[aprssig] APRS on all Radios!!!!

Scott Miller scott at opentrac.org
Sun Aug 17 12:47:40 EDT 2008

> Could it simply be PSK-31 encoded? What is the lowest carrier tone that can carrry PSK-31? Some APRS dongles already are starting to decode PSK-31.  And with say a 120 Hz carrier, it would seem that it would remain sub-audible?  We would of course add CRC checks to make each info packet complete.

I've decoded PSK-31 (sent by an OpenTracker) successfully at a carrier 
frequency of 62.5 hz.  Sounds like war drums on the subwoofer.

> If we used PSK-31 (sub audible) we would look carefully at the hamming coding to make sure we used an optimum format and did not just try to stuff APRS as-is into that pipe.

PSK-31 uses varicode to send printable characters.  No need to do that 
here, you can just use BPSK to send straight binary data.

Still, it sounds like there are some serious radio compatibility 
questions to be addressed.  I'm afraid I don't even know how the radio 
suppresses the PL tone - 100 hz is most certainly within the audible 
range.  Is everything filtered below a certain cutoff frequency, and if 
so, what's the cutoff?


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