Hi
In most cases, when you see an OCXO (or TCXO) begin to rise past a few thousand
seconds, you are either looking at aging or the room temperature.
Bob
On Dec 21, 2012, at 9:54 PM, Volker Esper <ail...@t-online.de> wrote:
> 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 saidj...@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,
>>>>> mag...@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
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> time-nuts mailing list -- time-nuts@febo.com
>>>>> To unsubscribe, go to
>>>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>>>> and follow the instructions there.
>>>>>
>>>>>
>>>>
>>>>
>>>>
>>>> _______________________________________________
>>>> time-nuts mailing list -- time-nuts@febo.com
>>>> To unsubscribe, go to
>>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>>> and follow the instructions there.
>>>>
>>>>
>>>
>>
>>
>>
>> _______________________________________________
>> time-nuts mailing list -- time-nuts@febo.com
>> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>
> <1_DF9PL_GPSDO_1_sigma(tau)_alle_MDEV_b.jpg><2_DF9PL_GPSDO_1_sigma(tau)(t)_alle_MDEV_b.jpg>_______________________________________________
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
