Magnus Danielson wrote: > Dick, > > Richard Moore skrev: > >> On Jan 8, 2009, at 2:58 AM, [email protected] wrote: >> >> >>> Message: 6 >>> Date: Thu, 08 Jan 2009 11:51:50 +0100 >>> From: Magnus Danielson <[email protected]> >>> Subject: Re: [time-nuts] GPSDO time constant >>> To: Tom Van Baak <[email protected]>, Discussion of precise time and >>> frequency measurement <[email protected]> >>> For ThunderBolt owners it is pretty straightforward to adjust the >>> TC and >>> damping, which is very nice. Use this oppertunity! >>> >> So, Magnus (and Tom), what damping factor do you suggest for a TBolt? >> I'm running a verrry long TC now. If 1.2 is not actually critically >> damped, what value would be? Any guesses? BTW, I really like that >> plot of Tom's that tracks the oven and then gets better from the GPS... >> > > Assuming that damping factors match classical analysis of damping, then > the square root of 2 is the answer... 1.414 or there abouts. > > I would be more conservative than that. I would consider damping factors > such as 3-4 or so. I have no support from measurements on GPSDOs but it > is reasonable that the rise of gain at and near the PLL frequency we see > for other systems will occur and result in similar effects even here. > This gain raises the noise floor and amount of gain is directly coupled > to the damping factor. It's just standard PLL stuff all over again. The > only difference is that we view the result in ADEV or MDEV views. > > Cheers, > Magnus > > Hej Magnus
For a second order loop, the noise bandwidth is minimised for a fixed time constant by choosing a damping factor of 0.5. Using a damping factor of 1.414 increases the noise bandwidth by about 60%. Using a damping factor of 0.7071 only increases the loop noise bandwidth by about 6%. A damping factor of 0.3 increases the noise bandwidth by about 13%. Bruce _______________________________________________ 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.
