[GreenKeys] OT: aprs radio stuff

[Eric]

On 11/26/2013 11:41 am, gil at baudot.net wrote:

> So first question: does anyone have experience with this aprs stuff or
> general packet? Any advice at all?
> 
> When I see a packet on the waterfall, from my MT-400 or from outside,
> I do see the spectral energy clustered between the markers at 1200 and
> 2400 (yellowish), with a bit more energy at the markers (reddish), so
> that makes sense. I can set the MT-400 to key just 1200 or 2200 and
> they both look good on the waterfall as well. When I have the MT-400
> key both, I was expecting to see both, but I see the energy appearing
> at 1700 -- I guess that makes sense.
> 
> However, the decoded packets from me have no lat/long that I can see,
> and some garbled data as well. Is some of the data ascii text and some
> binary?
> 

I find it pretty befuddling too, the whole system seems to have 
developed
over many years by gradual accretion instead of any kind of design :)


> More garbled data, and no lat/long:
> 
> 1:Fm KB7PLO-1 To S3RTSX Via KB0BWG-1*,WIDE2-1 <UI F/R Pid=F0 Len=29>
> [17:00:33R]
> `'Nxl|xv/'"7{}|!%%x'S|!wcd!|3
> 
> No lat/long -- this guy is using a byonics module as well:
> 
> 1:Fm N6BG To APT314 Via KB0BWG-1*,WIDE2-1 <UI F/R Pid=F0 Len=19>
> [17:01:11R]
>> MicroTrak FA v1.42
> 

I believe the "garbled" looking data is MIC-encoded reporting format 
data.
This is a compression method used to squeeze more telemetry into a 
packet
and I guess became mostly-standard at some point. There's some 
discussion
of it in http://www.users.cloud9.net/~alan/ham/aprs/aprs.pdf
but there are probably better references out there.


eric