Ais Transponder Software Software Defined Radio

Just tune manually until the signals are properly centered, or set the PPM offset correctly.

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.

Ais Transponder Software Software Defined Radio

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.

If you have not bought a dongle yet, see the Buy RTL-SDR page for information, and the check out the Quickstart Guide for an easy setup routine with SDRSharp.

You will also need to have an audio piping method installed and set up.

Audio piping will allow the audio from SDRSharp to be passed to a decoding program.

You can use either windows stereo mix, VB-cable (free) or virtual audio cable (paid with trial version).

So if your radio set up is more than 75 kilometers away from any boats, you will probably not be able to receive AIS signals.

AIS is also considered a line of sight signal, meaning that if there are large buildings or mountains in the way of your antenna and the boats, AIS signals could be blocked.

Because of this reason it is important to put your antenna as high up as possible.

However, sometimes home made antennas work even better and they of course are cheaper.

The antenna consists of one vertical 14 wave element connected to the center of the coax cable and four or more grounding elements pointing towards the ground at 45 degree angles which are connected to the coax shield.

A good way to calculate the exact element lengths required for 162 MHz is to use the calculator available here.

One element is connected to the center pin, and the other is connected to the coax shield.

The collinear antenna has very high omnidirectional gain directed towards the horizon.

This means it will receive signals best from sources that are near the horizon, which is where ships will be.

As it is made out of coax cable almost entirely, it is a very cheap antenna to build.

A Yagi is a very directional antenna, meaning that it will only pick up signals in the direction it is pointed.

The advantage is that with directionality we can get a very large signal gain, which allows reception of further and weaker signals.

A slim-jim antenna can be easily made on a budget using common 300 Ohm twin lead ribbon cable.

A page showing a twin lead slim-jim is here, but that version is designed for 145 MHz.

To calculate the correct lengths for AIS, this calculator can be used by inputting 162 Mhz into the frequency box.

Open SDRSharp, set your audio piping method in the Audio output drop down box, and tune to an AIS frequency (161.975 MHz or 162.025 MHz).

In SDR, the signals may not appear exactly on the AIS frequencies, since the RTL-SDR is not frequency accurate (unless you have a RTL-SDR with TCXO).