[time-nuts] Trimble Resolution SMT GG weirdness

[David]

On Tue, 23 Apr 2013 19:05:53 +0200, Attila Kinali <attila at kinali.ch>
wrote:

>On Tue, 23 Apr 2013 09:49:19 +0400
>Daniel Ginsburg <dginsburg at gmail.com> wrote:
>
>> Not perfect, but should be reasonably good. It's an external magnetic antenna on my windowsill.
>> Anyway, +-400ns I'm seeing translates to +-120m in position. My surveyed location is better than this.
>
>Windowsill? So you have only partial view of the sky?
>Then those 400ns sound about right. Said Jackson reported a couple
>of months back that a LEA-6T showed about 1us (IIRC) jitter until
>he avaraged the position for a couple of days (weeks?) to get the
>real position. After that, the jitter was much better.
>He also send some nice graphs of those measurements. You might want
>to look for them in the archives.
>
>			Attila Kinali

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.
:)

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.

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