[time-nuts] Trimble Resolution SMT GG weirdness

[Attila Kinali]

On Tue, 23 Apr 2013 14:36:45 -0500
David <davidwhess at gmail.com> wrote:


> I always suspected something like this was at work.
> 
> This would explain the ambiguous 1uS specification common in GPS
> receivers that are not intended for rigorous timing applications which
> I asked about a couple months ago.  I did not ask the right question.
> :)

There is more to that than just sky view. Navigational and timing
receivers differ slightly in the way they solve the equations.
How and what exactly, i don't know, but guess it's optimizations
for the common use case in timing receivers (fixed position, high
precision time but low precision position required)
 
> With this in mind, I would assume that averaging over multiples of 12
> hours would be necessary for maximum accuracy and days would be
> required to account for atmospheric transmission effects.  Now I have
> a much better idea about how good the disciplined oscillator will need
> to be.

If you go for 12h integration time, you have to have a very good
temperature compensation (ofcourse under the assumption you have
a very stable oscillator in the first place).

> A receiver intended for timing applications using position hold should
> allow accurate locking in a hundredth the time or less.

I think you overestimate what a timing receiver can do and what not.
You cannot compensate for atmospheric effects with just a single
frequency receiver unless you use WAAS/EGNOS/... and even that is
not super accurate. For reference, u-blox specifies their timing models
as being within +/-40ns and their navigational models being within +/-100ns.
>From what i know about how these things work, that factor two is about
what i would expect in imporvement in precision, probably even less.
(those numbers are under "ideal" conditions, with good antenna position)


			Attila Kinali
-- 
The people on 4chan are like brilliant psychologists
who also happen to be insane and gross.
		-- unknown