I'll be looking for that blog post. By the way, how did the burnt out EtherDue go? I remember saying after you had taken your last set of pictures that you'd popped it...!
On Mon, Sep 15, 2014 at 6:48 AM, Andrew Rodland <and...@cleverdomain.org> wrote: > Neil, > > I'm working on a blog post now, I'm hoping to have it complete by > Monday or Tuesday. I'll send a followup here when it's posted. > > On Sun, Sep 14, 2014 at 11:47 AM, Neil Schroeder <gign...@gmail.com> > wrote: > > I have nothing constructive to add at this time but I would truly enjoy > > reviewing your design and build logs/notes. > > > > > > > > On Sunday, September 14, 2014, Andrew Rodland <and...@cleverdomain.org> > > wrote: > > > >> Hi all, > >> > >> I've got some figures in from my clock, and I figured I would post > >> them here in hopes of getting some eyes on them and some help with > >> interpretation. > >> > >> Reference is a Spectracom NetClock 9183 with OCXO option. Frequency is > >> good to better than 10^-9, PPS is specified as +/- 50ns. > >> > >> Instrument is an HP 5335A (in lovely condition given that it was built > >> in 1985 according to the serial number) in time difference mode. > >> > >> My clock is quantized at 10MHz, so you wouldn't expect better than > >> 100ns accuracy. But I added -50ns to the offset in software, making it > >> zero in on the edge where the offset is 0 counts 50% of the time and > >> -1 count the other 50%. (Dithering provided by noise in the system and > >> the Resolution-T's own sawtooth). This seems to have worked better > >> than expected. > >> > >> (On a side note: this means that the gain of my control loop is > >> obviously pretty non-linear inside of 1us. Anything I should read > >> about that?) > >> > >> So far I've done two 24-hour runs, one with PLL and FLL constants at > >> 3600s, and one with them at 7200s. > >> > >> Phase plot: > >> 3600s: http://i.imgur.com/LLfYgXe.png > >> 7200s: http://i.imgur.com/zUbgNHc.png > >> > >> Both keep within +/-20ns the majority of the time, which is better > >> than I expected given the specs of both clocks. 1us offset is > >> deliberately added at the PPS output of my clock to make the 5335A > >> happy. > >> > >> Frequency plot: > >> 3600s: http://i.imgur.com/7GoXdoF.png and > http://i.imgur.com/rjBa7gf.png > >> 7200s: http://i.imgur.com/KcyGT3r.png and > http://i.imgur.com/GZH4Pcl.png > >> > >> Both have similar envelopes that seem to reflect the quantization more > >> than anything (100s averaging shrinks the envelopes by very close to a > >> factor of 100x). 7200s looks like it has some kind of oscillation with > >> 2000s period, which is worth looking into. > >> > >> MDEV: > >> 3600s: http://i.imgur.com/RmAcAwT.png > >> 7200s: http://i.imgur.com/xO7aYf9.png > >> > >> ADEV was a perfectly straight line so I didn't bother. MDEV displays a > >> little more structure, but I'm not really clear on the interpretation. > >> > >> TDEV both: http://i.imgur.com/YamRIui.png > >> > >> I like TDEV. Same information as MDEV but since it turns slope=-1 to > >> slope=0 it makes this kind of graph more readable. The two plots are > >> within each other's error bars, so any difference between them might > >> be imaginary, but they depart at 1000s, which probably corresponds to > >> the 2000s oscillation. > >> > >> I guess I'm seeking general input on where I should go next -- do the > >> graphs tell me anything interesting? Should I keep working on the > >> control loop even though it already manages to keep things within half > >> a clock tick? Or should I start looking for ways to reduce the > >> Ethernet jitter since that's the dominant source of error in the use > >> that I care about? > >> > >> Andrew > >> _______________________________________________ > >> time-nuts mailing list -- time-nuts@febo.com <javascript:;> > >> To unsubscribe, go to > >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > >> and follow the instructions there. > > _______________________________________________ > > time-nuts mailing list -- time-nuts@febo.com > > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > and follow the instructions there. > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.