I have a number of revisions of the John Vig tutorial in my Manual pages. The most recent was sent to me directly by John but I am not sure if it has the notes. www.ko4bb.com Go to Manuals and search for Vig
Didier KO4BB On Thu, Sep 26, 2019 at 7:03 AM Chris Caudle <[email protected]> wrote: > On Wed, September 25, 2019 5:45 pm, Taka Kamiya via time-nuts wrote: > > discussions take place both for GPSDO with Crystal Oscillators and > > Rubidium modules. It appears there are two types of each. > > 1) fixed frequency type (less jitter) > > 2) frequency agile type (more jitter) > > That is a bit oversimplified. GPSDO is "GPS disciplined oscillator," > meaning that the output frequency of the oscillator is forced to follow > the inverse of the time measurements derived from the Global Positioning > System. > Obviously if the oscillator has to follow another reference it cannot > truly be fixed frequency on the output, but there are various different > ways that the frequency can be varied. Depending on the important > parameters for your needs the differences in mechanism may or may not be > important. > > > I've read frequency agile Rb modules (ones you can change output > > frequency) is one kind of Rb (sa.22c and fe5650, etc), and there is > > another one that you cannot change frequency. (ie. T-bolt, PRS10, etc). > > You are mixing different types of equipment together, so it is a little > difficult to know what you are asking. > FE5650, PRS10 and SA.22C are rubidium frequency standards. A rubidium > frequency standard is fundamentally an OCXO which is slaved in a frequency > lock loop to a way to measure atomic transitions in rubidium vapor. There > are various systematic errors which pull the frequency of that atomic > transition measurement, so a rubidium standard will commonly have an > adjustment mechanism that can adjust the output frequency far enough to > compensate for those systematic errors, but you need a more accurate > device for comparison for that adjustment to be worthwhile. > > A Thunderbolt is a complete GPS disciplined oscillator system which > accepts GPS signals from an antenna, and outputs 10MHz which is slaved so > that on average there are always 10 million output transitions per > GPS-derived second estimation, and outputs a pulse once per second which > occurs on the transition of the GPS-derived second estimation. > > When the GPS signal is not available for some reason (antenna failure, GPS > system problems, etc.) the GPS disciplined oscillator has to run in > undisciplined mode. Over that time the corrections to the oscillator > frequency are not available, so only the intrinsic stability of the > oscillator used sets the long term stability of the output frequency. In > that particular case (no GPS available) a GPSDO using a rubidium > controlled oscillator as part of the design will have more stable long > term frequency than an oven quartz oscillator. > While GPS signal is available to measure and control the output frequency > there is little difference between an ovenized quartz and a rubidium > controlled (which recall also has an ovenized quartz oscillator driving > the output, but has a control loop using rubidium vapor transitions to > correct any frequency drift of the quartz oscillator). > > > Words like phase noise and PLL are thrown out often in discussions. > > A very good place to start is searching for John Vig oscillator tutorial. > John Vig has a lengthy presentation about all things relating to > oscillators, if you can find the version which includes the notes along > with the presentation slides you can spend a couple of days studying that > > > Is this because frequency agile type has the ultimate output from PLL > > (subject to jitter) and fixed frequency type is from OCXO? > > Mixing different types of things into a single question again. > The term PLL is phase locked loop, it is a particular type of control loop > design which measures the edge transitions of a reference frequency input, > the edge transitions of an output signal, and controls the output so that > the edges match the reference. > You can phase lock quartz, rubidium, pendulum. Maybe an hour glass, but > the only transition I can think of is when you turn the hour glass over, > so that would be an impractical PLL. > > > Even in main well known brands, I understand PRS10 > > and sa.22C and fe5650 are fundamentally different. > > I guess they are all "GPS disciplined" in some way > > No, SA.22C and FE5650 have no connection to GPS, they are not GPS > disciplined in any way as stand alone devices, but can be used as part of > a full GPS disciplined oscillator design. The SA.22C has a > pulse-per-second (PPS) input, so it can be connected to GPS, but that gets > into a lot of secondary questions relating to how that PPS is derived and > whether it helps or hurts overall stability. > > -- > Chris Caudle > > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
