[time-nuts] HP 106B quartz frequency standard...the story so far

WarrenS warrensjmail-one at yahoo.com
Thu Aug 6 14:43:07 UTC 2009


Jim

If your data is accurate and complete,
Looks like your OXCO's aging rate changes from 
+2*e-10 per Hr  to  +6*e-10 per Hr  to -1e-9 / Hr  
when you change it's oven temperature a little.

Hard to believe your limited data and that the effect is not caused by something else,  EXCEPT:
My New Tbold OXCO has been doing almost the exact same thing as you described over the last week.
Its aging rate will switch from 
 -5*e-10 per Hr, (-1e-8 per day) to 
+2.5e-10 per Hr (+0.5e-9 per day). 
and All I do is change its case temperature a few Deg.
And Do note these aging rates are 10 to 100 + times what they should be, and have no sign of getting better.
so even if they have not had time to fully stabilize as some suggest, THEY ARE still BAD.

In my case this is consistent and repeatable over minutes, hrs, and days, I have not tried weeks yet, 
and there is a magic temp in the center that is under a deg wide that the aging rate seems to be about zero.
In my case the value of the two Aging rates does not seem to be a function of temperature or time.
The temperature change causes more like a switch between the two values with a very narrow zero aging rate range in the middle.
For the non believers a have attached one of many of the Lady Heater plots that I have recorded over the last week
The OXCO effect is independent of the Tbolt's mode, It can be in discipline mode, hold over mode or disable mode but of course the way the Tbold responses to the OXCO aging is dependant on which mode it is in.

The bright side is, If I can not get it replaced, at least it becomes a great Kalman testing tool.
Because of all the data I have taken and varied test, I now know a lot more about how the Kalman filter responses.
My Tbolt's  Kalman filter has a first order correction factor for aging, Plus its temperature correction factor. 
If I'm careful with what data I feed it, so as not to confuse it with the difference between temperature effects and time effects, 
It can learn a new Aging rate in 4 hours, and still know it has a zero TC temperature.
If I am not careful, It confuses temperature effects and times effects and its responds is way off in holdover.

warren

***************

----- Original Message ----- 
From: "Jim Palfreyman" <jim77742 at gmail.com>
To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
Sent: Wednesday, August 05, 2009 10:38 PM
Subject: Re: [time-nuts] HP 106B quartz frequency standard...the story so far


OK, I'm puzzled. Can someone with a good knowledge of OCXOs explain my
observation. This is my HP 106B double ovened quartz oscillator, but
I'm sure the theory applies generally.

It's easiest to show these observations as made-up but approximate
numbers an hour apart. Say the device is set to 5.000 000 000 MHz and
then measurements are done on a 5370B with a GPSDO as an external
reference. (Note that the 5370B has more jitter than shown below when
measuring frequency, but by following it for a minute or so you can
see what numbers it hovers around.)

Connect an HP rubidium (to prove it's not a measurement error):

Hour     0,  1,  2,  3,  4,  5
5.000 000 000 
5.000 000 000 
5.000 000 000 
5.000 000 000 
5.000 000 000 
5.000 000 000

My 106B as it currently is running:
5.000 000 000 
5.000 000 001 
5.000 000 002 
5.000 000 003 
5.000 000 004 
5.000 000 005

If I turn the inner oven control in one direction (presumably the
hotter way) a fraction of a turn and then sit back and watch:
5.000 000 000 
5.000 000 003 
5.000 000 006 
5.000 000 009 
5.000 000 012 
5.000 000 015

If I turn the inner oven control the other way (a bit further past the
original point):
5.000 000 000
4.999 999 995   
4.999 999 990   
4.999 999 985   
4.999 999 980   
4.999 999 975


What I don't understand is why changing the oven temperature cause the
frequency to continually increase or decrease. If you look at Quartz
temperature curves (and I'm presuming this is an AC cut since SC
wasn't invented until 1976) they show a frequency offset dependent on
temperature. But I'm not getting an offset, I'm getting a steady
increase - all the time.

Sure I can find my sweet spot where it moves minimally (as it is now)
but that is hard to improve and seems to be sitting on a knife edge.

The only other thing to note is that my power supply rail is a few
volts too high (see previous post). Could this be the cause?

If what I'm seeing is normal I'd love to have it explained to me!

Regards,

Jim


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