If you want to monitor digital modes that use FSK or PSK (e.g. POCSAG, FLEX, ERMES and AIS), you get the best results if you use the unfiltered audio from your receiver. You can find that signal at the discriminator of your receiver. A discriminator is the 'heart' of an FM receiver. After the discriminator, audio filters and amplifiers follow that may heavily distort a digital signal. If you want to decode and monitor digital (FSK and PSK) systems seriously, a discriminator tap is an absolute prerequisite.

This program contains algorithms to demodulate and decode AIS messages sent by ships and coast stations. You will need to connect it to the discriminator output of a VHF receiver to make it work.

SeaTalk is a simple interface for networking Raymarine/Autohelm marine equipment so that all devices of a ship can exchange and share their data. SeaTalk is a proprietary solution of Autohelm and not compatible with NMEA or CAN. Unfortunately Raymarine keeps the technical details of SeaTalk secret. To assist users who want to develop hard- or software to connect their devices to the SeaTalk bus these pages uncover some of the mysteries. Part 3 adds hints how to interface SeaTalk with a PC.