AIS information is not audio frequency.
Class A AIS uses what is called SOTDMA (Self-Organizing Time Division Multiple Access) transmission
protocol. In short, this means that an AIS will use two frequencies to alternate its trasmission cycle four slots ahead. AIS operates between 156 and 162 MHz but can vary in that range depending on the countries VTS.
Now, the modulation type for AIS is GMSK or FSK depending on what the AIS is transmitting.
An AIS will transmit two sentences basically.
$AIVDM - This sentence contains all the other ships static and voyage data that the host AIS is seeing.
$AIVDO - This is your own static and voyage data.
What is static data?? Static data is that data that describes your vessel and will include, but is not limited to, the following:
- Ship Name
- Call Sign
- IMO Number
What is voyage data? Voyage data is data that is particular to the voyage you are currently on and may contain, but is not limited to,
- Souls on board
- Time to Destination
AIS data is just that over the airwaves....data. Think of AIS as the same as DSC
, teletype or fax with respect to whether you can audibly understand it or not.
NOW!! There are VHF radios out there that can take a NMEA
feed from an AIS unit and display AIS data on thier screens. I'll let you guys figure out who those companies are