[aprssig] APRS Telemetry Question
noskosteve at yahoo.com
Sat Oct 13 14:01:29 CDT 2012
Thanks Lynn & Hessu,
I have it now.
Lynn, I understand most of the (Printable) packet contents. Didn't intend for you to explain that. I didn't know if there was an unprintable bit/byte ahead of the payload that defines message vs. Telem. I now see that the":" in Telem is the 'preamble' delimiter, not part of the payload and that a message has two.
Yes; 101 is a bear to extract info from. It really helps if you understand it all before trying to read it... as all you Gurus do... (;-)
I now see that the delimiter for the packet "overhead" is the (first) colon (":"). __*THEN*__ comes a byte which lets us know if it is a standard message (:), or telemetry (T).
So, a message looks like: xxx_Overhead_xxx::message text... (BLN also)
Whereas Telem looks like: xxx_Overhead_xxx:T#telem data...
.... Other restrictions/requirements acepted...
SO... the *second* colon (:) kicks me out of the telemetry bucket and into the message bucket.
If the local digi wasn't ignoring me or down, I could have sent some packets to see this. I had written some code to look at sending messages for EMAIL and APRSLink email, but the data I collected was not raw, but what comes out of the serial port on these radios.
Of course, If I write my own software I CAN send & receive telemetry as a text message with a D7/D700... It just wouldn't show up in the other clients as telem.
> PS. I haven't re-checked aprs101.pdf, but I do believe
> the # is required. ...
As I said, APRS101 that I have (aug 2000) does not mention the #. It only shows it in the example. Therefore, the Telemetry data payload packets MUST begin with "T#nn" (and perhaps "T#n") not just "T" as 101 states.
With the data type definition being the "T" it seems to me that the "#" is redundant and a wasted byte, no?
Thanks, Steve, K9DCI
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