[time-nuts] Re: Thunderbolts

[Bob kb8tq]

Hi

Trimble mentions the E oscillator in a couple of places. They also seem to only
talk about holdover in very vague terms. They never tie down anything that 
would track back to the stability of the OCXO. If it *is* a high(er) performance 
OCXO, I find that all a bit weird. 

The ADEV plot they show looks a lot like the fine old TBolt we all know and love ….

Bob

> On Jul 21, 2021, at 9:48 AM, Dana Whitlow <k8yumdoober at gmail.com> wrote:
> 
> 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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