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[aprssig] USNS and APRS

Bob Bruninga bruninga at usna.edu
Mon Jun 1 10:02:17 UTC 2009

>Bob, any thoughts on using USNG with APRSTT?

The beauty of APRStt is that it is a LOCAL system, SIMPLEX rnage only from the sender.  Thus, each APRStt is set up to match the needs of its users (usually one club) and this is independent of how APRStt might be used somewhere else.

And APRStt can use any grid system, lat/long, SAR GRIDS, Mile marks, and even flea-market spaces at Dayton.  And any one APRStt can support many of these at the same time if needed.

At our first system in Dayton, we defined the position format to be Bxy*  Just one digit in X and one digit in Y.  But the spec has always said there would be xxyy, xxxyyy, xxxxyyyy versions for greater precision, or greater coverage area.  

So after dayton, we formalized this as follows.  There are 10 possible Position formats that can be implemented in any instance.  In most cases, only the one that is applicable at any parcicular APRStt will be used.  But that does not prevent the engine from accepting more than one if needed.  Here are their definitions:

B0x*        One of 10 special positions
B1xy*       1 digit XY  ( 10 mi in 60 mi area) (default)
                       (or 1 mi in 10 mi area)
                       (or.1 mi in  1 mi area)
B2xxyy*     2 digit XY   ( 1 mi in 60 mi area) (default)
                      (or .1 mi in 10 mi area)
                      (or 60 ft in  1 mi area)
B3xxxyyy*   3 digit XY  ( .1 mi in 60 mi area) (default)
                      (or 60 ft in 10 mi area)
B4xxxxyyyy* 4 digit XY  ( 60 ft in 60 mi area) (default)

B5zzzmm*    at bearing zzz range mm miles 
B6EEENNN*   SAR UTM Grid - Easting and Northing 
B7RRRMMM*   Road RRR, Milemark MMM 
B8......*   Table interpolation
B9...   *   TBD

What we used at Dayton is now B1xy*.  This added digit also is kind of a redundant check to make sure the proper number of digits has been received for a given posit.

Back to the original question,  So what each XY grid represents and how much precision is independent of whether it is UTM or LAT/LONG or USNS.  That is established at se-up time at that location.

Again, dont panic at all the options.  Usually, only one format will be used in a given applcation depending on the area covered and the degree of precision desired.  At Dayton, we only used B1xy*.  At the 2010 Scout Jamboree, we will use B2xxyy* because the published map that will be in the hands of every scouter will have an XX YY grid already on it.

Hope that helps

Bob, Wb4APR

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