[FARC] APRS Learning Snack - Fixed Station Position Packet

[m.e.whitmore at comcast.net]

Joe,

Thanks for the APRS info.  This is the kind of stuff that I like.  The real nuts and bolts nity gritty stuff.

Look forward for more.
 
Mark

----- Original Message -----
From: "Joseph M. Durnal" <joseph.durnal at gmail.com>
To: "Maryland ARC Frederick" <farc at mailman.qth.net>
Sent: Tuesday, September 20, 2011 3:57:36 PM
Subject: [FARC] APRS Learning Snack - Fixed Station Position Packet

There was so much I didn't discuss at last night's FARC meeting.  Over
the next few weeks, I'm going to send short informative e-mails about
different APRS functions, this is the first of those e-mails, I hope
to have time to follow up with e-mails on a mobile station packet,
object packet, weather packet, and a message packet.

***APRS Fixed Station Position Packet***

An APRS packet is a standard AX.25 UI (connectionless) packet
formatted in a specific way, here is an example of what you'd see on
the TNC.

NE3R>APX200,WIDE1-1,WIDE2-1:=3925.63N/07726.00WxPHG3000Frederick ARC APRS Demo


"NE3R>" = The source of the packet

"APX200," = The "destination", in practical application, it isn't
really the destination because APRS packets don't have a specific
destination, but it is an available AX.25 field, and makes good use of
the bytes in a packet to identify the APRS software generating the
packet, in this example, APX200 stands for Xastir version 2.00.

"WIDE1-1,WIDE2-1" = the packet path, 3 hops in this case, once
digipeated looks like N3KTX-2*,WIDE1*,KV3B-1*,WIDE2*

":" = The separator for addressing/routing and APRS info

"=3925.63N/07726.00WxPHG3000Frederick ARC APRS Demo" = the APRS
information, which I'll break down further below

"=" = APRS datatype, this one represents an APRS position without a
time stamp from a messaging capable station, others "!" = Position
without time stamp without messaging (a digipeater is a good example),
";" = Object, "@" position with timestamp

"3925.63N/07726.00W" = the position data, but the / is important to
the APRS symbol definition

"x" = the second part of the symbol, combined with /, the x displays
an X for XAPRS/Xastir (linux software), symbols for cars />, trucks
/k, houses /-, etc can be used.  There are many symbols, alternate
symbols, and overlays.  See www.aprs.org/symbols/symbolsX.txt &
http://www.aprs.org/symbols/symbols-new.txt for more info.

"PHG3000" = optional power height & gain info, important for
digipeaters and fixed stations (your software should calculate this)

"Frederick ARC APRS Demo" = A free-form comment

***End***
73 de Joseph Durnal NE3R
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