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[aprssig] Local Traveler Repeater Freq Objects

Robert Bruninga bruninga at usna.edu
Thu Feb 1 01:29:47 UTC 2007

> > immediate area, etc. I was told that many of the repeater 
> > owners would simply not authorize the broadcasting of 
> > this information due to concerns about vandalism or jamming.

That is why APRS has always supported position ambiguity.  It
has ambiguity settings of 0.1, 1 and 10 miles.  Just input the
repeater object with an ambiguity of 1 mile.  The format for
ambiguity is simply placing SPACE characters in the least
significant bytes.  

Instead of 3859.11N/07629.11W which is an exact position to 60
feet, instead enter 3859.  N/07629.  W and it will yield only a
1 mile accurate position.  Unfortunately many folow-on
APRSclones never implemented this fundamental principle and will
plot the station INCORRECTLY at 3859.00N/07629.00W which is

Nothing should be plotted there, unless the station is on a map
scale such that the ICON itself is larger than 1 mile.  Then it
can be plotted.  Below that mapscale, it only plots as a circle
of the size of the ambiguity.  This way there is absolutely no
potential for missinterpretation on the receive end.

Only a few APRS clients do it properly.


> Sounds a little paranoid to me, but I know there are guys out
> that get a little nervous about these things.   Any Amateur
> operator worth their salt could find the repeater via
> finding anyway.  But we are digressing a bit...
> >Or perhaps the precision of the coordinates sent out over 
> APRS could be
> >diluted somewhat so that the general location information 
> would still be
> >useful, while helping to allay repeater owners' concerns.
> Definitely not a problem at all.  In this APRS application,
> repeater coordinates do not have to be dead on accurate.  Even
if the
> object is a couple of miles from the actual repeater site, it
> gets the key information out which is the frequency and
> location.  The point is not for users to locate the actual
> site, but rather to get the information necessary to use the
>  This should keep alleviate any of the repeater owners'
> -- 
> A.J. Farmer, AJ3U
> http://www.aj3u.com
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