Over on our Forums xynium has told us about his recently released an AIS decoder called PNAIS which appears to directly connect to the RTL-SDR and decode AIS data. After decoding it then outputs the decoded NMEA data via UDP, which could then be received and used in map plotting software such as OpenCPN.
AIS is and acronym for Automatic Identification System and is a system used by ships to broadcast position and vessel information.
Hak5, a popular YouTube technology show has recently been dedicating a bunch of episodes to RTL-SDR projects. Recently we posted about their efforts with ADS-B, and some GNU Radio tutorials. Their most recent video discusses AIS (Automatic Identification System) which is a system similar to ADS-B which ships use to transmit their location to create a modern GPS based radar system.
The Hak5 video discusses how AIS works and also shows how to use an RTL-SDR to receive it. In their tutorial they use SDR#, VBCable and ShipPlotter to receive and view AIS data on map. Note that we also have an AIS tutorial here.
AIS enthusiast K2NCC has posted in our forum a link to a PDF document he has created showing how to use SDR#, AISMon and AIS Dispatcher to report AIS data to marinetraffic.com and aishub.net. Marinetraffic.com and Aishub.net are websites which aggregate AIS data from various contributors around the world.
AIS is an acronym for Automatic Identification System and is a type of modern GPS based radar system similar to ADS-B used by mariners to help avoid collisions at sea.
YouTube user k2nccvids has posted a video showing him decoding and plotting both AIS channels simultaneously on a Windows PC with free software. To do this he uses SDR Console and two AISMon instances. SDR Console is a general purpose SDR GUI that supports the RTL-SDR. One of it’s major advantages over other SDR software is that it can tune to multiple signals in the same swath of tuned bandwidth simultaneously and output their audio to different virtual audio cables.
k2nccvids used two AISMon instances, each one connected to a separate virtual audio cable outputting AIS audio from SDR Console. He set AISMon to output decoded UDP packets on two different ports. Then he created two UDP listeners in OpenCPN for plotting, one for each port.
Blogger OZ9AEC has written a post on his blog showing how he made a 2-channel AIS receiver using the RTL-SDR, GNU Radio and GNUAis. AIS is a radio protocol used by boats to broadcast their position and speed which is then used to create a type of radar system to help avoid collisions. AIS signals are transmitted periodically on one of two channels. Two channels are used to improve capacity and help avoid interference if two signals from different boats are broadcast at the same time.
Before this, most AIS receiver implementations we’d seen that used the RTL-SDR received only on a single channel. OZ9AEC’s GNU Radio program receives on both channels simultaneously like a commercial AIS receiver does and is thus a better receiver. He eventually plans to get this receiver to run on a Beaglebone.
See his post for instructions and to download the GRC files.
Update: Another AIS decoder known as gr-ais is also capable of 2 channel AIS, and bristromat from Reddit has written a tutorial on setting it up and running it with OpenCPN.
On a new blog called ‘Software Defined Radio for Mariners‘ aimed at mariners wanting to get into cheap software defined radio with the RTL-SDR, the author has posted an article for beginners on choosing a type of AIS antenna to build.
He reviews the performance of multiple homemade AIS antennas with his RTL-SDR, and finds that a Monopole antenna with two radials gave the best value/performance trade off.
He has also written a hardware guide article, explaining some of the most common antennas adapters and cable ends that might be found.
YouTube user Drvarnick has posted a good video tutorial on getting AIS decoding set up with the RTL-SDR using the free OpenCPN, AISMon, SDRSharp and VBCable Windows software programs.
We also have an AIS decoding tutorial blog post posted earlier in the year that shows similar steps at this link.
Large ships and passenger boats are required to broadcast an identification signal containing position, course, speed, destination, and vessel dimension information to help prevent sea collisions. This system is known as the "Automatic Identification System" or AIS for short. There are dedicated AIS receivers intended to be used on boats, or by hobbyists, but they can be expensive. A radio scanner, or the cheap RTL-SDR software defined radio (or a more advanced SDR such an Airspy) can be used to receive these signals, and with the help of decoding software, ship positions can be plotted on a map.
This tutorial will show you how to set up an AIS receiver with the RTL-SDR. Most parts of this tutorial are also applicable to other software radios, such as the Funcube dongle, Airspy and HackRF, or even regular hardware scanners if a discriminator tap is used, but the RTL-SDR is the cheapest option.
Safety Warning: This probably should not be used a navigational aid on a boat as the field reliability of the RTL-SDR or other software radios is not proven. This guide is intended for land based scanner hobbyists.
Note, tracking ships with AIS is very similar to tracking aircraft with ADS-B, which is another project that may interest you.
An AIS radar example is shown by YouTube user Vinicius Lenci who uses an RTL-SDR, SDRSharp and ShipPlotter. This video also shows what a strong AIS signal sounds like.
