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

Gary E. Miller gem at rellim.com
Tue Nov 7 17:42:50 EST 2017

```Yo MLewis!

On Tue, 7 Nov 2017 16:44:05 -0500
MLewis <mlewis000 at rogers.com> wrote:

> 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)

Yeah, one of my test locations has similar issues.  It leads to some
'interesting' results.

> 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?

I think it is reasonable as a worst case.  Basically a 1D model of a
3D problem.  With good sat angles, the 3m location change will be
trigonomically smaller for a sat at an angle.

But, as I said, given that GPS only resolves to 90 ns, the worst case
+/- 13 ns is noise.

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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