Message: 7
Date: Fri, 21 Dec 2012 09:27:29 -0800
From: Said Jackson<[email protected]>
To: Discussion of precise time and frequency measurement
<[email protected]>
Cc: Discussion of precise time and frequency measurement
<[email protected]>
Subject: Re: [time-nuts] Z3805A cooling requirements?
Message-ID:<[email protected]>
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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<[email protected]>
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 [email protected]:
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,
[email protected]
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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