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

Mark Spencer mspencer12345 at yahoo.ca
Fri Dec 21 17:42:21 UTC 2012


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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> >>> 
> >>> 
> >>> 
> >>>
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> > <DSCF1758_bb.jpg>
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> 
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> End of time-nuts Digest, Vol 101, Issue 152
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