[time-nuts] ✘NEO-M8N vs. NEO-M8T

Achim Gratz Stromeko at nexgo.de
Mon May 21 14:41:23 EDT 2018


Gary E. Miller writes:
> Which I always thought was pointless, that only works for a fixed
> antenna.  Any GPS in a fixed position lab will have a good rooftop
> antenna with clear skyview.

Except when it doesn't and then the ability to survive on fewer
visible/good satellites without going into holdover is most welcome.

> Except that requires a post process step, so not useful for real time.

No, you can very much use it to inform a consumer of the PPS in realtime
about the sub-quantization phase shift and have the PLL take this error
refinement into account.

> I just looked at the 'U-blox 8 Receiver Description' and it makes no
> mention of sawtooh anything.  Is that in a different doc?

No, it's in there, look for the UBX-TIM series of messages, specifically
TOS and TP.  However, it talks about offsets of the time pulse, not a
sawtooth.

But there's a more specific description for series 6 timing receivers,
most if not all of which will be applicable to your series 8 module as
well:

https://www.u-blox.com/sites/default/files/products/documents/Timing_AppNote_(GPS.G6-X-11007).pdf

> I'll also test Surevey-In mode to see how much that helps.

_Any_ error in the surveyed position will show up as timing error that
also depends on the GPS constellation.  I think Lady Heather provides a
special plot to map these deviations to the GPS sky tracks.


Regards,
Achim.
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