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[aprssig] Is my PIC-E transmitting incorrect LAT tracking data

Tapio Sokura oh2kku at iki.fi
Tue Jan 9 05:41:42 UTC 2007


EXT-Maetta, John wrote:
> Is my TAPR PIC-E is transmitting incorrect LAT data.  My location is
> 34.xxxxN, 120.xxxxW which is in grid CM94.
>  
> The PIC-E is transmitting the following LAT data: 3xxxxx.  Shouldn't it
> be sending Sxxxxx for a LAT?  The APRS spec is a bit confusing but I
> think I can manualy decode MIC-E APRS packets correctly.

If you look at the APRS 1.01 specification PDF file pages 43 and 44, 
you'll see the following:

1) The first character of the destination field contains both the first 
latitude digit (tens of degrees) and message bit A. Nothing more, 
nothing less. Especially note that the N/S indicator is encoded in the 
4th character.

2) Thus for 30 degrees (north or south), the first character can be 
either 3, D, or S. The only difference between these is the message bit 
A, which can be either zero, one (custom), or one (standard). A '3' says 
that the message bit A is zero.

The mic-e message bit table on page 45 says that if message bit A is 
zero, the possible messages are "committed", "special", "priority", 
"emergency" or "custom" messages 4-6. So you probably have one of those 
messages configured in your pic-e.

   Tapio





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