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[aprssig] APRS 101 Perhaps this'll work...

Steve Noskowicz noskosteve at yahoo.com
Tue Nov 27 23:16:01 UTC 2012


 

The coeficients are in another message.  A clear version of trhe spec couldn't hurt, but the Telem section of the spec is one of the easier to understand, though it still has some details poorly explained.

Summary:
Telem takes several messages.
One for the parameter names.
One for the coeficients of that equation.
One for the units.
One for some binary bits of data.

THEN you send the actual data.

I'd paste the spec section here, but there are tables that get all goofed up, even in Word.  I copied a bit here   Steve, K9DCI

Telemetry Report Format

The AX.25 Information field can contain telemetry data. The APRS Data
Type Identifier is T.
The report Sequence Number is a 3-character value — typically a 3-digit
number, or the three letters MIC. In the case of MIC, there may or may not be
a comma preceding the first analog data value.
There are five 8-bit unsigned analog data values (expressed as 3-digit
decimal numbers in the range 000–255), followed by a single 8-bit digital
data value (expressed as 8 bytes, each containing 1 or 0).
The Kantronics KPC-3+ TNC and APRS Micro Interface Module (MIM) use

On-Air Definition of Telemetry Parameters

In principle, received telemetry data may be interpreted in any appropriate
way. In practice, however, an APRS user can define the telemetry parameters
(such as quadratic coefficients for the analog values, or the meaning of the
binary data) at any time, and then send these definitions as APRS messages.
Other stations receiving these messages will then know how to interpret the
data.
This is achieved by sending four messages:
• A Parameter Name message.
• A Unit/Label message.
• An Equation Coefficients message.
• A Bit Sense/Project Name message.


----------------------------------------------------------
--- On Tue, 11/27/12, Dave B <dave at g8kbv.demon.co.uk> wrote:

> Can't get near that APRS101.pdf doc,
> all our AV/antimalware screams at 
> me, and blocks downloads of PDF's from that
> site!   Odd...  (Unless 
> something has got in to that file?)
> 
> But get the overall drift of what is needed it from your summary.
> "value = A x v^2 + B x v + C" where 'v' is the value sent in the 
> telemetry packet.
> 
> Perhaps that info could go in the document too, to be complete, with 
> perhaps a reference link to the APRS101 document.
> 
> Regards.
> 
> Dave G0WBX.
> 
> On 26 Nov 2012 at 17:38, J T wrote:
> 
> > 
> > Those are the standard APRS telemetry coefficients.
> Refer to page 70
> > of the APRS spec:
> > ftp://ftp.tapr.org/aprssig/aprsspec/spec/aprs101/APRS101.pdf
> > 
> > To summarize: the value = A x v^2 + B x v + C, where
> 'v' is the value
> > sent in the telemetry packet (packet type T).
> > 
> > --- On Mon, 11/26/12, Dave B <dave at g8kbv.demon.co.uk>
> wrote:
> > > http://aprstw.blandranch.net/Telemetry%20Parameters.pdf
> > 
> > Hi.
> > 
> > What do the figures in the EQNS columns relate to?
> Multipliers, 
> > divisors, dB corrections, or ???
> > 
> > Nice to have all that in one place, but more info
> needed please as to
> > how to use that info, WRT data received off air, to get
> the value
> > monitored, however that is done.
> > 
> > 
> > 
> 
> 
> 
> 
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>
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