Ship AIS (How to receive…)

Brief description

Ship AIS (Automatic Identification System) is a ship identification and location system which uses two frequencies on the Marine VHF band. Information on technical aspects and how the system is used can be found here. This page purely describes how I receive the signals and forward data to the Vessel Finder and Marine Traffic mapping websites (other AIS tracking websites are also available).

AIS is an essentially “line of sight” system, so range is restricted by factors such as the field of view of your antenna, the quality of the signal, height of the transmitting antenna and the transmitter power. Further factors include the prevailing radio propagation conditions, which can extend the range by several times under certain conditions, or bad weather which can reduce range due to increased wave heights.

There are two frequencies for system resilience, but it is not essential to receive both in order to receive all targets in range. The frequencies are 161.975 and 162.025 MHz (marine channels 87B and 88B). A reception mode of Wide FM with an I.F. bandwidth of around 15 kHz works for me.

I use a Discone mounted on the chimney at 15m agl (102m asl) and an RTL R820T USB dongle receiver connected to my PC via a USB cable. This feeds an instance of the SDR Console v3 software which is running two virtual receivers. The outputs of the receivers are fed to the left and right legs of a VAC (Virtual Audio Cable). The VAC is received by a small piece of software called AIS Dispatcher (from AIS Hub). This software compiles AIS data packets for distribution via TCP over the internet to the web services. An account is required in order for them to identify your station and give you a TCP port on which to forward the data. Submission of data to these sites is a free service, and you do not get paid for submitting your data. Some sites do, though, offer free subscriptions to their services in exchange for the data.

AIS Channels and AIS data bursts
AIS Dispatcher
Locally received targets displayed in the OpenCPN application
Extended range to 300+km thanks to tropo propagation
Receive range over past few days logged on