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

scott at opentrac.org scott at opentrac.org
Mon Oct 9 17:50:18 UTC 2006


It's not all about going faster.  Data rate alone is never going to be the
way to fix the system.

I'm also not convinced that a cellular style system is ever going to
succeed.  Hams are good at developing high elevation repeater sites, and
it's much easier to build and manage a few large systems than a bunch of
small ones that might need to be in inconvenient places.  Home-based systems
are another matter, but we'll never have them in all the right places.

Run timeslotting with 200 msec slots, have digis provide at least some loose
coordination of slot assignment (overlapping coverage areas and odd band
openings complicate assignment schemes) and you could have hundreds of
stations on a single channel with a cycle time of a few minutes.  Now, add a
multichannel receiver at the digi site (maybe gnuradio based) and you can
multiply that capacity by the number of channels available.  The dedicated
downlink from the digi can run at 9600 with no collisions, so you could
still get all of the local traffic by listening to a single frequency.

Baud rate is NOT the primary limiting factor in APRS.  We could probably
increase our channel capacity by 50% if we could just get everyone to set a
reasonable txdelay and stop using long comments on every packet.  I see way
too many short Mic-E packets with a 30-character comment tacked on to every
position report.  Not to mention D700's with half-second txdelays...

Scott
N1VG

> -----Original Message-----
> From: aprssig-bounces at lists.tapr.org 
> [mailto:aprssig-bounces at lists.tapr.org] On Behalf Of Andrew Rich
> Sent: Monday, October 09, 2006 10:35 AM
> To: TAPR APRS Mailing List
> Subject: RE: [aprssig] 9600b UHF APRS IS THE FUTURE OF APRS
> 
> Why stop there ?
> 
> Aircraft use PPM at a 1Mb rate and can send positions in 
> 112us at a 1/2
> second rate.
> 
> Just need some smart ham radio operators to try
> 
> 
> 
> -----------------------------------------
> Andrew Rich
> Amateur radio callsign VK4TEC
> email: vk4tec at tech-software.net <mailto:vk4tec at tech-software.net>
> web: http://www.tech-software.net
> Brisbane AUSTRALIA
> 
> 
> 
> -----Original Message-----
> From: Gregg Wonderly [mailto:gregg at wonderly.org]
> Sent: Tuesday, 10 October 2006 3:29 AM
> To: TAPR APRS Mailing List
> Subject: Re: [aprssig] 9600b UHF APRS IS THE FUTURE OF APRS
> 
> 
> Joel Maslak wrote:
> > It's not the coverage that's the problem,  it's the number 
> of users in
> > the collision domain and the size of the  aloha circle vs. 
> digipeater
> > location and user paths.
> 
> Not to be picky, because you did qualify that statement, but 
> it is exactly
> the
> coverage that increases the number of users and the size of the aloha
> circle.
> So, a system which can cover less area (at reasonable HAAT given the
> expected
> coverage area), will have a better performance margin from my 
> perspective.
> 
> Gregg Wonderly
> W5GGW
> 
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