At 02:17 PM 26/03/2003 +1000, Birding Services Brisbane wrote:
I had not used two Magellan GPS units for a few months until last week. I
have had great difficulty getting them to give readings here at Nundah in
Brisbane. They will usually find one or two satellites but not lock in to
a position. Both have new batteries and have been recalibrated. There
are no obvious obstacles in the way - trees, buildings etc. A friend at
St Lucia is also having problems.
Are others having problems too? Is George Dubya to blame?
According to this story on Forbes
http://www.forbes.com/home/2003/03/25/cx_ah_0325gps.html
the US military has no intention of reducing the accuracy of civilian GPS
by restarting Selective Availability (SA) which was turned off in the year
2000. What they can and quite possibly are doing is using jamming to
distort GPS signals over a small area. That shouldn't affect us in Australia.
According to a discussion at
http://slashdot.org/article.pl?sid=03/03/23/2035250&mode=thread&tid=167&tid=99
on Slashdot (slashdot.org - "News For Nerds, Stuff That Matters"), there
are many areas in the world that are having problems with GPS, not due to
jamming, rather because one satellite went dead and hasn't been replaced.
The current plan is to spread out the sats in that orbital ring (the B
plane) to help fill up the gap but that will result in more outages in more
places for short times compared to the current 1/2 hour outages seen
directly in the flight path. The
<http://www.navcen.uscg.gov/gps/default.htm>NavCen
(http://www.navcen.uscg.gov/gps/default.htm) are recommending that you
change your mask angle to 5 degrees if it is set higher (many people use 15
degrees).
You can see the problems on
<http://www.peterson.af.mil/GPS_Support/reports/uclas_world_dop.gif>this
map (http://www.peterson.af.mil/GPS_Support/reports/uclas_world_dop.gif) .
The black areas are where GPS isn't going to give a 3d position and the red
areas are where it wont get a 4d (3d+time) fix. The dark blue will have
issues if any part of the sky is blocked.
Sorry to say that the Pacific coast of northern NSW and southern Queensland
is dark blue... Maybe check your mask angle and see if setting it to 5
degrees makes a difference?
Cheers
Paul Foxworthy
Birding-Aus is on the Web at
www.shc.melb.catholic.edu.au/home/birding/index.html
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