RTL-SDR AIS Ship Tracking

Introduction

• AIS: Automatic Identification System.
• RTL
• SDR: Software Defined Radio
• Also: ADS-B (Automatic Dependent Surveillance-Broadcast) for aircraft surveillance. 1090 MHz

Need a radio dongle, antenna. Use Arduino and RPi.

RTL-SDR V3

My dongle seems to be original, according to https://www.rtl-sdr.com/rtl-sdr-blog-v-3-dongles-user-guide/

V3 Datasheet is at https://www.rtl-sdr.com/wp-content/uploads/2018/02/RTL-SDR-Blog-V3-Datasheet.pdf

• Install the custom drivers in order to make the V4 work
  • RTL-SDR Blog driver fork from https://github.com/rtlsdrblog/rtl-sdr-blog.
  • Release.zip file from the Releases page. For SDR# extract the rtlsdr.dll file from the x86 folder to the SDR#. For most other x64 programs, use the rtlsdr.dll file in the x64 folder.

Software

Frequencies 161.975 MHz and 162.025 MHz, thus by adjusting the frequency to 162.000MHz we can listen to both frequencies. Marine VHF is narrow band (NFM) Ch16 is on 156.8MHz.

SDRSharp, SDR#

• https://www.rtl-sdr.com/sdrsharp-users-guide/
• https://airspy.com/download/

SDR#, brief tutorial:

• set your audio piping method in the Audio output drop down box
• tune to an AIS frequency (161.975 MHz or 162.025 MHz). the signals may not appear exactly on the AIS frequencies (the RTL-SDR is not frequency accurate (unless you have a RTL-SDR with TCXO)). Tune manually until the signals are properly centered, or set the PPM offset correctly.
• adjust the RF gain such that the signal is strong, but the noise floor is low.
• use a program for decoding:
  • AISdeco2 not working anymore (2024)
  • SDRangel: https://github.com/f4exb/sdrangel/blob/master/plugins/feature/ais/readme.md and Wiki Home
  • AIS Catcher: https://github.com/jvde-github/AIS-catcher?tab=readme-ov-file

AISCatcher

https://www.youtube.com/watch?v=8wRIYuFXOqE

• In built-web server:

  AIS-catcher -v 10 127.0.0.1 -M DT -N 8100

• Use external data from https://airspy.com/directory/:

  AIS-catcher -v 10 127.0.0.1 -M DT -N 8100 y 37.136.93.253 5000

AirSpy

OpenCPN is a plotter.

AISmon

SDRangel

• Wiki https://github.com/f4exb/sdrangel/wiki
• More than only a AIS decoder.
• See https://www.youtube.com/watch?v=zugH-7yn-Mc for more information, and Jeremy Clark's web page https://jeremyclark.ca/wp/telecom/rf-signal-propagation-calculations_splat/
  • https://jeremyclark.ca/wp/telecom/rtl-sdr-for-ais-marine-weather-on-sdrangel-opencpn/
  • https://jeremyclark.ca/wp/telecom/rtl-sdr-for-ais-on-sdrangel-opencpn/

AIS Data received

• Date. Eg: Tue Jun 18 2024
• Time. Eg: 12:07:49
• MMSI: Maritime Mobile Service Identity. Eg: 230011000
• Country. Eg:
• Type. Eg: Static data report // Standard Class B equipment position report // Ship static and voyage related data // Position report (Scheduled) // Position report (Interrogated) // Data link management message // Base station report //
• Id. Eg:
• Data. Eg: Type: Vessel - Sailing Vendor ID: SRTH%GM Callsign: OH8682 // Type: Vessel - Pleasure craft Vendor ID: AMC@ANM Callsign: OH6573 // Name: MAIJU // Lat: 91° Lon: 181° Speed: 102.3 knts Course: 360° Status: Moored // Lat: 59.5295° Lon: 24.7398° Speed: 24.2 knts Course: 339.7° Status: Under way using engine // Lat: 59.5168° Lon: 24.8398° Tue Jun 18 09:37:29 2024 GMT // IMO: N/A Callsign: ES2735 Name: AHTO-28 Type: Pilot vessel Destination: MUUGA //
• NMEA 0183(?) (National Marine Electronics Association). See https://pypi.org/project/pyais/ Eg: !AIVDM,1,1,,,13KIo6P000QiV=:R2p;u2Db@2H59,0*4b // !AIVDM,1,1,,,13KtJ`04PaQiHGJR0w6j2GWT0D2I,0*08

// !AIVDM,1,1,,,347eHF50P0QiIBRR0qsWLFgN2000,0*2e
// !AIVDM,2,1,1,,54cac6429V2GQ1=2221LTi<tr20QDl8E:22222169p;975SV091AE33888888,0*73

!AIVDM,2,2,1,,8888888880,2*5c

• Hex. Eg: 14420221e2025bcd4854cc4800003594d40520000000000000000000003d0baf92485a497914515604ef2df8624814c00000000000 // 0441fbd883e0000871275fa2059611b9ffac008364
• Slot. Eg:

NMEA

NMEA 0183(?) (National Marine Electronics Association). See https://pypi.org/project/pyais/ or https://gpsd.gitlab.io/gpsd/AIVDM.html

• Comma-separated fields, eg !AIVDM,1,1,,B,15MwkT1P37G?fl0EJbR0OwT0@MS,0*4E
  • !AIVDM: the sentence is an AIS message in the "VDM" (VDO Message) format.
  • 1,1: the total number of sentences in the message and the current sentence number, respectively.
  • Blank
  • B: the communication channel. In this case, the channel is "B".
  • 15MwkT1P37G?fl0EJbR0OwT0@MS: the message in Six-bit ASCII.
  • 0*4E: a checksum.
• Eg, Position Report" message: position, course, and speed.

Eg: !AIVDM,1,1,,,13KIo6P000QiV=:R2p;u2Db@2H59,0*4b // !AIVDM,1,1,,,13KtJ`04PaQiHGJR0w6j2GWT0D2I,0*08
// !AIVDM,1,1,,,347eHF50P0QiIBRR0qsWLFgN2000,0*2e
// !AIVDM,2,1,1,,54cac6429V2GQ1=2221LTi<tr20QDl8E:22222169p;975SV091AE33888888,0*73

!AIVDM,2,2,1,,8888888880,2*5c

Theory -- AIS decoding

https://www.rtl-sdr.com/rtl-sdr-tutorial-cheap-ais-ship-tracking/

Radio Dongle

https://www.rtl-sdr.com/buy-rtl-sdr-dvb-t-dongles/

https://www.ebay.com/str/rtlsdrblog

https://www.ebay.com/itm/283144516411?mkcid=1&mkrid=711-53200-19255-0&siteid=0&campid=5338814417&customid=&toolid=20012&mkevt=1

Antenna

The frequency of AIS signal is 161.975 MHz and 162.025 MHz, and have the max range of about 70 km. Is is a line of sight signal. I wish to have 180 degrees view.

I decided to make two different Yagi antennas both working at 162.0 MHz. Both antennas have the reflecting and driven (dipole) elements, and two (2) or three (3) directional elements. The dimensions (given by k7mem, using non-metallic boom, boom diameter 20mm and element diameters 2.5 mm) are following:

Antenna dimensions with cumulative spacing

	Gain	Hor beam width	Refl pos	DE pos	D1 pos	D2 pos	D3 pos
2 Element Lengths	4.007 dBd	Nan deg	0	370.11
			907.55	901.08
3 Element Lengths	5.382 dBd	75.9 deg	0	370.11	508.91
			907.55	901.08	840.99
4 Elements Lengths	6.756 dBd	59 deg	0	370.11	508.91	842.01
			907.55	901.08	840.99	835.12
5 Elements Lengths	8.003 dBd	52.0 deg	0	370.11	508.91	842.01	1239.88
			907.55	901.08	840.99	835.12	827.89

Driven element is a dipole element [or actually a half-dipole], thus the length should be $\ell ={\tfrac {1}{2}}\lambda ={\tfrac {1}{2}}{\frac {c}{f}}={\frac {1}{2}}{\frac {299792458}{160\times 10^{6}}}={\tfrac {1}{2}}\times 1.85=0.925$ (m). A slightly different number for speed of light (speed of radio waves in the antenna; $v\approx 0.97c$) makes the $\ell$ to be $\ell =0.8975$ m. The driven element has an additional parallel wire connecting its two ends, and is called a folded dipole. Thus two nearly identical radiating currents are generated. See loop antenna. Folded dipole consists of a split dipole and an unbroken impedance transformer, and those two elements are connected together at both ends. The gap should be fixed to keep the wires at a constant separation distance. Spacing is the distance between the two parts of the driven element.

Positioning of the driven element.

There are three (3) common mounting types of driven elements: below, top or middle (see the image). Actually the mounting point do not matter. A good method to connect the wires to the driven element is to flatten the ends and attach the wire with a small nut and bolt, or use soldering iron.

Feeding. Normally the feeding impedance is 300 Ω. Impedance matching (if 75 Ω coaxial cable)

https://www.k7mem.com/Ant_Yagi_VHF_Feed.html#Mounting

https://www.k7mem.com/Ant_Folded_Dipole.html#Page_Top

https://www.k7mem.com/Ant_Yagi_VHF_Feed.html

Material: Common 1/4" copper tubing is often a good choice, or aluminum tubing, or #14 AWG electrical wire (diameter 1.6 mm and area 2.08 mm2).

Other antenna types I considered:

• Quarter wave / dipole. One vertical 1/4 wave element connected to the center of the coax cable and 4 (or more) more grounding elements pointing towards the the ground at 45 deg. A quarter wave antenna calculator: https://jeroen.steeman.org/Antenna/Quarter-Wave-Antenna-Calculator
• Coax collinear antenna. Very high omnidirectional gain. Multiple short coax cables where the outer conductor is connected to the inner conductor in an alternating fashion.
• Slim Jim.

https://arundaleais.github.io/docs/ais/aerial.html

Refs:

• https://www.rtl-sdr.com/rtl-sdr-tutorial-cheap-ais-ship-tracking/
• https://www.waves.utoronto.ca/prof/svhum/ece422/notes/13-folded.pdf

Raspberry Pi AIS

I will use an old Raspberry Pi 2B model for this.

1. Allow SSH: GUI: Preferences -> Raspberry Pi Configuration -> Interfaces -> SSH.
2. Start to CLI, no graphical user interface: Preferences -> Raspberry Pi Configuration -> System -> Boot To CLI.
3. User name: mol, server name: raspi.
4. Find the IP address using a Windows: Wireshark and use the following display filter eth.addr[0:3] == B8:27:EB.

Aim: To listen the data and to send it to a MySQL database for further usage. Also, take some photos.

• https://ranous.wordpress.com/wp-content/uploads/2018/02/rtl-sdr4linux_quickstartv2-18.pdf
• https://github.com/jvde-github/AIS-catcher
• https://www.klofas.com/blog/2021/ais-decoding-with-rtl-sdr-dongle/
• https://www.satsignal.eu/raspberry-pi/AIS-receiver.html
• https://github.com/mcqn/shpi-ais
• https://github.com/dgiardini/rtl-ais
• https://www.sarcnet.org/ais-receiver.html
• https://forums.raspberrypi.com/viewtopic.php?t=115380
• https://www.stripydog.com/kplex/