[time-nuts] ublox NEO-M8T improved by insulated chamber?

MLewis mlewis000 at rogers.com
Tue Nov 7 16:44:05 EST 2017


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?

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.walenius at 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
> 	gem at 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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