[aprssig] The APRS AX.25 Frame
Lynn W. Deffenbaugh (Mr)
ldeffenb at homeside.to
Wed Sep 21 09:38:45 EDT 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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