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: GP Antenna

This is the radiation pattern: GP Antenna

And now the VSWR: GP Antenna

The final antenna was measured and tuned using a VNA: GP Antenna 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.