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[aprssig] Parallel UHF APRS level-4 node system.

Phillip B. Pacier ad6nh at arrl.net
Tue Dec 28 19:44:40 UTC 2004


John Denison wrote:

> Icom has a system called the D-STAR which operates at 128k on 1.2 and 
> 10 GHz. I've just started getting into packet, but from a newbie point 
> of view, I wonder why 1200 baud is still being used. We left 1200 baud 
> behind years ago in computer modems, so why is ham radio still 
> lingering behind? If high speed data occurs on wireless routers at 2.4 
> GHz, then there is no reason why we can't meet or exceed that standard 
> with our own implementations.

I am currently conducting tests in So. Cal. with APRS at 9600 baud.  
Still a far cry from 802.11 type speeds, but still about 4 times faster 
than 1200.  A couple of reasons that 1200 baud has remained is that the 
higher speeds require much higher bandwidths.  Our amateur allocations 
at VHF do not allow for anything above 9600, and that is due to 
bandwidth.  Another reason that APRS has survived on 1200 is that it 
seems to work better when moving.  That is one of the tests we are set 
to conduct here in So Cal is how to overcome the increased negative 
effects of doppler as the baud rate increases.  At any rate, one plan is 
to possibly have fixed stations move to a 9600 channel and leave mobiles 
at 1200.  Finally, the cost issue comes into play.  There is so much 
1200 equipment available for so cheap that this is what we use.

73
Phil - AD6NH

>





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