Quote:
Originally Posted by AdamY
I dont get why we cant make one of these. If you could take a VHF, tune it to the frequency and then feed that undisciminated signal into a laptop using a standard stereo mini cable you would be in business, this should be doable for much less than the prices these AIS systems are charging.
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It could be done if somebody felt like putting the effort in to it. There are two frequencies to
monitor; it is unclear to me whether you can get by monitoring only one. The data rate is too high (9600 bps) to use the speaker output from the
radio, so you need to get the FM discriminator output directly. The sound card input should have a high enough sampling rate to distinguish the bits.
After that, it's "only" a matter of writing a program to extract the HDLC frame from the audio input, extracting the data from the transmitted packet, and finding a way to do something useful with the data. Probably you would end up writing a Windows device driver that looks like a
serial port sending
NMEA data, so it would
work with existing applications.
The hard part of all this is the detail of design and programming. If you did this as a
commercial endeavor, you would have expensive
software instead of expensive
hardware. (ok, you still need the
radio...) If you do it as a hobby, your time is free.