Category: Marine

Marine Vessel AIS and AirNav ShipXplorer

AirNav systems are a company that run, one of the big ADS-B aggregation tracking sites for tracking aircraft around the world. They also run a similar platform called ShipXplorer for tracking marine vessels using AIS data. The team at AirNav have provided us with a nice explanation of what AIS is and how it works. They note that they also sell a modified RTL-SDR with AIS filters and an LNA built in.

Presumably AirNav are seeking feeder volunteers for their ShipXplorer service with the submission of this post. We receive no compensation for this post and do not endorse one aggregator over another.

Below is the text from AirNav:

How Does the Automatic Identification System (AIS) Work


Automatic Identification System (AIS) is a crucial technology used for monitoring and tracking the movements of vessels at sea. It has become an essential tool for ensuring maritime safety, security, and efficiency. In this blog post, we will explore how AIS vessel tracking works, its benefits, limitations, and future prospects.

How Does AIS Vessel Tracking Work?

AIS is an automatic tracking system that uses transceivers installed on ships to transmit vital information such as position, speed, course, name, call sign, type of ship, and destination. This data is then received by terrestrial or satellite-based AIS receivers and transmitted to various stakeholders, including shore-based authorities, other ships, and online platforms. The information is displayed in real-time, allowing users to monitor the movement of vessels with pinpoint accuracy.

There are two types of AIS messages: Class A and Class B. Class A messages are mandatory for all ships over 300 gross tons, while Class B messages are optional but recommended for smaller vessels. Class A messages have a higher transmission power and update rate than Class B messages, making them more reliable for long-range detection.

AIS operates principally on two dedicated frequencies or VHF channels: AIS 1: Works on 161.975 MHz- Channel 87B (Simplex, for the ship to ship) AIS 2: 162.025 MHz- Channel 88B (Duplex for the ship to shore), which provide a range of up to 20 nautical miles for terrestrial stations and up to 1,000 nautical miles for satellite systems. The system uses Time Division Multiple Access (TDMA) technology to avoid signal collisions and ensure seamless communication between multiple vessels and base stations.

Benefits of AIS Vessel Tracking

AIS vessel tracking offers numerous benefits, including enhanced safety, improved operational efficiency, and better decision-making capabilities. Some of these benefits include:

  1. Improved Collision Avoidance
    By providing accurate information about a vessel's location, speed, and direction, AIS helps prevent collisions and reduces the risk of accidents. Ships can use this information to maintain safe distances from each other and navigate crowded waterways safely.
  2. Increased Efficiency
    AIS enables ships to optimize their routes and fuel consumption, leading to increased efficiency and cost savings. By sharing their positions and intentions, vessels can coordinate their movements and avoid wasting time and resources on unnecessary maneuvers.
  3. Enhanced Search and Rescue Operations
    In case of emergencies, AIS provides critical information that helps search and rescue teams locate and assist distressed vessels quickly. The real-time data provided by AIS allows responders to make informed decisions and allocate resources effectively.
  4. Better Decision Making
    AIS data can be integrated with other systems, such as weather forecasting tools, to help shipping companies make informed decisions about their operations. For example, they can adjust their schedules based on predicted weather conditions or reroute their vessels to avoid congested areas.

Limitations of AIS Vessel Tracking

While AIS vessel tracking is a powerful tool, it does have some limitations. These include:

  1. Limited Coverage
    Although AIS signals can travel up to 20 nautical miles via terrestrial stations, this coverage may not be sufficient in remote or offshore areas where there are no base stations. Satellite-based AIS systems address this limitation but come at a higher cost.
  2. Potential Security Risks
    Since AIS transmissions are unencrypted, there is a potential risk of interception and misuse by malicious actors. However, measures such as frequency hopping and encryption can mitigate these risks.

Future Prospects of AIS Vessel Tracking

As technology advances, AIS vessel tracking is expected to evolve and offer even greater benefits.

  1. Integration with Autonomous Shipping
    Autonomous ships rely heavily on sensor data for navigation and collision avoidance. AIS integration with autonomous shipping systems could enhance situational awareness and improve overall safety.
  2. Real-Time Cargo Monitoring
    AIS could be used to track individual cargo containers in real-time, enabling logistics companies to monitor their shipments more accurately and efficiently.
  3. Environmental Monitoring
    AIS-equipped vessels could collect environmental data, such as water temperature, salinity, and pollution levels, helping researchers and policymakers better understand and manage marine ecosystems.


AIS vessel tracking is an indispensable tool for enhancing maritime safety, security, and efficiency. While it has some limitations, advancements in technology continue to expand its capabilities and applications. As shipping becomes increasingly digitalized, AIS will remain a cornerstone of maritime communications and surveillance.

The SHipXplorer AIS Optimized RTL-SDR

AirNav Systems Launch AIS Aggregator

AirNav Systems are behind the RadarBox ADS-B tracking aggregator, one of several companies that use data obtained by volunteers running RTL-SDR dongles to collect ADS-B flight data from all over the world.

Recently they've launched a new project called which is a marine AIS aggregation service. Like RadarBox, ShipXplorer relies on volunteers running receiver stations all around the world. AIS is an acronym for 'Automatic Identification System', and in a similar way to ADS-B on aircraft, AIS allows the real time tracking of marine vessel positions. 

To help enthusiasts with AIS reception, AirNav have also launched an AIS optimized RTL-SDR dongle. At the moment we're not exactly sure how this dongle works, as it advertises NMEA output with no add-on programs required. So this may imply it has some onboard processing. But reviews imply that it is just an RTL-SDR dongle with TCXO. We are currently inquiring with AirNav Systems. UPDATE: We have clarified with AirNav and confirmed that the dongle is an RTL-SDR dongle with AIS modifications (LNA & TCXO). There is no onboard processing and the advertising text was an error. 

AirNav Systems write:

Some great news on a new product we've been developing for the last year and that's just been released.
As you know our company has been in the industry for over 20 years, offering innovative and unique flight (RadarBox) tracking solutions. We supply multi-million USD companies with reliable/accurate worldwide real-time flight information and the portal has now over 1.3 million accounts registered.

I'm reaching out to you to introduce you to AirNav System's ship tracker,, which we launched a few months ago 
ShipXplorer is a vessel tracking website that tracks global vessel movements in real time. ShipXplorer was developed to cater to the increasing navigational and tracking challenges faced by the maritime industry. In addition to offering professional maritime tracking solutions, the platform is also available for public use, with features and services specially developed for the burgeoning maritime enthusiast and vessel spotting community. Screenshot
ShipXplorer Screenshot
ShipXplorer Screenshot Screenshot Screenshot
In addition to our recently launched ship tracking portal, we have a variety of AIS hardware, such as dongles and AIS antennas. 
ShipXplorer AIS Dongle:
This high-performance dual channel AIS USB Receiver decodes AIS transmissions and enables the reception of AIS messages and data directly onto devices such as a Raspberry Pi or Laptop.
ShipXplorer AIS Optimized RTL-SDR Dongle
ShipXplorer AIS Optimized RTL-SDR Dongle

ShipXplorer AIS Antenna:
ShipXplorer's omnidirectional AIS Antenna is optimized for long-range, dual channel (Channel A and B) 162 MHz VHF reception. It also ships with a 30 ft cable (SMA connector). Meant for outdoor use, this antenna is built with a fiberglass & aluminum alloy and can weather prolonged exposure to the elements.

ShipXplorer AIS Antenna
ShipXplorer AIS Antenna
ShipXplorer Sea Range AIS Receiver:
SeaRange is ShipXplorer's newest 162 MHz, dual channel, AIS receiver. This brand-new model includes an added filter and an inbuilt amplifier designed to optimize AIS reception on both 162.025 MHz & 161.975 MHz frequencies.
And we are currently working on expanding our AIS coverage globally. 
ShipXplorer Sea Range AIS Receiver
ShipXplorer Sea Range AIS Receiver
ShipXplorer website:

ShipXplorer hardware:

Sharing AIS Data with ShipXplorer: 
And recently, we've also introduced the possibility of sharing AIS data with us using the AIS Dispatcher:
Some of the benefits feeders receive for sharing data with ShipXplorer include: 
  1. Free Business Account Access (benefit from all possible website features for free, while sharing data with ShipXplorer) 
  2. Dedicated Whatsapp, Facebook & Telegram Groups
  3. Access to ShipXplorer' MyStation page where users can monitor all traffic received by their own units.

SDRangel Now Available on Android: Mobile ADS-B, AIS, APT, Digital Voice, POCSAG, APRS, RS41 Radiosonde Decoders

SDRangel is a free open source software defined radio program that is compatible with many SDRs, including RTL-SDRs. SDRAngel is set apart from other programs because of it's huge swath of built in demodulators and decoders.

Thank you to reader Jon for writing in and noting that SDRangel has recently been released for Android as a free Google Play download. This is an amazing development that could open up many doors into portable decoding setups as the Android version supports almost every decoder implemented on the desktop version. Jon writes:

It includes most of the functionality of the desktop version of SDRangel, including:

  • AM, FM, SSB, Broadcast FM and DAB, AIS, ADS-B, Digital Voice (DMR, dPMR, D-Star, FreeDV), Video (DVB-S, DVB-S2, NTSC, PAL), VOR, LoRa, M17, Packet (AX.25), Pager (POCSAG), Radiosonde (RS41), Time signal (MSF, DCF77, TDF and WWVB) modems.
  • RTL SDR, Airspy, Airspy HF, LimeSDR, HackRF and SDRplay support via USB OTG as well as networked SDRs
  • 2D and 3D signal analysis in both time and frequency domain with statistical measurements of SNR, THD, THD+N, SINAD, SFDR and channel power
  • Satellite tracker, star tracker, maps and rotator controller

It should work on Android 6 and up. It’s a straight port of the desktop application, so although it will run on a phone, probably best used on a large tablet with a stylus or mouse.

SDRangel on Android
SDRangel on Android

ESAR – Extraordinarily Simple AIS Receiver written in C

Thank you to Richard Gosiorovsky for submitting his latest SDR project called ESAR (Extraordinarily Simple AIS Receiver). AIS stands for Automatic Identification System and is used by marine vessels to broadcast their GPS locations in order to help avoid collisions and aide with rescues. An RTL-SDR with the right software can be used to receive and decode these signals, and plot ship positions on a map.

Richards code comes as raw C code, so you will need some knowledge on C code compiling to use it. Being so simple, the code is also a great resource for learning how to access data from an RTL-SDR, and write a decoder. Richard writes:

[ESAR] takes less then 300 lines of programming code and no additional software is necessary (like SDR# or audio piping).

It was intended mainly as exercise in digital signal processing.

All you need is RTL-SDR dongle with driver and rtl_tcp command. Simple dipole antenna is sufficient. If all this you have just compile C code (in the attachment) using MS Visual Studio.

Before running ESAR run rtl_tcp command with this parameters:

rtl_tcp.exe -f 162e6 -s 300000 -a -p 2345 -g 48.0

It comes with GNU licence so converting output to NMEA format or any graphical output is free choice of other SDR enthusiasts.

Richard has shared the C code file directly with us, and it can be downloaded from our server here.

ESAR Code Screenshot

Demonstrating the New 3D Maps in SDRAngel

In December of last year we posted about a video demonstrating the many features that the SDRAngel software comes standard with. Recently they've added a new feature which are 3D maps that can be used to visualize signal data.

In the latest video demonstration they show these 3D maps projecting NOAA weather satellite images onto a 3D globe and at the same time tracking the NOAA satellites over the globe as it produces imagery. They also show the software visualizing a 3D model of aircraft on the globe, using live ADS-B data to show aircraft maneuvers when taking off, cruising and landing. With multiple SDRs they also show how the visualization can be combined with air traffic voice. Finally they also show marine vessels being visualized via live AIS data. There appear to be a wide range of vessel 3D models implemented.

A List of Crowd Sourced SDR Data Exchanges

Over on Reddit u/onemindisbuddha has put together an interesting list highlighting the number of crowd sourced data aggregators that use RTL-SDRs or similar hardware.

A common example of a data aggregator that makes use of RTL-SDRs is most of the flight tracking websites, such as FlightAware and FlightRadar24. Contributors to the service will usually set up RTL-SDR + Raspberry Pi based receivers that feed ADS-B aircraft data received from the local area to these websites. Data from contributors from all over the world are then combined onto a single map, allowing for a global live picture of aircraft traffic.  

Some other examples on the list that use RTL-SDRs include Amateur Radio APRS tracking, marine traffic, police/EMS audio feeds, train traffic, weather audio feeds, satellite ground station feeds and general web based remote SDR access. Added to the list are also aggregators based on other devices for applications like lightning detection and seismic activity reporting.

Aggregators List Partial Screenshot

SDRAngel Features Overview: ADS-B, APT, DVB-S, DAB+, AIS, VOR, APRS, and many more built-in apps

SDRAngel is a general purpose software defined radio program that is compatible with most SDRs including the RTL-SDR. We've posted about it several times before on the blog, however we did not realize how much progress has occurred with developing various built in plugins and decoders for it.

Thanks to Jon for writing in and sharing with us a demonstration video that the SDRAngel team have released on their YouTube channel. From the video we can see that SDRAngel now comes stock with a whole host of built in decoders and apps for various radio applications making it close to an all-in-one SDR platform. The built in applications include:

  • ADS-B Decoder: Decodes aircraft ADS-B data and plots aircraft positions on a map
  • NOAA APT Decoder: Decodes NOAA weather satellite images (in black and white only)
  • DVB-S: Decodes and plays Digital TV DVB-S and DVB-S2 video
  • AIS: Decodes marine AIS data and plots vessel positions on a map
  • VOR: Decodes VOR aircraft navigational beacons, and plots bearing lines on a map, allowing you to determine your receivers position.
  • DAB+: Decodes and plays DAB digital audio signals
  • Radio Astronomy Hydrogen Line: With an appropriate radio telescope connected to the SDR, integrates and displays the Hydrogen Line FFT with various settings, and a map of the galaxy showing where your dish is pointing. Can also control a dish rotator.
  • Radio Astronomy Solar Observations: Similar to the Hydrogen line app, allows you to make solar measurements.
  • Broadcast FM: Decoding and playback. Includes RDS decoding.
  • Noise Figure Measurements: Together with a noise source you can measure the noise figure of a SDR.
  • Airband Voice: Receive multiple Airband channels simultaneously
  • Graves Radar Tracker: For Europeans, track a satellite and watch for reflections in the spectrum from the French Graves space radar. 
  • Radio Clocks: Receive and decode accurate time from radio clocks such as MSF, DCF77, TDF and WWVB.
  • APRS: Decode APRS data, and plot APRS locations and moving APRS enabled vehicles on a map with speed plot.
  • Pagers: Decode POCSAG pagers
  • APRS/AX.25 Satellite: Decode APRS messages from the ISS and NO-84 satellites, via the built in decoder and satellite tracker.
  • Channel Analyzer: Analyze signals in the frequency and time domains
  • QSO Digital and Analog Voice: Decode digital and analog voice. Digital voice handled by the built in DSD demodulator, and includes DMR, dPMR and D-Star.
  • Beacons: Monitor propagation via amateur radio beacons, and plot them on a map.

We note that the video doesn't show the following additional features such as an analog TV decoder, the SDRAngel "ChirpChat" text mode, a FreeDV decoder and several other features.

SignalsEverywhere: Decoding HF WEFAX Weather Fax with an Airspy HF+ Discovery SDR

Over on YouTube Sarah is back this week with a new video on her channel SignalsEverywhere. In this video she shows how to decode HF WEFAX (weather fax) images using an Airspy HF+ Discovery software defined radio with a YouLoop antenna. HF weather faxes are daily weather chart images transmitted as an analogue signal over the HF bands by coastal stations. They are mostly used by ships at sea.

First Sarah shows where to find a lists of WEFAX frequencies and schedules for her area, and then goes on to demonstrate a WEFAX signal being received and decoded using SDR#, VB-Audio Cable and the FLDIGI decoder.