Counter OCXO behaviour
Hello,
recently I tried to trim the Racal Dana
1992 04E internal reference, using the
GPS pps as a reference. I'd like to ask
a pair of questions...
-
First is about the method.
I'm using the counter TI to measure it's
own OCXO. The GPS is starting the count,
the internal reference 10MHz (on the rear
there is a reference output connector)
stops the count and I log the result
as I've done before with other oscillators.
Is this a correct procedure? -
Second, is about the behaviour of the OCXO
after trimming. The OCXO seem not that stable
after the trimming, like if the crystal started
to age faster than before trimming, and now is
slowly stabilizing.
It's like the retrace of the crystals I've read
about, but the instrument was never powered down
in the last month. And it's oven has been on for
the last year. Will a crystal retrace also
after retrimming?
The frequency of the crystal is slowing, in the
first hours after the trimming rapidly, and now
more slowly. After few days the frequency seem
to be slowing somewhere around 1x10^-10 per day.
Unfortunately I havent logged the counter for
enough time before the trimming, but it measured
the same Rb with less than 3 digits of difference
(3x10^-10) in last 6 monthes.
Thanks,
Fabio.
Is it manually adjusted right at the oscillator? If so, just opening it
up and sticking a screwdriver in there gives it a thermal shock, and the
adjusted element will have mechanical stress that has to settle out too
- the value can change for a while.
Ed
The Racal Dana 1991/1992 OCXO has a big pair of pan head screws
exposed on the back. One is coarse adjust and one is fine adjust. I
have the TCXO version which also exposes the adjustment on the back so
you do not have to open anything to get to it.
You can see them here:
On Mon, 14 Jan 2013 12:34:04 -0800, Ed Breya eb@telight.com wrote:
Is it manually adjusted right at the oscillator? If so, just opening it
up and sticking a screwdriver in there gives it a thermal shock, and the
adjusted element will have mechanical stress that has to settle out too
- the value can change for a while.
Ed
On Mon, 14 Jan 2013 21:14:23 +0100, Fabio Eboli FabioEb@quipo.it
wrote:
Hello,
recently I tried to trim the Racal Dana
1992 04E internal reference, using the
GPS pps as a reference. I'd like to ask
a pair of questions...
- First is about the method.
I'm using the counter TI to measure it's
own OCXO. The GPS is starting the count,
the internal reference 10MHz (on the rear
there is a reference output connector)
stops the count and I log the result
as I've done before with other oscillators.
Is this a correct procedure?
I just measured the GPS pulse output directly with the counter. I got
the same calibration results measuring frequency or period. With time
interval, I used the delay feature to set the minimum measurement
duration.
- Second, is about the behaviour of the OCXO
after trimming. The OCXO seem not that stable
after the trimming, like if the crystal started
to age faster than before trimming, and now is
slowly stabilizing.
It's like the retrace of the crystals I've read
about, but the instrument was never powered down
in the last month. And it's oven has been on for
the last year. Will a crystal retrace also
after retrimming?
The frequency of the crystal is slowing, in the
first hours after the trimming rapidly, and now
more slowly. After few days the frequency seem
to be slowing somewhere around 1x10^-10 per day.
Unfortunately I havent logged the counter for
enough time before the trimming, but it measured
the same Rb with less than 3 digits of difference
(3x10^-10) in last 6 monthes.
My 1992 has the TCXO and I noticed the least significant digit
drifting after trimming. At least with the 1992 TCXO, I decided the
last digit was not worth worrying about which is pretty much the case
with all of my other counters although my 1992 is about the best of my
bunch.
Ed wrote:
Is it manually adjusted right at the oscillator? If so, just opening
it up and sticking a screwdriver in there gives it a thermal shock,
and the adjusted element will have mechanical stress that has to
settle out too - the value can change for a while.
The 04E standard used in the military surplus 1992s (which are by far
the most common 1992s in the US) is typically labeled "9462 454879,
Rev. A". There has been a fair bit of discussion on the list about
these -- a search of the archive will turn up a number of threads.
Yes, they do tend to take a long while to settle after
adjustment. So long, in fact -- and with oscillatory gyrations above
and below the starting frequency -- that I have speculated on-list
that the adjustment may not be a direct adjustment of the tuned
circuit (e.g., with the usual capacitor on the crystal), but rather
an adjustment to the oven controller setting the crystal temperature.
Because the oscillators are sealed assemblies, I'm not aware of
anyone who has taken one apart for analysis -- so the reason for this
behavior must be considered unknown until we know what is going on inside.
Best regards,
Charles
I answer here to all, thank Ed David and Charles for your thoughts.
David, LOL, you posted the pic of the exact counter in question.
Not a similar unit, I mean it's exactly that 1992 that is being
measured ;)
The pictures on eevblog show the early measurements I made with
the counter. One of the Rb wasmeasured to about 10MHz+60mHz.
After a while (I think a pair of monthes) the reading was slightly
over 10MHz+70mHz and remained there for more than 6 monthes, until
I trimmed the counter few days ago.
The trimming is very touchy, and the simple opening of the screw on
the rear is traumatic: the frequency rises for a pair of minutes and
then it takes a while to return to the previous level.
Talking about this OCXO, how much is it good?
I mean for who has eperience with many OCXO is
this a good unit, or it's an average one?
Is this the kind of stability and reaction that can
be expected by an OCXO useful for GPSDO (less the
EFC control of course)?
Measuring this OCXO, just now I'm starting to feel the precision
of the FE5680, or 5682. It's so easy to set the Rb to follow
GPS closely for days...
I have some pics of the measurements I made, they are a little messy,
I hope can be fun and interesting to see:
This was before touching anything, top right the phase between
the GPS and OCXO:
http://www.flickr.com/photos/14336723@N08/8382126024/
it was slow by about 7x10^-9. This was the first trim attempt:
http://www.flickr.com/photos/14336723@N08/8382125734/
and this the last trims, the dips in phase are evident, they
happen when I open the calibration screw on the rear:
http://www.flickr.com/photos/14336723@N08/8381043177/
and at last these are logged after last trim action:
http://www.flickr.com/photos/14336723@N08/8381044033/
I tried to extract more data from last log:
http://www.flickr.com/photos/14336723@N08/8382126108/
Here I made the first and second derivative in time of the phase,
data are heavily averaged, so are not very accurate. The
10MHz period error (vs. GPS) changed from -0.8x10^-10 soon after
the trim, to +1x10^-10 after two days (top right).
The OCXO period was rising from almost 2x10^-15 soon after the
trim to 1.3x10^-15 after two days (bottom left).
Seem the stabilization will take a while...
Fabio.
Il 2013-01-15 00:08 Fabio Eboli ha scritto:
Trying to be more clear:
10MHz period error (vs. GPS) changed from -0.8x10^-10 soon after
the trim, to +1x10^-10 after two days (top right).
Top right is change of phase in time, i.e. period error
measured using GPS as reference.
The OCXO period was rising from almost 2x10^-15 soon after the
trim to 1.3x10^-15 after two days (bottom left).
Bottom left is change of period error in time,
1.3x10^-15 per second is around 1.1x10^-10 per day,
if I'm not mistaken, more than typical unit's aging
stated by datasheet.
Seem the stabilization will take a while...
Fabio.
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Hi all,
Will someone know what it could be?
http://www.stben.net/DSC_0338.JPG
http://www.stben.net/DSC_0339.JPG
Thanks for your help.
Bye,
Jean-Louis
It's a part of an oven regulator.
----- Original Message -----
From: "Jean-Louis Noel" jln@stben.net
To: "Discussion of precise time and frequency measurement" time-nuts@febo.com
Sent: Tuesday, January 15, 2013 11:24 AM
Subject: [time-nuts] hammond 77589
Hi all,
Will someone know what it could be?
http://www.stben.net/DSC_0338.JPG
http://www.stben.net/DSC_0339.JPG
Thanks for your help.
Bye,
Jean-Louis
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Hi Jean-louis,
It looks very much like the main crystal in a Symmetricom Rubidium unit that I
tried changing a crystal in. In my case the crystal was made by Bliley. It is
about the same size as the standard 8 lead TO-5 integrated ciruit case except
that it had just three leads on the bottom just like your unit.
Is your roughly the same size ? Do you know or have a picture of what it came
out of ?
Bill....WB6BNQ
Jean-Louis Noel wrote:
Hi all,
Will someone know what it could be?
http://www.stben.net/DSC_0338.JPG
http://www.stben.net/DSC_0339.JPG
Thanks for your help.
Bye,
Jean-Louis
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.