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 -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
