[aprssig] GPS question
Stephen H. Smith
wa8lmf2 at aol.com
Sat Dec 8 15:36:45 CST 2012
On 12/8/2012 4:26 PM, Andrew Rich wrote:
> I am not sure I have asked this before but I will ask it again.
> I have a GPS on the side of a building and it can only see half the sky - to
> the north
> What is curious - is that when plotted on google earth - the postion is north
> of where it should be
> I will move it into full view of the sky and see what that does
> - Andrew -
A gps receiver should be able to function normally WITHOUT seeing the entire
sky; they do this all the time on car dashboards.
Most likely you either have the unit set for a datum other than WGS84 (the
GLOBAL grid system created by and for GPS).
Or the device is being confused by reflections from nearby structures. Since
GPS works by timing the difference in time of arrival of signals from multiple
satellites, multipath reflections that add to path length (and thereby delay
the time of arrival of signals) will translate directly into a shifted
position. In downtown large-city "urban canyons" of glass-faced high-rise
buildings that bounce the 1575 MHz GPS signals every which way, it's not
uncommon to see GPS "go nuts" and jump back and forth several blocks.
-------------- next part --------------
An HTML attachment was scrubbed...
More information about the aprssig