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[aprssig] APRS Telemetry Question

Heikki Hannikainen hessu at hes.iki.fi
Fri Oct 12 18:45:58 UTC 2012


On Fri, 12 Oct 2012, Steve Noskowicz wrote:

>  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.

Ok, that's just a text message. You can't put telemetry data there.

You can use it to transmit the coefficients and parameter names, though.

>  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'.

Can send parameter names ("Channel is Temperature") within a text message.

Cannot send telemetry data ("Current temperature is 10").

> 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?

No.

> 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".?

Telemetry looks like this in the raw packets:

2012-10-12 10:13:37 UTC: 
KI6TSF-8>APOTRS,N6ZX-3,WIDE1*,qAR,K6MJW-10:T#27,018,021,050,010,000,00000000

A text message looks like this:

2012-10-09 06:47:56 UTC: 
DO2ML-9>APDR11,TCPIP*,qAC,T2TUENL::DJ1JAY-14:GUGGUG{3

Note that the first : after the packet path is just a separator character 
to separate path and the packet's data. The second : in the above text 
message is actually within the packet's data portion, and it tells us it's 
going to be a text message, and the recipient callsign follows that.

> Q: Is the "#" required or optional?

It's required.

> 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?

Depends on the recipient, but it shouldn't be completely ignored - it 
should be used to drop old packets which arrive out of order.

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

APRS101.pdf can be confusing at times, I can agree with that. :)

Bulletins are actually sent using the same format as text messages, they 
only have BLN as the first three characters of the recipient callsign. 
Compare http://aprs.fi/bulletin/ with the raw packets of the stations 
transmitting those.

   - Hessu




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