[time-nuts] time-nuts Digest, Vol 101, Issue 152

Volker Esper ailer2 at t-online.de
Sat Dec 22 02:47:12 UTC 2012

```Said,

Unfortunately I don't have the equipment to measure the phase noise of
an HP 10811 (yet).

But I did some work on evaluating the results of my fan experiment.
Within this posting 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.

1 hour ago, I switched off the fan and laid back the aluminium cover. We
wait and see.

And now, dear time nuts, it's time to go to bed.

Volker

Am 21.12.2012 18:53, schrieb Said Jackson:
> Mark,
>
> Your plot still shows excursions of +/-1E-010, about 100x higher base noise than the Z3801A/Z3805A are capable of achieving. Wonder where that noise is coming from? This noise is probably much higher than the thermal effects.
>
> The original post was the question "does my Z380xA have reduced stability if I add a fan" or similar, I think the answer is shown to be "yes".
>
> Volker, I wonder if you also see fan-induced spurs in the phase noise from 1Hz to 100Hz. I would not be surprised if the fan vibration adds significant spurs to the 10811A crystal.
>
> Bye,
> Said
>
>
> On Dec 21, 2012, at 9:42 AM, Mark Spencer<mspencer12345 at yahoo.ca>  wrote:
>
>> This plot should show the frequency change more clearly.   (Same data just presented differently.)
>>
>> It seems to me that the noise goes may be going down a bit for a minute or so just after the fan is turned on but I don't believe these plots provide conclusive evidence of this.
>>
>>
>> Regards
>> Mark Spencer
>>> Message: 7
>>> Date: Fri, 21 Dec 2012 09:27:29 -0800
>>> From: Said Jackson<saidjack at aol.com>
>>> To: Discussion of precise time and frequency measurement
>>>      <time-nuts at febo.com>
>>> Cc: Discussion of precise time and frequency measurement
>>>      <time-nuts at febo.com>
>>> Subject: Re: [time-nuts] Z3805A cooling requirements?
>>> Message-ID:<83CE0384-2996-4155-B51B-9D79910B29AA at aol.com>
>>> Content-Type: text/plain;
>>> charset=us-ascii
>>>
>>> Great plots guys!
>>>
>>> Looking at these results I think my original claim still
>>> holds: ADEV goes up when a fan is involved versus no fan,
>>> even on a double oven 10811..
>>>
>>> Clearly visible on the 10811, maybe not so much on the MV89
>>> but that unit seems to have frequency moves into the xE-010
>>> region on Marks plot so maybe the effect is just a bit
>>> hidden?
>>>
>>> Bye,
>>> Said
>>>
>>>
>>> On Dec 21, 2012, at 5:44 AM, Volker Esper<ailer2 at t-online.de>
>>> wrote:
>>>
>>>> ...and the picture of the experiment...
>>>>
>>>>
>>>>> 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
>>> 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
>>>>>
>>>>> 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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>>>> <DSCF1758_bb.jpg>
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>>>
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>>> End of time-nuts Digest, Vol 101, Issue 152
>>> *******************************************
>> <MV89A Fan turned on at 460 seconds v2.png>
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