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[aprssig] The APRS AX.25 Frame

Lynn W. Deffenbaugh (Mr) ldeffenb at homeside.to
Wed Sep 21 13:38:45 UTC 2011


Agreed.  That's probably sufficient detail with a reference to 
aprs101.pdf if anyone wants to know more.

You might mention that the trailing characters on the packet are part of 
the source identification as described at:

http://aprs.org/aprs12/mic-e-types.txt

That way when they see their own Kenwood-generated Mic-E packets going 
by "in the raw", they don't wonder about the ] or > and = and say "but 
that's not in my comment" and plow through the menus to deconfigure 
something that isn't there.

Lynn (D) - KJ4ERJ - Author of APRSISCE for Windows Mobile and Win32

On 9/21/2011 9:32 AM, Joseph M. Durnal wrote:
> I need to think about the mic-e packet.  Obviously, if one takes their
> TNC and watches the 144.39 data go by on the terminal, they'll see a
> lot of mic-e.  I'm still working on how far into the weeds I should
> go.  I could keep it simple and just say that the destination address
> contains the encoded latitude, NS/EW,&  message and the info field
> contains the encoded longitude, course speed,&  symbol.  I don't think
> most of my audience will find much more than that very useful.
>
> On Wed, Sep 21, 2011 at 4:13 AM, Ian Wade G3NRW
> <g3nrw-radio at ntlworld.com>  wrote:
>> ___Original Message_________________________________________
>> From: Joseph M. Durnal<joseph.durnal at gmail.com>
>> Date: Tue, 20 Sep 2011   Time: 15:09:29
>>
>>> I'm trying to explain an APRS packet to many non-APRS users and I want
>>> to get it right, but I've confused myself
>>>
>>
>> Hi Joseph
>>
>> To get the full information you need, take a look at the APRS
>> Specification:
>>
>>     http://www.aprs.org/doc/APRS101.PDF
>>
>> This includes all the details of packet structure, APRS commands etc.
>>
>> When writing the specification, I wrote an APRS decoder (APRSDEC) that
>> breaks down each received packet into readable English:
>>
>>     http://homepage.ntlworld.com/wadei/aprs.htm
>>
>> Here is a snippet of the APRSDEC output:
>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>
>> Record #3
>> G3NRW*>APRS:!5157.97N/00029.38W-                              ~ Basic
>> posit
>>   APRS Data Type= Posit w/o time. No APRS
>>   Lat= 51 deg 57.97 min N  Long= 0 deg 29.38 min W
>>   Icon= House QTH VHF   Overlay= (none)
>>
>> --------------------------------------------------------------
>> Record #4
>> WB4APR*>APRS:!5157.97N/00029.38W-                             ~ Exactly
>> the same posit, but Bob is a long way from home!
>>   APRS Data Type= Posit w/o time. No APRS
>>   Lat= 51 deg 57.97 min N  Long= 0 deg 29.38 min W
>> **QUESTION: Is this lat/long position reasonable?
>>             It seems a long way from home for this callsign.
>>   Icon= House QTH VHF   Overlay= (none)
>>
>> --------------------------------------------------------------
>> Record #5
>> G3NRW*>APRS:TheNet X-1J4!5157.97N/00029.38W-                  ~ "TheNet"
>> string preceding posit
>>   APRS Data Type= Posit w/o time. No APRS
>>   Lat= 51 deg 57.97 min N  Long= 0 deg 29.38 min W
>>   Icon= House QTH VHF   Overlay= (none)
>>
>> --------------------------------------------------------------
>> Record #6
>> G3NRW*>APRS:@012345z5157.97N/00029.38W-                       ~ Basic
>> posit with timestamp
>>   APRS Data Type= Posit w/ time. With APRS
>>   Day= 01  Time= 23 hours 45 mins UTC
>>   Lat= 51 deg 57.97 min N  Long= 0 deg 29.38 min W
>>   Icon= House QTH VHF   Overlay= (none)
>>
>> --------------------------------------------------------------
>> Record #7
>> G3NRW*>APRS:@5157.97N/00029.38W-                              ~ Same
>> again, but timestamp missing (a common mistake)
>>   APRS Data Type= Posit w/ time. With APRS
>> **WARNING: Bad/missing timestamp. Rest of data may not decode correctly.
>>   Lat= 61 deg 58.47 min N  Long= 111 deg 41.36 min W
>>   GPS Fix= Current   NMEA Source= RMC   Compression Origin= Digipeater
>> conversion
>>   Course= 216 deg   Speed= 2 knots (2.3 mph  3.7 kph  1.0 m/s)
>>   Icon= **INVALID ICON   Overlay= **BAD OVERLAY CHAR 'N' not allowed with
>> this symbol
>>
>> --------------------------------------------------------------
>> Record #8
>> G3NRW*>APRS:!5157.97N/00029.38W-/A=000056                     ~ /A=
>> altitude
>>   APRS Data Type= Posit w/o time. No APRS
>>   Lat= 51 deg 57.97 min N  Long= 0 deg 29.38 min W
>>   Icon= House QTH VHF   Overlay= (none)
>>   Altitude= 56 feet (17 meters)
>>
>> --------------------------------------------------------------
>> Record #9
>> G3NRW*>APRS:=5157.97N/00029.38W-023/050                       ~ CSE/SPD
>>   APRS Data Type= Posit w/o time. With APRS
>>   Lat= 51 deg 57.97 min N  Long= 0 deg 29.38 min W
>>   Icon= House QTH VHF   Overlay= (none)
>>   Course= 023 deg   Speed= 050 knots (57.5 mph  92.6 kph  25.7 m/s)
>>
>> --------------------------------------------------------------
>> Record #10
>> G3NRW*>APRS:=5157.97N/00029.38W-.../...                       ~
>> Indeterminate CSE/SPD
>>   APRS Data Type= Posit w/o time. With APRS
>>   Lat= 51 deg 57.97 min N  Long= 0 deg 29.38 min W
>>   Icon= House QTH VHF   Overlay= (none)
>>   Course= (Indeterminate) deg   Speed= (Indeterminate)
>>
>> --------------------------------------------------------------
>>
>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>
>>
>> Go to http://aprs.fi for a good source of raw data to play through
>> APRSDEC.
>>
>> Also, someone else in this thread mentioned MIC-E. The details of MIC-E
>> packets are explained in the specification, and my MICENC encoder
>> program (also at http://homepage.ntlworld.com/wadei/aprs.htm) lets you
>> generate a MIC-E packet from a standard uncompressed packet.
>>
>> Hope this helps.
>>
>> --
>> 73
>> Ian, G3NRW
>>
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