[time-nuts] Z3801A - notes on the hp58533a GPSDO

[David I. Emery]

On Sat, Jan 13, 2007 at 09:01:50AM -0500, Tim Shoppa wrote:
> "David I. Emery" <die at dieconsulting.com> wrote:
> > 	Which leaves the other question,  from reading the 58540A
> > literature, manual and other material available I concluded four years
> > ago that it adjusted the 1 PPS timing to track GPS once locked to GPS by
> > adjusting the EFC for the OXCO (I quite distinctly remember a statement
> > being made in the documentation that the 1 PPS and 10 MHz phase
> > relationship is fixed with no abrupt jumps of one clock tick in the 1
> > PPS or 10 MHz once locked). I have not dug up the documentation recently
> > to see if I can find this statement again, but I am pretty sure that it
> > is true.
> 
> It's true by definition - it is a phase locked loop. You even
> included the correct proviso about requiring lock. Contrast with
> frequency locked loops (which are surprisingly awkward for most
> applications) which seems to be some people's mental models.

	I see your point, an architecture with the VCXO derived 1 PPS
output NOT coherent with the 10 MHz would be somewhat unnatural and hard
to use in a system and presumably virtually ALL GPSDOs do phase lock the
10 MHz to the GPS time base rather than just frequency locking to it.

	There are, however, some subtle differences between a loop
optimized to make the best estimate of 10 MHz possible given the OCXO
used and one optimized to make the 1 PPS the best possible approximation
to UTC.

-- 
   Dave Emery N1PRE,  die at dieconsulting.com  DIE Consulting, Weston, Mass 02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."