When applied to meter movements this is called geotropism. Robert G8RPI
--- On Fri, 14/8/09, Magnus Danielson <[email protected]> wrote: > From: Magnus Danielson <[email protected]> > Subject: Re: [time-nuts] Gravity and OCXOs > To: "Discussion of precise time and frequency measurement" > <[email protected]> > Date: Friday, 14 August, 2009, 9:02 AM > Murray Greenman wrote: > > Rick is right. > > > > The effect you see when turning your GPSDO upside down > will be > > predominantly the direct gravitational effect on the > OCXO crystal and > > its mountings. You see this with any OCXO, and the > good ones will have a > > '2G turnover' or other G rating quoted. > > > > For example, the well known HP 10811A specification > says 'Gravitational > > Field: <4 x 10^-9 for 2g static shift (turnover). > That's fairly typical. > > > > I just measured the effect on a good C-MAC 10MHz OCXO > (similar to those > > used in many recent GPSDOs) and measured 40mHz p-p, or > exactly 4e-9. > > > > It's complicated in the GPSDO because the correction > mechanism (via GPS > > 1pps) is much slower than the rate at which you can > change the > > gravitational effect. Rb references simply have a > faster loop and will > > correct the G effect more quickly. > > If you care about that speed, you use GPSes which has > higher speeds and you don't use a PPS since as you pointed > out is unfit for it. Also, if you care about it, you'd use > sensors to sense the gravity and use that for the bulk > adjustment, if a low sensitivity crystal isn't enought or > available in matching specs. > > The PPS is just an arbitrary limit. > > 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. > _______________________________________________ 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.
