MARINETRAFFIC.COM
“DIY VHF AIS RECEIVER”
GENERAL INSTRUCTIONS ON HOW TO USE YOUR VHF TRANSCEIVER AS AN AIS
RECEIVER AND SHARE DATA WITH MARINETRAFFIC.COM
A cost efficient alternative to dedicated AIS receivers is to use a cheap or readily available
VHF radio transceiver and a PC equiped with a basic sound card (with line-in) to decode AIS
messages. In order to do so you must tap into the radio's discriminator output (unfiltered audio).
The equipment setup must look like below:
Very few cheap VHF transceivers have a dedicated discriminator output available. In most
cases the user must modify the unit in order to gain access to the unfiltered audio feed required for
AIS signal decoding.
This requires basic electronics knowledge and basic to intermediate soldering skills
(depending on the transceiver type).
The best source for info / guides / howto's , covering a vast array of VHF radio makers /
models is:
http://www.discriminator.nl/ais/index-en.html
When modification is required the concept is to find the receiver IC in the unit's main board,
identify the pin that carries the discriminator signal and solder a basic RC filter between that pin
and the chassis ground. This is done in order to eliminate the 455KHz IF component of the FSK
signal which distorts the audio feed.
The desired output resides between the filter output and the chassis ground. An example of
said modification on a “COMMTEL COM103” transceiver looks like this:
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