[aprssig] Automatic omni DF query

Wes Johnston, AI4PX wes at ai4px.com
Mon Feb 9 13:50:32 CST 2009

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.


On Mon, Feb 9, 2009 at 2:44 PM, Scott Miller <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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Where there's silence, there is no Hope.
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