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

[J. L. Trantham]

Are you just seeing the transient as it reaches a new equilibrium of
temperature after which it would reduce to a background drift rate or is
this the observation after it has stabilized?

Joe 

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Jim Palfreyman
Sent: Thursday, August 06, 2009 12:38 AM
To: Discussion of precise time and frequency measurement
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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