[OZAPRS] Odd data path
an at comms.net.au
Tue Jun 14 21:02:34 AEST 2016
in Mic-E encoding, the X.25 destination address contains the encoded position, and some other data, in 7-bit printable ASCII characters:
- 6 latitude digits
- 3-bit mesg identifier
- N/S W/E indicator
- longitude offset indicator
- S = LAT 3, mesg bit A = 1
- T = LAT 4, mesg bit B = 1
- 5 = LAT 5, mesg bit C = 0
- 4 = LAT 4 N/S indicator = S
- S = LAT 3 long offset = 100
- 9 = LAT 9 W/E indicator = E
ie. latitude of 34 degrees 54.39 minutes South, in the Eastern hemisphere, message id = 1 1 0, ie. En Route
The longitude can be calculated from the long offset and information field.
The specs is documented here: http://www.aprs.org/doc/APRS101.PDF, page 44.
On 14 Jun 2016, at 3:14 pm, Norm McMillan <vk3xci at gmail.com> wrote:
> The bit I don't understand is the ST54S9. I always thought that this defined the TNC device and usually starts with AP for APRS followed by a string to ident the tnc?
> Now I look a little closer at the data-stream I see quite a few SWU1U4, S7T9Y5... hmmm all six element strings starting with S?
> A brief explanation or link?
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> OZAPRS at aprs.net.au
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