[time-nuts] Calibration and temperature

Magnus Danielson magnus at rubidium.dyndns.org
Sat Nov 29 12:40:40 UTC 2008


Lux, James P skrev:
> 
> 
> On 11/28/08 11:27 AM, "Bill Hawkins" <bill at iaxs.net> wrote:
>> Has any work been done on temperature compensation of quartz or other
>> oscillators to avoid the expense, space, and power of ovens? The
>> oscillating material must have a repeatable temperature curve, of
>> course.
> Look at MCXOs, a very clever technique using the different between third
> overtone and fundamental to measure the temperature of the rock.

The fundamental and third overtones have different temperature 
dependencies. The difference is essentially linear, so by dividing the 
third overtone down by three or tripping the base frequency and then 
compare them in a mixer to get the beat frequency and count that, 
adjustment to the frequency can be performed, often through a DDS 
clocked at the third overtone.

The traditional suppression of major resonances becomes slightly 
different in the oscillator core, since now both the fundamental and 
third overtones is wanted. It is however not a big mystery.

You could use this temperature sensing technique to with an OCXO 
solution to let the inner oven be sensed in the crystal. A combined 
solution would both feed forward and feed backwards.

The MCXO and many others is very well presented in the big presentation 
that John Vig has 
(http://www.ieee-uffc.org/freqcontrol/tutorials/vig3/vig3.ppt). In 
general, there is plentifull of good information to read at:
http://www.ieee-uffc.org/fcmain.asp?view=review#tutor

Reading through that and parts of the NIST T&F archive should elivate 
your knowledge pretty fast and it is all for free. Just costs you the 
time to read.

Cheers,
Magnus




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