[aprssig] Q: What's the Omni DF Formula

[Robert Bruninga]

> Reading the spec, I see the PHG circle 
> formula, but not the Omni DF circle formula.  
> Can anyone provide it?

Its in the original docs: http://aprs.org/APRS-docs/DF.TXT

> I made an Excel spreadsheet with a nifty 
> bubble chart and somewhat of a size 
> approximation, but would like to use the 
> formula that is (hopfully) determined by 
> more than my (highly, of course) educated guesses.

Basically a not-heard circle is the same size as the PHG circle.
As the signal gets stronger, the circle size gets smaller
because obviously the signal has to be closer.
Actually, it is the same at the PHG calculator, but instead of P
for Power, let P = 10/S where S is the reported signal strength.
For S = 0, I think I forced it to S=.5 to avoid a singularity.

So a signal report of 1, is the same as a PHG circle for a 10W
station.
A signal of 2 is the same size as a PHG circle for a 5W station
and so forth.

Please note, that years back, in APRS1.1, the size of the PHG
circle was HALVED for display of actual mobile ranges.  Iin this
case, for DFS, do not divide the circle by half.

Bob, WB4APR
> 
> FINALLY, an up to date APRS Beginner Guide - 2009.
> Direct link:
> http://k9dci.home.comcast.net/APRS Beginner Guide - K9DCI Ver
5-1.pdf 
> OR
>   http://K9DCI.home.comcast.net 
>     Click the APRS Beginner INFO link under Contact
> 
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> 
>   http://k9dci.home.comcast.net/
> 
> 
> --- On Sun, 7/19/09, Heikki Hannikainen <hessu at hes.iki.fi>
wrote:
> 
> > From: Heikki Hannikainen <hessu at hes.iki.fi>
> > Subject: Re: [aprssig] Q: NOGATE Method(s)
> > To: "TAPR APRS Mailing List" <aprssig at tapr.org>
> > Date: Sunday, July 19, 2009, 10:37 AM
> > On Sat, 18 Jul 2009, Steve Noskowicz
> > wrote:
> > 
> > > Steve Dimse <steve at dimse.com>
> > wrote:
> > >> !x! was implemented as a shorthand for the
> > internet standard...
> > >> 
> > >> ...I implemented it in findU...as a way to allow
> > hams to
> > >> opt out of having their positions stored on findU,
> > ...
> > >> Years ago we settled on NOGATE and RFONLY...
> > > 
> > > I was hopin' cuz' on the D700 & D7 changing
> > between two different status texts is easier than the
> > path.  No biggie.  Easier to remember anyway.
> > 
> > I hadn't seen this in any of the specifications, so it's
> > not implemented in aprs.fi yet. It seems useful, so I'll put
> > it in the code now. Is it documented somewhere else than the
> > mailing list archives?
> > 
> > The feature doesn't seem to be really used, I only have a
> > single station in my database using it, and it has last
> > transmitted in May 2009. I'll delete that track now. :)
> > 
> > Steve Noskowicz should make a note that Steve Dimse said:
> > 
> >   "I added !x! in order to allow mic-e users to add it
> > to their comment text... "
> > 
> > That's *comment* string, not the *status* message. They're
> > two different things. The comment is transmitted together
> > with position packets, and our server-side software can
> > conveniently drop the position packet if !x! is seen in the
> > beginning of the comment text. The separate status packet
> > might be only transmitted much later, or it might be lost.
> > 
> >   - Hessu, OH7LZB
> > 
> > 
> > _______________________________________________
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> > aprssig at tapr.org
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> > 
> 
> 
>       
> 
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