[time-nuts] Z3805A cooling requirements?

Volker Esper ailer2 at t-online.de
Sat Dec 22 02:54:50 UTC 2012


Here come the curves...

You'll find two diagrams. The first (named "1_DF9PL...") shows five MDEV 
curves (Modified Allan Deviation), each of them measured at different 
times. Total time span is 30.5 hours.

At small tau values (up to 1000 s) only a slight increase of sigma over 
time can be noticed. However, at a tau of 5000 s or greater you can 
watch sigma making a big bump. Ok, that's what we expected before.

In diagram no. 1 it's somewhat fussy to recognize the change of a 
particular sigma(tau). Now, that we've got curious, we want to see, how 
the sigma(tau) changes over time. So I've been providing a second 
diagram ("2_..."), where sigma(tau) is a function of the time.

You can see, for example, the curve of tau=20480s developing a big hump, 
and falling back to a proper value after about 1800 minutes. All curves 
at a tau greater or equal 2560 do so.

At smaller values the curves are esentially less affected, but - they 
are not back at their starting value after 1800 minutes (30 hours)! You 
could guess, that the hump moves up to longer times with increasing 
sigma - but it doesn't. There is something significantly different below 
tau=2560s.

What is it?

Volker



Am 21.12.2012 14:42, schrieb Volker Esper:
> (oh, I've got to split the posting)
>
>> The picture enclosed can give you a first impression. What we see is
>> the difference time between the GPS signal and the OCXO (blue)
>> ("PPS-TI"), which is an HP 10811. In red we can see the EFC. The total
>> span is 24 h.
>>
>> Before I applied the fan, the noise was at a maximum of about +/- 20 ns.
>> Some hours after starting the fan the noise is much greater. That should
>> have a significant impact on the ADEV.
>>
>> I don't put the ADEV curves here, I make up for it when the EFC
>> compensation is completely out of the scope, that will be in about 12
>> hours. I don't have the ADEV at 1 s, but the ADEV at 10 s has been
>> almost constant. The ADEV at about 1000 s has a nasty bump now.
>>
>> IMHO that fits to the physical facts: the airflow will surely not affect
>> the 10 s ADEV since the OCXO tries its best to isolate the oscillator
>> from short time temperature influences. However, the turbulent air flow
>> that I applied will influence the longer time ADEV.
>>
>> Have a nice solstice
>>
>> Volker
>>
>>
>>
>>
>> Am 21.12.2012 12:44, schrieb Volker Esper:
>>>
>>> Yes, I made such a setup, it's now running 22 hours. I'll post the
>>> results in two hours or so (if nothing evil happens to the earth,
>>> meanwhile).
>>>
>>> Volker
>>>
>>>
>>> Am 21.12.2012 03:35, schrieb SAIDJACK at aol.com:
>>>> Wish I had more time to play with this setup.
>>>>
>>>> How about fellow time nuts spend some time and present similar test
>>>> data on
>>>> their OCXO's to compare?
>>>>
>>>> I was interested in the 1s to 100s ADEV, and my runs were from 8
>>>> minutes to
>>>> 20 minutes, certainly enough time to capture data for 1s to 100s ADEV
>>>> measurements..
>>>>
>>>> bye,
>>>> Said
>>>>
>>>>
>>>> In a message dated 12/20/2012 14:17:59 Pacific Standard Time,
>>>> magnus at rubidium.dyndns.org writes:
>>>>
>>>> On 12/20/2012 01:34 PM, Bob Camp wrote:
>>>>> Hi
>>>>>
>>>>> Temperature transients are not a good thing for an OCXO. If you
>>>> deliberately use the fan to create a transient, then yes the OCXO will
>>>> not be
>>>> happy. The question it - what happens after the transient has settled
>>>> out? The
>>>> plot you have still looks a lot like a step function.
>>>>
>>>> I agree. Temperature steps stresses the OCXO oven loop and easily
>>>> creates a gradient over the crystal. As the oven loop tracks in, the
>>>> frequency returns to around normal. The trouble with forced air over a
>>>> crystal is that the metal shield couples very well and acts like a heat
>>>> sink. A think plastic cover over it and forced convection doesn't have
>>>> the same effect. There is even being used by at least one vendor. Works
>>>> very well for the extra cents of manufacturing cost.
>>>>
>>>> The HP10811 is recommended to be put in a airflow-quiet corner of the
>>>> world. Look at it's mounting in the HP5370A/B for instance.
>>>>
>>>> Cheers,
>>>> Magnus
>>>>
>>>>
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>>>>
>>>
>>>
>>>
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>>
>
>
>
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