Wegmatt dAISy Owner's Manual - page 10
6 Tips for good AIS reception
dAISy is not the most sensitive AIS receiver out there. But you we can help it to excel with some basic
measures.
6.1 Antenna
If everything else is optimal, almost any antenna tuned to the VHF band will do. I used a simple wire cut
to length for my first prototypes. However, a good antenna will greatly improve results.
AIS messages are broadcast on two channels around 162 MHz, which is in the maritime VHF band. This
means that any antenna sold as “marine VHF antenna” will be a good start.
The short VHF “rubber duck” antennas are cheap and will work at short distance. As long as you check
whether 162 MHz is inside the supported frequency range, you can even ignore the “marine” and save a
few bucks. However, the more broadband the antenna, the worse the reception quality.
A step up are VHF whip antennas. These are steel rods about 1 meter (3.5ft) long. While bulky, these
don’t cost much more than the “rubber duck” but provide superior results. Personally, I use the TRAM
1600-HC which cost around US $40.
There are many more options, which I did not explore myself yet. This article gives a great overview of
the topic:
http://sdrformariners.blogspot.com/2013/08/ais-antenna-shootout.html
Note: dAISy uses a BNC connector for its antenna input. Depending on the antenna
you buy (or build), you might need an adapter. In the U.S. I can recommend
coaxrf.com for a good selection, reasonable prices and fast shipping.
The AIS antenna should be separated as far as possible from the voice VHF antenna to avoid
unnecessary interference. The best separation is achieved by vertically separating the antennas or at
least mounting them on opposite sides of a vessel.
To avoid damaging dAISy’s receiver, the antenna should be mounted at least 3 meters away from, or at
least out of the transmitting beam, of high-power transmitters such as radars or other VHF antenna
installations.
6.2 Location, location, location
Good AIS reception requires line of sight.
A few building and trees between you and your targets aren’t ideal, but you will still be able to catch a
few messages. Hills and mountains however are almost certain showstoppers. A clear view of the water
and your targets is ideal.
In my experience the most important factor is the height of the antenna above sea-level (or lake-, river-,
wherever-level the ships are). Sitting at the beach or on the deck of a boat will work. Mounting the
antenna on the mast of your boat, or standing on the observation deck of a cruise ship is better. A hill
overlooking the harbor is great. Climbing that 2000m mountain that towers over the coast is AIS heaven.