Hi Adrian, Actually no. This ADEV is a plot of the sawtooth-corrected 1PPS signal from the GPS receiver (LEA-6T) measured by the TIC in my GPSDO against the output of its OCXO.
Bob ________________________________ From: Adrian <rfn...@arcor.de> To: Bob Stewart <b...@evoria.net>; Discussion of precise time and frequency measurement <time-nuts@febo.com> Sent: Tuesday, September 2, 2014 11:24 AM Subject: Re: [time-nuts] OCXO Phase Noise Measurement in Primitive Conditions Bob, to me your ADEV plot looks pretty exactly like a measurement system noise floor plot with its typical 10/decade shape. I would assume that you connected the same signal to both counter inputs, or, both sources have been phase locked. Adrian Bob Stewart schrieb: > Hi Bob, > > I take it that the 3 segment ADEV pretty much defines a GPSDO. So, is my > plot an indication that I'm riding the OCXO too hard to get the results I > think I should be getting? What I think I should be getting is a flat phase > line. But is a GPS receiver, even after applying quantization error > corrections, accurate enough to give that? I see three things at play here: > hardware, software, and my expectations. I'm trying to figure out which one > (or several) of these needs to be addressed. I suppose I could hook the Rb > back up and see the effect on the ADEV of the Rb vs OCXO as I loosen the gain > values. > > > Bob > > > > ________________________________ > From: Bob Camp <kb...@n1k.org> > To: Bob Stewart <b...@evoria.net>; Discussion of precise time and frequency > measurement <time-nuts@febo.com> > Sent: Tuesday, September 2, 2014 6:38 AM > Subject: Re: [time-nuts] OCXO Phase Noise Measurement in Primitive Conditions > > > Hi > > Your ADEV is (mostly) a plot of 1-2 ns resolution out over your sample range. > It’s not a “typical” three segment ADEV. It’s more likely that any departure > from a straight line is random rather than systematic. Yes I’ve spent a lot > of time looking at random plots that I was *sure* had significant information > in them….. > > Bob > > > On Sep 1, 2014, at 9:31 PM, Bob Stewart <b...@evoria.net> wrote: > >> Hi Poul, >> >> I've made a few hardware changes and some software changes, and I was >> wondering if you (and/or others) would take a look at this plot. The green >> is phase over 70,000+ seconds with ~100ps resolution, while the blue is the >> ADEV. (The sharp departures in phase are from large temperature changes and >> not quite perfect temperature compensation software.) I don't see your >> horizontal line down at the bottom, but there are some worrying horizontal >> lines between about 3tau and 150tau. Should I take that to mean that I have >> some noise/oscillations from about 1/3Hz to 1/150Hz? Those up at about >> 150tau I think I can see by eye on another plot of different data. I've got >> a lot of data collected from this run (still running) including pTerm, >> iTerm, dTerm, and tTerm (temperature) updates to the DAC. I hope to try to >> tease something out of that later, though the pTerm and iTerm are mostly >> +1,0,-1 stuff. FWIW, in real terms, the dGain is at about 4.2. The phase >> starts to get ugly if I bring it much below that. iGain is .01 and pGain is >> .05. There are misc damping and limiting factors applied, as well. >> >> >> Just about ready to do a second board with updates from what I've learned, >> so any help is appreciated. The plan is to release the source code at some >> (not too) future date and make boards available, if there's interest. But >> I've still got a lot to do before that. >> >> >> http://evoria.net/AE6RV/TIC/ADEV3.png >> >> >> Bob >> >> >> >> >> ________________________________ >> From: Poul-Henning Kamp <p...@phk.freebsd.dk> >> To: Bob Stewart <b...@evoria.net>; Discussion of precise time and frequency >> measurement <time-nuts@febo.com> >> Sent: Thursday, August 28, 2014 1:04 AM >> Subject: Re: [time-nuts] OCXO Phase Noise Measurement in Primitive Conditions >> >> >> -------- >> In message <1409175707.2080.yahoomail...@web142706.mail.bf1.yahoo.com>, Bob >> Ste >> wart writes: >> >> This looks like a step in the right direction. >> >> The "correct" allan plot will have a clearly visible horizontal >> segment somewhere in the 100-10000 second range (depending on OCXO quality). >> >> This is where the GPS long-term stability "takes over" from the OCXO's >> better short-term stability. >> _______________________________________________ >> 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.
