[time-nuts] Re: Thunderbolts

[Dana Whitlow]

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 <kb8tq at n1k.org> 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 <k8yumdoober at gmail.com>
> 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 <
> time-nuts at lists.febo.com>
> > 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
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