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[aprssig] old formats

Bill Vodall WA7NWP wa7nwp at jnos.org
Thu Jan 5 18:01:26 UTC 2006


>>  So not all of those microseconds of air time is wasted.
> 
> 
> Well it may not be many microseconds, but in % it's between 200% and 
> 500% the size of APRS formated packets. Grabbing 3 examples from an old 
> log file:
> 
> $GPGGA sentence: 69 byte payload
> standard APRS position report, with time, speed, and heading: 35 bytes
> standard APRS position report, position only: 20 bytes
> Mic-E packet from a D700: 14 bytes

Redo your calculations with the txd and ax25 overhead.  D700 adds a half 
second TXD chirp before sending the ax25 info before sending the 14 
bytes of data.

It's less for other devices but still significant and makes the overall 
difference between packet types far smaller.

> This also does not address altitude; you need two different NMEA strings 
> to get complete position and heading information from a balloon, but a 
> "dumb" tracker is _so_ dumb it can do it in a single packet using about 
> 10 or 15% of the air time (and battery power!) of the KPC-3+.

I agree completely.  Use dumb trackers for balloons and rescue dogs. 
Anywhere else they're limiting what can be done with packet/APRS.

Bill





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