 162 MHz. This leads to a wavelength of 1.851 m. For a groundplane antenna the radials and the radiator is expected to have a length of lambda/4, which is 0.4626 m.
Antenna
For testing a designed a ground plane with 2 radials instead of the usual 4. The only reason is that this antenna can be better hung up in front of a window. For simulation I used xnec2c and the measurements are done withe the VNWA3 by DG8SAQ. Overall some more tuning needs to be done, but it is working for now.
CM --- NEC2 Input File created by xnec2c 3.0 --- CE --- End Comments --- GW 1 51 0.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00 4.70000E-01 1.10000E-02 GW 2 51 1.00000E-02 0.00000E+00 0.00000E+00 3.40000E-01 0.00000E+00 -3.30000E-01 1.10000E-03 GW 3 51 -1.00000E-02 0.00000E+00 0.00000E+00 -3.40000E-01 0.00000E+00 -3.30000E-01 1.10000E-03 GW 8 15 0.00000E+00 0.00000E+00 0.00000E+00 1.00000E-02 0.00000E+00 0.00000E+00 1.50000E-03 GW 9 15 0.00000E+00 0.00000E+00 0.00000E+00 -1.00000E-02 0.00000E+00 0.00000E+00 1.50000E-03 GE 0 0 0.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00 EX 0 1 1 0 1.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00 FR 0 20 0 0 1.40000E+02 3.15789E+00 2.00000E+02 0.00000E+00 0.00000E+00 0.00000E+00 NH 0 0 0 0 0.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00 NE 0 10 1 10 -1.35000E+00 0.00000E+00 -1.35000E+00 3.00000E-01 0.00000E+00 3.00000E-01 RP 0 19 37 1000 0.00000E+00 0.00000E+00 1.00000E+01 1.00000E+01 0.00000E+00 0.00000E+00 EN 0 0 0 0 0.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00
The result looks as following. First the antenna itself:
This is the radiation pattern:
And now the VSWR:
The final antenna was measured and tuned using a VNA:
Reciever
I tried a Funcube Pro+, a HACKRF and a RTL SDR. But, for now I have a dAISy via USB attached.
Software:
One can use OpenCPN. The dAISy comes as /dev/ttyACM0 with 38400 Baud. The connection to aprs.fi is rather simple and requires the aisdispatcher:
./aisdispatcher-x86_64 -r -d /dev/ttyACM0 -s 38400 -H 127.0.0.1:5000
and the ais_json script:
./ais_json.py
The latter needs to be configured in settings.py.