Bob, I'm aware of the hump, but it's so much smaller than what I see from GPSDO that I don't mind it too much.
My current usage scenario is that I use one or more GPSDOs as a reference for tweaking one of my Rb stds to reasonable conformance with GPS. Frequency noise on either gets in the way of doing this most accurately, and greatly extends the observation time required to do a good tweak job. I "observe" with the aid of a home-built quadrature demodulator and a duan-channel DSO running in very slow "roll mode", with its two channels driven by I & Q outputs of the demod. Thus I can learn a lot just by an occasional glance at the display as I happen to pass near the 'scope in the course of other activities. I currently own a new CNS *Clock II* and three older T'Bolts. The CNS unit has a very fast tracking loop, with an estimated time constant of only a very few seconds (not user- adjustable). It's 10 MHz output is incredibly noisy, with frequent frequency excursions of several PPB either way. But at least it does not have much trouble with ambient temperature sensitivity. The T'Bolts have user-adjustable time constant, and I've spent a lot of time playing with those. For very short TC settings the GPS noise dominates the picture, and for very long settings ambient temperature fluctuations on the GPSDO's VCXO dominate. I keep going back to the CNS clock because although its frequency fluctuations are more severe, I find it's easier to visually estimate tweak amounts. My desire is to maintain an Rb within 10 PPT most or all of the time with little or no manual attention. In response to your latest, I'm sure I saw mention of a double-oven in connection with the T'Bolt E, on the Trimble site. But perhaps this is an extra cost option. Thanks for mentioning this. As an amusing side note I occasionally rely on a local taxi service, and one of the regular drivers' last names is Trimble. Perhaps I should inquire if there is any connection :-) Dana On Wed, Jul 21, 2021 at 8:20 AM Bob kb8tq <[email protected]> wrote: > Hi > > With the PRS-10 you get that hump in the ADEV. I’m not saying that it’s > the > end of the world, but it really does bug me that it’s there …. > > Bob > > > On Jul 20, 2021, at 10:03 PM, Dana Whitlow <[email protected]> > wrote: > > > > Bert, remember that I need a very long locking loop time constant > setting in > > order to smooth out GPS noise, so in a sense the GPSDo is *almost* in a > > holdover state anyway, all the time. > > > > Probably the smartest thing for me to do is to buy a spanking new PRS-10, > > with the PPS locking feature present. Then I could just leave it locked > to > > GPS most all the time, but disconnect the PPS and let it go into holdover > > on the rare occasions when I need a few hours of even better stability. > > > > Dana > > > > > > On Tue, Jul 20, 2021 at 6:56 PM ew via time-nuts < > [email protected]> > > wrote: > > > >> There is a lot of misinformation out there. It is not the OCXO that > >> changes, Bruce did extensive testing and I did some too. The Vectron is > >> super, would like to know what is in it but do not want to open one. > Once > >> warmed up the stable OCXO temperature is a main contributor to the board > >> temperature. Using a Dual Oven may give you a warm feeling but only > adds 1 > >> more Watt of stable heat to the board making the temperature change > >> smaller. The OCXO is important during Hold Over and that is why it is > >> there. The changes are the DAC which is updated once a second. Very > >> temperature sensitive. Cheap. We have done the tests 10811, OSA 8600, > FRK > >> and M100. For fun did use a cheap small OCXO, no performance change. Was > >> done in Juerg's temperature stable basement. See attached picture. > >> > >> Bert Kehren > >> My experiences with the T'Bolt have not been entirely satisfactory. If > I > >> set the loop > >> lime constant long enough to get a satisfying smoothing of the GPS > noise (a > >> few hundred > >> seconds), then the thermal sensitivity of the VCXO on the T'Bolt rears > its > >> ugly head and > >> I see a lot of my HVAC system cycling instead. The T'Bolt E supposedly > has > >> a double- > >> oven XO, so I'd like to give that a try. But my wallet says "whoa"! > >> > >> According to Bodnar, his units do have some choices in the time constant > >> setting. > >> I've been considering ordering a Bodnar just for frequency agility, but > >> have been > >> holding off out of concern for the complications of dealing with a > foreign > >> supplier. > >> > >> Dana > >> _______________________________________________ > >> time-nuts mailing list -- [email protected] -- To unsubscribe > send > >> an email to [email protected] > >> To unsubscribe, go to and follow the instructions there. > > _______________________________________________ > > time-nuts mailing list -- [email protected] -- To unsubscribe > send an email to [email protected] > > To unsubscribe, go to and follow the instructions there. > _______________________________________________ > time-nuts mailing list -- [email protected] -- To unsubscribe send > an email to [email protected] > To unsubscribe, go to and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] -- To unsubscribe send an email to [email protected] To unsubscribe, go to and follow the instructions there.
