From: "Matt Ettus" <[EMAIL PROTECTED]> Subject: Re: [time-nuts] low-g OCXO GPSDO Date: Thu, 5 Jun 2008 10:25:43 -0700 Message-ID: <[EMAIL PROTECTED]>
> > A "normal" OCXO would drift significantly when being turned around in any > > direction. > > I've actually been wondering about what physical mechanism that causes > this. I could understand how it could cause a phase shift, but I > can't envision the cause of frequency shift. Does anyone know? Anything that deforms the actual crystal will slightly change the acoustical waveequation and thus the frequency. Crystals also deforms due to electrostatics, which have been used by NIST for finegrained phase modulation. The interested can make the exercise to model the crystal in detail by solving the Schröder equations and the various stress mechanism and then how that changes the acoustical waveequations. It's that "simple". :) Actually, today I have been looking for articles relating to Kalman filter estimation of exponential frequency drift. The traditional phase, frequency and frequency drift does not match data very well. Curve-matching shows much better aggrement with exponential frequency. However, normal curve-matching does not match well with real time estimation. Most articles seems to use the linear drift. Ah well. Cheers, Magnus _______________________________________________ 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.
