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

Gregg Wonderly gregg at wonderly.org
Mon Oct 9 18:06:14 UTC 2006


Bob Bruninga 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...
>>
>>Don't forget "packet time" is also part of the equation.  
>>A 9600 baud network with packets 1/4 the size of a 1200 
>>baud network can handle 4X the number of users in its 
>>Aloha circle.
> 
> 
> BUT, in order to make 9600 baud work at UHF, you first have
 > to make up a 9 dB RF link penalty, and a few dB decoding penalty.
 > This requires you to have to install 4 times as many digipeaters
 > for the SAME performance.

The distance to the digi is smaller, so that 9db loss, is not such a dramatic 
situation, and antennas can make it a non-issue.

> Now, once you have installed 4 TIMES the number of digis, you now 
 > have much smaller CELLS and can stuff in 16 times as many users.

4 times the equipment for 16times the bandwidth?  We must be crazy to want that 
kind of upgrade huh?  Have a look at our UHF linked system at 
http://www.w5ias.com/status.  It covers have a state for reasonable voice 
services from HTs.  We don't try and fill all the low areas in the far east and 
SE of OK, but, from the hill tops, you can work the system.  I think that people 
just need to go try it to see whether the numbers all fall in line, or if there 
are certain system characteristics that change things.

Maintaining the current expectations for the use of APRS, is going to cause it 
to be pushed asside by other technologies with more bandwidth and better 
characteristics.  D-Star, Celluar, WI-FI/WI-MAX (standardization at a massive 
scale), all provide a lot more bang for the buck.  It's either time to start 
working on the next generation, or time to take the idle path of waiting to be 
overrun, and then dump everything and start over.

Gregg Wonderly




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