Hi Richard: I neat idea.
I would think there are three key measurements: TI1 = GPS-A TI2 = GPS-B TI3 = A-B Of these A-B is the most precise and the other two with GPS involved are much lower stability. In your proposed method only the poor time intervals are being measured. So I would think the approach would be make all three measurements at the same time then in a perfect world you could solve three equations in three unknowns. But I suspect that the errors will not exactly balance. So you could split the closing error in two and assign half to A and half to B. Have Fun, Brooke Clarke http://www.prc68.com/P/Prod.html Products I make and sell http://www.prc68.com/Alpha.shtml All my web pages listed based on html name http://www.PRC68.com http://www.precisionclock.com http://www.prc68.com/I/WebCam2.shtml 24/7 Sky-Weather-Astronomy Web Cam Richard H McCorkle wrote: > Hello Time-Nuts, > I am currently disciplining two MTI260 oscillators in a > dual standard to a common GPS timing receiver 1PPS with > two highly modified Shera style controllers that use a > 100 MHz TIC with sawtooth correction and a 23-bit DAC. > Phase samples are accumulated over identical 30-second > periods between updates and the updates are logged over > identical sample intervals from both controllers using > a common receiver. When the phase data from the two > controllers are compared there is a striking similarity > in the short-term phase variations in both data sets > when both oscillators are locked. > Extreme care was taken to minimize coupling between > the oscillators by using separate power supplies, > physical separation, and shielding of the two systems > and their associated wiring. Intentionally varying the > frequency in either of the oscillators has no visible > effect in the phase data from the other oscillator so > I don’t believe injection locking is occurring between > the oscillators. > The MTI260 has very good short-term stability so I am > assuming the short-term phase variations of nanoseconds > per update seen in both data sets are predominantly the > result of changes in the GPS 1PPS timing. I am wondering > if anyone on the list has explored the concept of using > the common phase variations from multiple disciplined > high-stability oscillators driven from a common GPS > receiver to determine the actual GPS variation (using a > 3-corner hat analysis) and apply that information in the > disciplining routines to improve oscillator short-term > stability. > I am considering a methodology of doing comparisons of > A to GPS in controller A, B to GPS in controller B, and > then having the two controllers share their phase data > and do a comparison in each controller to determine the > common GPS variation and correct the raw phase data before > calculating the EFC. Each controller outputs the combined > phase effects of the GPS and its oscillator and by sharing > the phase data between two controllers fed by a common > receiver I believe the GPS variations in the raw phase > data could be eliminated using simple PIC math as shown > in the following equations using Gp as the GPS phase, Ap > as the A oscillator phase, and Bp as the B oscillator phase. > > Controller A raw phase data = (Gp + Ap) > Controller B raw phase data = (Gp + Bp) > Difference in readings = (Gp + Ap) – (Gp + Bp) = (Ap – Bp) > A reading – difference = (Gp + Ap) – (Ap – Bp) = (Gp – Bp) > B GPS difference = (Gp + Bp) + (Gp – Bp) = (Gp * 2) > GPS phase data = (Gp * 2) / 2 = Gp > Controller A corrected phase data = (Gp + Ap) – Gp = Ap > Controller B corrected phase data = (Gp + Bp) – Gp = Bp > > One concern I have is a 3-corner hat is generally > performed on three sources of similar stability. In > this case the short-term stability of the two MTI260 > oscillators will be much better than the GPS short-term > stability and I am questioning how valid the data will be. > I would appreciate any comments on the concept, flaws in > the methodology, or pitfalls that might result during > implementation before I attempt this in a working system. > > Thanks for your input, > > Richard > > > > > _______________________________________________ > 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.
