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[aprssig] APRS Telemetry Question

Steve Noskowicz noskosteve at yahoo.com
Fri Oct 12 18:18:49 UTC 2012



--- Heikki Hannikainen wrote, that Steve Noskowicz wrote:
> > Q:  Is Telemetry a standard APRS message? ...
> 
> Well, it's a standard APRS message / packet (that's a
> slightly ambiquous wording), but telemetry data is not
> transmitted in a TEXT message or bulletin. It's an APRS
> packet type of it's own, starts with a T# (text messages
> start with a ':').

Let me try this from another perspective:

  With these radios we can send what I call a "standard APRS text message" via the knob-twiddle method or an added keyboard/W2FS-adapter.
  Now...
  All the data in "telemetry messages" is ASCII, so... My intent of this question is to determine whether the D700/D7 radios can send a telemetry 'message'.
  These radios *also* allow a "stardard APRS text message" to be sent by sending the text into the serial port using an all ASCII message command "AMSG 00,...".  The text following that command is a text message and the rest of the packet is whatever is appropriate for a "standard APRS message".
  _If_ the only difference is that the Telem message starts with T and sequence number, then these radios can do it.


Q:  One way to re-word this question is:  If, on a D700, I send a message via the knob-twiddle method that starts with T#001, then comma sep groups of 3 ASCII digits, would it be interpreted as Telemetry?  OR, is there some other "sfuff" in a "true" Telemetry packet that distinguishes it as Telemetry and NOT an ordinary message? - OTHER than the fsct that the message is 'to itself".?


I also see some inconsistencies...
  APRS 101 says a Telem msg starts with a "T" and a three character sequence number, but shows "T#xxx" and does not mention the "#" character elsewhere.   
Q: Is the "#" required or optional?

Q:  I also see that KI6TSF-8 has only 2 characters in the sequence numbers, so aparently the telemetry sequence number length is not fixed, and possibly ignored anyway...no?


> On the other hand, telemetry channel names and coefficients
> are sent in APRS text messages 

APRS 101 mentions bulletins....making this confusing.



> If you wish to see what each packet decodes to...:
> http://aprs.fi/?c=raw&call=OH7RDA&limit=50&view=decoded

  As I look at KI6TSF-8 packets, I see that everything up to and including the ":" is the same for the Wx and Telem packets.  This sugests that the only difference between WX, Telem and ordinary messages is the payload (and the destination since a real message goes to another call).  Therefore it appears that Telemetry is simply a regular APRS message with a correctly formatted payload portion...  no?


73, Steve, K9DCI



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