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[aprssig] Automatic omni DF query

Scott Miller scott at opentrac.org
Mon Feb 9 20:00:43 UTC 2009


That's the 'optional footprint' part, which is defined in the APRS spec 
- not sure how much it's supported, though.

Scott
N1VG

Wes Johnston, AI4PX wrote:
> On the tracker side, we need to think about making sure we limit "who" 
> will answer.  querying every tracker in the world and then them 
> answering could be akin to a DDOS attack, eh?
>  
> Maybe we need a range parm on the tracker to limit it's range to 100km 
> by default from the query station?  Of course it could/should be user 
> adjustable, but default low.
>  
> Wes
> 
> On Mon, Feb 9, 2009 at 2:44 PM, Scott Miller <scott at opentrac.org 
> <mailto:scott at opentrac.org>> wrote:
> 
>     My new T2-301 trackers are frequency-agile and can measure incoming
>     signal strength, so it occurred to me that it'd be useful to define an
>     APRS query that'd cause all capable stations to QSY their receive side
>     to the specified frequency for a second, take a reading, and then come
>     back and report what they heard in omni-DF format.
> 
>     Before anyone asks, these particular units won't work for 121.5 - I've
>     only been able to get them to receive as low as 127 MHz.
> 
>     Based on some experimentation with a service monitor, it looks like the
>     usable RSSI range is roughly -128 dBm to -68 dBm.  If I'm reading my
>     conversion chart right, for a 50-ohm system that's a little more than
>     the standard S0-S9 range.  Seems kind of low at the top end, but I'll
>     have to do some field testing and see what I get.
> 
>     What I'm thinking of is something like this:
> 
>     ?DF146.520?<optional footprint>
> 
>     The response should be a DFSshgd omni-DF extension followed by the
>     frequency.  I'd prefer the frequency to be a standard part of that
>     response, so clients could be made smart enough to separate out multiple
>     DF plots.
> 
>     Comments or suggestions?
> 
>     Scott
>     N1VG
> 
> 
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> 
> 
> 
> -- 
> Wes
> ---
> Where there's silence, there is no Hope.
> 
> 
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