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

Volker Esper ailer2 at t-online.de
Sun Dec 23 02:30:58 UTC 2012


Thank you very much for the advice, I didn't know that at all...
Volker


Am 22.12.2012 22:26, schrieb Alan Melia:
> Volker.....look at the subject line, the posting is in your hands, you
> dont need to just use the reply button, as somone did with a "digest"
> which forked the thread.. This means all the posing under "Digest...."
> are hidden from view and searching. You can edit the subject line but
> this does not always return to the old thread if you use he reply
> button. I think it depends on the mail client.
> Alan
> G3NYK
> ----- Original Message ----- From: "Volker Esper" <ailer2 at t-online.de>
> To: "Discussion of precise time and frequency measurement"
> <time-nuts at febo.com>
> Sent: Saturday, December 22, 2012 8:44 PM
> Subject: Re: [time-nuts] time-nuts Digest, Vol 101, Issue 152
>
>
>>
>> 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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>>>>>>> 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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