On Dec 2, 2008, at 1:59 AM, Ulrich wrote: > Message: 6 > Date: Tue, 2 Dec 2008 10:59:05 +0100 > From: "Ulrich Bangert" <[EMAIL PROTECTED]> > Subject: Re: [time-nuts] Thunderbolt settings > > Dick, > to be honest, I did even some more things concerning the TBolt. Find > attached the results of an measurement where the oscillator > disciplining > has been disabled and the internal PPS comparison has been logged over > some time. So it is free running OCXO vs. GPS. The falling slope in > the > left is much due to GPS jitter averaging out with longer observation > times. The ascending slope is much due to the OCXO reacting to > environmental conditions. This measurement would indicate that > 1000-2000 > s is a good value for the time constant. However, I did not have the > heart yet to use such a big value. Neveretheless I use 1200 s TC in my > DIY GPSDO made from an M12+ and an FTS1200. > > I think that also an clarification is necessary what exactly different > manufactures mean by "time constant". I am using the term "time > constant" in the same sense as Stanford Research do in their PRS10 > manual, where they talk about the pll's "natural time constant". > When a > sudden step in OCXO frequency is noticed by the pll it will react > to it > by changing the EFC voltage. It is exactly the "natural time constant" > that the pll needs to bring the OCXO frequency to its original value. > The pll reaction as a whole lasts much longer since it wants to bring > the phase difference back to zero. > > Best regards > Ulrich
Ulrich, thanks so much. I have upped the Loop TC using the TBolt monitor sw to 4000.0 secs, a bit over an hour. I really have no idea what that actually means, but the TBolt seems to be happy. I have no way that I know of to do an Allan Var measurement, so I don't know if this is a sweet spot or not. In the plot (thanks for that) can I assume that disciplining will keep the right end of the slope falling for a while? Dick Moore _______________________________________________ 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.
