[aprssig] APRS Telemetry Question
Lynn W. Deffenbaugh (Mr)
ldeffenb at homeside.to
Fri Oct 12 13:42:21 CDT 2012
An APRS message, such as those sent by the APRS-capable radios, is a raw
packet data type of colon (:). A telemetry packet is a raw packet data
type of capital T (T). No, an APRS-messaging radio cannot send telemetry
That said, you might be able to transmit telemetry DEFINITION packets
because those are just specially-formatted APRS message (:) packets.
Transmitting the definitions will allow suitably-capable client
applications like aprs.fi and/or APRSISCE/32 and others to interpret,
scale, and label subsequent telemetry data. However, the client
application in question must be operating when you knob-twiddle and
transmit the definitions. This would be true for aprs.fi which is
(nearly) 24x7, but may not be true of other APRS applications.
Also, here's a quick "anatomy of an APRS packet" that might explain why
the stuff in front of the colon is the same for two different packets.
MYCALL = Source station's callsign (may include -SSID)
> = Humanly readable separator between source and destination calls.
TOCALL = Packet-defined "To" callsign, but used as an "Application
Identifer" in APRS. (Note that this is also replaced with part of the
coordinate information for a Mic-E-formatted position packet)
,PATH1,PATH2 = Requested (or used if * present) path components
: = Humanly-readable separator between header and payload (not to be
confused with the : datatype for an APRS message as that's the first
character of payload)
APRSPacketPayload = The actual APRS packet payload. The first character
describes the datatype of the remainder of the payload.
So, an APRS message will have a ::MSGCALL : as the delimiter and first
part of the payload. A telemetry packet would have :T#nnn as the
delimiter and first part of the payload.
Hopefully this helps. aprs101.pdf is packed with good stuff, but it
takes numerous bed-time readings to grok it all.
Lynn (D) - KJ4ERJ - Author of APRSISCE for Windows Mobile and Win32
PS. I haven't re-checked aprs101.pdf, but I do believe the # is
required. Some clients use the sequence to detect duplicate and/or
missing telemetry packets.
On 10/12/2012 2:18 PM, Steve Noskowicz wrote:
> --- 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.
> 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...:
> 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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