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[aprssig] APRS radios

Heikki Hannikainen hessu at hes.iki.fi
Sun May 25 09:33:30 UTC 2008


   Hi,

On Sat, 24 May 2008, Bob Bruninga  wrote:

> APRS is really quite simple.  There are only 4 types of packets, 
> position, status, message and queries.  All one has to do is capture 
> them and display them.  And provide a simple user interface...

   Its really quite complicated. There are so many different types of 
packets, and so many different types of packets for the same purpose (a 
position packet), with a large amount of options and extensions and 
special cases. Like the one here, a message suddenly isn't a message, but 
a bulletin, because the destination callsign has a special prefix. It 
could be so much simpler and still have all the same features. I know, it 
seems too late to fix it... but it really cannot honestly be called 
'simple'.

   I know it's a massive task to implement APRS on a big computer, using a 
scripting language which is very good for implementing string parsers. 
It's even more work in C. It must be really, really hard to implement all 
of it properly in a tiny embedded device with very little memory.

   Luckily embedded CPUs are getting more powerful and have more memory to 
spare than before, so the manufacturing cost of adding APRS in a radio 
comes mostly from writing the code and adding a GPS chip. If the protocol 
spec would be smaller, it'd be cheaper to do it.

   Don't get me wrong, I think APRS is pretty damn cool. I spent most of my 
spare time last year implementing an user interface for it, and had a lot 
of fun in the process. Just don't call it simple. :)

   - Hessu





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