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[aprssig] 9600b UHF APRS IS THE FUTURE OF APRS

scott at opentrac.org scott at opentrac.org
Sun Oct 8 21:44:43 UTC 2006


Steve's right.  Just cranking up the baud rate is NOT the way to improve
APRS.  Even implementing a simple slotted ALOHA scheme would double channel
capacity for APRS.  And if you're going to require all new infrastructure,
better to do it right with better channel access control, forward error
correction, a more compact packet structure, and standards for maximum TX
delay.

The AK-47 didn't get to be the world's most popular assault rifle by being
the most accurate, the most deadly, or the fastest firing.  Rather, it's
been that successful because it's cheap, simple to operate, and it gets the
job done while being very forgiving of mistreatment.  The same is true of
APRS on 1200 baud AFSK.  Many, many APRS users would have never gotten into
it if they hadn't been able to use any old FM voice rig.  Most won't follow
it to 440 if it means buying expensive new equipment that doesn't give any
clear benefit.

Scott
N1VG

> Unfortunately UHF 9600 baud AX-25 is not eight times more 
> speed for a  
> little more money. There are serious problems with it, things like  
> increased path loss and multipath. Deviation setup is critical so it  
> does not lend itself to the modern appliance operator ham. Finally,  
> throughput is far less than an eight-fold increase when considering  
> short messages like APRS uses.
> 
> A lot of money to build a new infrastructure for maybe twice the  
> bandwidth. In my opinion worldwide APRS never will transition to UHF  
> 9600 baud, and never should. There are situations where it may be  
> worthwhile for local areas to use it as a supplement, but I 
> don't see  
> that it could ever become the primary mode of APRS.







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