[aprssig] APRS on all Radios!!!!
bruninga at usna.edu
Sun Aug 17 10:28:33 EDT 2008
In fact, we could make it by directional and be full APRS on all voice repeaters.! Mobiles send in their sub-audible APRS data on the uplink, and the repeater streams the local APRS situation on the repeater output. HAMHUD devices (or modified RC-D710 display heads give all the mobile display functionality!
> Sounds like DPL commonly called DCS.
Yes, in fact, this has been considered many times in the past for APRS, but no one has done it. We could use a less verbose protocol for shortest possible packet length.
> Needs careful thought/design.
> This is a problem for Phase modulated rigs
> because of ... low freq components...
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.
The dongles on the user end and repeater end would be bidirectional. They would do these things:
1) Convert mobile GPS input to PSK string and TX it.
2) Receive PSK strings and convert to APRS for sending over to APRS or for local display on existing devices, clients, internet, etc..
3) Receive local APRS (at the repeater) and convert to PSK for streaming to all mobiles.
4) Have a SQUELCH OUTPUT bit for the repeater so that the sender of this DPL(PSK) data can also be heard on that repeater like all other PL users.
Remember, this is a UNIQUE service on a VOICE repeater. Thus, the repeater dongle can FILTER, TRAP, and focus only on LOCAL information only of immediate value in the coverage area of that repeater, not the 10,000 square miles worth of SPAM that floods the area on normal APRS. THus the stream would be able to paint a pretty good picture in few minutes.
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.
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