Category: Marine

New Windows AIS Decoder For the RTL-SDR: AISRec

Over on YouTube user Jane feverlay has uploaded a video showing a new AIS decoder called AISRec for Windows that he has developed.

AIS is an acronym for Automatic Identification System and is a system used by ships to broadcast position and vessel information. By monitoring AIS transmissions with the RTL-SDR we can build a boat radar system. We have a tutorial on this here.

The new software is not free, but he offers a trial version that limits the run time to 20 minutes and 5000 max messages. The paid version removes these limits and also decodes both AIS channels simultaneously. The program monitors data from the RTL-SDR and sends decoded data out via UDP. Software such as OpenCPN can then be used to display the AIS data on a map.

We tested the trial version on our machine and found that it worked well at decoding AIS messages. To download the trial go to http://pan.baidu.com/s/1pJiEzEV and enter the code kn44. The download site is in Chinese, but it is obvious where to enter the code. We found the software to be virus free, but remember to always scan unknown software like this yourself. The full price of the software is unknown, but purchasing instructions are given in the trial download readme. The author also writes that his software now supports the Airspy, but not in the trial version.

Note that we discovered that the software doesn’t use a PPM correction setting as expected. Instead it uses a frequency shift setting. To set the shift in the AISRec.ini file, we had to calculate freqshift = 162.025 MHz – frequency of the second AIS channel as shown in SDR# with no PPM correction set.

Another similar software program that was released earlier is PNAis.

New AIS Decoder for the RTL-SDR: PNAIS

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.

PNAIS
PNAIS Decoder

Hak5: Identify and Locate Ships Via AIS Transmissions

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.

Identify And Locate Ships Via AIS Transmissions!, Hak5 1610

K2NCC’s Guide to AIS Reporting for the RTL-SDR

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.

Map from Aishub.net
Map from Aishub.net

Decoding 2x AIS Channels with SDR Console, AISMon and OpenCPN

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.

2-Channel AIS Receiver with RTL-SDR and GNUAIS

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.

Two channel AIS Block Diagram

Software Defined Radio for Mariners: AIS Antenna Design Review

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.

AIS Monopole Antenna

AIS Decoding Video Tutorial with OpenCPN, AISMon and RTL-SDR

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.

RTL-SDR AIS Reception-Decoding