[time-nuts] Thunderbolt stability and ambient temperature

Don Latham djl at montana.com
Thu Jun 11 14:00:37 EDT 2009

I have a General Radio 100KHz crystal oven that is inside a crafted wood
box. The oven uses a mercury thermometer with a pair of wires sealed in
the side to implement a bang-bang servo. The wood box will thus smooth out
the square wave heat pulse. I think it came from something like an LR-1
Navy signal generator as a calibration standard. I need to put an
oscillator circuit on it in order to characterize its behavior. It's on
the FIFO to-do stack...

Arnold Tibus
> Ed,
> and the big group
> I did run such a 10811 without the outer heater connected and without
> any insulation around as replacement for the original insulation and box
> but I did not see any fluctuations beside the normal behaviour of a 10811.
> (I have to admit that I did not yet run precision records, neither for the
> heater current nor for the frequency output. I see what I have to do
> soon!)
> This model is obviously adjusted inside to work best in an encreased
> environment of around 40 to 45 deg. C .
> I think as Ulrich does explain, blocking the heat flow significantly must
> deteriorate the regulating loop parameters. The life time of the
> oscillator
> electronics outside the stabilized crystal element will as well
> decrease...
> A good idea in fact to put the standard in a stable area and very slow
> varying temp range of around 15 deg. C underneath the house
> fundaments...I will think about!
> Did anybody ever think to apply wood as stabilizing element around an
> oscillator? Wood behaves a bit strange, it is on one side a not bad
> insulator and it does have as well a quite high heat storage capacity!
> (Oak with around 2.4 J/g, K., Lambda 0.17 W/m.K,,
> Pine around 2.7 J/g.K., Lambda 0.14 W/m.K.
> Water around 4.18 J/g.K., Lambda 0,604 W/m.K.
> Copper has 0.385 2.4 J/g, K., Lambda 401 W/m.K. at 25 deg. C. )
> I consider wood a very intersting material, cheap and easy to work...
> Arnold
> On Thu, 11 Jun 2009 09:22:00 -0600, Ed Palmer wrote:
>>Ulrich, when you changed the thermal characteristics around your 10811,
>>how 'crazy' did it become?
>>According to your theory, there should be differences in the schematics
>>of the oven controllers between the single and double oven variants of
>>the 10811.  Last year I picked up a couple of those double oven 10811s
>>from China that had the outer insulation removed.  I wonder if I could
>>see any anomalies in its operation with no outer insulation and only the
>>inner oven operating.
>>Ulrich Bangert wrote:
>>>> I'm not talking about crystal ovens, I'm talking about
>>>> timekeeping kit in general: how to filter high frequency
>>>> temperature fluctuations out, so the PLL does not have to
>>>> deal with them.
>>> Ok, but in this general case you have to accept the fact, that
>>> filtering
>>> high temperature fluctuations is only ONE part of the engineering job.
>>> The
>>> second task (which I tried to point at) is: When you do already have a
>>> closed loop temperature regulation system inside what you plan to built
>>> around it, then you need to manage the filtering without mal
>>> interaction of
>>> the local temperature controller with your additional filtering stuff.
>>> The
>>> art is to make the closed temperature loop inside see only smaller
>>> temperature fluctuations but No changes otherwise.
>>> If you apply an overall change in temperature insulation to the ambient
>>> you
>>> will make the work of the inside temperature controller a lot harder
>>> because
>>> it is not prepared for that. In the aluminium box that i wrote about I
>>> have
>>> for an experiment replaced the air between the 10811 and the outer box
>>> with
>>> a material that has a significant lower temperature conductivity than
>>> standing air. You can easily watch the temperature controller go crazy
>>> with
>>> that. For a second experiment I have replaced the air with a material
>>> having
>>> lots more of thermal conductivity than air and you can watch the
>>> temperature
>>> controller go crazy with that too. You don't need sophisticated
>>> temperature
>>> measurement equipment to see the controller go crazy, just watch the
>>> frequency of the oscillator. This will tell you all about it.
>>> Things are different, if you have an influence on the controller's
>>> regulation parameters (which you do not have with a ready bought
>>> device). If
>>> you do have, then your additional provisions for filtering and
>>> insulation
>>> can easily be included into the thermal model that the temperature
>>> controller has to handle and will lead to different operation
>>> parameters of
>>> the controller. That will of course work and that is why I compared
>>> your
>>> suggestions to designing a new oven (for xtal or rubidium or whatever).
>>> Best regards
>>> Ulrich Bangert
>>>> -----Ursprungliche Nachricht-----
>>>> Von: time-nuts-bounces at febo.com
>>>> [mailto:time-nuts-bounces at febo.com] Im Auftrag von Poul-Henning Kamp
>>>> Gesendet: Donnerstag, 11. Juni 2009 12:50
>>>> An: Discussion of precise time and frequency measurement
>>>> Betreff: Re: [time-nuts] Thunderbolt stability and ambient temperature
>>>> In message <E182724B9FCE4B9F9E914BCC4F374401 at athlon>, "Ulrich
>>>> Bangert" writes:
>>>>>> For PLL steered devices, you want your device enclosed by a
>>>>>> thermal mass which is again enclosed by a layer of thermal
>>>>>> isolation.  The goal is to filter/average all rapid (daily ?)
>>>>>> external temperature influences, only letting through such
>>>>>> slow variations (seasonal ?) which the PLL can comfortably
>>>> cope with.
>>>>> My impression with this thread is that two sligthly different things
>>>>> are being discussed here:
>>>>> Some posters explain how a crystal oven shall be designed as
>>>>> Poul-Henning does with his words above. Absolute correct, no doubt
>>>>> about it!
>>>> I'm not talking about crystal ovens, I'm talking about
>>>> timekeeping kit in general: how to filter high frequency
>>>> temperature fluctuations out, so the PLL does not have to
>>>> deal with them.
>>>> The above advice applies to GPSDO's and Rb's and Cs's as well
>>>> as TCXOs, OCXOs and voltage references.
>>>> Poul-Henning
>>>> --
>>>> Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
>>>> phk at FreeBSD.ORG         | TCP/IP since RFC 956
>>>> FreeBSD committer       | BSD since 4.3-tahoe
>>>> Never attribute to malice what can adequately be explained by
>>>> incompetence.
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Dr. Don Latham AJ7LL
Six Mile Systems LLP
17850 Six Mile Road
POB 134
Huson, MT, 59846
VOX 406-626-4304

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