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

Volker Esper ailer2 at t-online.de
Sat Dec 22 20:44:44 UTC 2012


Plot 1: MDEV of the time interval reported by GPSDO
Yes, Said, that are important issues.

By the way: I'm now writing in two threads, I don't know, why the 
original thread ("Z3805A cooling requirements?") was splitted... Can we 
please move to the original thread?

I am sure, that the noise of the GPSDO PPS-TI data is much to high to 
recognize the effects. I'm going to make a new setup, where I'll compare 
the GPSDO PPS with an external oscilator, e.g. an HP 10544 or the "high 
stability reference" within my SMX signal generator.

Volker


Am 22.12.2012 05:07, schrieb Said Jackson:
> 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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>>>>>
>>>>>
>>>>>
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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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>>
>> <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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