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

Said Jackson saidjack at aol.com
Sat Dec 22 04:07:24 UTC 2012


Hi Volker,

What is being plotted here? Efc? Time interval as reported by the GPSDO? External counter versus a stable reference?

It looks like the resolution is approaching 10ns/s (1E-08 at 1s), and that the short term effects may be hidden in this noise?

The effects are clearly visible in your first GPSCon plot, not sure if we can see the short term noise in these plots..

The 10811 I had tested went from ~3E-012 at 100s to ~2E-011 when the fan was on, I think both values are quite a bit below the noise floor of your plot so probably hard to measure.

Bye,
Said

Sent from my iPad

On Dec 21, 2012, at 6:47 PM, Volker Esper <ailer2 at t-online.de> wrote:

> 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
>> 
>> Sent from my iPad
>> 
>> 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
>>>> 
>>>> Sent from my iPad
>>>> 
>>>> 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
>>>>>> 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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>>>>> 
>>>>> <DSCF1758_bb.jpg>
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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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> 
> <1_DF9PL_GPSDO_1_sigma(tau)_alle_MDEV_b.jpg>
> <2_DF9PL_GPSDO_1_sigma(tau)(t)_alle_MDEV_b.jpg>
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