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[aprssig] APRS on all Radios!!!!

Scott Miller scott at opentrac.org
Sun Aug 17 22:49:41 UTC 2008


PSK-31 isn't like 1200 baud packet where we've got zillions of different 
non-upgradeable hardware devices to work around.  Almost all 
implementations are entirely in software - there's no need to make the 
protocol so convoluted just to use some existing software that's not 
really what you want anyway.

I meant what I said about breaking out of the text mindset.  I know it's 
difficult when BASIC is what you've always worked with, where string 
manipulation and floating point math are effortless but dealing with 
binary data can be a bit of a pain.  But show a little mercy to us 
embedded systems developers, with no FPUs and RAM measured in hundreds 
of bytes!

Scott
N1VG

Bob Bruninga wrote:
>> Please, can't we just have a fixed-length 
>> binary message? 
> 
> Yes, that is what I was proposing.  Fixedfields for all APRS data.  Then give that to the stock PSK-31 varicode system so that it was compatible completely with that system.  Being able to montior it or decode it with any off-the-shelf PSK-31 decoder would be a powerful tool.
> 
>> Start using varicode (or any Huffman code) 
>> and you've got to worry about designing 
>> for the worst case data.
> 
> No, beacuse the text to varicode to text algoirthms are done.  Built into all PSK-31 applications.  SO that is outside the scope of a PSK-31 approach.  I agree compeltey with fix-length fields for the APRS data (prior to PSK-31 varicoding).
> 
>>  Callsigns don't have the sort of letter 
>> distribution you see in natural language. 
> 
> Yes, but the average bit length for random calls is still only about 6 bits each.  SO ther is no penalty.
> 
>> Stop thinking in terms of text strings, 
>> and think about data structures.
> 
> I like the text strings for trounbleshooting especially if using off-the-shelf PSK-31.  The data structure would be fixed length fields.
> 
> But I agree, if there is no interest in using off-the-shelf PSK-31 for all the advanatages of TX, RX, monioring, and troubleshooting, then binary makes sense too.  But not if the only tool for using it is the only decoder itself.  Then there are no options for troubleshooting.
> 
> Bob, WB4APR
> 
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