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[aprssig] APRS DF reporting

scott at opentrac.org scott at opentrac.org
Wed Nov 22 18:50:11 UTC 2006

> I disagree, it is a very improtant issue.  Bearing lines have 
> an estimated length relative to the knowledge of the person 
> doing the bearing line.  That information must be included in 

Speaking as someone who once spent a night chasing a marine EPIRB across an
inland mountain range, I disagree.  The COSPAS/SARSAT hit gave a false
impression of where the search area should be, and all of our a priori
assumptions were wrong.  I think I'd prefer to start with a generous
estimate of the maximum possible range and use that.  If the lines all
disappear before reaching convergence, you're searching in the wrong place.

Ultimately, it should be up to the client software to limit the length of DF
lines.  Especially in the case of a SAR operation, you're likely to have
more drivers than skilled DF operators.  Even if you only have one, they
should be at the mapping console interpreting what they're seeing and
directing the searchers.  Having them ride along with an autonomous DF
system that has no user interface other than an on/off switch would be a

For manual DF bearings, there's obviously a little more operator skill
involved.  Still, I don't think it's ever safe to guess at the range.  I've
been on t-hunts where the transmitter was a tiny unit buried underground
with a 19" wire antenna shoved into a dry weed (ok, that was me), and others
where the transmitter was a 60-watt mobile with a 4-element quad pointed
straight at the starting point.

And around here, every once in awhile your kerchunker might turn out to be
someone talking on a repeater in Hawaii...


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