[time-nuts] ublox NEO-M8T improved by insulated chamber?
jimlux at earthlink.net
Tue Nov 7 21:14:11 EST 2017
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
> 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
>> page 54) of 90 ns.
>> 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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