[Xastir] Question about APRS GPS position precision

[Richard Polivka, N6NKO]

Jim,

Most GPS units are good to 4 decimals. Any higher precision requires 
post-processing or L1/L2 reception (not avail in consumer equipment). 
When you factor in multipath and all the other variables, 4 decimals is 
quite good but it takes time and patience - think searching for a 
geocache in a forest. Plus, at four decimals, on a patch antenna minus 
ground plane, it is quite unstable.

Plus, I have a feeling that when Bob B. designed APRS, he was not 
looking at this being used for what we are doing.

Until the data output is smoother and better accuracy, five decimals in 
- broadcast 4 - rewrite the standard, this may be the best for now.

73 from 807,

Richard, N6NKO


Jim Tolbert wrote:
> Hi, all..........
>
> I have been told that the limiting factor in position precision is the 
> APRS system transmission standard-- that transmissions are limited to 
> 1/1000th of a degree or approximately +/- 60 feet.   Is this true?  If 
> so, why?
>
> If not, what is the limiting element in the final display of tracker 
> position on Xastir?
>
> For those of you using Xastir for Search & Rescue, do you run on the 
> APRS frequency or a different (quiet) frequency?   What are the 
> arguments for each school of thought?   We are going to be running 
> some field tests in the near future with a variety of equipment 
> setups....  does anyone have suggestions of things we should test?  We 
> have a list, but new ideas and comments would be appreciated from 
> those that have already taken the stumbles<grin>.
>
> Many thanx.............. jt
>