[time-nuts] New to list and GPSDO questions

[Richard H McCorkle]

Chis,

Over time without phase correction the analogy would be more like
zig to the right, correct to go straight, zig to the right, correct
again, and keep repeating this sequence ad infinium as the source
ages in predominantly one direction. Each time the phase shifts in
the same direction and before long you are on a different road a
full clock cycle to the right and continuing to shift in the same
direction. The total number of clocks over the period has changed
from the ideal even though the average frequency has been correct.
So over the short-term the right number of cycles occur, but over
the long term there is an increasing error from the ideal number
of clock cycles as the period increases.
  If all you need is a frequency that is stable over short periods
then the phase is of no concern. But when using a scope or TIC to
compare a device under test (DUT) to the reference to determine its
Adev over longer periods then you need the phase of the reference
to be constant over the maximum measurement period (typically 4-5
days for a 1-day Adev value) to determine the DUT long-term drift.
  By keeping track of the total accumulated count from an arbitrary
starting point (i.e. when the reference sample is taken) and adding
6800 HEX each update the reference count would represent the ideal
count after X updates if no drift had occurred. Comparing the
current count to this ideal gives the total change since the
arbitrary reference was first stored. By adding steering to keep
the actual sample count at the ideal value then over the long-term
there would be no drift as it would be corrected out. The actual
phase to GPS isn't the important factor - the change in the phase
over long periods (like a day or week) is as it represents an error
in the total number of counts over that period and a reduction in
the long-term stability.

Richard


>
> I'm with Bob in that I don't really understand this description.
>
> And what are we trying to be in phase with? the 1PPS?
> Is it possible to reproduce the actual phase of the
> clock in the GPS birds once it has been through my GPS
> and come out as 1PPS?
>
> I picture the EFC steering the car straight down the road.
> And you want to adjust not just the drift to the right but
> steer back to the center of the lane.  I think I get
> that part.  I don't get who is setting the lane
> and why I should care.
>
> Do the statistics (ADEV, etc.) show that this is an improvement?
> If I'm doing my slow zigzag down the center line or the
> right shoulder, again, do I care?
>
> Chris
> w0ep
>
>
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
>