On 11/7/17 1:44 PM, MLewis wrote:
Yo Gary!
With a strictly SSE skyview, I still regularly get signals from sats to
my NW. When they're at the right elevation and heading, their signals
pass over me and reflect back at me from a tall building. When running
my M8T with the position unlocked, and those NW sats are getting a
reflection and reporting in, (although the reflecting building is
further away to the SE) my GPS position drifts up to 300' to my south (S
of SSE). (reported position goes for a walk, staggering across the
parking lot, wanders through a park with an occasional loop, across a
road, then sits down for a while, before wandering back)
Is it reasonable to use the 9" ~= 1 ns for:
running with a fixed & correct survey position, and NW sats reflecting a
signal to me, that 300' drift would equate to a (300' x 12") / 9" =
400, for a ballpark 400 ns error?
No.. in free space it's about a foot per nanosecond.. 9" is 0.75
velocity factor, reasonable for coax, for instance, depending on the
dielectric.
Thanks,
Michael
On 07/11/2017 3:40 PM, Gary E. Miller wrote:
Yo Lars!
On Tue, 7 Nov 2017 20:32:19 +0000
Lars Walenius <lars.walen...@hotmail.com> wrote:
Another question: If You have an error in the surveyed position of
say 3meters and you receive all of the available satellites in all
directions how much will this really affect your timing?
I'll oversimply a bit by repeating Adm. Grace Hoppers famous giveaway.
When asked, she handed out 9 inch long peieces of wire, and said: that
is a nanaosecond.
3m is about 118.11 inches is about 13 ns. So worst case, skipping the
3D math, yoy get about +/13 ns.
Which is small compared to the published GPS time resolution
(IS_GPS_200H,
page 54) of 90 ns.
RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
g...@rellim.com Tel:+1 541 382 8588
Veritas liberabit vos. -- Quid est veritas?
"If you can’t measure it, you can’t improve it." - Lord Kelvin
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